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Neuroscience > Cranial Nerve 8 > Flashcards

Cranial Nerve 8 Flashcards

1
Q

The anatomy of the ear can be broken down into 3 sections, what are they?

A
  1. External ear
  2. Middle ear
  3. Internal ear
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2
Q

what are the 3 structures of the external ear?

A
  1. auricle (pinna)
  2. external auditory canal
  3. ear drum (tympanic membrane)
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3
Q

what is the auricle (pinna)?

A

outer ear structure

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4
Q

what is the external auditory canal?

A

a tube connecting the auricle to the ear drum

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5
Q

what is the ear drum?

A

also called tympanic membrane

sheet across external auditory canal composed of:

epidermis, epithelium, and CT fibers (elastic)

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6
Q

what is the middle ear?

A

the small air-filled cavity within the ear

composed of 5 structures

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7
Q

what structures are inside of the middle ear?

A
  1. auditory ossicles
  2. oval window
  3. round window
  4. tensor tympani and stapedius muscles
  5. opening to the auditory tube (eustuchian tube)
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8
Q

what are the auditory ossicles?

A

the 3 smallest bones in the body:

malleus

incus

stapes

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9
Q

what is the malleus?

A

“the hammer”

connects ear drum to anvil (incus)

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10
Q

what is the incus?

A

“the anvil”

connects hammer to stirrup (stapes)

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11
Q

what is the stapes

A

“the stirrup”

connects anvil to oval window

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12
Q

what is the oval window?

A

a membrane covered opening into perilymph of cochlea

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13
Q

what is the round window?

A

a membrane covering opening in to the perilymph at the other end of the cochlea

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14
Q

what innervates the tensor tempani and stapedius muscles?

A

tensor tympani (V3)

stapedius (CN 7)

these contract to prevent damage to middle ear structures by loud noise

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15
Q

why is there an opening to auditory tube(eustachian tube) in the middle ear?

A

the opening connects the middle ear chamber to nasopharynx (upper throat) to equilibrate pressure in the ears

(the pop you hear during swallowing)

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16
Q

what is inside of the inner ear?

A
  1. bony labyrinth
  2. membranous labyrinth
  3. Vestibulocochlear nerve
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17
Q

what is the bony labyrinth in the inner ear?

A

a series of 3 structures lined by periosteum and containing perilymph

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18
Q

what are the 3 structures within the bony labyrinth?

A
  1. semicircular canals
  2. vestibule
  3. cochlea
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19
Q

what are the semicircular canals?

A

contain the sensory receptors (crista ampullaris) for equilibrium (angular)

lie at right angles in 3 geomtric planes within the inner ear

20
Q

what is the vestibule within the bony labyrinth?

A

contains sensory receptors (macula) for equilibrium (linear)

21
Q

what is the cochlea?

A

a part of the bony labyrinth that contains sensory receptors (spiral organ of corti) for hearing

22
Q

what is the membranous labyrinth?

A

sacs and tubes inside the bony labyrinth that have the same shape as the inside of the bony labryinth.

it is filled with endolymph

made up of 4 structures

23
Q

what are the 4 structures found within the membranous labyrinth?

A
  1. utricle - membranous sac → connected to semicircular canals
  2. saccule- membranous sac → connected to utricle
  3. membranous semicircular canal
  4. cochlear duct for hearing
24
Q

List the ganglia for the 1st order neurons of the Vestibulocochlear nerve

A
  1. vestibular branch → S/I vestibular ganglia
  2. cochlear branch → spiral ganglia
25
Q

what makes up the hearing apparatus within the spiral organ of corti?

A

a hair cell layer on the basilar membrane arranged around the spiral core of the cochlear bony labyrinth (modiolus);

hair cell stereo cilia are embedded in a matrix = tectoral membrane which does not move

26
Q

Define pitch and amplitude pertaining to sound waves

A
  1. pitch = frequency of sound waves
  2. amplitude = size of sound wave

pitch + amplitude = tone

27
Q

Describe the hearing pathway

(from outside the ear all the way to the spiral organ of corti)

A
  1. sound wave directed to eardrum by auricle and external auditory canal
  2. sound waves cause ear drum to vibrate
  3. vibration is amplified and transmitted to oval window by auditory ossicles
  4. pressure waves in peri- and endolymph
  5. pressure waves bend stereo-cilia of hair cells (in spiral organ of corti) embedded in tectoral membrane
  6. this produces a change in the pattern of signaling from the spiral organ of Corti
  7. this stimulates the peripheral process of the auditory sensory neuron
28
Q

is the direction of bend in the stereo-cilia of hair cells in the tectoral membrane important? How?

