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Human Physiology 2 - Unit 1 - Zach H. > Lecture 9: Auditory Senses > Flashcards

Lecture 9: Auditory Senses Flashcards

1
Q

What is the conduction pathway sequence?

A
  • tympanic membrane
  • malleus
  • incus
  • stapes
  • oval window
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2
Q

What are the 3 auditory ossicles?

A
  • malleus (hammer)
  • incus (anvil)
  • stapes
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3
Q

What does the malleus attach to?

A

tympanic membrane

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4
Q

You know the malleus attaches to the tympanic membrane, but what does it articulate with?

A

incus (anvil)

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5
Q

What auditory ossicle is located between the malleus and the stapes?

A

incus (anvil)

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6
Q

What does the stapes insert into?

A

oval window

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7
Q

What are the openings of the middle ear (tympanic cavity)?

A
  • Oval Window
    • the stapes attaches to the membrane covering the oval window
    • the oval window opens into the scala vestibuli
  • Round Window
    • this membrane-covered region is at the end of the scala tympani
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8
Q

What are the two muscles found in the inner ear?

A
  • tensor tympani
  • stapedius
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9
Q

What does the tensor tympani insert on and what is its function?

A
  • inserts on malleus
  • pulls handle of malleus inward
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10
Q

What does the stapedius insert on and what is its function?

A
  • inserts on the stapes
  • pulls stapes outward
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11
Q

Which 2 muscles contract reflexively in response to loud sounds in order to dampen the vibrations of the auditory ossicles?

A
  • tensor tympani
  • stapedius
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12
Q

Where is the round window located within the middle ear?

A

This membrane-covered region is at the end of the scala tympani.

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13
Q

What attaches to the oval window in the middle ear? Also, what does the oval window open into?

A
  • stapes attaches to the membrane covering the oval window
  • the oval window opens into the scala vestibuli
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14
Q

True or False:

The tympanic membrane surface area is about 17 times that of the surface area of the stapes.

A

True

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15
Q

What increases the force from the ossicular lever system to the cochlear fluid by 22x?

A

The tympanic membrane suface area being 17 times that of the surface area of the stapes.

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16
Q

What provides the impedance matching between the air and the fluid?

A

Tympanic membrane and auditory ossicles.

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17
Q

What does the tensor tympani do?

A

pulls handle of malleus inward

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18
Q

What does the stapedius muscle do?

A

pullls stapes outward

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19
Q

What effect do the opposing forces caused by the ossicular musclular system have?

A

Reduce sound transmission - protection mechanism to shield the inner ear from damage due to intense sound.

  • These two forces oppose each other and thereby cause the entire ossicular system to develop increased rigidity, thus greatly reducing the ossicular conduction of low-frequency sound, mainly frequencies below 1000 cycles/sec.
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20
Q

What is the function of the attenuation reflex?

A
  • protect the cochlea from damaging vibrations caused by excessively loud sound
  • to mask low-frequency sounds in loud environments.
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21
Q

What effect do the stapedius and tensor tympani muscles have on a person’s sensitivity to his or her own speech?

A
  • Another function of the tensor tympani and stapedius muscles is to decrease a person’s hearing sensitivity to his or her own speech. This effect is activated by collateral nerve signals transmitted to these muscles at the same time that the brain activates the voice mechanism.
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22
Q

What is impedance matching?

A

Middle ear is an efficient impedance transformer. This will convert low pressure, high displacement vibrations into high pressure of the air into, low displacement vibrations suitable for driving cochlear fluids.

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23
Q

How would hearing sensitivity be affected in the absence of the ossicular system and the tympanic membrane?

A
  • In the absence of the ossicular system and tympanic membrane, sound waves can still travel directly through the air of the middle ear and enter the cochlea at the oval window.
  • However, the sensitivity for hearing is then 15 to 20 decibels less than for ossicular transmission—equivalent to a decrease from a medium to a barely perceptible voice level.
  • Harder to hear!
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24
Q

What are the major components of the cochlea?

A
  • Scala vestibuli
  • Scala media
  • Scala tympani
  • Reissner’s membrane
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25
Q

Which components of the cochlea make up the three side-by-side coiled tubes?

