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303 Cards in this Set
- Front
- Back
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anatomy and fn of external ear
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made up of auricle and external auditory meatus
fn - collects sound waves and funnel them down to the tympanic membrane - which vibrates when sound hits it |
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anatomy of middle ear
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ear ossicles in tympanic cavity
ear ossicles - three bones that connect tympanic membrane with inner ear a. malleus - embedded in tympanic membrane and articulates with teh inus b. incus - articulates w/stapes c. stapes - footplate of the stapes forms a hatch-like covering over the oval window (fenestra vestibule) of inner ear |
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fn of middle ear
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sound waves cause vibration of typanic membrane which results in mvmt of the ear ossicles
footplate of the stapes operates in piston like fashion to generate pressure waves in the fluid of the inner ear pressure waves are transformed into nerve impulses by receptor cells of the inner ear |
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acoustic middle ear reflex
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very loud sounds cause excessive mvmt of ear ossicles which results in the generation of large pressure waves in the innner ear - could damage the receptors in the inner ear and lead to partial deafness
this reflex counters this by inhibiting the mvmt of the ear ossicles - accomplished by contraction of the tensor tympani mm attached to the malleus - innervated by V - and the stapedius mm - attached to stapes innervated by N VII - superior olivary nuc, brain stem auditory nuc 0 activated by loud sounds and innervates the motor neurons that innervate the tensor tymoani and stapedius mm |
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bony labyrinth
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space in petrous temporal bone that contains membranous labyrinth
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membranous labyrinth
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system of membranous (soft tissue) tubes that are suspended in the fluid (perilymph) that fills the bony labyrinth
filled with fluid endolymph |
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vestibule
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bony
- contains utricle and saccule - membranous - oval window - covered over by footplate of |
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three semicircular cannals
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bony
semicircular ducts - membranous located in each semicircular cannal |
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anatomy of cochlea
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bony - shapped like a snails shell - spirals for 2 1/2 turns
cochlea duct - membranous - contained in bony chochlea - spirals for 2 1/2 turns scala vestibule - space that lie abv the cochlear duct throughout its spiral course - cont with vestibule at base of cochlea scala tympani - space that lies bellow the cochlear duct - membrane over the round windo seperates it from the tympanic cavity - at base of cochlea |
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fnal aspects of cochlea
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1. mvmt of the stapes - results in the generation of pressure waves in the perilymph of the vestibule
2. pressure waves travel up the scala vestibule and then transmittted across the cochlear duct 3. transmission across the cochlear duct activates the receptor apparatus in the cochlear duct (organ of corti) 4. pressure waves reach scala tympani 5. travel down scala tympani and dampen out at the membrane covering the round window |
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basiliar membrane
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forms floor of cochlear duct
adjacent to scala tympani |
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organ of corti
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spiral organ
- supported by basilar membrane - found all along the spiral course of the cochlear duct contains a. hair cells = auditory receptors |
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hair cells
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found in organ of corti
audidtory receptors apex of hair cells - contain hairs - stereocilia that extend outward and contact (inner hiar cells) or are embedded in (outer hair cells) the overlying tectorial membrane (a gelatinous membrane) - base of hair cells - synaptic contacts made w/ peripheral processes of the first order neurons of the auditory system - hair cells are presynaptic (contain synaptic vesicles) - and the first order neurons are postsynaptic |
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first order auditory neurons
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cell bodies in cochlear spiral ganglion - located along inner edge of cochlear duct along its entire spiral course
bipolar neurons - central processes form cochlear division of VIII n - peripheral processes are postsynaptic to hair cells |
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fn aspects of organ of corti
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1. pressure waves generated by stapes ravel up the scala vestibuli
2. the vibration causes a displacement of the basilar membrane and results in a shift in the position of the overlying hair cells 3. tectorial membrane is relatively stationary and does not move when pressure waves strike it 4. since tips of hair in contact w/tectorial membrane - the shift in position of the hair cells causes the hairs to bend 5. bending results in depolarization of hair cells 6. produces the release of nt from synaptic vesicles at the base of the hair cells -which depolarizes the peripherial processes of the first order neurons of the spiral ganaglion |
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tonotopic localization
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inner ear - regional differences in the basilar membrane
1. base of cochlea - basilar mem is narrow and stiff - is max displaced by (more sensitive to) high frequency tones (high) pitch - high tones tend to excite hair cells and first order neurons at the base of the cochlea 2. apex of the cochlea - basilar mem is wide and pliable - maximally displaced by *more sensitve to( - low frequency tones (low pitch) - therefore low tones tend to excite hair cells and first order neurons at the apex whole spectrum of audible tones is represented in an orderly manner in the cochlea and cochlear gang = tonotopic localizaiton |
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Ascending auditory pathway first order neurons
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bipolar neurons in cochlear ganglion
1. peripheral processes - receive synapses from hair cells 2. central processes - form cochlear div of CN VII runs in internal auditory meatus along w/facial VII - cochlear n fibers - SSA - enters brainstem at jnct of pons and medulla - fibers bifurcate - one branch synapses in dorsal cochlear nuc and the other in the ventral cochlear nuc |
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ascending auditory pathway second order neurons
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dorsal and ventral cochlear nuclei
1. axons (secondary auditory fibers) bundle together and cross to the contralateral side of the brain stem - each of these bundles is called an acoustic stria - axons from the dorsal and ventral cochlear nuclei take different courses a. axons from the ventral cochlear nuc - course ventral to the inf cerebellar peduncle and cross to the contralateral side of the lower pons - crossing fibers form a fiber bundle that is trapezoid shaped when seen in cross section - trapezoid body - after crossing in the trapezoid body fibers either synapse in the sup olivary nuc or enter the main ascending auditory tract (called the lateral lemniscus) these second order auditory fibers in the lateral ascend through the pons and finally synapse in the inf colliculus of the lower midbrain b. axons from the dorsal cochlear nuc - course dorsal to the inf cerebellar peduncle and cross to the contralateral side to the trapezoid body - like axons of the ventral cochlear nuc - axons from the dorsal coclear nuc either enter the lateral lemniscus and course to the inf colliculus and or synapse in the superior olivary nuc both also synapse in the ipsilateral nuc |
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ascending auditory pathways in thrid order neurons
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superior olivary nuc
1. axons from both ipsilateral and contralateral cochlear nuclei synapse in ezch sup olive 2. Since SO neurons can analyse the tiem differentialthat it takes for impulse to reach it from the two ears - SO very imp for the localizaition of sound - also involved in middle ear reflex - origin of efferent cochlear bundle Axons from SO enter the ipsi and contralateral lateral lemniscus - therefore auditory impulses arising from each ear ascend through the brain stem in both the left and right lateral lemniscus = as a result auditory info from one ear eventually reaches both the L and R auditory cortex - so each ear is represented bilaterally in ascending auditory path |
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Lateral lemniscus
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contains 2nd order axons from cochlear nuclei and 3rd order axons from the sup olivary nuclei
- located lateral and dorsolateral to the medial lemniscus which ascends through pons and terminates in the inf colliculus of midbrain |
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nuc of lateral lemniscus
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relay nuc located w/in the lateral lemniscus in the middle and upper pons
-surrounded by fibers of the lateral lemniscus some of which synapse in the nuc - the axons of the neurons in this nucleus join the lateral lemniscus and ascend =both nuc of lat lemniscus and inf colliculus have commissural fibers that further contribute to the bilateral representation of each ear in the auditory path |
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inf colliculus
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its axons form the brachium of the inf collliculus which ascends through the upper midbrain lateral to the sup colliculus
terminates in the medial geniculate nuc of the dorsal thalamus - the most caudsal thalamic nuc |
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Medial geniculate nuc
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auditory nuc of the thalamus
1. crude awareness of sound at the level of MGN 2. sends fibers to the primary auditory cortex - fibers to cortex are termed auditory radiations - fibers course through a portion of the internal capsul that passes beneath the lentiform nuc - sublenticular protion of the internal capsule |
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primary auditory cortex
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area 41
1. located on the ant transverse temporal gyrus (of Heschl) 2. cortical processign of auditory info is imp for appreciating the meaning of sound - iding sounds - understanding speach - appreciating music 3. area 41 projects to surrounding auditory asssociation areas - including area 42 on post transverse tempral gyrus and area 22 on sup temporal gyrus - these are sites of auditory memory storage and are critical for understanding the meaning of sound |
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Ascending Auditory Pathway
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1.first order - bipolar neurons of cochlear ganglion
2. second order neurons - dorsal and ventral cochlear nuclei 3. most cross some dont in the trapezoid body 4. Sup olivary nuc and then to lateral lemniscus or straight to lateral lemniscus 5.inf colliculus via brachium of the inf colliculs 6. medial geniculate nucleus 0 auditory nuc of thalamus 7. primary auditory cortex area 41 8. auditory association areas 42 post transverse temporal gyrus or 22 sup temporal gyrus |
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bilateral lesion of the auditory cortex
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rarely observed
1. inability to appreciate the meaning of sound (can't understand speech) 2. still have crude awareness of sound since medial geniculate is intact |
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unilateral lesion of the auditory cortex
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pts have no obvious hearing loss in either ear bc impulses from each ear can go up the ascending auditory pathway contralateral to the lesion to reach the contralateral auditory cortex
- however, pts may have impaired sound localizaiotn - sophisticated audiometric testing may show slight loss of hearing acuity in the ear that is the contralateral lesion |
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unilateral lesion of the medial geniculate
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pts have no obvious hearing loss in either ear bc impulses from each ear can go up the ascending auditory pathway contralateral to the lesion to reach the contralateral auditory cortex
- however, pts may have impaired sound localizaiotn - sophisticated audiometric testing may show slight loss of hearing acuity in the ear that is the contralateral lesion |
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unilateral lesion of the lateral lemniscus
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pts have no obvious hearing loss in either ear bc impulses from each ear can go up the ascending auditory pathway contralateral to the lesion to reach the contralateral auditory cortex
- however, pts may have impaired sound localizaiotn - sophisticated audiometric testing may show slight loss of hearing acuity in the ear that is the contralateral lesion |
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unilateral lesion of the auditory nerve or cochlear nuclei
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- hearing loss in the ipsilateral ear
-common cause of auditory nerve lesion = acoustic neuroma - benighn tumor - removed by surgery (aka acoustic neurinoma) - benign schwann cell tumor of the CNVIII in int auditory meatus - ringing in ears (tinnitus) frequently precedes hearing loss |
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descending auditory pathway
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involves most of the same tracts and nuclei of the ascending pathway but descents rather than ascends - bilateral multisynaptic pathway from auditory cortex to hair cells
- fewer fibers than the ascending pathway - sup olove not the cochlear nuc - projects to the hair cells via the "efferent cochlear bundle" - its fibers exit the brain stem in the vestibular poriton of CN VIII bilaterally -fibers cross to the auditory n and synapse w/the outer hair cells in the organ of corti -efferent fiber activation changes of the outer hair cells, which changes the stiffness of the tectorial membrane - this affects the sensitivity of the hair cells to particular frequencies of sound |
