CSD 302
Terms
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vertebral arteries
- paired arteries which supply the muscles of the neck, spinal cord, and cerebellum. inside the skull, the two vertebral arteries join up to form the basilar artery.
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basilar artery
- It arises from the confluence of the two vertebral arteries From the basilar artery arises the anterior inferior cerebellar artery (supplying the superior and inferior aspects of the cerebellum), Fx= supplies the brain with oxygen-rich blood. Origin of la
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anterior inferior cerebellar artery
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passes backward to be distributed to the anterior part of the under surface of the cerebellum. Arises from the basilar artery.
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labyrynthine artery
- a long slender branch of the basilar artery, arises from near the middle of the artery; it accompanies the acoustic nerve through the internal acoustic meatus, and is distributed to the internal ear.
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5. Spiral modiolar artery:
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medial to the scala vestibuli, it gives off several branches which further divide to supply several different areas. 3 diff areas:
a. Spiral ganglion & Auditory nerve
b. To lateral wall/stria vascularis < - 6. Radiating Arterioles
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to lateral wall/stria vas (runs over SV) there is another set of radiating arterials that run to the spiral limbus and organ of corti
- 8. Vessel of tympanic lip
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right underneath the organ of corti. Closest a vessel gets to a hair cell
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9. Vessel of the basilar membrane:
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vessel that is on the underside of the basilar membrane, in the arcuate zone.
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11. Spiral modiolar vein:
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carries the venous blood out, next to the scala tympnai.
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12. Arteriovenous shunt:
- The passage of blood directly from arteries to veins, without going through the capillary network.
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afferent innervation
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1. Afferent: have soma in the spiral ganglion. Two types of spiral ganglion cells:
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type 1
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large, the dark line around the soma is part of the myelin sheath; they are by far the majority of the total of all ganglion cell. have a single ending radially connected to IHCs. RADIAL AFFERENTS
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type 2
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the myelin sheath is not nearly as prominent. Small cell bodies. 5-20 %. OUTER HAIR CELLS! from habenula, cross on the floor of the tunnel of corti and outer spiral bundles--> OHC
- 2. Habenula Perforata
- The perforations along the tympanic lip of the spiral lamina giving passage to the cochlear nerves. All nerve fibers pass through the habenula perforata…
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i. intraganglionic spiral bundle.
- The olovo-cochlear bundle enters the modiolus and forms this. It spirals in rosenthals canal near the scala tympani.
- b. Olivocochlear bundle:
- the axons of the neurons from the “medial system” and “lateral system” join and leave the brainstem here.fibers exit the brainstem on the vestibular nerve, join the cochlear nerve in the inner ear, and terminate on OHC.
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c. Anastomosis of oort:
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olivocochlear bundle jumps to the cochlear system here. The olovo-cochlear bundle enters the modiolus and forms the
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1. LATERAL SYSTEM efferents
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1. LATERAL SYSTEM efferents these nerve fibers make axodendritic connections on the type 1 spiral ganglion cells. (they don’t actually make contact with IHC).
- 2. Medial system efferents
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axons cross the middle of tunnel of organ of corti after leaving the habenula. Then they branch and make synaptic contacts on the bases of several OHC.
- Otic placode
- forms the otic pit and the otic vessicle, giving rise eventually to th organs of hearing and equilibrium.
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otic pit
- deepens and becomes the otocyst
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Otocyst
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embryonic vesicle from which the parts of the interal ear are developed. it elongates and forms 2 regions. the utricular and saccular region.
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utricular region (from otocyst)
- differentiates into the semicircular canals and ducts and the christa amp and the utricle and muculae
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saccular region (from otocyst)
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differentiates into the saccule and cochlear duct
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inner (lesser) epithelial ridge
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is what differentiates into the spiral limbus and the IHC and the inner pillar
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outer epithelial ridg (lesser)
- differentiation --> includes the outer pillar, deiter cells and hensen cells and OHC.
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branchial groove
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an external embryonic groove between contiguous branchial arches. --> EAR CANAL! this grove gives rise to a deep invagination, the MEATAL PLATE, which opens up eventially.
