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138 Cards in this Set

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what are the three neurons in each somatosensory pathway?
primary (ganglion cell), secondary (projection cell AKA axon decussates which crosses body - why left side of brain controls right side of body), and tertiary (thalamic cell which projects message to sensory cortex)
what are the two somatosensory tracts of the upper and lower body and what is the difference between the two?
the DCML tract which has its first synapse in the medulla before the decussation to the contralateral side, thus the message travels ipsilaterally up the cord from the site of sensation. The spinothalamic tract has its first synapse in the dorsal horn of the cord ipsilateral to the sensation site, then the projection cell decussates to the contralteral side for travel up the cord.
what types of sensations are on the DCML? the spinothalamic tract?
DCML - discrimative touch and proprioception
spinothalamic - pain and temperature
receptive fields on the skin contain what two areas?
an excitatory center and an inhibitory surrounding area to help localize touch to one area.
how does lateral inhibition work?
when an area is stimulated, the nerve fires, at the first synapse, there are inhibitory interneurons at the synapse which act to inhibit the sensory tracts of the areas next to the stimulated area.
what trends do the receptor fields follow as we move more distal?
they become smaller and have greater innervation density
what is the term for the cause of a depolarization of a sensory receptor membrane? since this is different for each type of receptor, what is the result of many receptors acting?
adequate stimulus. each receptor makes a unique contribution to somatic sensation.
what is the function of these receptors?
1. meissner's
2. merkel's
3. pacinian
4. ruffini's
5. petritrichial
6. free endings
7. muscle spindle
8. golgi tendon
1. rapid movement of an object over the surface of the skin
2. pressure, form and texture
3. high frequency vibration
4. stretching of the skin, joint capsule etc
5. hair movement
6. light touch
7. muscle length, movement and velocity
8. muscle tension
what is receptor adaptation and what receptors do this?
decrease in receptor potential with continued stimulation; all receptors do this and they are either slow or rapid adaptors
what are possible mechanisms of receptor adaptation?
Na or Ca channel inactivation, K channel activation, or physical properties of the connective tissue capsule
what receptors are slow adaptors?
merkel's, ruffini, nociceptor (pain), temp, muscle spindle, golgi tendon
what are rapidly adapting receptors?
meissner, pacinian, peritrichial
in terms of AP's what is the difference between slow and rapid adapting receptors
Rapid adaptors only illicit AP’s at onset and cessation of a stimulus while slow adaptors illicit AP’s throughout the stimulation
classify axons by thickness (amount of myelin thus velocity) from thickest to thinnest?
type I (A alpha), type II (A beta), type III (A delta), and type IV (C - this one is unmyelinated)
what types of sensory receptors utilize type I and II axons? where on the dorsal root are their axons located?
discriminative touch, pressure, pain and proprioception. Use the medial division of the dorsal root
what types of sensory receptors utilize type II and III axons?
light touch
what types of sensory receptors utilize type III and IV axons? where on the dorsal root are their axons located?
pain and temperature, and they use the lateral division of the dorsal root
what is the congenital disease in which the pain and temp fibers are insensitive?
CIPA, congenital insensitivity to pain and anhydrosis
large fibers tend to enter what neuro tract? small fibers?
dorsal funiculus, lissauer's tract
what are the three possible routes of the sensory fibers once they synapse in the dorsal horn?
follow usually tracts for conscious sensation, synapse with an interneuron form a reflex, or go to the cerebellum for muscle coordination
protopathic fibers are defined as what and what tract do they follow? epicritic fibers?
protopathic fibers are less refined and more primitive. they will come back first after nerve injury and are poorly localized and painful. they follow the spinothalamic tract. epicritics are the opposite of the protopathics and they follow the dorsal cloumn medial lemniscus (DCML)
each dermatome overlaps the one next to it by how much?
one half of the adjacent dermatome
what will happen to sensation in the corresponding dermatomes if 3 consecutive dorsal roots are lost?
complete loss of sensation in the intermediate dermatome and partial loss in the adjacent dermatomes.
what are the 5 types of thalamic nuclei?
specefic, sensory and motor, nonspecefic (intralaminar), association, and reticular (GABAergic neurons that modulate activity of all other thalamic nuclei, it is the only nuclei that does not project to the cortex)
what thalamic nuclei project to the somatosensory cortex?
the ventral posterial medial and lateral
how are dermatomes organized in the cortex?
adjacent dermatomes are adjacent in the cortex
from medial to lateral, how are fibers organized in the dorsal funiculus? spinothalamic tract?