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fn of descending pathway
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auditory sharpening - inhibition of background noise so we can better hear the sounds we want to attend to (increase of singal-to-noise ration)
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hearing testing
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simplest method - cover one of pts ears w/hand and test the hearing of the other ear by seeing if the pt can hear a whispered voice, tick of a watch, or a tuning fork
audiometric testing - audiometers are sophisticated electronic instruments that present the pt w/different frequencies and intesnities of sound in order to test hearing thresholds |
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Deafnesss
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1. conduction deafness
2. sensorineural deafness differentiated by the Rinne and webster tests - both test depend on the fact that the cochlea can be directly activated by conduction of sound throughthe bones of the skull - air conductio nis more efficient than bone conduction |
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conduction deafness
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caused by malfunction of the transmission of sound throug hthe middle ear
causes: 1. otitisi media - build up of fluid - most common in deafness of young kids 2. osteosclerosis (fusion of stapes to bone surrounding the oval women - most common in acults |
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sensorineural deafness
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casued by damage to the cochlea, auditory n , or cochlear nuclei
common causes: 1. loss of hair cells in the organ of corti due to infections, degeneration, chronic exposure to loud sounds 2. damage to the auditory n from acoustic neuromas |
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Weber test
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a vibrating tuning fork is placed on the forehead and the pt is asked were do ou hear that
- do you hear the noise in the center of your head or is it lounder on one side or the other norm - sound appears to come from center of forehead abn - sound will appear to be louder in the normal ear b/c the deaf ear cannot hear sound even by bone conduction with a middle ear conductive hearing loss the sound will appear to be louder in the deaf ear - b/c bone conduction is equal in the 2 ears but the deaf ear hears no background noise from the air |
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rinne test
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vibrating tuning fork is placed first on the mastoid bone and then over the ear cannal
pt asked where is the sound louder behind your ear or in your ear norm = louder when over air since air conduction is greater than bone conduction in conduction deafness the sound will be heard only when the tunign fork is held against the mastoid bone since it cannot be conducted via the norm route through the middle ear |
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extramedullary vessels - spinal cord
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nonsegmental and nonsymmetric blood supply
9-12 a - vascularization of entire spinal cord via 3 vertical channels single ant spinal a and paired post spinal a |
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anterior spinal artery
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in pia mater extending caudally from its origin on the vertebrals to the level of the 4th cervical system
from here it is augmented by the terminal branches of several spinal medullary aa that enteer the intervetebral foramen and course along the internal aspects of their respective roots give no branches to roots before enter dura and reach substance of cord a few spinal medullary a augment spinal ant spinal a making ant spinal a an anastomotic channel - single continuous vessle or channel |
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post spinal aa
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many sml nutritive contributions from various levels
nonsegmental spinal medullary aa arise more frequently from L than R in thoracic and lumber regions |
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cervicothoracic zone
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entire cervical cord and the first 2 or 3 thoracic segments
- upper 4 cervical segments supplied by ant spinal a - a single trunk formed by contributions from each vertebral a - no other source of vessels lower 4 cervical segments and first 2 thoracic segments - including cervical enlargement posses independent blood supply 2-3 non segmental spialmedullary vessels from the intratransverse part of the vertebral a |
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artery of the cervical enlargment
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a single vessel ariving w/.C7 or C8 root
arises from deep cervical branch of the costocervical trunk |
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collateral circulation to cervical enlargement
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occipital a
ascending cervical a other branches of costocervical trunk zone of poor collateral circulation occurs abt T4 boundary btw cervicothoracic and midthoracic zones |
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spinal branch of the posterior intercostal a
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T4-T8 midthoracic zone
supplied by a single vessel derived from the thoracic aorta abt the level of T7 disease of aorta - secondaryily causes in j to spinal cord |
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thoracolumbar zone
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last few thoracic levels and lumbar enlargement
depends on a single vessel that arises from the abd aorta - becomes the ant spinal a by branching into a sml ascending and large descending branch enters w/ thoracic n (T9-T12) |
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anastomotic loop of the conus
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rich anastomosis to conus medullaris formed by union of the causdal ends of the andt and post spinal vessels
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intramedullary arterial system of spinal cord
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intrinsic vessels that supply the gray and white matter
consists of central a and peripheral arterial system |
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central a
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supply the central part of spinal gray matter and white matter
branches of ant spinal a penetrate ventral median fissure at ventral white commisure pass to one half of the cord and the adjacent one to the other half anastomose = overlapping |
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pial arterial plexius
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from ant and post spinal arteries on spinal cord surface
system of the cord includes penetrating branches of this pial arterial plexus |
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peripheral artery
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- vessels supply bulk of white mater and greater part of dorsal horns
term arterioles of the central and peripheral intramedullary vessels form an extensive capillary network cap more numerous in gray mater - neuronal cell bodies - greater metabolic needs |
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vertebral-basilar system
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the human brain stem receives its arterial supply
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vertebral aa
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enter foramen magnum and converge on the ventral surface of the medulla in a groove btw the pyramid and olive
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basilar a
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formed from the uniting of the vetebral aa
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L vertebral a
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frequently larger in caliber than the R
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posterior cerebral arteries
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basilar artery bifructates at upper pons
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branches of the intracranial part of vertebral and basilar a
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two types
extrinsic - superficial a intrinsic - penetrating a |
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superficial brain stem arteries
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vertebral arteries -
- ant and post spinal rami - post inferior cerebellar arteries (PICA) - ant spinal rami originate from the medial aspects of both vertebrals curve medially and unite at the medullar or upper cervical level post spinal rami - arise as distinct -branches of the vertebral arteries, but may branch from postinf cerebrellar a - supplies the posterior medulla Post inf cerebellar aa - arise from vertebral aa - asymmetrical in origin and caliber - tortuous in course - forms a ccranially drected loop near the aperturess (poorly defined gap btw the cerebellum and medulla - bends inf and medially btw brain stem and cerebellar tonsil - enters 4th ventricle - asscending roots emerge near glossopharyngesal and vagal roots - give off penetrating vessels that enter the lateral medulla |
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Posterior inferior cerebellar arteriesanterior inferior cerebellar artery
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- comes directly from the basiliar arrtery
- may come from a stem common to it and the internal auditory artery - penetrating branches from undersurface enter pons w/rootlets of facial n and distrubute to the lateral part of the inf pointine tegmentum |
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internal auidtory artery
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doesn't contribute blood supply to brain stem
supplies the roots of vestibulococchlear and facial nn and the inner ear originates from basiliar - shares common origin w/ant inf cerebellar a |
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superior cerebellar a
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last large branch of basilar a before its bifurcation
symmetrical w/large diameters pass around brain stem along the upper border of the pons occulomotor n emerges btw sup cerebellar a and post cerebral a - provides blood to inf colliculus - via one of the small rami - supply the superior cerebrallar surface - branches descend along the middle of the vermis - larger branch ends in the cerebellar dentate nuc |
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post cerebral a
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terminal branches of basiliar
- 30% of the time one (L) retains its embryological relationship with ipsilateral internal carotid flow of blood from basiliar into larger encircle the brain stem at the tentorial notch suppy: - cerebral peduncle and sup colliculi -gives off the post choroidal a w/ other sml rami to supply the thalmus - major distribution - posteromedial cerebral cortex |
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posterior communicating artery
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arises from internal carotid and passes horizontally to join the post cerebral a
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vestibulocochlear n
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hearing n two roots - one cochlear n
special somatic afferent - responsible for a special exteroceptive sensation that relates us to our enviro |
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modiolus
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central cone of trabecular bone supporting the cochlea
somata of the bipolar neurons - primary neurons in the auditory path |
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cochlea
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spiral 2 1/2 turns - within tempporal petrus bone
- 3 fluid filled membranous compartments - coclear duct - scala vestibuli and scala tympani |
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auditory receptors
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aka sensory hair cells - on the sensory epithelium of the cochlea on the basilar part of the spiral membrane in the cochlear duct
- set at an angle to one another and named by their position relative to the modiolus inner and outer non-neural hair cells modified receptors for auditory stimuli extend throughout the cochlea |
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spiral ganglion
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primary neurons - bipolar - of the auditory path
- cell bodies in the modiolus - peripheral processes take an intricate course passing in the modiolus to synapse at the base of the sensory hair - central processes form cochlear root of the bestibulocochlear n |
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cochlear root of vestibulocochlear n
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central processes of primary neurons in auditory path
myelinated fibers in each n enter at the obtuse angle at the jnct of the pons, medulla, cerebellum = cerebello-pontine angle dorsal surface and lat of the inf cerebellar peduncle enter and bifurcate into ascending and descending branches to dorsal and ventral cochlear nuclei or secondary cochlear gray matter |
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cerebello-pontine angle tumor
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could impinge vestibulocochhlear n or facial n
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dorsal and ventral cochlear nuc
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vol half or 1/3 the vol of the ventral nuc
secondary neurons in path nt btw cochlear afferents and secondary cochlear neurons is glutamate or aspartate |
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auditory secondary neurons
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from cochlear nuclei
ventral bundle ascends and spreads through the medial lemniscus to the opposite side of the brain stem contributing to the trapezoid body dorsal - form dorsal bundle that decussates near ventricular floor after decussation turn and ascend in the lateral lemniscus |
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trapezoid body
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trapezoid shaped are of intermingled secondary auditory fibers and neuorons of the lower pons
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lateral lemniscus
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ascending auditory pathway
shifts as it ascends crossed and uncrossed fibers from the dorsal and ventral cochlear nuclei, sup olivary nuclei, and nuclei of the lateral lemniscus |
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stimulation of the upper brainstem
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causes a smooth, synchronous, low pitched note - buzzing like a bee or humming or sounds w/a musical quality like a ringing bell