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pharyngeal pouch:
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extends laterally toward the first branchial groove where it meets the ectoderm.
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meatal plate
- invagination of the first branchial groove which gets very deep during embryonic development in vertibrates.
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aurricular hillocks
- bumps on the branchial arches. they are derived from meso, the skin part covering them is ectoderm. they fuse together to form the pinna.
- traveling wave in cochlea:
- rapid wave prop at base, it slows as appraches the peak. amplitude of the vibnration increases slowly with distance basal to the pea. amplitude of vibes decreases rapidly with distance apical to the peak.
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basal end most sensitive to:
- ~25,000 Hz
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apical end most sensitive to:
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~100 Hz or so
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cochlear amplifier
- the mechanisms that produce the enhancements in the living ear as opposed to the dead ear. enhances sensitivity to low level tones, frequency selectivity.
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in dead ear observe:
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decreased sensitivity and a drop in the CF at a place
- nonlinearity:
- the response of the living BM is NOT LINEAR!! as you increase the input level for a certain freq you see greater change in the responce of the freq below the CF at that freqs place.
- becuse coch amp is most effective for freq near resonance suggests...
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that the active process somehow acts to reduce the damping of BM.
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in coch the OHC appear to act as....
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force generators in part of a positive feedback process which reduces the apparent damping of the BM.
- Gain
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(amplitude of response)/(amplitude of stimulus). if gain is not constant then the response is nonlinear. the gain is not constant.
- characteristic frequency of a place:
- the freq that evokes the greatest response along the BM at threshold level.
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distortion product emissions
- present 2 stim tones simultaneously.then examine the distortion signals. the 2 stim must be close enough in freq that their traveling wave patterns overlap allot. the dist prod OAE's are identified via spectral analysis.
- transdution channels
- specialized gates or channels in the cell membrane of the hair cell which can either be open or shut depending on position of the hair bundle. not selective to K or N. towards kino = more trans ch open = greater dep = excited.
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transduction characteristic saturation:
- can become saturated in either direction. the point where cells response saturates for the inhib direction is close to resting Vm. = easy to depolarize from resting but inhib displacements can produce on ~ small hyperpol.
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AC intracellular receptor potential
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the time variation of the hair cell membrane potential.
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DC receptor potential
- the shift of the average membrane potential away from the resting potential during a stim. independent of freq.
- as stim freq is increased the hair cell basolateral membrane...
- begins to act like a low pass filter. --> amplitude of ac receptor potential decreases. DC DOSNT CHANGE.
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cellular basis for cochlear amp:
- in the cochle, the OHC appear to act as force generators in part of a + feedback loop that reduces the apparent damping of BM. 2 proposed models
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prestin somatic motility
- OHC in a dish change their length when stimulated electrically. protein prestin responsible for this. VOLTAGE DEPENDENT. causes the OHC to lengthen and shorte
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hair bundle motor
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model based on the cochlear amplifier arising from an active force generated by the sterio directly involving the transduction mech.
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spontaneous activity (AP)
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characteristic of all neurons in aud nerve....AP occur without stim. if the Ca++ volt dependent channels activeate then the cell releases NT. due to coordinated release there is big enough EPSP to get AP...
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rate intensity fx
- relates the sound level of the stim to the rate of aps over some range of sound level between where we just barely detect an increase and where the rate saturates.
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dynamic range
- range of stim levels that cause a change in the rate of AP's
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High SR neurons vs low SR neurons
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high sr neurons usually have a lower threshold then the low SR neurons do. they also have a smaller dynamic range.
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phase locking
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the fact that the prob of generating an AP in spiral ganglion cells varies within one period of the stimulus, depending directly on the waveform of the hair cell receptor potential.
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volley pitch principle
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Cells must be organized into
squads and fire in volleys (volley
principle). -
tuning curve
- The threshold tuning curve is a convenient way to represent the minimal stimulus levels that activate a part of the auditory pathway to the extent that the response exceeds some predefined criterion threshold.