DF: SLTC (sacral, lumbar...)
ST: CTLS
what is the specefic pathway from thalamus to cortex in terms of sensory info?
ventral posterior nu of thalamus through the posterior limb and internal capsule then to the postcentral gyrus and paracentral lobule
in terms of the areas of brodmann, where are tactile and proprioceptive fibers located in the cortex?
tactile: 3b and 1
proprioceptive: 3a and 2
the unit of organization of senses, one unit per type of receptor, in the cortex is what?
cortical column
what type of sensations are highly dependent upon cerebral cortex analysis? what types are not?
epicritic (discriminative) are dependent, protopathic (pain and temp) are not, thus you can feel pain at the thalamic level
the postcentral gyrus and paracentral lobule makeup the main part of the sensory cortex. how is it organized from lateral to medial, in terms of parts of the body? what is another name for this area?
oral cavity, face (trigem), hand, arm, trunk (C and T), hip, leg, feet (L and S) this area is AKA as S1
what arteries supply the thalamus? where do they come from? the internal capsule...?
the thalamoperforating and thalamogeniculate which come from the posterior cerebral artery. the internal capsule is supplied by lateral striae from the middle cerebral artery
what are some properties of the DCML
phylogenetically new, seen in well developed primates, large myelinated axons, small receptive fields, high innervation density to the periphery and is the principle sensory input to the somatosensory cortex.
what are the three epicritic sensations sent through the DCML and define each.
discriminative touch (duh), stereogenesis (recognition of objects by touch alone), graphesthesia (touch recognition of letters or numbers drawn on the skin), vibratory sense, and proprioception (sense of body position and movement)
how is discriminative touch tested?
by the 2 point touch threshold
would you be able to distinguish two points touchin at the same time within 5mm on the back and the fingers?
no the back has larger receptor fields and the points need to be 50 to 70 mm apart
what receptors sense vibrations and how are they tested?
pacinian cropuscles which can be tested by a tuning fork at 130 to 200 cps
what receptors sense proprioception?
muscle spindles, golgi tendon organs, and joint receptors
what do all epicritic sensationss have in common
?
they all require a high degree of spatial and temporal resolution via small receptive fields and large rapidly conducting axons
what sense is severly compromised with DCML lesion?
vibratory sense
most primary afferents in the DCML do what in the dorsal column?
bifurcate to form a long ascending and short descending branch
some primary afferents in the DCML will synapse where in the dorsal horn and with what axons?
in the nucleus proprius and synapse with neurons whose axons then enter the dorsal column
what part of the dorsal column do DCML afferents ascend? what is the exception?
above T6 ascend in the more lateral fasciculis cuneatus while below T6 ascend in the more medial fasciculus gracilis. the exception is that some proprioception ascends in the dorsal part of the lateral faniculus
what nuclei in the medulla do the DCML afferents synapse on? where in the medulla are they located?
arm and upper body -> nucleus cuneatus which is lateral
leg and lower body -> nucleus gracilis which is more medial
after synapsing in the medulla, where do DCML messages go (differentiate between upper and lower body)?
fire on the sensory decussation and cross the midline to form the medial lemniscus which has a vertical orientation near the midline of the medulla. Upper body sensations are more dorsal while lower body is represented ventrally
the medial lemniscus assumes what position in the pons? how are upper and lower body sensations oriented here?
horizontal in the pons, upper body is medial, lower body is lateral
where are the DCML fibers located in the midbrain and where do they eventually synapse?
they move laterally as they ascend and are dorsolateral to the red nuclei in the midbrain. They eventually synapse in the VPL of the thalamic nucleus
where do fibers of the spinothalamic tract project and what are they called?
spinoreticular fibers to the brainstem reticular formation, spinotectal or spinomesencephalic to the superior colliculus and periaqueductal gray, spinothalamic to the thalamus, and spinohypothalamic to the hypothalamus. (note few fibers project to the thalamus)
what are the protopathic sensations conveyed over the spinothalamic tract?