A
  • Scala vestibuli
  • Scala media
  • Scala tympani
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26
Q

What is the function of the Reissner’s membrane (vestibular membrane)?

A
  • Separates scala media from scala vestibuli.
    • because of the thinness of Reissner’s membrane, the scala media and vestibuli are considered to be a songle chamber as far as sound conduction is concerned.
    • Reissner’s membrane maintains a special fluid within the scala media.
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27
Q

Which membrane separates the scala media from the scala tympani?

A

Basilar Membrane

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28
Q

Which membrane separates the scala media from the scala vestibuli?

A

Reissner’s membrane (vestibular membrane)

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29
Q

How does the change in length of fibers along the basilar membrane from the oval window to the apex of the cochlea relate to their frequency of vibration?

A
  • Length increases from oval window to apex of the cochlea (helicotrema).
  • Diameter of the fibers decrease from oval window to the apex of the cochlea.
  • Result of this:
    • stiff, short fibers near the oval window beat at a high frequency.
    • long, limber fibers near the apex of the cochlea vibrate at a low frequency.
30
Q

How many fibers does the basilar membrane contain?

A

20,000 - 30,000 fibers that project from the modiolus of the cochlea to the outer wall.

31
Q

Are the fibers at the distal end of the basilar membrane fixed or not?

A
  • Distal ends of the fibers are not fixed but are embedded in the basilar membrane.
  • Fibers can vibrate.
32
Q

Fill in the Blank:

Stiff, short fibers near the oval window beat at a _____ frequency.

A

high

33
Q

Fill in the Blank:

Long, limber fibers near the oval window beat at a _____ frequency.

A

low

34
Q

What is the function of the Organ of Corti?

A

Generates nerve impulses in response to vibration of basilar membrane.

  • sensory receptors of organ of Corti are hair cells:
    • single row of internal hair cells
    • 3-4 rows of external hair cells
    • set on top of basilar fibers
35
Q

What do hair cells (sensory receptors) of the organ of Corti stimulate?

A

Nerve fibers that lead to the spiral ganglion.

36
Q

How is a rigid unit of hair cells created in the organ of Corti?

A

Outer ends of hair cells are tightly attached to reticular lamina, supported by rods of Corti, which are attached to the basilar fibers.

This creates a rigid unit.

37
Q

True or False:

In the organ of Corti, sterocilia from the hair cells touch or are embedded in the overlying tectorial membrane.

A

True

38
Q

What does the bending of hairs in the organ of Corti cause?

A

Bending of the hairs in one direction depolarizes them and bending them in the opposite direction hyperpolarizes them.

39
Q

In the organ of Corti, what do neurons in the ganglion send axons to, and via what cranial nerve?

A

Send axons via the cochlear nerve (CN VIII) into the upper level of the medulla.

40
Q

The movement of which fibers causes movement of the reticular lamina?

A

Basilar fibers

41
Q

What does the movement of the reticular lamina cause on hair cells?

A

Movement of the reticular lamina causes shearing forces on the hir cells against the tectorial membrane.

  • Thus, whenever basilar membrane moves, hair cells become excited.
42
Q

How many stereocilia do each hair cell have on its apical border?

A

100

43
Q

On which side of the hair cell are stereocilia longest?

A

Stereocilia are longer on the side farther from the modiolus.

44
Q

What creates a mechanical transduction that opens 200-300 potassium channels resulting in a depolarization of the hair cell membrane?

A

When cilia are bent in direction of the longer ones, a tensile force is created on the shorter cilia.

** remember: stereocilia are longer on the side farther from the modiolus **

45
Q

Is the scala media filled with endolymph or perilymph?

A

endolymph

46
Q

Is the scala vestibuli and scala tympani filled with endolymph or perilymph?

A

perilymph

47
Q

What is the concentration of endolymph with regards to potassium and sodium?

A

Endolymph contains:

  • high [potassium]
  • low [sodium]
48
Q

What is the concentration of perilymph with regards to potassium and sodium content?

A

perilymph contains:

  • low [potassium]
  • high [sodium]
49
Q

What is the millivolt difference between endolymph and perilymph?

A
  • +80 mV difference between endolymph and perilymph (scala media is positive)
  • = endocochlear potential
50
Q

What is the endocochlear potential?