or thin tinny sound - ticking, sizzling, swishing, clicking, or cricketlike o or a deep note - roaring or rumbling = contralateral preponderance of response ipsilateral too sml to be successfully stimulated |
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inferior colliculus nuclei
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additional neurons are found here
multilaminar and richly interconnected via the commissure of the inf colliculus |
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stimulation of inf colliculus
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causes loud noise in ipsilateral ear and a similiar but fainter noise in contralateral ear
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brachium of inf colliculus
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connect lateral lemniscus to medial geniculate body of the dorsal thalamus
- ventral division of it - where pitch reaches consciousness and loudness - fibers are reduced in number and size in the elderly |
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stimulation of the medial geniculate nucleus
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causes ringing referred to center of the head or buzzing heard bilaterly but mainly in contralateral ear
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transverse temporal gyri
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coorespond to broadmann's areas 41 and 42 = two parralel areas
part of the supeiror temporal gyrus primary auditory cortex |
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acoustic radiations
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orderly projections from medial geniculate neurons to primary auditory cortex
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sublenticular part of internal capsule
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how acoustic radiations reach the temporal lobe
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primary auditory association cortex
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lateral aspect of the sup temporal gyrus - areas 42 and 22
sounds are localized, interpreted w/previous auditory experience discriminated, and recognized/ understood only one distinguishes a sound but both are essential for localization comparison btw two cortices of sound's direction and speed of transmission and loudness tonotopic localization denotes that tones of different frequences are represented low tones rosttrolatterlly higher tones caudomedially point to point projections from sites in the cochlea |
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median zone
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supplied by the intrinsic vessels from medial arteries on the ventral surface of brain stem
most central arteries are the longest - supply median plane structures- 1. hypoglossal 2. abducent 3. trochlear, 4. oculomotor nuclei 5. supply the roots that emerge near the median plane - except trochlear 6. medullary pyramids 7. medial corticospinal fibers 8. medial bundles in cerebral peduncle 9. medial longitudinal fasciculus 10. medial lemniscus 11. medial part of inf olive |
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paramedian zone
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branches of vertebrals at the level of medulla
in pons and midbrain arise from basilar and post cerebral a supply: 1. most of inf olive 2. motor paths in basilar pons 3. sensory paths dorsolaterally 4. outer 2/3 of cerebral peduncle in midbrain 4. red nucleus in midbrain |
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lateral zone
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arteries never exted to median plane or floor of 4th ventricle except in pons
supply: 1. root of glossopharyngeal 2. root of vagus 3. tract and nucleus solitarius 4. inf and sup salivatory nuclei 5. nucleus ambiguus 6. trigeminal spinal tract and nucleus 7. spinothalamic tracts 8. vestibular nuclei 9. VTT 10. facial nuc 11. inf cerebellar peduncle 12. upper pontine tegmentum 13. sup cerebellar peduncle 14. laterala lemniscus 15. long ascending tracts greatest number of vascular inj in the brain stem involves arteries of the lateral zone |
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dorsal zone
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go to brain stem structures that form the roof of the ventricular system
supply: 1. tectum 2. nucleus gracilis 3. nucleus cuneatus 4. lateral cuneate nucleus 5. dorsal part of inf cerebellar peduncle 6. dorsal vagal nuc 7. dorsal nucleus solitarius |
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Median medullary syndrome
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structures involved include roots of hypoglossal n
pyramid maybe ML and hypoglossal nuc |
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median mesencephalic syndrome
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strucutres involved
roots of oculomotor n corticobulbar and corticospinal tracts (ventral version) oculomotor nuclei bilaterally (dorsal version) |
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paramedian mesencephalic syndrome
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structures involved are the roots of oculomotor n and red nuc
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lateral medullary syndrome
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root of nuclei of glossopharyngeal n
trigeminal spinal tract and nuc lateral tectotegmentospinal tract LST VTT inf cerebellar peduncle inf and medial vestibular nuclei |
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inferolateral pontine syndrome
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strucutres involved
- roots and facial nucleus - trigeminal spinal nuc and tract - lateral spinothalamic tract - lateral tectotegmentospinal tract |
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superolateral pontine syndrome
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structures involved
- sup cerebellar peduncle - lateral spinothalamic tract - vtt - lateral tectotegmentospinal tract |
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dorsal mesencephalic syndrome
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sup colliculus
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vestibular receptors
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detect orientation
detect mvmts |
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vestibular portions of bony labryinth
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1. 3 semiciruclar canals: ant (sup), post, lat
- at right angles to each other enables them to monitor head mvmts in all spatial planes 2. vestibule - btw semicircular cannals and cochlea - saccule and utricle - contains macula which detect head orientation and linear mvmt suspended in fluid - perilymph of vestibular bony labyrinth isvestibular membranous labyrinth - contains endolymph - semicircular ducts utricle and saccule |
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semicircular ducts
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one in each semicircular cannal
continuous w/utricle of the vestibule - dilated portion = ampulla - vestibular receptor in each ampulla = crista ampullaris - monitors head mvmt - rotation in their spatinal plane - b/c receptors are the main part of vestibular apparatus monitoring head mvmt - kinetic labyrinth |
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utricle
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found in bony vestibule
- contains a vestibular receptor - macula utriculi - |
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saccule
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found in bony vestibule
contains vestibular receptor - macula sacculi - monitor head position- which detects head orientation and detects linear mvmt called - static labyrinth |
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crista ampullares - cupula- rotation of head
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in ampula of semicircular ducts located on a creest of CT in each ampulla
cubpula - originates from apex of crista and extends across lumen of the ampulla filled w/endolymph at rest straight up ( a gelatinous structure) - rotation of head in the plane of the semicrcular duct causes mvmt of the endolymph which deflects the cupula - moves it toward the vestibule - activates hair cells in the crista - causes depolarization - rotation of head in the same plane but in opoosite direction this deflects the cupula in the opposite direction - away from vestibule - inhibiting or hyperpolarizing the hair cells in the crista |
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hair cells of crista ampularis
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receptor cells
- apex of hair cells - hairs( stereocillia and one kinocilium) extend outward and embedded in the cupula - a geletinous structure - kinocilium is always located on the same side relative to the stereocilia - side facing the utricle - base of the hair cells - contain synaptic vesicles and are presynaptic to the peripherial process of the first order vestibular neurons |
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scarpa's ganglion
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aka vestibular ganglion
- first order neurons - bipolar neurons located in the lateral part of the internal auditory meatus - peripherla processes - postsynaptic to hair cells - central processes - form the vestibular portion of CN VIII |
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hair cells fn
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hair cells have a tonic depolarization - always secretion of nt
1. rot of head in plane of semicircular duct produces mvmt in endolymph pushing the cupula in one direction 2. causes bending of the hairs of the hair cells 3. hairs are bent towards the kinocilium - haircells depolarized - activating first order neurons is increased if bent away from kinocillium the hair cells are hyperpolarized and activaation of first order neurons is decreased |
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maculae structure
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macula utriculi and macula sacculi - same structure but utriculi is horizontally oriented and sacculi is vertically oriente
hair cells - receptor cells - apex - hairs (stereocilia and one kinocilium) extend outward and are embedded in a gelatinous otolithic membrane. - the kinocilium is alwayys to one side of the stereeocillia but its exact position varies in diff parts of the macula - base - hair cells are presynaptic to peripherial porcesses of the first order vestibular neurons (cell body's in the vestibular ganglion) - otolithic membrane - contains crystals called otoliths "earstones" otoliths aka statoconia - geatinous membrane - heavier than endolymph = otolithic membrane is heavy |
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maculae fn
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hair cells have tonic depolariztion - constant baseline activation of 1st order neurons
- tilt head in one direction causes the otolithic membrane to siink in the endolymph bending the hair cells - if bent towards kinocilium hair cells are depolarized and activation of neurons is increased - bent away hiar cells are hyperpolarized and activation of neurons decreases - some are hyperpolarized and some are depolarized - CNS decodes this pattern to determine the position of the head linear accelerations of the head- the otolithic membrane will bend hairs of cells due to its inertia and delayed mvmt relative to hair cells - as head movs forward otolithic membran moves backward - as head moves backward otoltiic mmembranemoves forward |
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first order neurons of vestibular system
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innervate both maculae and cristae - scarpa's vestibular ganglion
- bipolar located at the tlat end of int auditory meatus -peripheral postsynaptic hair cells - central processes- form vestibular portion of vestibulocochlear n SSA - runs through int auditory meatus and neters brain stem at pons-medulla jnct - some fibers run along medial aspect of inf cerebellar peduncle and synapse in cerebellum in the focculonodular lobe - vestibular part of cerebellum - most run beneath the inferior cerebellar peduncle and synapse in the vestibular nuclei - travels w/internal labryinthine artery |
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vestibular nuclei
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- 2nd order neurons in the vestibular system
- located medial to the inf cerebellar peduncle in the floor of the 4th ventricle "vestibular area" of 4th ventricle extends from medulla to pons lateral nuc - pons medulla jnct - right where fibers come in inf nuc - many fibers run through it extends well into the medulla - medial to and adjoining the inf cerebellar peduncle - verticcal fibers medial nuc - medial to inf and lat nuc - lacks fiber bundles sup nuc - extends into middle 1/3 of pons - sup to lat and med nuclei |
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outputs of vestibular nuclei
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different from others sensory systems b/c
- projections are widespread - mostly to areas involved in motor fn 1. Cerebellum 2. Spinal cord - lateral vestibulospinal tract - medial vestibulospinal tract 3. nuclei of CN II IV and VI 4. reticular formation 5. thalamus and cortex |
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output of vestibular nuclei to cerebellum
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primary and secondary vestibular fibrers reach this via flocculonodular lobe - vestibulocerebellum)
fn - conveys proprioceptive info abt porientatiuon and mvmt of the ehad to the cerebellum - imp for maintaining balance and regulating posture |
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lateral vestibulospinal tract
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IPSILATERAL
part of the vestibular system - originates in lat vestibular nuc - runs in the ventral funiculus - overlaps vetral spinothalamic tract - terminates in medial portions of ventral horn at all levels of spinal cord fn - maintains equilibrium by reg mm tone of extensor mm ends at upper lumbar levels inj - body, head and chin show deviations |
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medial vestibulospinal tract
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BILATERAL
- originates i nmedial vestiublar nuc - descends in medial longitudinal fasciculus - terminates in medial portions of ventral horn at cervical levels - motor neurons innervating neck and arm mm = fn - regulates mm tone of neck in order to support and stabilize the head during mvmts - vestibulocolic reflex also have projections going course medially, decussates, MLF ends at cervical spinal levels |
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outputs of vestibular nuclei to CN
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II, IV, VI
up MLF - vestibuloocular mvmts to maintain gaze fixed on objects as head mvoes adjusts position of eyes to compensate |
