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Head and Neck Physiology > Auditory System > Flashcards

Auditory System Flashcards

1
Q

What is sound?

A

Sounds are audible variations in air pressure
- Many sources of sound produce variations in air pressure that are rhythmic

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2
Q

What is sound frequency?

A

Sound frequency is the number of sound cycles per second (Hertz)
- We perceive high- frequency waves as having a higher pitch
- We perceive high-intensity waves as louder

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3
Q

What frequencies do people hear at?

A

Our auditory system can respond to pressure waves over the remarkable range of 20 Hz to 20,000 Hz

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4
Q

What is pitch?

A

high or low tone
- determined by the frequency

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5
Q

What is intensity?

A

amplitude
- Sound intensity determines the loudness we perceive
- loud sounds having higher intensity

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6
Q

What sound intensity damages the ears?

A
  1. Noise above 70 decibels (dB) over a prolonged period of time may start to damage your hearing.
  2. Loud noise above 120 dB can cause immediate harm to your ears
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7
Q

Describe the outer ear?
Function?

A
  • Pinna to tympanic membrane/ear drum
  • The “pre amp” – makes sound waves stronger
  • Pinna for humans has a poor design (too flat on head) so try “cupping” ears and see how sound quality improves
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8
Q

Describe the tympanic membrane?

A
  • A thin semi-transparent partition between the outer ear and middle ear.
  • Covered by epidermis and lined by simple cuboidal epithelium.
  • Tears usually heal in a month
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9
Q

Histology of the external auditory canal?

A

The external auditory canal is lined with hairs and specialized sweat glands called ceruminous glands
- Ceruminous glands secrete cerumen /earwax

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10
Q

2 important functions of earwax?

A
  1. Keeps skin in ear canal soft (lubrication)
  2. Keeps bugs out (they don’t like the taste)
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11
Q

Parts of the middle ear?

A
  1. Back of tympanic membrane
  2. 3 small bones (malleus, incus and stapes)
  3. Eustachian /auditory/ pharyngotympanic tube
    - Sound waves change to mechanical energy in the middle ear
    - Separated from inner ear by the round and oval windows
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12
Q

Describe the set-up of the ossicles in the middle ear?

A
  • The handle of the malleus is attached to the inner wall of the tympanic membrane
  • The head of the malleus is attached by a tiny synovial joint to the incus, which is in turn attached by a tiny synovial joint to the stapes.
  • The foot plate of the stapes is held in place in the oval window by a flexible annular ligament
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13
Q

Function of the ossicles?

A

Transmit vibrations from the tympanic membrane to the oval window

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14
Q

Why can`t sound waves simply directly move the membrane at the oval window?

A
  • the cochlea is filled with fluid, not air
  • The fluid in the inner ear resists being moved much more than air does (i.e., fluid has greater inertia), so more pressure is needed to vibrate the fluid than the air can provide.
  • The ossicles provide this necessary amplification in pressure
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15
Q

When will the pressure at the oval window become greater than the pressure at the tympanic membrane?

A
  1. the force on the oval window membrane is greater than that on the tympanic membrane
  2. the surface area of the oval window is smaller than the area of the tympanic membrane.
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16
Q

How does the middle ear increase pressure at the oval window?

A

force applied onto a larger area (tympanic membrane) is concentrated onto a smaller area (oval window)
- The force at the oval window is greater because the ossicles act like levers
- increases pressure by 20 times

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17
Q

What are the muscles of the middle ear?

A
  1. The tensor tympani muscle
    - innervated by the trigeminal nerve
    - is anchored to bone in the cavity of the middle ear at one end and attaches to the malleus at the other end
  2. The stapedius muscle
    - innervated by the facial nerve
    - also extends from a fixed anchor of bone and attaches to the stapes
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18
Q

Function of the muscles of the inner ear?

A

When these muscles contract, the chain of ossicles becomes much more rigid, and sound conduction to the inner ear is greatly diminished

19
Q

What is the attenuation/acoustic reflex?

A

The onset of a loud sound triggers a neural response that causes the tensor tympani and stapedius muscle to contract the chain of ossicles becomes much more rigid, and sound conduction to the inner ear is greatly diminished
Note: Sound attenuation is much greater at low frequencies than at high frequencies
- Since the reflex suppresses low frequencies more than high frequencies, it is thought to be activated when we speak, so we don’t hear our own voices as loudly as we otherwise would

20
Q

What is a limitation of the attenuation reflex?

A

the attenuation reflex has a delay of 50–100 msec from the time that sound reaches the ear
- Does not offer much protection from very sudden loud sounds
- damage might already be done by the time the muscles contract.

21
Q

Functions of the Eustachian/auditory tubes?

A
  1. Drain cells/tissue
  2. Equalize air pressure between outside air and middle ear cavity
    - Normally closed, opened when yawning, chewing, swallowing
22
Q

What are the clinical correlates for the Eustachian tube?

A

The most common type of ear infections (otitis media) is caused by pathogens that travel from the throat and nose via the auditory tube
- Children more susceptible because their auditory tubes are shorter, narrow, almost horizontal (45° tilt in adults) which decreases drainage efficiency

23
Q

Describe the structure of the auditory tube?

A

The first third of the tube beginning at the middle ear is surrounded by bone and the remainder is surrounded by an incomplete ring of elastic cartilage
- The meeting point of the bony and cartilaginous portions is called the isthmus

24
Q

Describe the importance of the auditory tube?

