Ear - Inner ear

Question 0

Nerve in the inner ear

Answer 0

Two divisions of CN VIII - cochlear and vestibular

Question 1

What are the two portions of the inner ear?

Answer 1

Vestibular portion (balance) - semicircular canals and structures of the vestibule
Cochlear portion (auditory sense)

Question 2

What makes up the vestibular component of inner ear

Answer 2

Uticle, saccule (2 maculae, 1 in the uticle and 1 in the saccule) and 3 semcircular canals.
Determine the position and motion of the head to maintain balance

Question 3

Describe the uticle and saccule structure

Answer 3

Lied by epithelium
Elaborated in two spots, or maculae
In maculae, the simple squamous becomes simple columnar with as many as 5-0100 stereocilia and a single kinocilium. Sensory structures

Question 4

Describe the semicircular canals

Answer 4

Three - horizontal, frontal, saggital.
Each contains a semicircular duct which are continuous with the uticle
Ampullae are located at the junction of the semicircular ducts and the uticle (expansions in the diameter of the ducts)
Most of the structure is lined with epithelium by the ampullae is elaborated to form sensory units called the cristae ampullaris (like maculae in the uticle/saccule)

Question 5

What are the ampullae? Relation to cristae ampullaris?

Answer 5

3 ampullae - one per semicircular duct / uticle joint
3 cristae ampullaris - one per ampullae and site of sensory cells (simple columnar with stereocilia and single kinocilium

Question 6

What is the function of sensory cells in the maculae?

Answer 6

Transduce mechanical stimulation into neural impulses

Question 7

Describe the effect of bending hairs in the maculae

Answer 7

One direction depolarizes and the other direction hyperpolarizes

Question 8

What are type I hair cells?

Answer 8

Axon terminal completely invests in the rounded base

The apical surface has a single kinocilium and a cluster of specialized stereocilia

Question 9

What are type II hair cells?

Answer 9

Axon terminals in the form of small terminal boutons

Kinocilum and stereocilia are present

Question 10

What are support cells?

Answer 10

Surround hair cels and provide nutrients

Question 11

What is the otolithic membrane?

Answer 11

An overlying gelatinous mass that the stereocilia and the kinocilia extend into. Contains calcium carbonate particles known as otoliths

Question 12

What is the function of otholiths?

Answer 12

Mass contributes to inertial force that will cause displacement of the otholithic membrane and thus the bending the hair

Question 13

Describe the orientation of the maculae

Answer 13

At right angles to each other (saccule and utricle)

They are now sensitive to static head position and linear acceleration in two major body planes

Question 14

Describe the function of the sensory cells in the semicircular canals

Answer 14

Movement of endolymph bends the hairs that are embedded in an overlying gelatinous mass
The cristae in the ampullae of the semicircular ducts are sensitive to rotational movement of the head in the three major body planes

Question 15

Utricle detects?? Semicircular canal detects?

Answer 15

Utricle - linear motion

Semicircular canal - rotation

Question 16

What is the cochlea?

Answer 16

A snail-shell shaped canal within the temporal bone. The cochlear duct is suspended within the cochlear region of the membranous labyrinth

Question 17

Describe the structure of the cochlear duct

Answer 17

External walls - stria vascularis attached to the wall of the bony cochlea. Superior to that is the vestibular (Reissner’s membrane). Inferior is the basilar membrane.
Internal walls lined by epithelial cells. Those that are taller and specialized for sensory reception are in the organ of Corti

Question 18

What is the Reissner’s (vestibular) membrane?

Answer 18

Separates the cochlear duct from the scala vestibuli. Superior portion of the cochlea.

Question 19

What is the basilar membrane?

Answer 19

Separates the cochlear duct from the scala tympani and supports the organ of corti. Inferior portion of the cochlea

Question 20

The cochlear duct is filled with?

Answer 20

Endolymph

Question 21

The scala vestibuli and the scala tympani are filled with?

Answer 21

Perilymph, part of the bony labyrinth

Question 22

Describe the organ of corti

Answer 22

Contains sensory cells that are columnar epithelial which rest of the basilar membrane.
There are NO kinocilia

Question 23

What are the two populations of hair cells in the organ of corti

Answer 23

Single row near the central axis called inner hair cells

Three rows of cells farther away from the axis called outer hair cells.

Question 24

What is the tectorial membrane?

Answer 24

The gelatinous mass in which the tips of the stereocilia of the hair cells of the organ of corti embed in

Question 25

Describe the path of sound into the ear

Answer 25

Enters at the tympanic membrane. The foot of the stapes transmits pressure wave to the perilymph of the cochlea. This sets up a differential between the peilymph of the scala tympani and the endolymph of the cochlear duct. The basilar membrane vibrates. Because the basilar membrane and the tectorial membrane in the organ of corti are not connected the movement causes the bending of hair cells within the organ of corti. Signal!

Question 26

How is sound transmitted from the middle ear to the inner ear?

Answer 26

Vibration of tympanic membrane moves the ossicles and the stapes vibrates the oval window causing pressure wave in the perilymph of the scala vestibuli

Question 27

Describe resonance in the basilar membrane

Answer 27

Amplitude of pressure wave increases as a function of the frequency of sound. Amplitude peaks at the portion of the basilar membrane where resonance occurs.

Question 28

Describe frequency of sound in context of basilar membrane

Answer 28

The basilar membrane increases in width from the base of the cochlea towards the apex.
Higher frequency sounds are registered at the base and low frequency sounds register near the apex.
Certain cells are associated with these hair cells and the brain interprets their signals as different frequencies

Question 29

What is the function of the scala tympani?

Answer 29

Pressure waves transmitted from the scala vestibuli and into cochlear duct are mimicked in the scala tympani.
The scala tympani dissipates the sound waves through he round window in order to keep the basilar membrane from constantly being stimulated

Question 30

Stereocilia in the organ of corti sensory cells are found to be in what shape?

Answer 30

U-shaped in SEM

Question 31

What is otitis media?

Answer 31

infection of the middle ear that originates from pathogens traveling up the Eustachian tube from the nasopharynx.
Common in infants because of underdeveloped skull.
Recurring cases are treated with drainage tubes to allow fluid to drain from the middle ear through the tympanic membrane

Question 32

What is otosclerosis?

Answer 32

The formation of extra bone between the stapes and oval window or the stapes and incus which results in progressive deafness
Autosomal dominant hereditary defect

Question 33

What is sensory hair toxiticty?

Answer 33

Drug induced, irreversible damage of vestibular or cochlear sensory cells
Linked to antibiotics, diuretics, antimalarial drugs, nitrogen mustard, and salicylates

Question 34

What is acoustic trauma?

Answer 34

Noise induced hearing loss
Earliest damage occurs in the external hair cells of the organ of corti and is associated with deformation, swelling, and disintegration of the hair cells. Progressive injury leads to damage of supporting cells.
Tensor tympani and stapedius are not able to attenuate the sound