A

Yes

bend lateral direction → depolarization

bend medial direction → hyperpolarization

29
Q

T/F: different areas of the spiral organ of Corti are sensitive to different pitches?

A

TRUE

base = high pitch

apex = low pitch

30
Q

Describe the start of the auditory nerve pathway

(from recieving the signal to entering the brainstem)

A
  1. signal on bipolar neuron in spiral ganglia
  2. signals cochlear nerve
  3. cochlear nerve travels through petrous portion of temporal bone exiting the internal auditory meatus
  4. enters brainstem at junction of pons and medulla and synapses with dorsal and ventral cochlear nuclei in tonotopic manner
31
Q

what are the 3 destinations for the auditory nerve after it synapses with the 2nd order neurons in the cochlear nuclei?

A
  1. tectum → tectospinal head turning reflex
    1. inferior and superior colliculus
  2. medial geniculate body of thalamus → heads to auditory cortex next
  3. reticular formation → activates the CNS
32
Q

do fibers from the cochlear nucleus cross to the contralateral side?

A

most fibers do (at the trapezoid body)

some stay ipsilateral

but bilateral projections to the cortex allow discrimination of sound differences in each ear

33
Q

In order for us to have equilibrium we need what type of information?

A

linear acceleration → change in velocity when traveling in one direction

angular acceleration → change in velocity when rotating

34
Q

what is our organ of equilibrium?

A

Vestibular apparatus within the inner ear

35
Q

what are the 2 sensory receptors within the Vestibular Apparatus and what are they sensitive to?

A
  1. macula → linear acceleartion
  2. crista ampullaris → angular acceleration
36
Q

what/where are the macula?

A

2 thickened regions in the walls of the utricle and saccule

37
Q

what/where are the crista ampullaris?

A

elevations in the lumen of each semicircular canal

sensory receptors for angular acceleration

38
Q

describe the makeup of the macula

A
  1. support cells
  2. hair cells (containing stero cilia/microvilla)
  3. otolithic membrane
39
Q

how do the macula respond to stimuli?

A

body movement causes the otolithic membrane to move and bend the sterocilia of the hair cell resulting in either

depolarization/hyperpolarization of the membrane

this changes the pattern of excitation/inhibition from the utricle and saccula macula to the Vestibular nerve

40
Q

describe the makeup of the crista ampullaris

A
  1. support cells
  2. hair cells (contain sterocilia and kinocilia)
  3. cupula (gelatinous ECM in which the stereocilia are embedded)
41
Q

how does the crista ampularris respond to stimuli?

A

rotational movement of the head bends the sterocilia of the hair resulting in membrane depolarization/hyperpolarization

to change the pattern of excitation/inhibition from the crista ampullaris to the vestibular nerve

42
Q

When the crista ampullaris on the L side is depolarized, the one on the R side is _______

A

hyperpolarizaed

43
Q

Describe the Vestibular pathway

(from sensory receptors to brainstem nuclei)

A
  1. bending sterocilia of hair cell
  2. depolarize/hyperpolarize the hair cell
  3. change in pattern of excitation/inhibition of peripheral axon of bipolar neuron in vestibular ganglia
  4. central axon forms vestibular branch of vestibulocochlear nerve
  5. exit petrous portion of temporal bone at internal acoustic meatus
  6. enter brainstem at junction of pons and medulla
  7. Fibers head to S/I and M/L vestibular nuclei
44
Q

Fibers from the semicircular canals, utricle, and saccule all go to specific vestibular nuclei. List them

A
  1. semicircular canal (crista ampullaris) → superior and medial vestibular nuclei
  2. utricle maculae → lateral vestibular nuclei
  3. saccule maculae → lateral and inferior vestibular nuclei
45
Q

Where do the vestibular nuclei project to after receiving input from the crista ampullaris and maculae?

A
  1. cerebellum flocculonodular lobe
  2. cervical spinal cord head turning muscles
    • medial vestibulospinal tract
  3. both cervical and lumbar spinal cord extensor muscles
    • lateral vestibulospinal tract
  4. CN III, IV, VI nuclei (via MLF)
  5. MLF
46
Q

Where do vestibular nuclei that project to the MLF head next?

A

bilateral ventro-basal complex of the thalamus

then

premotor and other regions of cerebral cortex (post central and adjacent associative cortex dealing with head proprioception)

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