S2 Neuro Exam 5: Histology Of The Ear

Front 1

What is the external ear comprised of?

Back 1

skin over elastic cartilage (allows some sound defelection)

upper skin of meatus contains sebaceous glands & ceruminous glands that secrete cerum (ear wax)

(wax buildup can block meatus resulting in hearing loss)

Front 2

Obj.
Auditory segments of the external ear

Back 2

External auditory meatus-
cartilagenous tube partly w/i temporal bone
passage way for sound waves to reach tympanic membrane

Tympanic membrane-
"ear drum" located at end of meatus, connected to malleus of middle ear
vibrates with sound waves & transmits motion to malleus

Front 3

What are the 2 parts of the tympanic membrane?

Which is more flexible?

Back 3

pars tensa (5/6)- strong & fibrous
&
pars flaccida (1/6)- more flexible

Front 4

Describe the two collagen layers of the tympanic membrane

Back 4

outer-
radial

inner-
circular
covered by simple epithelium on outside & mucosa on inside

Front 5

Obj.
Auditory segments of the middle ear

Back 5

3 Ossicles (Malleus, incus, & stapes)

mechanical transduction chain btwn external & inner ear

malleus attached to middle of tympanic membrane (external)

stapes attached to oval window of vestibule (inner)

Front 6

The stapes, attached to the oval window by the annular ligament, transduces sound waves from ______ to _____ in the scala vestibule of the bony labyrinth

Back 6

from air (middle ear) to fluid (inner ear)

Front 7

What muscles attach to the malleus & stapes (for sound dampening= protect inner ear) & what are they innervated by?

Back 7

malleus-
tendon of tensor tympanic
trigeminal nerve (5)

stapes-
tendon of stapedius
facial nerve (7)

Front 8

Obj.
Auditory segments of the inner ear

Back 8

bony:
Cochlea
semicircular canals

membranous:
cochlear duct
semicircular ducts & ampullae

Front 9

Obj.
Vestibular segments of the inner ear

Back 9

bony:
(scala) vestibule - continuous w/ the subarachnoid space via cochlear aqueduct

membranous:
saccule & utricle

Front 10

The bony labyrinth is the space w/i the petros temporal bone. It is lined by fibrous periosteum that secretes ____________ via capilaries

Back 10

perilymph
(high Na+, low K+--> contributes electric potential)
(similar & continuous w/ CSF)

*surrounds all elements of membranous labryinth

Front 11

Obj.
Vestibular & auditory components of the Bony labyrinth

Back 11

vestibular-
scala vestibule- recieves sound from middle ear

auditory-
cochlea- coiled tube w/i temporal bone, wrapped around modiolus (including scala tympani portion)
semicircular canals

Front 12

What does the modiolus contain?

Back 12

afferent cell bodies for CN VIII (cochlear part)
spiral ganglion

Front 13

What are the 3 parts of the spiral tube that forms the cochlea?

Back 13

scala vestibuli & scala tympani (bony)
cochlear duct (scala media) (membranous)

scala vestibuli (connects to oval window)-->scala media-->scala tympani (connects to round window)

Front 14

The scala media/cochlear duct is separated from the scala vestibuli via ___________

& separated from the scala tympani via ____________

Back 14

vestubular (Ressiner's) membrane


basilar membrane (attached to bony cochlea via spiral lig & osseus spiral lamina of modiolus)

Front 15

Where is the Organ of Corti located?

What are the primary elements?

Back 15

on the basilar membrane w/i cochlear duct

hair cells (detectors), tectorial membrane (creates shear) & supporting cells (phalangeal cells, pillar cells) (structural, prevents collapse)

Front 16

Describe the structure of the basilar membrane (base of organ of corti)

Why is this significant?

Back 16

thinner/narrower at base, thicker & wider near helicotremma (thickens as ascends cochlear spiral)

Allows different frequency sounds to vibrate at different points (thickness)

Front 17

Describe the hair cells (Organ of Corti)

Back 17

hair = stereocilia w/ actin & linking proteins, w/o cilia

attached to cuticular plate, increase in height toward stria vascularis

Front 18

What is the function of the Organ of corti hair cells?