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outputs of vestibular nuclei to reticular formation
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activate:
1. RF neurons giving rise to the reticulospinal tracts - fn - maintains equilibrium by reg mm tone - influence spinal cord motor neurons directly v/vestibulospinal tracts and indirectly via RF ) 2. RF neurons w/projections to visceral nuclei of bs and sc - malfn - causes motion sickness - nausea vomiting, pallor, sweating, salivation etc - excessive stimulation |
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outputs of vesstibular nuclei to thalamus and cortex
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fn - conscious appreciation of body orientation
1. vestibulothalamic tract - bilateral - originates in vestibular nuclei - terminates - ventral post thalamic nuc (VPi) inf division 2. vestibular portions of the VP nuc projects to primary vestibular are aof cortex = poarietal vestibular area - located - rostral intraparietial sulcus just post to postcentral sulcus - when stimulated pts report dizziness and sensation of turning 3. another vestibular area - temporal vestibular area - located on sup temoral gyrus - rostral to auditory cortex - when stimulated pts report dizziness and sensation of turning - not sure how vestibular inf ogets there - sometiems acivated during temporal lobe epilepsiy - dizzy feeling assoc w/ seizure |
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inputs to the vestibular nuclei
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only major input besides vestibular n is cerebellum
fn - permits cerebellum to influence mm tone via vestibulospinal tracts |
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tessting vestibular fn
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several procedures that all involve examining eye mvmts after vestibular stimulation
ex-caloric test and rotatitn chari test - barany chair |
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lesions of labyrinth, vestibular n or vestibular nuclei
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produce similiar signs and symptoms - range from diruption of flow of vestibular impulses along the efferent projection pathways of vestibular nuclei
1. vertigo - conscious sense of rotation - caused by disruption in the trasnsmission of vestibular info to cerebral cortex 2. nystagmus and or deviations of the eyes - caused by diruption in the transmission of vestibular info to the cranial n nuclei innervating eye mm 3. unsteadineess, staggering, and postural deviations - caused by disruption in transmission of vesstibular info to the spinal cord and or cerebellum 4. visceral symptoms - nausea - caused by disruption in transmission of vestibular info to the visceral centers of the reticular formation |
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Reticular formation def
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forms the core of the brain stem and extends through medulla, pons, and midbrain
reticulum means net diffuse but organized network of neurons and fibers that form the core of the brain stem distict nuclei - not discrete clusters areas of RF that have distinct connections and fns |
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reticular formation structure
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3 zones aranged from medial to lateral - extends entire length
1. midline zone - aka raphe - several named nuclei - use serotonin as a nt 2. medial zone - forms medial 2/3 of RF - several named nuclei - very large neurons - provides most of the outputs of RF ("effector zone") 3. lateral zone - lat 1/3 of RF - sml cells - projects axons to medial zone - no significant projections beyond the RF |
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morphology of neurons of reticular formation
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dendrites - very long
- e xtend across much of brain stem in transverse plane fn - individual RF neurons recieve info from many diff tracts passing through brain stem and integrate this info axons - many branches - project widespread regions of the brain and spinal cord fn - individual RF neurons can activate many CNS regions |
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nt of reticular formation
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acetylcholine
monoamines - serotonin/dopamine. norepi DA and NE have similiar chem structure and are termed catecholamines monaminergic neurons are found in special neuron in special nuclei of the RF |
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FN anatomy of RF
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motor fn
visceral fn regulation of consciousness |
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reticulospinal tracts
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motor fn of reticular formation
-origin - medial zone - course - ventral/lat fuiculi of spinal cord - termination - all levels of spinal cord - mostly ipsilateral - synapse w/medial portions of ventral horn and intermediate gray matter btw ventral and dorsal horn fn- maintain posture by influencing activity of motor neurons innervating axial (postural mm) produce gross body mvmts by activating motorneurons innervating axial mm and proximal limb mm several imp motor regions of the brain modulate motor activity by activating the neurons of origin of the reticulospinal tracts - motor cortex via corticoreticular tract - cerebellum, basal ganglia, and vestibular nuclei projection of RF to CN nuclei that is analogous to the reeticulosponal tract |
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ascending vesstibulothalamic tract
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contralateral fibers from sup vestibular nuc to each lateral vestibular nuc
btw medial and lateral lemnisici monosynaptic connection |
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thalamic neurons of the ascending vestibulothalamic path
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VL, VPL, VPi
vestibular projection is sparse but defined bilateral VL and VPL nuc involved in vestibular aspects of motor cooordination VPi - involved in conscious appreciation of vestibular sensaiton |
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parietal vestibular cortex
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primary vestibular cortex
post part of postcentral gyrus at rostral tip of the intraparietal sulcus integrate vestibular and proprioceptive input including thta cased by mvmt and position of mm and joints visual input also plays a role |
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temporal vestibular cortex
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rostral part of the temporal operculum
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posterior insula
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part of vestibular cortex
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motion sickness
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projections to the dorsal vagal nuc influence nonstriated mm of the sotomach and provide for reverese peristalsis
-connections to nucleus solitarius provide for nausea nuc ambiguous underlie frequent swallowing and regurgitiation influence blood vessels and sweat glands to yield pallor and cold sweat phrenic nuc provide nec diaphragmatic mvmts that occuri n vomiting salivatory nuclei provide for excessive salivation |
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visceral fn of the RF
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visceral centers
- certain areas of RF are very imp for controlling specific visceral fns mainly located in medulla and pons centers for CV fn, resp, GI control etc visceral centers produce visceral response by projecting to visceral nuclei of the brains stem and spinal cord - spinal cord - symp and parasymp pregang neurons - brain stem - parasymp and special visceral efferent cranial n nuclei (GVE and SVE) |
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RF and regulation of consciousness
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most imp fn clinically
- vital for maintaining alertness and arousal - ascending reticular activating system ARAS - produces alertness, arousal, and attention by activating cerebral cortex - activates cortex indirectly via a projection to the talamus - reticulothalamic tract - part of CTT (cholinergic) - direct ascending monoamine patways to cortex also contribute to alertness and arousal |
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reticulothalamic tract
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origin - medial zone of the RF - pons and medulla
course 0 CTT of brain stem termination - intralaminar nuclei of the thalamus - different foorm most htalamic nuclei - instead of projecting to specific cortical areas the intralaminar nuclei have diffuse projections to all parts of the cortex thalamocortical projections form intralaminar nuclei -terminate in all areas of cortex = widespread activation of cortex assoc w/alertness, arousal and attention - assoc w/eeg activation |
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what activates ARAS
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1. Somatosensory
- ex - many fibers from the lateral spinothalmic tract terminate in RF - pain is an arousing stimulus - explains why smelling salts can jolt an individual to consciousness - smelling salts iirritate cutaneous endings of trigeminal n in nose - reach RF and activate ARAS 2 also visual, auditory and visceral sensory |
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lesions of RF caused by
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can be caused by:
1. vascular lesions or tumors of BS 2. tumors or hemmorrhages of cerebral hemisoheres causing uncal herniation 3. tumors or hemorrhages of cerebellum causing tonsilar herniation |
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signs of RF lesions
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1. disturbances of consciousness - most common
- caused by damage to ARAS - drowisiness to coma depending on severity to fleeting periods of unconsciousness to sleep 2. changes in mm tone and postural reflexes - caused by damage to reticulospinal tract - decerebrate rigidity seen w/midbrain lesions 3. disturbances in visceral fn - caused by damage to visceral centers and their pathways - disrupted CV and/or resp fn can be lifethreatening |
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serotonergic patways of RF
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fxns - descending pain inhibition
- ascending - sleep and mood 1. location of mneurons - midline raphe 2. projections - widespread - to cerebral hemispheres - imp for sleep and mood - to spinal cord - imp for pain inhibition |
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noradrenergic pathways of RF
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fxns - ascending - mood, attention, memory
location - several cell groups in RF of pons and medulla including locus ceruleus - upper pons - locus ceruleus - bloe spogn - visible in gross brain - projections - widespread - cerebral hemispheres - imp for mood, memory, attention |
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domaminergic pathways of reticular formation
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location - substantia nigra, ventral tegmental area medial to SN
projections - more restricted than those of serotonin and NE - substantia nigra to caudate and putamen 0 imp for motor fn - lesion = parkinsons Ventral tegmental area to forebrain areas involved in emotion (amygdala, prefrontal cortex, and the nucleus accumbens of the ventral striatum) - imp for bh and emo - excess dopamine release in prefrontal cortex and amygdala is assoc w/schizophrenia dopamine release in nucleus acucumbens is critical for pleasurable effects of addictive drugs fn - nigrostriatal - motor and mesolimbic -- bh and emotion |
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visceral fn of the RF
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visceral centers
- certain areas of RF are very imp for controlling specific visceral fns mainly located in medulla and pons centers for CV fn, resp, GI control etc visceral centers produce visceral response by projecting to visceral nuclei of the brains stem and spinal cord - spinal cord - symp and parasymp pregang neurons - brain stem - parasymp and special visceral efferent cranial n nuclei (GVE and SVE) |
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RF and regulation of consciousness
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most imp fn clinically
- vital for maintaining alertness and arousal - ascending reticular activating system ARAS - produces alertness, arousal, and attention by activating cerebral cortex - activates cortex indirectly via a projection to the talamus - reticulothalamic tract - part of CTT (cholinergic) - direct ascending monoamine patways to cortex also contribute to alertness and arousal |
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reticulothalamic tract
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origin - medial zone of the RF - pons and medulla
course 0 CTT of brain stem termination - intralaminar nuclei of the thalamus - different foorm most htalamic nuclei - instead of projecting to specific cortical areas the intralaminar nuclei have diffuse projections to all parts of the cortex thalamocortical projections form intralaminar nuclei -terminate in all areas of cortex = widespread activation of cortex assoc w/alertness, arousal and attention - assoc w/eeg activation |
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what activates ARAS
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1. Somatosensory
- ex - many fibers from the lateral spinothalmic tract terminate in RF - pain is an arousing stimulus - explains why smelling salts can jolt an individual to consciousness - smelling salts iirritate cutaneous endings of trigeminal n in nose - reach RF and activate ARAS 2 also visual, auditory and visceral sensory |
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lesions of RF caused by
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can be caused by:
1. vascular lesions or tumors of BS 2. tumors or hemmorrhages of cerebral hemisoheres causing uncal herniation 3. tumors or hemorrhages of cerebellum causing tonsilar herniation |
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signs of RF lesions
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1. disturbances of consciousness - most common
- caused by damage to ARAS - drowisiness to coma depending on severity to fleeting periods of unconsciousness to sleep 2. changes in mm tone and postural reflexes - caused by damage to reticulospinal tract - decerebrate rigidity seen w/midbrain lesions 3. disturbances in visceral fn - caused by damage to visceral centers and their pathways - disrupted CV and/or resp fn can be lifethreatening |
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serotonergic patways of RF
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fxns - descending pain inhibition
- ascending - sleep and mood 1. location of mneurons - midline raphe 2. projections - widespread - to cerebral hemispheres - imp for sleep and mood - to spinal cord - imp for pain inhibition |
