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40 Cards in this Set
- Front
- Back
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What is sound a measure of?
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Perception of wave (pressure (y axis) and compression/refraction is measured over time/distance (x-axis)
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What is intensity a measure of?
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Intensity is the amt of energy or power of the pressure waves.
*measured in terms of loudness-perception of that intensity -unit-dB (bel) |
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What is frequency a measure of?
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It's the repetitive nature of the wave that is measured in hertz (Hz) = cycles/sec
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What is the perception of frequency?
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Pitch
**20-20,000 Hz is the range of human perception |
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What are the components of the external ear?
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1. Pinna (auricle)
2. External auditory meatus 3. Tympanic membrane |
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What are the components of the middle ear?
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*ossicles=
1. malleus (contacts tympanic membrane) 2. incus 3. stapes (contacts cochlea) |
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What are the components of the inner ear?
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*it's a closed cavity filled with fluid
1. cochlea 2. semicircular canals (balance) |
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What are the characteristics of the cochlea?
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1. winds around on itself-bony 2 3/4 turns in temporal bone, snail appearance
2. Spiral ganglion-sensory neurons of the cochlea; cell bodies of auditory primary afferent fibers and their central portion forms the cochlear division of CN VIII 3. Basilar membrane (BM)-inside the cochlea, runs the length of it 4. Organ of Corti-located on the BM and it contains hair receptor cells that respond to pressure |
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What is characteristic of the organ of corti?
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-contains receptor cells that respond to pressure
-stereocilia are little hairs on top of the receptor cell with approx. 20 hairs on each cell -stereocilia insert on the gelatinous tectorial membrane so that vibration of basilar membrane causes oscillations of the hairs and therefore oscillation of membrane potential. -stereocilia of inner hairs do not attach to tectorial membrane |
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What makes the basilar membrane mechanically specialized?
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-because peak amplitudes of traveling waves are maximal at particular places along the BM; leads to excitation only at these areas along the BM
-High frequencies-best projected at base end of cochlea (approx 20,000 Hz) by the oval window -Low frequencies-apex of cochlea (and helicotrema, approx 20 Hz) |
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What is a kinocilium?
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-adjacent to the tallest stereocilia of each hair cell in the semicircular ducts, utricle, and saccule.
-not important for transduction, but for asymmetry/mechanical connections of the hair cells in which they persist |
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What is the structure and function of hair cells?
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-at the apical end (top) of hairs
-arranged in a graded fashion arrangement according to height. -if the action potential is towards the tall hairs, depolarization occurs (excitation) -if action potential is toward short hairs, then repolarization (inhibition) -intensity of wave is related to the degree of deflection -amt of depolarization/repolarization depends on how much stereocilia bend -stereocilia are functionally polarized |
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What are tip links?
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They are fine, elastic filaments between adjacent stereocilia
-they act like springs to allow stereocilia to bend together -tension opens mechanically-sensitive ion channels -these channels are located at the tips of stereocilia |
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Describe the transduction process.
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1. Displacement of BM causes movement/shearing action of stereocilia
2. Depolarization activates voltage sensitive Ca 2+ channels 3. Release of transmitter from hair cells 4. Action potentials in the spiral ganglion neurons (output of cochlea to CNS) |
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Auditory information is distributed bilaterally in the CNS, what branches do the neurons located in the spiral ganglion bifurcate into?
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*Dorsal cochlear and ventral cochlear nucleus (from pontomedullary junction of brainstem first)
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What is order of the core auditory pathway?
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1. Dorsal Cochlear nucleus-axons cross contralateral side of brain and ascend->
2. inferior Colliculus 3. Medial Geniculate Body of thalamus 4. Primary Auditory cortex (Transverse temporal gyrus of Heschl in temporal lobe) |
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What is the function of the core auditory pathway?
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*sound discrimination (both intensity/loudness and frequency/pitch)
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Describe the belt auditory pathway.
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1. ventral cochlear nuclei
2. superior olivary nucleus 3. inferior colliculus 4. medial geniculate 5. auditory association cortex (other areas of the temporal lobe) |
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What is the function of the belt auditory pathway?
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language comprehension (Wernicke's area is important, aphasia if dysfunction is present)
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What is the significance of the superior olivary nuclei?
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*It receives bilateral projections (from both ears) and this determines differences in the arrival in sound between both ears
*Spatial localization-computes interaural time and intensity |
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What is the anatomy of the vestibular apparatus?
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-it is a tubular structure (membranous labyrinth) suspended with bony labyrinth in the temporal bone.
-bony labyrinth is filled with perilymph (low K+, high Na+) -membranous labyrinth is filled with endolymph (high K+, low Na+) |
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What are the otolith organs? Where are they located and what are the functions?