Back 18

when linking proteins bend (toward tallest stereocillium), open or close (cepolarize/hypopolarize) mechanoelectric transduction ion channels -->
depolarization = influx of Ca2+ & K+

*works w. potential created by endolymph/perilymph
(ion channel sensitivity can be adjusted by motor tensioning system)

Front 19

Differentiate btwn outer & inner hair cells

Back 19

1 inner layer:
moved by fluid shear, contact basilar membrane
provide afferent to spiral ganglia dendrites
primary receptors for sound & frequency discrimination

3 outer layers:
contact tentorial membrane (gel secreted by spiral lamina)
recieve efferent info from superior olive
held by reticular lamina
contain prestin= contract when depolarized
serve as an amplification system

Front 20

What would a loss of outer hair cells lead to?

Back 20

increased auditory threshold & reduced frequency discrimination
loss of otoacoustic emissions

(otoacoustic emissions- sound produced by contraction from incoming sound pulse)

Front 21

The membranous labyrinth is filled w/ _______ secreted by stria vascularis (psueduostratified epithelium on lateral scala media)

Back 21

endolymph (low Na+, high K+, opp perilymph)

Front 22

Obj.
Describe sound transduction into action potentials

Back 22

Perilymph (high Na+, low K+) & endolymph (high K+, low Na+) create an electrical potential w/i inner ear

Organ of Corti is the site of actual transduction of sound into AP
Fluid sound waves bend hair cells in Organ of Corti, hair cell open mechanoelectric transduction ion channels--> depolarization--> influx of K+ & Ca2+ --> action potential

Front 23

Obj.
Vestibular & auditory components of the Membranous labyrinth

Back 23

vestibular-
saccule & utricle (connected via utriculosaccular duct)

auditory-
cochlear duct/scala media (attached to saccule via ductus reuniens)
semicircular ducts & ampullae

Front 24

The utriculosaccular ducts is connected to the endolymphatic sac via the ________________

What is the function of the endolymphatic sac?

Back 24

endolymphatic duct (runs through vestibular canaliculus)

allows pressure relief from rapid small volume changes

Front 25

What does the vestibular apparatus consist of?

What is its innervation?

Back 25

vestibule & semicircular canals w/ ampullae
(includes static & kinetic labryinth)

sensory via dendrites from vestibular ganglion

Front 26

Obj.
How do static vestibular components function
Describe histology

Back 26

components= utricle + saccule (both membranous)

fxn= detects linear motion (via maculae)

Front 27

What are maculae?

Back 27

neural transducers
-contain hair cells embedded in otolith membrane
-central strola dense w/ otoconia (surrounded by hair cells)
(otolith membrane secretes otoconia via supporting cells)

Front 28

How do vestibular hair cells differ from auditory hair cells?

Back 28

orientation & direction of depolarization/hyperpolarization detects linear accelerations (not frequencies)

Front 29

Differentiate btwn type I & II vestibular hair cells

Back 29

Type I cells- provide the primary afferent information to vestibular ganglia dendrites.

Type II cells- receive most of the efferent information from the vestibular nuclei and appear to regulate sensitivity.

Front 30

The macula of the utricle is oriented parallel to the base of the skull, while the maculae of the saccule is vertical
What does this do?

Back 30

allows detection in changes in the static position of the head

Front 31

Obj.
How do kinetic vestibular components function
Describe histology

Back 31

components= semicircular canals

fxn= detects rotary motion

Front 32

The semicircular canals of the bony labyrinth are oriented in 3 planes relative to the head. What are the components of the semicircular canals?

Back 32

membranous:
crista of ampulla
endolymphatic (vestibular) ducts

bony:
ampulla (connects w/ vestibule)

Front 33

What is the structure/function of the crista of the ampulla (membranous)?

Back 33

structure:
ridge of hair cells embedded in gelatinous membrane (= cupula), extending into opposite wall of ampulla

function:
detect transduction of angular motion

Front 34

How are hair cells w/i the ampulla stimulated?

Back 34

shear forces of fluid w/i the semicircular canals as a result of rotary head movements---> hair cells interpret angular movement of the head (via hyperpolarizing/depolarizing) for the CNS