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noradrenergic pathways of RF
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fxns - ascending - mood, attention, memory
location - several cell groups in RF of pons and medulla including locus ceruleus - upper pons - locus ceruleus - bloe spogn - visible in gross brain - projections - widespread - cerebral hemispheres - imp for mood, memory, attention |
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domaminergic pathways of reticular formation
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location - substantia nigra, ventral tegmental area medial to SN
projections - more restricted than those of serotonin and NE - substantia nigra to caudate and putamen 0 imp for motor fn - lesion = parkinsons Ventral tegmental area to forebrain areas involved in emotion (amygdala, prefrontal cortex, and the nucleus accumbens of the ventral striatum) - imp for bh and emo - excess dopamine release in prefrontal cortex and amygdala is assoc w/schizophrenia dopamine release in nucleus acucumbens is critical for pleasurable effects of addictive drugs fn - nigrostriatal - motor and mesolimbic -- bh and emotion |
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macula lutea
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yellow spot 5mm in diameter located central portion of retina in w/ visual axis
- therefore an objec int the center of the visual field (the object that the eye is looking at is projected onto the maucula lutea depression in the center of the macula lutea - fovea - so you don't have to go through so many layers in the retina -specific layers of the retina are diverted to the sides to make the depression of the fovea- exposes photoreceptors for greater visual acuity |
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optic disc
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akapapilla- medial to maculae lutea
- raised area where the opticn collects w/ retiea - no photoreceptors = blind spot aa and vv of retina enter and exit at opticdisc optic n surrounded by meningies - derived from neural plate -dura blends w/sclera - also surrounding the optic n is extension of subarachnoid space filled w/CSF increase in intracranial pressure due to tumor growing in cranial cavity - are transmitted to the CSF surrounding the optic n - interveres w/venous oputflow from retina and produces a swelling of optic disc = chocked disc or papilledema - imp sign of increased intracranial pressure central a and v go through n |
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rods
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lacking in fovea - more and more numerous as move to more peripherial parts of retina rots outnumber cones in the retina by 20:1
more sensitive to light - allow us to see in dim light not capable of color vision synapse w/bipolar cells |
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cones
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distributioniss opposite that of rods - the fovea cont only cones number of cones gradually dec in more peripheral parts of the retina
- involved in discriminative aspects of vision - visual acuity 3 types - each sensitive to diff wavelengths of colors of light - red/green/blue - lack of one or more types = color blindness synapse w/bipolar cells |
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bipolar cells
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primary neurons pof visual system
intraneurons - including axonless amacrine cells - also found in bipolar cell layers synapse w/ ganglion cells of retina |
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ganglion cells
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secondary neurons of visual system
axons of ganglion cells course along inner surface of retina and converge at optic disc to form optic n (CN II) |
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cells of retina
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rods, cones, bipolar cells, ganglion cells
light must go through innner layers of retina to reach photoreceptors these layers |
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retinotopic organization
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precise point -to -point topographical organization to the visualsystem which extends fro m the retina all the way to the visual cortex
- lesions in diff parts produce very characteristic visual deficits |
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visual field
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extent of the external world seen by the eye when the gaze of the eye is fixed
- test each eye separately using sophisticated perimetry devices or by confrontational method |
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confrontational meethod
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face pt have pt cover one eye and have pt fix the gaze of the of the uncovered eye on your nose
wiggling fingers and gradually bring them into the visual field pt tells you when the ycan first see fingers test each quadrent separately upper nasal, upper temporal lower nasal lower temporal |
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lens and image
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lens inverts visual image
therefore the nasal half of visual field projects to the temporal half of the retina temporal half of visual field projects to nasal half of retina upper half of visual field projects to lower half of retina lower half of visual fiel projects to upper half of retina |
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visual pathway n -> tract
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1. optic n
- fibers all originate in retina on that side - fibers are retinotopically organized 2. optic chiasm - fibers from nasal half of retina (representing temporal half of visual field) cross to reach contralateral optic tract - fibers from temporal half of retina - representing nasal half of the visual field do not cross - pass through the lateral portions of the optic chiasm and enter the ipsilateral optic tract 3. optc tract - - runs from optic chiasm to lateral geniculate nuc of dorsal thalamus - each optic tract contains fibers carrying info from nasal visual field of the ipsilateral eye and temporal visual fild of the contralateral eye each optic tract conveys info from the contralateral visual field of both eyes let optic tract has a representation of the right visual field of both the left and right eyes |
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visual pathway lateral geniculate nuc of the thalamus
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- recieves info from the opposite visual field of botheyes via optic tract
- projects to the ipsilateral primary visual cortex via the geniculocalcarine tract("optic radiations" - fibers course through a portion of the internal capsule located behind the lenticular nuc - retrolenticular portion of of internal capsule - some fibers loop forward into temporallobe before coursing back to visual cortex = meyers loop go to primary visual cortex area 17 |
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primary visual cortex
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area 17
located on upper and lower lips of the calcarine sulcus aka striate cortex - stripped - b/c contains prominant stripe of myelinated fibers since visual cortex recieves fibers from ipsilatteral lateral geniculate the visual cortex contains a representation of the contralateral visual field representation of the visual fields - lower half of the contralateral visual field projects tothe upper lip of the calcarine sulcus upper half of the contralateral vissulal field projects to the lower lip of the calcarine sulcus - it is the fibers to the lower lip that course through the loop of meyer macular portion of the retina - center of visual field projects to the caudal 1/3 of the visual cortex more periperal parts are representedin the rostral 2/3 |
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lesions of the visual system
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most visual disturbances are caused by dx of the eye and lens not by dx of the CNS - glaucoma and cateract
b/c topographical organization of the visual pathway lesion at various points along the pathway produce very distinctive visual field defects - |
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monocular blindness
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lesion of optic n to one eye
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bitemporal hemianopsia
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tunnel vision
cant see temporal visual field of either eye lesion of optic chiasm |
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homonymous hemianopsia
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same half of each visual field is missing
caused by lesion in the optic tract - contralateral to half of vision missing can't see L visual field = R optic tract inj |
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upper quadrant anopsia
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due to lesion of meyers' loop on contralateral side
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optic n lesion
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only ipsilateral eye has visual field defects = lesion in front of optic chiasm
complete lesion = blindness partial lesion = sml blindspot = scotoma |
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optic chiasm lesion
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bitemporal hemianopsia = lack of sight in the temporal visual fields of both eyes
damage to fibers from nasal halves ofboth retinas crossing in opticchiasm common cause - pituitary tumor -b/c pituitary stalk right behind it = this + headache |
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optic tract lesion
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contralateral homonymous hemianopsia
homonymous defect = defect that involves the same side ofthe visualf field of both eyes defect is contralateral b/c it is contralateral visual field which is represented in optic tract and optic radiations and visual cortex |
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lesions of optic radiations and visual cortex
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usually incomplete contralateral homonymous hemianopsia since lesion usually involve only part of the structures
- ex loop of meyer complete lesion of visual cortex would be expected to produce a contralateralhomonymous hemianopsia - w/central part of visual field which projects upon macular part of the retina is spared - macular sparing |
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olfactory systems receptor/modality
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forms rhinencephalon
modality - smell SVA Receptors - olfactory system are also the first order neurons - olfactory receptor cells - of olfactory epithelium located on the roof of the nasal cavity or just below the cribiform plate of the ethmodi bone -ORC - bipolar neurons that differentiate from basal cells - constant turnover -life span 4-6 weeks |
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peripheral processes of the ORC
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extend to the epithelial surface where they form a dilation - olfactory vesicle - that gives rise to several long nonmotile cilia
-cilia posess membrane prot that are receptors (olfactory receptor proteins) for odorous chem - many diff olfactory receptor proteins - thought that the odor of a substance is due to the differential activation of different classes of olfactory receptor proteins - perhaps located on a distinct subpop of olfactory receptor cells binding of odorants to olfactory receptor protein depolarizes the ORCs via a g-protein receptor mediated mech - linked to the opening of ion channels some individuals are odor blind for specific odors due to the lack of specific subtype of olfactory receptor protein |
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central processes of the ORC
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form axons that pass through the holes of the cribriform plate in thin buncles called olfactory fila - which constitute the olfactory n (CN I) enter the olfactory bulb and synapse wit the second order neurons of the olfactory system (mitral cells)
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mitral cells
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second order neurons of the olfactory pathway - in olfactory bulb
- olfactory nerve axons synapse w/the tufted end of the apical dendrites of mitral cells in spherical structures called glomeruli - axons of mitral cells form the olfactory tract which courses through the olfactory stalk - not to be confused w/olfactory n - to reach several olfactory areas in cerebral hemispheres also GABAergic inhibitory interneurons in the olfactory bulbe -- granule cells and periglomerular cells - actually granule cells outnumber the mitral cells - granule cells have no distinguishable axon - their processes fn as both dendrites and axons - they form dendodendritic synapses w/lateral dendrites of mitral cells |
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olfactory tract
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runs through olfactory stlak and splits ot form the medial and lateral olfactory stria which outline the olfactory trigone
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medial olfactory stria
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a branch of the olfactory tract
some fibers in this stria may synapse in the medial portions of the olfactory trigone other fibers may course towards the septal region and then run through the ant commisure to reach the contralateral olfactory bulb |
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lateral olfactory stria
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most fibers from the olfactory tract enter this stria
terminate in 2 main cerebral olfactory areas that appear to be involved in the conscious appreciation of olfactory stimulation: a. olfactory cortex - located along the surface of the olfactory trigone and in the temporal lobe near the uncus b. amygdala - superficial (corticomedial) part of the amygdala located along the sup (hidden) surface of the uncus |
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temporal lobe epilepsy and uncinate fits
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TLE is the most common type of epilepsy
since it involves abn activation of the cortex and amygdala in the region of the uncus it is often assoc w/olfactory hallucinations - usually the perceived odors are unpleasant - burnign smell and occur just prior to the onset of the seizure |
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output targets of the cerebral olfactory areas
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1. hypothalamus
- from olfactory cortex via the medial forebrain bundle which runs along the base of the brain from the region of the septum and olfactory trigone through the hypothalamic region - from the amygdala via stria terminalis runs along the medial aspect of the tail and body of the caudate - in response to olfactory stimulation the hypothalamus can generate visceral responses (salivation) and behavior responses (feeding) via it's connections w/the brian stem 2. orbital surface of the frontal lobe - imp in odor discrimination via direct projections from the olfactory cortex and indirect projections via relay in the dorsomedial nuc of the thalamus |