A

Cells lining middle ear absorb air (negative pressure) thus constant supply from Eustachian tube is necessary

25
Q

What happens when the auditory tube is blocked?

A

When the tube is blocked, the eardrum is sucked into the middle ear (pain, pressure, hearing loss)

26
Q

What causes blockage of the auditory tube?

A
  1. inflammation of nasal lining narrows opening or passageway
  2. nasal allergy
  3. obesity (excess fat deposits along passageway)
27
Q

Fullness in the ears can be alleviated by?
How?

A

Fullness in the ears (negative pressure in middle ear) can be alleviated by ‘popping’ the ears
- Yawning or swallowing opens the eustachian tube by contracting the tensor palatini muscles
Note: The hook-shaped arrangement of the Eustachian tube cartilage keeps the tube in the normally closed state.
- The tube is opened when the cartilage hook is uncurled by action of the tensor palatini muscle

28
Q

What is the cochlea?

A

Snail-shaped, pea-sized, filled with fluid

29
Q

What does the cochlea consist of?

A
  1. the scala vestibuli
    - perilymph similar to CSF
    - low K+ (7 mM) and high Na+ (140 mM) concentrations]
  2. the scala media
    - endolymph with ionic concentrations similar to intracellular fluid
    - high K+ (150 mM) and low Na+ (1 mM).
  3. the scala tympani
    - perilymph similar to CSF
    - low K+ (7 mM) and high Na+ (140 mM) concentrations
30
Q

Describe the cochlea’s role in hearing?

A
  • At the base of the cochlea, the scala vestibuli meets the oval window and the scala tympani meets the round window.
  • Inward motion at the oval window pushes perilymph into the scala vestibuli.
  • Because the fluid pressure has nowhere else to escape, the membrane at the round window bulges out in response to the inward movement of the membrane at the oval window
31
Q

What is the cochlear aqueduct?

A
  • A small canal in the bony labyrinth that contains the perilymphatic duct, which drains perilymph into the cerebrospinal fluid of the subarachnoid space
  • The lateral end arises from the scala tympani
32
Q

What is the endolymphatic sac and duct?

A
  • In the membranous labyrinth
  • drain endolymph from the auditory and vestibular apparatus
  • the sac acts as both a reservoir for endolymph and the site for reabsorption into the epidural space
33
Q

Describe the organ of Corti?

A
  1. on the surface of the basilar membrane
  2. Contains a series of electromechanically sensitive cells, the hair cells (20,000).
    - Hair cells are specialized epithelial cells
    - Each hair cell has about 100 stereocilia on its apical border
    - They extend above the reticular lamina into the endolymph
    - They are sandwiched between the basilar membrane and a thin sheet of tissue called the reticular lamina
  3. The rods of Corti (pillar cells) span these two membranes and provide structural support
34
Q

Name and describe the cells of the organ of corti?

A
  1. inner hair cells
    - Hair cells between the modiolus and the rods of Corti (about 4500 form a single row)
    - tips of sterocilia end just below the tectorial membrane
  2. outer hair cells
    - Cells farther out than the rods of Corti are called outer hair cells (12,000–20,000 arranged in three rows)
    - tips of sterocilia end in the gelatinous substance of the tectorial memmbrane
35
Q

Function of hair cells?

A

Generate nerve impulses in response to sound vibrations

36
Q

What is an important structural component of hair cells that aids in auditory signal transduction?

A
  1. Stereocilia become progressively longer on the side of the hair cell away from the modiolus
  2. The tops of the shorter stereocilia are attached by thin filaments to the back sides of their adjacent longer stereocilia
37
Q

Describe auditory signal transduction?

A
  1. Whenever the cilia are bent in the direction of the longer ones, the tips of the smaller stereocilia are tugged outward from the surface of the hair cell.
    - This causes a mechanical transduction that opens 200 to 300 cation-conducting channels
  2. K+ influx from the surrounding scala media fluid into the stereocilia,
    depolarization of the hair cell membrane
  3. The entry of K+ depolarizes the hair cell, which opens voltage-gated calcium channels.
  4. Ca2+ influx triggers the release of the neurotransmitter glutamate, which activates the spiral ganglion fibres lying postsynaptic to the hair cell
38
Q

Describe the centralauditory pathways?

A

Afferents from the spiral ganglion enter the brain stem in the auditory–vestibular nerve.
At the level of the medulla, the axons innervate the dorsal cochlear nucleus and ventral cochlear nucleus ipsilateral to the cochlea where the axons originated
From the cochlear nucleus, auditory info is transmitted to
superior olivary nuclei (pons, decussation)
lateral lemniscus (midbrain)
inferior colliculus (midbrain)
medial geniculate nuclei (thalamus)
All levels of the central auditory system receive and process information from both the ipsilateral and contralateral sides

39
Q

What is otitis externa?

A

inflammation of outer ear

40
Q

What is otitis media?

A

inflammation of middle ear

41
Q

What is cholesteatoma?

A

benign tumour)
a skin-lined cyst that begins at the margin of the eardrum and invades the middle ear and mastoid

42
Q

What is hearing loss?

A
  1. Conductive hearing
    - damage to or obstruction of the outer or middle ear
  2. Sensorineural hearing loss
    - gradual loss of hearing resulting from an abnormality in either the inner ear, the auditory nerve, or both
43
Q

What is tinnitus?

A

ringing in the ear
1. exposure to loud noise
2. normal aging
3. infections

Head and Neck Physiology (18 decks)

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