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Anat & Phys W6

Inner Ear Structure

QuestionAnswer
Importance of Organ of Corti. Responsible for picking up sound at the peripheral level. It is the auditory transducer and where the nerve supply ends. Organ of Corti runs the length of the cochlear duct.
What is within the Organ of Corti? 1) Hair Cells (receptor cells) 2) Nerve endings for receptor cells 3) Supporting cells
What is the ceiling of the Organ of Corti? Tectoral membrane
Composition of Tectorial Membrane. Collagen and proteins. TM resembles more of a "gelatanous flop" than a regular membrane.
What are the attachment points of the Tectorial Membrane. TM only attaches at ONE end, spirl limbus of osseous spiral lamina (ONLY IMMOBILE part of the Organ of Corti). Thought to be supported by Hansen cells on the other side.
Name of the attachment point of the TM to the spiral limbus. Vestibular lip
How are stereocilia of OHC attached to TM? Stereocilia of OHC articulate with the TM through ridges. OHC are NOT physically attached to the TM.
Name of the ridges of the TM where the stereocilia of the OHC articulate. Kimura's membrane
Briefly describe the movement of the TM and the BM in relation to one another. B/C the TM is immobile at one end it moves differently than the BM. This causes a shearing action of the stereocilia of the OHCs within the organ of corti.
Reticular lamina Forms ceiling of the sensory (receptor) cells and the supporting cells of the Organ of Corti. Forms the upper border of the space of Nuel. Seperates endolymph from internal structures of the Organ of Corti.
Fluid "in" Tunnel of Corti. Why would it be in it? Cortilymph. In the tunnel b/c if endolymph was in the tunnel then it would throw the chemical balance off, killing the unmyelinated neurons.
Forms the reticular lamina. Phalanges of the Deiters' and inner phalangeal cells, and by the inner and outer pillar cells. The phalanges mushroom at the top as do the inner and outer pillar cells and form a tight junction that compose the reticular lamina.
What penetrates the reticular lamina? What fluid is it bathed in? The stereocilia of the hair cells. Bathed in endolymph.
Composition and charge of endolymph. Low sodium and high in potassium. Charge of +80mV.
What fluid is the hair cells bathed in? Cortilymph
Composition and charge of cortilymph. High sodium and low patassium. Charge is neutral.
Lateral wall of the cochlea. Spiral ligament and stria vascularis. Spiral ligament falls between the stria vasularis and wall of the otic capsule.
Composition and purpose of the spiral ligament. Made of connective (fibrous) tissue. Provides overall support to BM and Reissner's membrane.
What is the tension of the BM? The BM is NOT under any tension. If you make a slit in the BM then the edges do not curl or draw apart.
Two functions of the stria vascularis. Potential for secretory and absorption functions. Seems that stria vascularis has a role in regulating potentials. Absorbs oxygen. Stria vascularis has high concentration of capillaries.
3 types of cells in the stria vascularis. 1) Marginal cells 2) Intermediate cells 3) Basal cells All three cell types seem to play a role in the metabolism of the structure.
Describe the marginal cells of the stria vascularis. 1) Epithelial cells forming single layer 2) Lines lateral wall of scala media 3) Rich in mitochondria 4) Seem to be associated w/ ion channels and pumps
Where are the capellaries in the stria vascularis? In the middle, along with the intermediate cells.
Describe the intermediate cells of the stria vascularis. 1) Lateral to marginal cells 2) Rich in melanin 3) Seems to be integral to contributing to charge that gets pumped through the marginal cells, contributing to endocochlear potential
Describe the basal cells of the stria vascularis. 1) Faces the perlymphatic side of the spiral ligament 2) Multiple layers, interleaved 3) Tight junctions b/w them limits the flow of ion movement through the intermediate cells.
Location of the highest endolymphatic charge. At the spiral ligament and stria vascularis. Mounting evidence that stria vascularis is the source of endolymphatic potential and also endolymph. Suggests stria vascularis is an ultra filtrate of blood serum.
What can an overactive stria vascularis cause? Can cause cochlear hydrops, just like EVA can cause it.
