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ANP1106 > hearing and balance > Flashcards

hearing and balance Flashcards

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1
Q

What are the 3 major ear regions and their functions?

A

External (outer) ear: Hearing only (collects sound)

Middle ear (tympanic cavity): Hearing only (amplifies sound)

Inner ear: Hearing + equilibrium

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2
Q

Auricle (pinna)

A

shell-shaped structure surrounding ear canal that
functions to funnel sound waves into auditory canal
▪ Helix: cartilaginous rim
▪ Lobule: fleshy earlobe

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3
Q

External acoustic meatus (auditory canal)

A

▪ Short, curved tube lined with skin bearing hairs, sebaceous
glands, and ceruminous (earwax) glands
▪ Transmits sound waves to eardrum

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4
Q

Tympanic membrane (eardrum)

A

– Boundary between external and middle ears
– Thin, translucent connective tissue membrane
– Vibrates in response to sound
– Transfers sound energy to bones of middle ear

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5
Q

The middle ear (tympanic cavity)

A

a small, air-filled, mucosa-lined cavity in temporal bone
– Flanked laterally by eardrum
and medially by bony wall
containing oval and round
membranous windows

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6
Q

Epitympanic recess

A

superior portion of middle ear (roof of cavity)

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7
Q

Mastoid antrum

A

canal for communication with mastoid air cells in mastoid process

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8
Q

Pharyngotympanic (auditory)
tube

A

connects middle ear to
nasopharynx
- Usually flattened tube, but
can be opened by yawning or
swallowing to equalize
pressure

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9
Q

Auditory ossicles

A

– Malleus: the “hammer” is secured to eardrum
– Incus: the “anvil”
– Stapes: the “stirrup” base fits into oval window

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10
Q

Which muscles protect against loud sounds?

A
  • Tensor tympani (attached to malleus)
  • Stapedius (attached to stapes)
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11
Q

What nerves control these muscles?

A
  • Tensor tympani: Trigeminal (CN V)
  • Stapedius: Facial (CN VII)
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12
Q

How do the auditory ossicles connect to each other?

A
  • Synovial joints link: Malleus → Incus → Stapes
  • Suspended by ligaments
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13
Q

What is the bony labyrinth?

A
  • A system of channels and cavities through bone
  • Contains perilymph fluid (CSF-like)
  • Has 3 regions: Cochlea (hearing), Vestibule, Semicircular canals (equilibrium)
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14
Q

What is the membranous labyrinth?

A
  • Membrane-lined sacs/ducts inside bony labyrinth
  • Contains endolymph (K⁺-rich fluid)
  • Follows bony labyrinth contours
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15
Q

What is the vestibule and what does it contain?

A
  • Central egg-shaped cavity of bony labyrinth
  • Contains two sacs:
    Saccule: Continuous with cochlear duct
    Utricle: Continuous with semicircular canals
  • Sacs house equilibrium Receptor region called maculae (respond to gravity/head position)
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16
Q

Describe the semicircular canals’ structure and function.

A
  • Three canals (anterior, posterior, lateral) in 3 planes
    *Snaking through each semicircular canal is a corresponding membranous semicircular duct, which communicates with the utricle anteriorly
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17
Q

Ampulla

A

enlarged area of
ducts of each canal that
houses equilibrium receptor
region called the crista
ampullaris

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18
Q

What is the cochlea and what is its function?

A

a spiral, conical, bony chamber about the size of a split pea. extends from vestibule

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18
Q

What is the crista ampullaris and what does it do?

A
  • Equilibrium receptor in each ampulla
  • Detects rotational head movements
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19
Q

What is the modiolus in the cochlea?

A

a bony pillar around which the cochlea coils. It provides the central structure of the cochlea.

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20
Q

What is the cochlear duct?

A

known as the scala media, the cochlear duct is the membranous part of the cochlea that runs through its center and contains endolymph.

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21
Q

What is the spiral organ (organ of Corti)?

A

The spiral organ is located within the cochlear duct

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22
Q

What is the scala vestibuli?

A

part of the bony labyrinth, begins at the oval window, and contains perilymph. It is continuous with the vestibule

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23
Q

What is the scala media (middle scala)?