crude/light touch, pain, temperature, and sexual/pressure (needa use it)sensations.
how can alesion to the bowel bladder sensation portion of the spinothalamic tract not eliminate sensation from any region of the pelvis?
these sensations are conducted bilaterally, thus a unilateral lesion will not eliminate sensation from any lesion of the pelvis
describe the spinothalamic pathway in the spinal cord.
afferents enter through the dorsal horn, bifurcate to ascending and descending branches, some enter the dorsal horn and synapse with interneurons or projection neurons in the posteromarginal nucleus, substntia gelatinosa, or nucleus proprius. Axons of porojection neurons cross the ventral white commissure and form the contralateral spinothalamic tract which is found in the ventral part of the lateral funiculus and continues to the brainstem.
what is the organization of fibers in the spinothalamic tract? how does this compare to the DCML?
anything above T6 (upper body) is medial while anything below T6 is lateral. This is the inverse of the DCML
after traversing the spinal cord, the spinothalamic tract differentiates into neospinothalamic and paleospinothalamic parts. what are the pathways of each of these? functions of each?
neospinalthalamic projects to the VPL (&PO) nuclei of the thalamus whose axons then pass through the posterior limb of the internal capsule to synapse in the S1, S2, and insula. the main functions of the new part are crude touch and fast pain (S2 appears to have a special role in perception and tight localization of fast pain, projections from S1 to S2 may help localize this pain). The paleospinothalamic part projects to nonspecefic (intralaminar) thalamic nuclei, VPL and PO thalamic nuclei, spinoreticular fibers (reticular formation), spinotecal (tectum and periaqueducatal gray), and spinohypothalamic. the reticular formation also projects to the ARAS (ascending reticular activating system that modulates consciousness... the brain battery)
what is the path of the spinothalamic tract in the brainstem?
it traverses the lateral medulla in the ventrolateral tegmentum and above the basillar pons lateral to the medial lemniscus in the ventral pontine tegmentum, in the midbrain it is dorsolateral to the red nucleus and DCML fibers
sensory input to the reticular formation comes from where?
cranial nerves and spinothalamic tract
the only sense mediated by the reticular formation is what? waht is the pathway?
slow pain and the affective nature of it.
spinothalamic tract or trigeminal nucleus project to the reticular formation, then synapse on the intralaminar nuclei in the thalamus and finally project to the cerebral cortex
what are the characteristics of coma and how can it occur?
abnormal unconscious state that cannot be aroused from as opposed to sleep, slowed respiration and heart rate, diminshed responses to pain, depressed reflexes. causes can be depression of cerebral function or brainstem/thalamic lesion
levels of consciousness and alertness are modulated by a bunch of factors... name some.
ARAS (major role from cholinergic neurons in the rostral pons like pedunculopontine and laterodorsal tegmental nuclei appear to play a major role), the reticular formation (influences cholinergic neurons in basal nuclei and histamniergic tuberomammillary nuclei in the hypothalamus), and noradrenergic and serotonergic neurons of the brainstem also modulate cortical function
the paleospinothalamic projection to the tectum does what?
involved in the reflex eye and head movements in response to tactile stimulation
the paleospinothalamic projections to the periaqueductal gray does what?
provide info about pain to a pain inhibiting system centered in the PAG
the periaqueductal gray sends its antinociceptive (pain inhibiting) messages where? what is the result?
noradrenergic nuclei and medullary serotonergic raphe nuclei of the brainstem which project to the dorsal horn where enkephalinergic interneurons inhibit pain transmission
what are some causes of peripheral neuropathy?
infection (leprosy, diptheria...), autoimmune disease (GBS), metabolic disorders (vit B deficiency, heavy metal poisoning, drugs), endocrine disorders (diabetes), and gene mutations (charcot-tooth marie syndrome)
characteristics of peripheral neuropathy?
sensory loss in glove and stocking distribution, pain, parasthesias, damage of axon itself or myelin sheath, may prefer small or large diameter fibers or for sensory or motor fibers, diminished reflexes, paresis or paralysis
characteristics of radiculopathy?