A

+80 mV

51
Q

Which type of lymph are the lower bodies of hair cells surrounded by?

A

perilymph

** NOTE: low [potassium]; high [sodium] - in scala tympani & vestibuli **

52
Q

What type of lymph are the tops of hair cells that project through the reticular lamina bathed by?

A

endolymph

** NOTE: high [potassium]; low [sodium] - in scala media **

53
Q

With respect to perilymph, what is the intracellular potential of hair cells?

A

-70 mV

54
Q

With respect to endolymph, what is the intracellular potential of hair cells?

A

-150 mV

55
Q

What is the “place principle”?

A

Nervous system detects sound frequencies by determining positions along the basilar membrane that are most stimulated.

56
Q

Nervous system detects sound frequencies by determing positions along the basilar membrane that are most stimulated.

A

Place Principle

57
Q

What is a decibel?

A
  • a 10-fold increase in sound energy is called 1 bel
  • 0.1 bel is called 1 decibel
  • 1 decibel represents an actual increase in sound energy of 1.26 times
58
Q

Explain how the auditory system determines loudness?

A

Loudness is determined by the auditory system in 3 ways:

  1. as sound becomes louder, amplitude of vibration of basilar membrane and hair cells also increases so that the hair cells excite the nerve endings at more rapid rates.
  2. as amplitude of vibration increases, it causes more and more of the hair cells on the fringes of the resonating portion of the basilar membrane to become stimulated
    • thus, causing spatial summation of impulses - that is, transmission through many nerve fibers rather than through only a few
  3. outer hair cells do not become stimulated significantly until vibration of the basilar membrane reaches high intensity, and stimulation of these cells presumably apprises the nervous system that the sound is loud.
59
Q

Describe the relationships between frequency and pressure in decibels.

A
60
Q

How does the frequency range that can be heard change with age?

A

As you get older you can hear higher frequencies.

61
Q

What are the components of the nervous system pathway in order?

A
  • spiral organ of Corti
  • dorsal and ventral cochlear nuclei
  • superior olivary nucleus
  • lateral lemniscus’ nucleus
  • medial geniculate nucleus (thalamus)
  • auditory cortex
62
Q

In the auditory pathway, where does decussation occur between right and left pathways?

A

Brainstem

63
Q

What is the relationship between the auditory tracts and the RAS?

A

Many collateral fibers from the auditory tracts pass directly into the reticular activating system of the brain stem (RAS).

  • this system projects diffusely upward in the brain stem and downward into the spinal cord and activates the entire nervous system in response to loud sounds.
64
Q

Where are the dorsal and ventral cochlear nuclei of the auditory nervous pathway located?

A

upper part of medulla

65
Q

Once fibers synapse in the dorsal and ventral cochlear nuclei of the upper medulla, where do second-order neurons pass through and then terminate at?

A

Second-order neurons pass mainly to the opposite side of the brain stem to terminate in the superior olivary nucleus.

**a few second-order fibers also pass to the superior olivary nucleus on the same side**

66
Q

Explain how a person determines the direction from which sound comes.

A
  • A person determines horizontal direction from which sound comes by two principle means:
    1. the time lag between the entry of sound into one ear and its entry into the opposite ear (functions best at frequencies below 3000 cycles/sec
    2. the difference between the intensities of the sounds in the two ears (operates best at higher frequencies because the head is a greater sound barrier at these frequencies)

** these mechanisms cannot tell whether the sound is emanating from in front of or behind the person or from above or below - this descrimination is achieved mainly by the pinnae of the two ears **

67
Q

What is the difference between primary auditory cortex and the auditory association areas?

A
  • Primary Auditory Cortex -> directly excited by projections from the medial geniculate body.
  • Auditory Association Areas -> excited secondarily by impulses from primary auditory cortex, as well as some projections from thalamic association areas adjacent to the medial geniculate body.
68
Q

In people with old-age type nerve deafness, is air conduction or bone conduction better?

A

Air conduction until a frequency of 8000 and a loss of 40 decibels.

69
Q

In people with air conduction deafness, is air conduction or bone conduction better?

A

Bone conduction is better.

70
Q
A

Human Physiology 2 - Unit 1 - Zach H. (9 decks)

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