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testing of the olfactory system
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each nostril tested separately
closing the oposite nostril determien if pt can detect odors - coffee, sinnamon, lemon and tobacco) the inability to smell - anosmia may be more awayre of loss of taste since flavor of food is highly dependent on odor |
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comon lesions producing anosmia
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most common = head cold w/inflammation of nasal mucosa
olfactory groove meningioma - benign tumor in the floor of the ant cranial fossa that can damage the olfactory bulbs and olfactory tract fracture of the cribriform plate - common in automobile accidents and othere head trauma - result in severing of the olfactory n fibers - smell may be restored as the olfactory receptor cells turnover and contribute new axons to the olfactory fila |
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gustatory system
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modality - taste SVA
taste buds, which contain gustatory receptor cells are found on the dorsum and sides of the tounge as well as on the epiglottis, soft palate, and pharynx 1000's of taste buds on one papille taste buds w/particular sensitivities (sweet, sour, salty, bitter, unami) are concentratted on particular parts of the tounge where they are found on various types of papillae (foliate fungiform, circumvallate |
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bittter
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back of tounge
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sour
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side of tounge
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sweent/ unamai
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front half of tounge
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salty
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very tip and sides of front half of tounge
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gustatory receptor cells
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formed by differentiation of basal cells - constant turnover
life span = 2 weeks - apical part of cell - has microvilli that extend into taste pore which are sensitive to substances dissolved in saliva - individual taste buds and their gustatory receptor cells are differnetially sensitive to at least 5 primmary tastes - sweet, sour, salty bitter, unami (aa, including monosodium glutamate) - taste of a substance is due to the different proportions of the four primary tastes that it contains - much of what we norm consider tastes is actually flavor which depends on the integration of taste and smell transduction mech for activating (depolarizing) diff gustatory receptors: 1. salty : sodium ions enter the cell via sodium channels 2. sour - acidic - H ions enter the cell via H ion channels 3. sweet, bitter, umamo - activation of G-prot coupled receptors which open ion channels via second mesangers basal part of cell - oresynaptic to peripherial processes of first order neurons of the gustatory system - depolarization of the gustatory receptor cell results in release of transmitter which activates a first order neuron |
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first order neurons of gustatory pathway
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ganglion ceslls of cranial nn VII, IX, X
VII - taste buds on ant 2/3 of tounge IX - taste buds on post 1/3 of tunge including circmvallate papillae X taste buds on epiglottis and pharynx |
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second order neurons of the gustatory pathway
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gustatory nuc - rostral part of the nucleus solitarisus
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ascending gustatory pathway
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origin - gustatory nuc
course - CTT - ipsilateral 2 main targets of termination - hypothalamus - taste info can be integrated w/olfactory input from cerebral olfactory areas - influences feeding centers of hypothalamus - medial (small celled) part of VPM - the gustatory -related medial VPM projects to gustatory area of cortex located in and around area 43 at base of central sulcus - adjacent to somatosensory representation of tounge - also extends on to the dorsal insular cortex - these cortical areas are involved w/the consious appreciation of taste - irritative lesions near the gustatory cortex can cause seizures sthat are preceded by gustatory hallucinations - a disagreeable taste) |
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gustatory tsting
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have pt stick out tounge and apply a cotton swab moistened w/ dilute solns of sugar, salt, quinine, or vinegar.
test each side of the toungue separately inabillity to taste = ageusia partial loss of taste - hypogeusia - more common |
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unilateral loss of taste
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commonly occurs w/lesions of facial n
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bilateral loss of taste
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may occur in cancer pts undergoing chemo and in pts w/ diabetes
taste acuity usually declines naturally after age 50 |
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parasympathetic innervation of the eye - preganglionic neurons
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edinger-westphal nuc - sometimes called the accessory oculomotor nucleus
pregang fibers run in the oculomotor n - synapse in the ciliary ganglion |
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parasympathetic innervation of the eye - postganglionic neurons
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ciliary gangilion
post gang axonxs innervate sphincter pupillae mm and ciliary mm - sphincter pupilae constricts pupil (miosis - if abn ) - contraction of ciliary m reduces the tension in the suspensory lig of the lens - the lens, in turn, is able to assume a rounder shape - increase s the refractile poer of the lens for close vision - accomodation of the lens |
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pupil size
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due to the balance of the actions of sphicter pupillae (parasymp) and dilatory pupillae (sym) ( called mydriasis if abn)
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pupillary light reflex testing
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shine light into one eye this should result in papillary constriction in the illuminated eye (direct light reflex/ direct response ) and the other as well "consensual light reflex or consensual response"
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anatomical basis of the pupillary light reflex
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retinal projections to pretectal area
- branches of some fibers in optic tract bypass the lateral geniculate and course to the pretectal area via a fiber bundle called the branchium of the sup colliculus - the pretectal area is just in front of the sup colliculus (tectum ) and adjacent to the post commisure - pretectal area projects to edinger-westphal nuc - edinger -westphal nuc innervates sphinceter pupillae mm via the ciliary ganglion 2 reasons why direct and consensual response are obtained 1. optic n fibers reach both ipsilateral and contralateral pretectal area bc some cross in chiasm and some dont 2. each pretectal area projects t both ipsilateral and contralateral edinger-wetphal nuc carried out by oculomotor n |
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lesion of optic n in right eye and pupillary light reflex
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illuminate right eye
- direct response - no - consensual response in L eye - no illuminate left eye - - direct response = yes - indirect response = yes |
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lesions of oculomotor n in R eye and pupillary light reflex
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illuminate right eye
- direct response - no - consensual response in L eye - yes illuminate left eye - - direct response = yes - indirect response = no this lesion may also cause ipsilateral ptosis, abduction, limitations of eye mvmt, dilation (mydriasis) as well as diplopia |
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accomodation -convergence reflex testing
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aka near reflex
ask pt to keep eyes fixed on your finger - held abt 5 feet from pts face then bring your finger w/in one foot of pts face 3 things should happen: 1. convergence of eyes - contraction of medial rectus mm - nec to maintain gaze on close object 2. accomodation of lens - contraction of ciliary m - rounding up of lens inc its refractile power this is nec tot maintain focus on a close up object 3. pupillary consstriction - contraction of sphincter pupillae mm - sharpens image of close object on retina- light coming through peripheral portion of the lens is brought to a diff focal point than light going through central poriton of lens. this discrepancy is accentuated when objects are close to the lens. pupillary constriction eliminates peripheral light from reaching lens and retina) |
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anatomical basis of accomadation-convergence reflex
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1. activation of visual cortex by retina
2. visual cortex projection to pretectal area and or sup colliculus via internal capsule and brachium of superior colliculus 3. activation of edinger-westphal and oculomotor nuc 4. contraction of sphincter pupillael cilliary, and medial rectus retina -> LGN->visual cortex --via optic radiations and brachium of SC --> pretectal area a/o sup colliculus -> oculomotor nuc -> CN III -> medial rectus -= convergence sup colliculus -> edinger wetphal nuc - > CN III -> ciliary ganglion -> sphinct pup - pupillary constriction and ciliaryy mm -> accommodation bilateral - involves both eyes |
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lesion of cn III
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loss of reflexon the side of the lesion
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argyll-robertson pupil
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after the accommodation-convergence reflex involves many of the same nuclei and fiber bundles as pupillary light reflex there are diff
it is possible to have pupils which constrict when tested for accommodation-convergence reflex - but which don't constrict when tested for the pupillary light reflex commonly seen in syphilis when CNS is involved also seen sometimes in diabetes and multiple sclerosis |
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anatomy of pupillary dilation and the sympathetic innervation of the eye/face
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pregang neurons - interomediolateral cell column (T1-T3)
- pregang fibers course up symp trunk postgang neurons - sup cervical ganglion - post gang fibers surround internal carotid a and ascend to orbit and other parts of face and head - innervate: - dilator pupillae mm - tarsal mm - part of levator palpebral mm - sweat glands of face also innervated - tonically active |
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lesions that interrupt sympathetic innervation innervation of head
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like innervation of symp trunk = horner's syndrome
Ipsilateral of lesion symptoms: 1. miosis - norm the pupillary dilation caused by symp innervation is balanced by the pupillary constriction casued by the parasympathetic innervation. interruption of symp innervation leaves the constriction of parasymps unchecked - 2 pupils not of equal size = anisocoria 2. ptosis - drooping of the eyelid due to interruption in symp innervation of tarsal mm- partial ptosis 3. anhydrosis - lack of sweating of face |
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lesions that can cause a horner's syndrome
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1. lesions of the pregang fibers passing adjacent to the apex of the lung towards the symp trunk (lung cancer) or in the cervical part of symp trunk (due to trauma such as knife or bullet wonds)
2. lesions of the postgang fibers running in the wall of the internal carotid aa - due to atherosclerotid lesiosn of a 3. lesiosn of the lateral part of reticular formation - there is a descending sympathetic pathwya also called the lateral tectotegmentospinal tract that maintains tonic activation of sympathetic tone - this pathway may originate in the hypothalamus since it courses through lateral parts of the brain stem - lesions in the region often produce a horner's syndrome |
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optic n
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has several parts including
intraocular intraorbital intracanalicular intracranial part each one contains 1.1 mil fibers w/ variability btw nerves age related dec occurs in axonal number and density as well as photoreceptors over 40 |
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papillomacular bundle
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fibers from macula grouped together on lateral side of orbital part of optic n immediately behind eyeball
- esp vulerable to trauma or tumor shift to center of optic n as they approach chiasma |
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paramacular fibers
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fibers from retinal areas surrounding the macula are grouped together
- remaining peripherial fibersform peripherial retinal areas are grouped together peripheri=y in the n |
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optic chiasma
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indents the anteroinferior wall of 3rd ventricle
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lateral geniculate nuclei
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almost a 1 to 1 ratio btw optic tract fibers and lateral geniculate somata such that practically all the retinal ganglionic neurons synapse w/lateral geniculate somata
also a direct bilateral projection from the retina to the mesencephalic pretectal area and a direct retinal projection to to the sup colliculus - non geniculate connections imp for visual reflexes |
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geniculocalcarine tract
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optic radiations from lateral geniculate uc to primary visual cortex - area 17