dorsal root or dorsal root ganglion lesion resulting in loss of somatic sensation with a dermatomal distribution, pain and parasthesia, hyporeflexia and hypotonia
what are ataxia and romberg's signs? what do the sensory form of these two expressed together and a wide based gate indicate?
ataxia is clumsy uncoordinated movements. Romberg's sign is sway/instability with feet together measured with eyes open and then closed. More instability with eye closed indicates sensory deficit. If both of these deficits are seen and are sensory in natures, then DCML lesion should be suspected
severe epicritic loss in both legs may indicate what?
lesion of the dorsal funiculus of spinal cord (tumor maybe), lesions of paracentral lobule bilaterally, or tabes dorsalis (tertiary syphilis)
why does tabes dorsalis cause bilateral epicritic loss to the legs?
dorsal root ganglia in the lumbar area are degenerated and the larger diameter fibers are affected first.
what three systems does the brain use to sense positioning and how to move?
spinal proprioceptors (golgi tendon organs, muscle spindles, and joint receptor organs), vestibular proprioceptors (head orientation in space and antigravity muscles), and vision
what are the symptoms and pathophysiology of anterior cord syndrome?
bilateral analgesia, athermia, possible paralysis/paresis and bowel bladder incontinance. This is caused by lesions of sulcal branches of anterior spinal artery. The spinothalamic tract is affected.
syringomyelia is an example of what? What is syringomyelia? What is it associated with?
central cord syndrome (lesion of ventral white commissure). A cavity forms near the central canal of the cervical enlargement. Associated with spina bifida, arnold chiari malformation or years after trauma.
protopathic fibers synapse where compared to where they enter the cord?
about two segments superiorly
a brown sequard lesion causes what?
anesthesia at ipsilateral level of lesion as well as epicritic defect on down on ipsilateral side of lesion. Protopathic defect on contralateral side starting at two spinal segments caudally and continueing on down
what happens when a lesion occurs in the VPL nucleus in the thalamus?
contralateral hemianasthesia bc it effects both epicritic and protopathic senses
in a thalamic lesion, if the intralaminar nuclei are spared, what will happen?
thalamic pain, a slow, severe burning pain characterized by allodynia and dysethesia
what are the three characteristics of thalamic syndrome?
hemianesthesia, sensory ataxia, and thalamic pain
injury to the thalamus caused by stroke usually is due to what arteries?
lateral striate arteries and anterior choroidal artery
lesions to the cerebral cortex usually cause what?
loss of epicritic and protopathic senses, but mainly of epicritic senses
possible causes of segmental loss with pain and parasthesia are...
spinal nerve or dorsal root ganglion lesion
possible cause of epicritic loss to one side and protopathic to other side as well as motor losses?
spinal hemisection
possible causes of loss of epicritic sensation but not protopathic?
lesion of dorsal columns or medial meniscus
possible causes of bilateral epicritic deficit to the legs?
lesion to fasciculi gracilis, paracentral lobules, or tabes dorsalis
possible cause of epicritic defect in the arms?
lesion of medial lemnisci in the medulla or pons
possible cause of unilateral protopathic loss?
lesion in spinothalamic tract in contralateral medulla or spinal cord
what are the four possible causes of hemianesthesia and what are the other symptoms seen with each cause?
Ventral posterior nucleus lesion (thalamic pain also occurs), lesion of medial lemniscus and spinothalamic tract at pontine level or above. lesion of posterior limb and internal capsule of thalamus (paresis, paralysis and visual defects), lesion of postcentral gyrus (epicritics effected mainly, paresis and paralysis as well bc close to motor cortex)
bilateral loss of pain and temperature with an upper and lower level involved maybe due to ?
lesion of ventral white commissure
bilateral loss of pain and temp with an upper level involved as well as incontinanceand paresis/paralysis may be caused by...?
anterior cord syndrome
where are the cell bodies for the primary trigeminal sensory neurons?
mesencephalic nucleus (proprioceptive only) and trigeminal ganglion (some proprioceptive and all other senses)
the secondary sensory neuronal cell bodies of the trigeminal are found where?
main (chief) nucleus and spinal trigeminal nucleus
where are the protopathic senses and epicritic senses of the trigeminal nerve mediated?
protpathic in the spinal trigem nucleus and epicritic in the chief nucleus
where are the tertiary sensory neuron cell bodies of the trigeminal located and which mediate fast and slow pain?