A

the cochlear duct, part of the membranous labyrinth, and it contains endolymph

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24
What is the scala tympani?
part of the bony labyrinth, contains perilymph, and ends at the round window
25
What is the helicotrema?
region at the cochlear apex where (scala vestibuli and scala tympani) become continuous with each other.
26
What is the vestibular membrane and where is it located?
the "roof" of the cochlear duct, separating the scala media from the scala vestibuli.
26
What is the stria vascularis?
the external wall of the cochlear duct. It’s a highly vascularized mucosa that secretes endolymph.
27
What forms the "floor" of the cochlear duct?
the osseous spiral lamina and the basilar membrane
28
How are hair cells arranged in the spiral organ?
There is one row of inner hair cells and three rows of outer hair cells, positioned between the tectorial membrane and the basilar membrane.
29
What is the spiral organ (organ of Corti) composed of?
consists of supporting cells and cochlear hair cells, which are the receptor cells for hearing
30
What happens at the tympanic membrane when sound enters the ear?
Sound waves enter the external acoustic meatus, strike the tympanic membrane, and cause it to vibrate at the same frequency. Greater intensity causes greater membrane displacement.
31
What role do the auditory ossicles play in sound transmission?
They amplify and transfer vibrations from the tympanic membrane to the oval window, acting like a lever/piston system.
32
How does sound travel through the scala vestibuli?
Vibrations from the stapes push perilymph in the scala vestibuli. Because fluids can’t be compressed, the round window bulges outward to relieve pressure into middle ear cavity
33
What happens to low-frequency sounds in the cochlea?
They travel the helicotrema path—through the scala vestibuli, around the helicotrema, and down the scala tympani—but do not activate the spiral organ, so they are not heard.
34
What happens to audible/high-frequency sounds?
They take a shortcut through the cochlear duct, vibrate the basilar membrane, and stimulate hair cells, generating action potentials sent to the brain.
35
What is resonance in the basilar membrane?
It's the movement of specific regions of the basilar membrane in response to specific sound frequencies.
35
How does the basilar membrane change along its length?
Near the oval window: fibers are short and stiff Near the cochlear apex: fibers are longer and floppier
36
Which part of the basilar membrane responds to high-frequency sounds?
The base (near oval window) — short, stiff fibers resonate with high-frequency waves.
37
Which part of the basilar membrane responds to low-frequency sounds?
The apex (near helicotrema) — long, floppy fibers resonate with low-frequency waves.
38
What is the role of the basilar membrane in sound processing?
mechanically processes sound based on frequency before the signal reaches the receptors (hair cells).
39
What causes excitation of inner hair cells?
Movement of the basilar membrane deflects their stereocilia, which are embedded in the tectorial membrane and bathed in K⁺-rich endolymph.
40
What happens when stereocilia bend toward the tallest ones?
Tip links tighten Ion channels open K⁺ and Ca²⁺ enter → Depolarization
41
What happens when stereocilia bend toward the shortest ones?
Tip links relax Ion channels close Cell becomes repolarized or hyperpolarized
42
What is the function of tip links?
They connect stereocilia and open ion channels when pulled.
43
What do outer hair cells do?
Receive efferent signals from the brain Contract or stretch to adjust basilar membrane stiffness
44
What are the two functions of outer hair cell activity?
Amplify motion of the basilar membrane (fine-tuning inner hair cell response) Protect inner hair cells by decreasing motion in response to loud sounds
45
Describe the pathway that auditory signals take from the inner ear to the brain.
Cochlear receptors (inner hair cells) generate action potentials. - Signals travel in the spiral ganglion. - Afferent fibers form the vestibulocochlear nerve (CN VIII). - Signals synapse in the cochlear nuclei of the medulla. - Neurons project to the superior olivary nucleus (medulla-pons junction). - Signals ascend via the lateral lemniscus to the inferior colliculus (midbrain reflex center). - medial geniculate nuclues (thalamus) - axons project to the primary auditory cortex for conscious perception.
46
What is equilibrium and what sensory systems contribute to it?
Equilibrium is the response to head movements and relies on input from the inner ear (vestibular apparatus), eyes, and stretch receptors in muscles and joints.
47
What structures make up the vestibular apparatus and what do they monitor?
Vestibular receptors (in the vestibule) monitor static equilibrium (maculae). Semicircular canal receptors monitor dynamic equilibrium (cristae ampullares).
48
What are maculae and where are they located?
Sensory receptor organs located in each saccule and utricle wall that monitor static equilibrium and linear acceleration.
49
Describe the anatomy of a macula.
- Hair cells with stereocilia and a true kinocilium. - Stereocilia embedded in the otolith membrane, which is studded with otoliths (calcium carbonate crystals). - Hair cells synapse with vestibular nerve fibers.
50
What happens when hair cells bend toward or away from the kinocilium?
- Toward kinocilium: depolarization → increased neurotransmitter release → more APs. - Away from kinocilium: hyperpolarization → less neurotransmitter release → fewer APs.
51
52
What is the crista ampullaris and what does it detect?
Receptor for rotational (angular) acceleration. Located in the ampulla of each semicircular canal.
53
What is the function of the ampullary cupula?
A gel-like mass into which hair cells an supporting cells extent or project into; it bends due to endolymph movement during rotation, stimulating the hair cells.
54
Where is equilibrium information sent in the brain?
To vestibular nuclei in the brainstem and the cerebellum. This allows for fast, reflexive responses to prevent imbalance.
55
How does head movement bend hair cells?
Head tilts → density of otolith membrane lags due to inertia Stereocilia base moves with the rate of head → tips embedded in otolith pulled by membrane causes bending Bending opens ion channels → depolarization
56
Why do hair cells in opposite ears respond differently to rotation?
One ear depolarizes (excited) Other ear hyperpolarizes (inhibited)
57
movement of endolymph during movement
Endolymph in the semicircular duct lags behind due to inertia. This causes the ampullary cupula (gel-like cap over hair cells in the crista ampullaris) to bend in the opposite direction of the head movement. Bending of the cupula → hair cells are stimulated, leading to: Depolarization if bent toward the kinocilium. Hyperpolarization if bent away from the kinocilium. The brain interprets this bending as rotational movement.
58
movement of endolymph during deceleration or stopping
The endolymph keeps moving briefly because of inertia (even though your head has stopped). This causes the endolymph moves in the direction of the rotation and endolymp flow will bend cupula in the opposite direction of the initial movement. You may feel dizzy or like you’re still moving briefly

ANP1106 (8 decks)

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