axons from medial half of the lateral geniculate nucleus pass post to the sup lip of calcarine sulcus the gyrus below the calcarine sulcus is the lingual gyrus that becomes cont w/the parahippocampal gyrus and the gyrus sup tothe calcrine sulcus is the cuneus lat half of the lateral geniculate nuc carying impuses from inf retinal quadrents arch into rostral temporal region then extend as far forward as the tip of the temporal horn to abt the plane of the uncus then rich the inf lip of the calcarine sulcus - temporal loop of optic radiations ends along the calcarine sulcus of the occipital lobe = primary visual cortex area 17 fibers from macula end most posteriorly paramacular retina and peripheral retina end most anteriorly |
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primary visual cortex
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aka striate area
- sup and inf lips, banks, and depths of the calcarine sulcus of the occipital lobe surrounded by secondary or extrastriate visual areas 18 and 19 amt of myelin in the stria gradually reduces beginning in the 3rd decade - also occurs w/blindness , alzheimers or multiple infarct dementia |
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visual path
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great length - vulnerable to demyelinating dx
like MS<tumors of brain or pituitary , vascular lesions of the middle and post cerebral arteries and head inj |
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7 primary odors
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camphoric
muscky floral mint ethereal pungent putrid can judge odor qualitiy strength and pleasurable aspects |
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olfactory epithelium
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mucuous membrane of nasal cavity w/ olfactory receptor cells
- bounded by sup nasal concha and upper third of the nasal septum - olfactory receptal cells - axonal parts are unmyelinated => olfactory fila enter the olfactory bulb at the tip and along the ventral surface |
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medial olfactory stria
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synapse in course then project toward medial hemisphere wall - reach medial ant perforated substance before entering ant commisure
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lateral olfactory stria
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lat part of ant perforated substance
amydaloid body and ant insula |
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stria terminalis
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interconnects the corticomedial amygdala in temporal lobe w/hypotahlamus and subcallosal area
precommisural fibers turn infront of the ant commisure to reach subcallosal area postcommissural fibers turn behindant commisure to enter hypothalamus |
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orbitofrontal cortex
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3 prprimary olfactory corticcal areas including the
orbitofrontal cortex - post and lat spects - involved in discrimintion of odors inferior temporal gyrus and ant insula |
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dysosmia
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destorted sense of smell
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fungiform papillae
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on front of the tongue that contain 3-5 taste buds - sweet sensitive
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foliate papillae
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lateral border off the posterior tongue
1280 taste buds make up 1 sensitive to salty andsour tastes |
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circumvallate papillae
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post tounge
1000 taste buds on each - bitter |
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gustatory nucleus
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dorsal visceral gray aka gustatory part of solitary nuc
- fibers of facial n carrying gustatory impulses terminate in the rostral 1/3 of the gustatory nuc fibers of glossopharyngeal nerve IX carrying gustatory impulses terminate in the intermediate 1/3 of the gustatory nuc and ifbers of the vagal n carrying gustatory impulses terminate in the caudal 1/3 of gustatory nuc |
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ascending gustatory tract
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1. gustatory part of solitary nuc
2. ipsilateral ascends as CTT 3. terminating in parvocellaular part of VMpc 4. leave the level of sup colliculus of midbrain to enter hypothalamus - where olfactory and gustatory impulses correllated ipsilateral tract that travels in pontine tegmentum and dorsomedial mesencephalic tegmentum might cross in midbrain to reach contralateral dorsal thalamus |
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secondary ascending gustatory path
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thought to terminate in teh ventroposteromedial nuc of dorsal thalamus particularly in parvocellular part VPMpc
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parageusi
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perversions of taste or confusion abt taste
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decibel scale
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120 = painful - jet taking off
90 - very noisy - tracter trailer 70 - noisy - inside compact car 50 - moderate - avg class room 30 - quite - bedroom at night 10 - barely audible - soft whisper |
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fn of auditory system
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identification
localization communication |
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physical properties of sound
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sound waves
1. produced by vibrating objects which cause alternating phases of compression and rarefactions - basic sine wave frequency and amplitude characterize sound waves in air = 330 m/sec in water 1500 m/sec |
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4 features of waves
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1. waveform
2. phase 3. amplitude - sml amplitude = spft sound - high amplitude = loud sound 4. frequency - low freauency - low pitch - deep voice - high frequency - high pitch - squeeky |
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frequency
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measured in Hz hertz
human hearing ~20-20,000 Hz speaking voice 2,000 -5,000 Hz babies hear a little higher- loose high frequency hearing |
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doppler shift
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change in percieved pitch due to mvmt
frequency of sound changes when the sound source is moving pitch goes up as it moves toward u and then goes down as it moves away increased frequency = increased pich |
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intensity
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measured in decibels dB
dB = 20 x log Psound /Pthreshould for human hearing ratio to a subjective intesnity rather than arbitrary intensity as a base - sound pressure > 80 dB can be painful and damaging to auditory receptors sound pressure during norm conversation are 1000 times as great as threshold or 60 dB |
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auditory transduction
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outer ear - funnels sound and converts sound into physical vibration
middle ear- transmits vibrations to inner ear inner ear - converts fluid mvmts into neural firing receptor cells depolarize create an action pot and the more the AP the greater amt of nt they release |
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pinna
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filters frequencies to identify sound sources
- in lower animals - moved in direction of sound - in humans - little mvmt shape helpsto discern the source of sound in front vs behind head |
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external auditory canal
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amplifies 30-100x frequencies around 3k kHz (norm speech=)
some sounds are amplified better than others amplification greatet at 2-5 kHz speech range - sounds <20 Hz or >20,000hz are not amplified |
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impedence matching
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impedence = describes a mediums resistance to mvmt
sound waves in low impedance air to much higher imedence fluid - in middle ear occurs byboosting the pressure measured at tympanic membrane almost 200 fold by the time it reaches the inner ear - tympanic membrane is abt 17 times the size of the oval window - mechanical lever movement of the oscilles - forceful displacement of stapes against the oval window to move fluid in the cochlea (a 300lb gorilla wearing high heels) |
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intensity control
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dampens high intensity/pressure sounds
lever action of the ossicles middle ear mm - reduce sound pressure amplitude - deceases the mobility and transmission properties of the ossicles - mm contract reflexively in response to intense sounds - reduce sound pressure amplitude via decreasingmobility and transmission properties of the ossicles = decreases pressure of sounds reaching the inner ear tensor tympani mm - trigeminal n -> malleus stapedius m - facialn - > stapes contraction occurs just prior to vocalization and chewing |
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middle ear
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amplification
impedence matching intensity control |
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cochlea
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transfers sonically generated pressure waves into neural impulses
- two membranes divide the cochlea int o 3 compartments 2 are filled w/ perilymph - low K+, high Na+ 0 mV extracellular fluid 1 is filled with endolymph - high+ low Na+ - 80 mVintracellular fluid inner hair cells - 45 vibrating middle ear bones impacting on the oval window cause the fluid w/in thecochlea to virate this vibration stimulates the auditory receptors - hair cells on organ of corti |
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organ of corti
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2 groups of haircells lie onthe basiliar membrane
1. inner layer ofsingle row of hair cells - fine auditory discrimination - > 90 % of auditory n fibers innervate these cells 2 outer layer -consists of 3 rows of hair cells - detecting the presence of sound - 10% of auditory n fibers |
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auditory transduction
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in and out motion ofthe oval window is converted into an up and down motion of the basilar membrane displacing the stereocilia and opening stretch activated K+ channels
organ corti - down i. stereocillia - toward limbus ii. result = K+ channel closes iii hyperpolarization - Ca_ close organ corti - up i. stereocillia - away from limbus ii. result = K+ channel opens iii depolarization Ca+ flows in |
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tonotopy
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sound frequency sorts along the basilar membrane
the frequency of sound that activates a particular hair cell depends on the location of the hair cell along the basilar membrane - basilar membrane is the narrowest and stiffest at the base of the coclea near the oval and round window s and most complant at the apex of the coclear high frequency sounds passes through the organ of corti near the base of the coclea low frequency sounds pass through the organ of corti near the apexof the cochlea encoding frequency (pitch) - the auditory n fiber activated by a particualr frequency is similarly dependent on the location of the hair cell it innervates - low frequency - auditory n fiber can fire at same frequency as the sound wave - higher frequency pitch is coded based on tonotopy - placement - end of coclea is most complient |
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presbycusis
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loss of high frequency sounds
loss of hair cells at the base of the cochlea |
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intensity or loudness
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coded by the number of fibers activated
as intensity of sound inc a larger portion of the basilar membrane is vibrating so that more auditory n fibers are activated |
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tonotopy of CNS
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on primary auditory cortex
w/ lowest frequency most ventral and largest dorsal ventral - apex of coclhea dorsal - base of cochlea |
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localization < 3 kHz
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<3kHz
interneural time differnces 1. sound reaches L ear first if 2. action pot begins traveling in MSO -medial superior olive 3. sound reaches right ear a little faster 4. AP begins traveling to MSO 5. APs converge on MSO neuron that responds most strongly if their arrival is coincident |
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localization >2 kHz
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1. stronger stimulus to L ear excites L LSO
2. this stimulates also inhibits right LSO via MNTB interneuron 3. excitation from L side is greater than inhibition form right side - excitation to higher centers 4. inhibition from L side is greater than excitation from R side resulting in net inhibition on right - no signal to higher centers LSO - lateral superior olive MNTB - medial nucleus of the trapezoid body |
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tinnitus
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ringing in the ears
irritative stimulation of inner ear and/or vestibulocochlear n |
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conductive hearing loss
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- damage to external or middle ear
-lower the efficacy at which sound energy is transferred to the inner ear - external hearing aids fn to boost sound pressure levels |
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sensorineural hearing loss
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causes- congenital, infection of the inner ear, acoustical trauma, ototoxic drugs, presbyacusis (the hearing of the old)
hair cell death or damage to the 8th cranial n cochlear implants use an electrode array to stimulate the cranial n |
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function of the visual system
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create a mental image of the external world
a. image formaiton b. transduction- light energy into electrical signal c. encoding of image d. perception c. |
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optic principles
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optic principles :
light rays travel in all directions convergering lenses focus rays of light divergening lenses scatter rays of light parallel rays of light entering a converging lens will converge at the focal point |
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cornea
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along with the lens provide converging power of the eye