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Otolith organs give information about static position
-they are located in the vestibule (chamber separating the semilunar canals from the cochlea) -they respond to linear acceleration and head tilt -contains utricle and the saccule |
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What does the saccule respond to?
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-linear acceleration in the vertical plane
-an otolith organ in the vestibular apparatus |
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What does the utricle respond to?
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-linear acceleration in the horizontal plane
-an otolith organ in the vestibular apparatus |
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What do the semicircular canals respond to?
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They are 3 canals located at right angles to each other-superior, posterior, and lateral
-they respond to head rotation/angular acceleration |
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What is the vestibular apparatus filled with?
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*endolymph (opposite of nerves)
-filled with high concentration of K+ in comparison to adjacent cells -consist of sheets of hair cells that respond to mechanical stimulation (movement of endolymph with head movement) |
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What is the cellular anatomy of the hair cells?
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-embedded in a sensory epithelium
-hair cells are polarized by organization of cilia -group of stereocilia (small) and one large kinocilium |
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What is the cellular anatomy of the otolithic organs?
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*the otolithic membrane has a surface that consists of calcium carbonate crystals called-->OTOCONIA
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What is the cellular anatomy of the semicircular canals?
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*the tips of hair cells are embedded in a gelatinous substance called-->
CUPOLA |
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What sensory transduction occurs upon head movement? (results)
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-movement of the head causes endolymph to displace hairs cells and this results in either:
1. movement of otolithic membrane/organs 2. movement of cupula of the semicircular canals |
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What happens when stereocilia move toward the kinocilium?
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1. opening of the K+ channels (moves down its concentration gradient and into the cell)
2. Depolarization of hair cell-->infux of calcium ions which then... 3. Trigger release of NT (activates sensory CN VIII 4. Repolarization-as intracellular concentration of calcium rises to such a level that potassium begins to exit through the base of the cell. |
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What happens when stereocilia move away from kinocilum?
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*reduced frequency of action potentials
-repolarization |
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There are 1st and 2nd order neurons systems that CN VIII project to in the central neural pathways, what are they?
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1. 1st order neurons: most of CN VIII project to the vestibular nuclei in the medulla
-some afferents (minor): cerebellum 2. 2nd order neurons: a. CN III, IV, VI for eye movements b. cerebellum for balance c. spinal cord (motor nucleus) for posture, and standing erect |
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One of the reflex functions of the vestibular apparatus is positional reflexes. Which nerves does this involve and what is the goal?
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*Positional reflexes involve head tilt. The eye muscles rotate the eyes in a direction opposite that of the head tilt.
-Involves the "otolithic organs" of CN VIII -projects from vestibular nuclei to CN III, IV, VI -goal is to keep visual field in horizontal plane |
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Another reflex function of the vestibular apparatus is acceleratory reflexes. These involve 3-neuron circuits. What are the 2 types?
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1. angular acceleration of the head:
involves the vestibular-ocular reflex (VOR) -involves the semicircular canals (vestibular nuclei-->CN III, IV, VI) *eye movements stabilize the eyes in space during head and body movements to provide a stable visual target *conjugate eye movements (both move parallel) and eye direction is opposite to direction of head movement. |
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What is Nystagmus?
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*rapid back/forth eye movements and is not normal if following an object
-during head rotations that are too large for the VOR, it is interrupted with very rapid eye movements in the opposite direction (slow in one phase, fast in another) |
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What do the vestibulospinal fibers influence?
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*antigravity muscles and neck muscles
pathway: otolithic organs-->CN VIII-->vestibular nucleus-->spinal cord neurons -goal: control posture and stand erect; activate limb and trunk muscles to counter imposed movements **lateral and medial vestibulospinal tract |
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What disorder associated with the vestibular system is a disturbance of the fluid pressure in the inner ear? Symptoms?
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**Meniere's Disease-
-increased production of endolymph that can result in rupture of the laybrinth -symptoms: vertigo, imbalance, nausea/vomiting -hearing can be affected; decreased endolymph in cochlea **hallmark of vestibular disease |
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What is Benign Paroxysmal Positional Nystagmus (BPPN)?
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-it is where the otoconia break off and impair movement of cupula so you don't get the right signal when you move your head
-not life-threatning, sudden onset -symptoms: vertigo, imbalance, nausea, hearing is NOT affected because there isn't a problem with cochlea |
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What is alcohol-induced vertigo?
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-It's when the cupula and endolymph have the same density and not sensitive to gravity.
-Symptoms: illusion of movement; head tilts and activates semicircular canals a. intoxication: cupula (highly vascular) absorbs alcohol and becomes less dense than surrounding endolymph so the cupula begins to float b. hangover-alcohol leaves cupula first by uptake into endolymph so now the endolymph is less dense than cupula so the cupula sinks because it's heavier than usual. |