VPM nucleus and PO nuclei are the main thalamic projection of the trigem; they mediates fast pain and the intralaminar nuclei and reticular formation mediate slow pain
what trigem nucleus (and what part of that nucleus) receives all facial, oral, and nasopharyngeal pain and temp fibers including fibers of nerves VII, IX, and X?
the causal part of the spinal nucleus
what nucleus generates a chewing movement pattern while sleeping in order to maintain an airway?
Supratrigeminal nucleus (not it is inactivated in general anesthesia)
describe the path that forms the ventral trigeminothalamic tract.
secondary fibers from the spinal trigem and ventrolateral subdivision of the chief nucles cross the midline to form this tract and then lies down on the dorsal surface of the medial lemniscus and synapses on the VPM nucleus of the thalmic nuclei.
describe the path that forms the dorsal trigeminothalamic tract.
fibers from the dorsomedial division of the chief nucleus stay ipsilateral and project to the VPM
the spinal nucleus projects fibers to where?
the VPM, PO, intralaminar, and reticular formation
primary pain fibers of the trigem synapse where? How are these fibers organized in terms of the midline of the face?
the caudal part of the spinal trigeminal nucleus. The fibers from the midline of the face are more rostral in this nucleus
what is the path of the ARAS fibers?
sensory fibers project to the brainstem RF which then project to the intralaminar nucleus and then to the cerebral cortex
what is the path of the jaw jerk reflex?
muscle spindle of masseter signals proprioceptove fibers to the mesencephalic nuclei. A central axon then is sent to the motor nucleus of the trigeminal. Alpha motor neuron is then signalled. This all occurs on the mandibular division of the trigeminal
A strong jaw jerk reflex suggests what? A weak or absent reflex? Why?
strong suggests upper motor neuron lesion. Weak or absent is normal. This is bc this reflex is hard to illicit in most ppl, when it is strong it is hypereflexive, thus a upper motor neuron issue.
touch afferents of the trigem synapse where?
chief and spinal trigem nuclei
which trigem nuclei is used for touches that discriminative touch? crude touch?
chief nucleus, spinal nucleus
touch sensory projections from the chief nucleus that follow the ventrotrigeminothalamic tract take what path? dorsal trigeminothalamic tract? Which path is only for touch from the oral cavity?
contralateral VPM, ipsilateral VPM, dorsal trigeminothalamic tract
touch sensory fibers from the spinal trigem nuclei project to what thalamic nuclei?
contralateral VPM, intralaminar nuclei, and reticular formation
trigem fast pain fibers project where from the spinal nucles? slow pain fibers?
VPM and PO, intralaminar nuclei and reticular formation
nociceptors projecting pain to the spinal trigem nucleus may come from what nerves?
V, VII, IX, X
what is the path of the corneal reflex?
touching the cornea causes the trigem nuclei to send bilateral signals to the facial motor nucleus. Thus both eyes blink
what disease is characterized by severe facial pain illicited when the face is touched? What other pathology does this indicate if it is bilateral? What are treatments?
Trigeminal neuralgia, multiple sclerosis, anticonvulsants or surgery to alleviate the structure on the trigem nerve
how can alternating anlagesia occur? describe it. What syndrome is it part of?
lesion in rostral medulla affecting the spinothalamic tract and the spinal trigem tract, thus loss of pain in ipsilateral face and contral lateral side of the body.
at the level of the sensory decussation in the medulla, a lesion of the medial lemniscus and spinal trigem nucleus would cause what?
ipsilateral epicritic defect in the body and pain and temp defect on the face
lesions to the internal capsule-posterior limb cuase what trigem effects?
loss of most epicritic and protopathic senses (mainly contralateral), oral epicritic senses maybe preserved by the ipsilateral dorsal trigeminothalamic tract.
what senses are eliminated in a trigem tractotomy?
pain and temp, epicritics remain, but pain may return
rostral medullary compromise affecting the spinal trigem tract and spinothalamic tract are usually caused by what vascular lesion?
posterior inferior cerebellar or vertebral artery
what nerves are found in the geniculate, petrosal , and nodose ganglia?
the facial, glossopharyngeal, and vagus respectively
SVA fibers from VII, IX, and X synapse where? the secondary fibers then follow what tract and synapse where?
the gustatory nucleus which is the rostral part of the solitary nucleus. project bilaterally in the medial lemniscus and central tegmental tract and then synapse in the medial part of the VPM or the pontine taste area (parabrachial nucleus)
taste fibers that synapse in the VPM will then project where? taste fibers that synapse in the pontine taste area?
opercular post central gyrus and insula. limbic strucutres that mediate the affective quality of taste OR the hypothalamus which regulates feeding behavior.