Describe the inner border cells. 1) Slender, columnar cells 2) Seperate IHC from cells of the spiral sulcus
Describe the inner phalangeal cells. 1) Supports the IHC 2) Has a stalk that seperates the lateral sides of the IHCs.
What does the inner and outer pillar cells form? Forms the tunnel of corti. Contributes to the reticular lamina at the apical end of the cochlea.
Describe how the base of the pillar cells lie. 1) They lay on the BM and is broad and supportive. 2) Cells oriented at 45 degree angle. 3) Maintain a strong structural attachment between the reticular lamina and the BM, giving rigidity to the organ of corti.
Describe the outer phalangeal cells. 1) Also known as Deiters' cells. 2) Forms cups holding the ends of the OHC. 3) Sends fine processes or phalanges up to the reticular lamina leaving spaces between the OHCs
Describe the Hensen's cells. 1) Provides lateral support to the OHCs and support to the TM
Types of connections between with Hensen's and Deiters' cells may have. May have synaptic connections to type II nerve fibers (afferent) and possibly some efferent fibers as well.
Purpose of the cells of Claudis. Add strength to the BM.
Purpose of Bottcher's cells. Interspersed between BM and Claudian cells, support hair cells and may contribute to maintaining ionic balance in the cochlea.
What cells does the TM lie on? Hensen cells
How many rows and what is the arrangement of OHCs? IHCs? OHC - 3-4 rows; 12,000 OHCs; Maybe more OHCs at the apical end IHC - 1 row for the IHCs arranged on opposing sides of pillar cells; 3,500 IHCs For both of them the nerve fibers connect, but do NOT touch, cell bodies.
Shape and dimensions of the OHCs. Cylinder-shaped; ~10 micrometers in diameter; Length range from 10-90 micrometers (longer in regions tuned to low freqs and shorter in regions tuned to high freqs.
What is the important protein in OHCs? Electrical charge of OHCs? Nucleus location? Mitochondria location? Potassium channel location? 1) Protein = prestin (contributes to OHC ability to move) 2) ~ - 60mV charge 3) Nucleus located at basally. 4) Mitochondria located at base. 5) K+ channels lie at bottom of the HC, which control ion flow out of the cell after depolarization.
Shape of stereocilia on OHC configuration. Number of stereocilia on OHC on base/apex. Primary type of nerves. Form a "W;" Graded in length; ~150 stereocilia at the base and ~50 at apex; Primarily efferent nerves.
Shape and dimensions of IHCs. Flask-shaped; ~35 micrometers in length; ~10 micrometers at the widest point.
Nucleus location? Shape of IHC configuration? Mitochondria location? Nerve fiber type? 1) Central 2) "U" shaped configuration 3) Mitochondria are scattered throughout and are more dense above nucleus 4) Nerve endings are situated at base of the cell and primarily afferent fibers
Composition of Stereocilia? What bonds them together to move as one unit? Composed of packed actin filaments, bonded in paracrystalline array. Bonded together by sideways-running link called "cross-links." Some of actin filaments continue into a rootlet, and anchors stereocilium into cuticular plate. Base is electron dense.
Describe the cuticular plate. Formed by actin filaments arranged in a dense matrix. The cuticular plate is a gap with a basal body.
Kinocilium. Vestibular HCs and embryonic HCs have one that comes from basal body. Kinocillium is the tallest.
Describe the height of the stereocilia. Longest at the apex and becomes shorter toward base. Tallest are at the lateral part of organ of Corti (away from the modiolus).
How does depolarization happen? Stereocilia in endolymph (high K+ and +80mV charge); Inside HC is ~-60mV charge. These differences permit K+ flow into cell. Tip-links connect stereocilia; connects mechanotransduction channels, opens channels when cilia move, opens pores for K+ ion flow.
What is the hair cell tuning? Tuned along the length of BM. HCs have a characteristic frequency (frequency to which the cell best responds). Cells at basal end = high freq and apical end = low freq. Freqs outside characteristic freq have to be more intense to excite the HC.
Created by: duda713