avascular, transparent, pouter surface of the eye refractive power 2/3 of refractive power of the eye cannot be altered physiologically |
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glaucoma
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increased formation of the aqueous humor or blockage of outflow increases intraocular pressure
affects cornea |
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lens
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avascular transparent
refractive power - under physiological control accomodation |
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accomodation
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eye forms an image of an object on its retina by the process of accomodation - adjusting the refractive power of its lens
accomodation reflex - bulging of the lens - pupillary constriction - convergence lost with normal aging - presbyopia fornear things |
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cataracts
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opacities that develop as an individual ages on the lens
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myopia
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nearsightedness
-cornea is very steep - focal distance < distance to the retina - focal point is in front of the retina - distant objects are not focused on the retina - reduce the converging power of the eye w/diverging lens - normal in kids - out grow eye - runs in families |
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hyperopia
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cornea is too flat
- focal distance>distance to retina -focal point is behind retina - near objects are not focused on the retina - increase the converging power of the eye w/ a converging lens - born with it - but can accomodate when young b/c lens is so flexible - but when get older can't accomodate |
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astigmatism
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cornea is oval instead of spherical
- light focuses on more than one point in the eye resulting in blurred vision at distance or near - corrected by lenses or lasix |
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lasix surgery
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1. a micro keratome cuts a flap of superficial cornea
2.a laser beam is applied to sculpt the core to precise shape 3. flap is then settled back in position and it adheres on its own |
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morphology of retina
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6 layers
5 types of neurons bottom layer = photo receptors - pigmented epithelium - photopigment and membraneous disc |
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image formation
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cornea and lens
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cells of retina
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1. photoreceptors - rods and cones
2. bipolar cells 3. ganglion cells 4. horizontal cells 5. amacrine cells |
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anatomical distribution of photoreceptors
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retina - rods>>>cones
fovea diameter 1.2 mm cones>>>rods foveola = 300 micros - NO RODS 90 mil rods 4.5 mil cones cones - high acuity - concentrated in the foveola - no response toscatered light - response to light is quick |
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photopigment
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rods - phodopsin (blue-green)
cones - S cones have S opsin: blue M cones have M opsin: green L cones have L opsin: red |
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color deficiences
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missing L cones (4/100 males 1/400 females) 0 red color blindness long - wave length l opsin
RED AND GREEN X linked MEN MORE THAN WOMEN missing M cones (4/100 male 1/400 females) - green color blindness - m opsin- medium wave length missing S cones ( 1/20,000) - blue color blindness -s opsin - short wave light |
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rhodopsin
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opsin+retinal ( from vitamin A)
-when light hits retinal 11 cis retina -> alltransretinal => metarodopsin cis to trans photisomerization = metarhodopsin II Rods (as compared to cones) contain more rhodopsin. greater response for each photon of light Polarized for a longer time |
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sensory transduction
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transduction mechanism
1. metarhodopsin II activates transducin (g protein) 2. transducin activates phosphodiestersase 3. reduction of cGMP conc (phosphodiesterase cleaves cGMP) 4. cGMP dissociates from Na+ channels 5. Na_ channels close 6. hyperpolarization of the cell 7. electrotonicconduction - direct flow of electric current (not AP) in the cytoplasm to thesynaptic body - graded conduction of signal strength LIGHT HITS RHODOPSIN - stops Na+ from coming into the cell for ever rhodopsin activated= 800 transducin every activated phosphodiesterase = cleaves 6 cGMP closes abt 200 Na+ channels = huge amplification |
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in the dark
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depolarized
Na+ flowing in , cGMP bound to Na+ channels= release of nt dark = rod and cone cells releasing nt - resting membrane pot = -40 mV - high Na+ conductance of the outer segment - Na+ channels in open state by cGMP - nt is released |
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in light
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hyperpolarization
- photoreceptors are polarized by light - hydrolysis of cGMP - closing of Na+ channels - no synaptic release of nt |
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scotopic
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dark- cones are not active - cones ineffective can't tell colors = scotopic vision
- poor resolution of details - b/c fovea - visual acuity decreased (20/200) - entire fovea is blind spot - peripheral vision based upon silhouttes against a contrasting back ground loss of rods = night blindness = occurs as age niight vision increases longer in he dark |
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mesopic
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sun starts to rise - use cones and rods
decreased: - color discrimination - visual acuity -cone effectiveness |
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photopic
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- activates foveal cone cells
- color easily discerned - sharp images due to use of fovea (central vision) - rhodopsin in rods mostly bleached out - don't use rods lost of cones - macular degeneration - legal blindness |
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photoreceptors bipolar cells =ganglion cells light in the center
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bipolar - 2 types on- center and off-center both lie next to each other
light in center a. cone cell- hyperpolarization - no nt release b. on center bipolar cell - G prot coupled receptor inhibits the cell - disinhibits the oncenter bipolar cell - membrane depolarization - release of nt - depolarization and ap on the oncenter ganglion cell off center bipolar cell - ligand gated ion channels -hyperpolarization -no realeaseof nt - no depolarization oin the offcenter ganglion cell |
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photoreceptors bipolar cells =ganglion cells dark in the center
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a. cone cell- depolarization - nt release
b. on center bipolar cell - G prot coupled receptor inhibits the cell - membrane hyperpolarization - NO release of nt - no activity in oncenter ganglion cell off center bipolar cell - ligand gated ion channels - depolarization - realease of nt - depolarization in the offcenter ganglion cell |
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lateral inhibition
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horzontal cells are inhibitory
lateral connections btw rods, cones, and bipolar cells lateral inhibition - visual contrast |
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center-surround inhibition
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1. light in surround hyperpolarizes horizontal cell
2.decreases release of inhibitory nt GABA onto cone 3. depolarize the center cone terminal 4. greater release of glutamate from cone cell in the presence of light to the center 5. glutamate binds to the Gprot coupled receptor on the on-center bipolar cell 6. smlr depolarizations and less nt release 7. less activity in the on center bipolar cell 8. encodes relative intensity of stimulation compared to ambient levels.increases sensitivity to changes in luminance |
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center-surround inhibition inluminance contrast
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light in center = max AP on the oncenter gnaglion cells
light moved from center into the surround = decreasing activity of the gamglion cell light in the surround (outside of center) = inhibition of oncenter ganglion cell ( lateral inhibition) light not in center or surround = resting level of firing |
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light-dark edge
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responses of a population of oncenter ganglion cells whose receptive fields are distributed across a light dark edge
the neurons whose firing rates are most affected by thisstimulus either increased top point or decreased lowest point = which arethe neurons w/ receptive fields that lie along the light-dark border emphasizes the regions where there are differences in luminance |
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label line
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visual cortex
orientaiton - neurons in the visual cortex respond vigorously to light-dark bars or edges but only if the bars are presented at a particular range of orientations w/in the cells'receptive fields - straight up and down or twisted just diagonialy from this columnar organization - vertical - neurons w/same preferred orientaitons - oblique - neurons show a systemic change in orientation across the cortical surface Subtypes of neurons with preference for: - Orientation and position dependence - Orientation dependent but position independent - Length of a bar of light Direction selective for which a light moves across a receptive field binocularity - lateral geniculate nuc recieves inputs fromboth eyes - axons terminate in separate layers so that individual geniculate neurons are monocular - segregation remains in alternating eye specific coluns w/in a cortical layer = ocular dominance column |
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stereopsis
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depth perception
2 eyes look at worldfrom slightly different angle striate cortex fusing together the inputs from 2 eyes 3D image Each retina captures its own view. Two separate images are sent to the striate cortex. The two images arrive simultaneously and are united into one picture. The striate cortex combines the two images by matching up the similarities and adding in the small differences. The combined image is a three-dimensional stereo picture. |
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occular dominance
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in striate cortex the relative strength of inputs from the 2 eyesvaries from neuron to neuron
extremes are neuroons that respond almost exclusively to the L or R eye |
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ambylopia
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loss of acuity and diminished stereopsis
causes: anything that interferes w/clear vision in either eye during the critical period birth - 6 years - lazy eye - blockage of an eye due to cataract, trauma, lid droop, etc. - strabisimus - anisometropia patch |
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brightnes/intensity
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encoded by the firing rate of ganglion cells
low light - rods - so every rod that is stimulated by light contributes to overall response high light -cones - overall response is attenuated by receptors in the surround of the receptive field - lateral inhibition |
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contrast
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encoded when one ganglion cell is stimulated and its neighbor is inhibited - lateral inhibition
- neighboring cells respond in opposite ways at the border btw light and dark - in lightened portions of the border the center is illuminated while the surround is not - incresses on center ganglion activity in darkened poriton the surround is illuminated while center is not - decreases oncenter ganglion activity - when bothcenter and surround are illuminated or darkened - no change in ganglionic activity |
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form
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information abt form is decoded by cells w/in the primary visual cortex refered to as simple cells - centere surround receptive fields
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strabisimus
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(constant turn of one eye) – 5% of children
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anisometropia
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(different vision/prescriptions in each eye)
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depth
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depth info is provided by cells w/in the striate cortex
occular dominant cells are binocular (input from both eyes the amt of disparity btw the images perceived by each eye is used to assign depth to the image - depth perception is possible b/c each eye perceives a slightly different image |
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location
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retinotopic
receptotopic |
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size
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population of cells
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color
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wavelength
label lines |
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contours
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color/intensity change
label lines |
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motion
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label lines
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hypothalamus
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regulation of circadian rhythms
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pretectum
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reflex control of pupil and lens
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superior colliculus
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orienting movement of eyes and head
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