GVA fibers from the solitary nucleus convey fibers to where to help regulate what?
to the vital centers in the reticular formation (These fibers help regulate blood flow to different organs, GI tract motility, blood pressure and respiration), also sends to VPM and hypothalamus.
describe the path of the baroreflex.
axons that innervate the carotid sinus travel to the petrosal ganglion and have central axons that travel to the solitary nucleus and synapse. Neurons then project to the vasomotor (cardiovascular) center of the pons and the medulla. The center can influence the vagus to control heart rate and the sympathetic nerves to regulate vasomotor tone.
the vasomotor center can be divided into what two areas? What NT's does it use?
pressor (lateral reticular nu) and depressor areas (central reticular nu). GABA is used (inhibitory) bc the pressor area is tonically active.
describe the path of the chemoreflex.
petrosal ganglia cells with peripheral axons innervating the carotid body (detecting oxygen and carbon dioxide) have central axons that synapse in the solitary nucleus. These neurons project to the respiratory center of the pons and medulla. It can influence the phrenic nerve, vagus and sympathetics (control breathing rate and regulater airway caliber).
what are the three nuclei of the respiratory center?
inspiratory (solitary nucleus), expiratory (ventrolateral medulla RF), and pneumotaxic (parabrachial nucleus in the pons)
a spinal cord transection at C3 or above will result in what?
respiratory arrest bc of phrenic nerve
what are algogenic substances?
compounds that sensitize nociceptors causing hyperalgesia or activate nociceptor resulting in pain
pain follows what tracts?
spinal trigem/ventral trigeminothalamic or the spinothalamic.
what type of axons and what is the tract of fast pain?
type III fibers mediate pain reflexes and sharp well localized pain. They synapse in the posteromarginal nucleus of the dorsal horn. Project to the VPL and PO and to the SII and insular areas
what type of axons does slow pain use and what is the path it follows?
type IV fibers which mediate chronic, burning or aching pain as well as emotional (affective responses to them). They synapse with interneurons in the substantia gelatinosa of the dorsal horn. Then to the RF (including the PAG), intralaminar nuclei, and to the limbic structures (can influence the autonomic nervous system)
define thalamic pain.
nonspecefic and poorly localized pain on the side of the body that has lost its fast pain fibers. The slow pain projections in the intralaminar nuclei are still intact.
what are the characteristics of physiologic pain?
elicited by nociceptor stimulation and is sensitive to analgesics
peripheral sensitization to pain is associated with what?
allodynia (normally nonpainful stimuli become painful.
central sensitization to pain occurs when...?
chronic stimulation cuases projection neurons to become hypersensitive
neuropathic pain results from what and is treated with what?
from injury to the nervous system and treated with antidepressants and anticonvulsants
nerve entrapment or peripheral neuropathy may result in what?
pain and tinel's sign
visceral pain is transmitted bilaterally by what?
spinothalamic tract
what is referred pain and two examples?
pain felt at a related dermatome not the source. Angina and pain to the face from dental work
what are two examples of projected (radicular pain)?
tabes dorsalis and trigeminal neuralgia
what is the gate control theory (local pain modulation)?
an interneuron in the dorsal horn called gate cell receives synapses from both touch fibers and pain fibers. Touch fibers excite the gate cell while pain inhibits them. when the gate cells are excited, they inhibit transmission of pain by small myelnated and unmyleinated pain fiebres
endogenous opiods (enkephalin and dynorphin) are found in what neurons?
PAG, brainstem RF, and spinal cord dorsal horn.
what is the effect of morphine on the receptors for the endogenous opiods?
activates the antinociceptive pain pathway by suppressing inhibitory GABA interneurons allowing neurons to descend from the PAG