Lecture 7: Auditory and Balance

Question 1

Describe the main functions of the ear.

Answer 1

The ear is responsible for hearing and equilibrium (balance).

Question 2

Explain how fluids in the ear contribute to hearing and balance.

Answer 2

Fluids must be moved to stimulate the mechanoreceptors located in the internal ear, which are essential for both hearing and equilibrium.

Question 3

Define the three major areas of the ear and their functions.

Answer 3

The ear has three major areas: the external ear (hearing only), the middle ear (tympanic cavity, hearing only), and the internal ear (hearing and equilibrium).

Question 4

How are the receptors for hearing and balance activated?

Answer 4

Receptors for hearing and balance respond to separate stimuli and are activated independently.

Question 5

What are the components of the external ear?

Answer 5

The external ear consists of the auricle (pinna), helix, lobule, and the external acoustic meatus (auditory canal).

Question 6

Explain the function of the auricle (pinna).

Answer 6

The auricle (pinna) is a shell-shaped structure that functions to funnel sound waves into the auditory canal.

Question 7

What happens if the tympanic membrane is subjected to unequal pressure?

Answer 7

If pressures on both sides of the tympanic membrane are not equal, it cannot vibrate efficiently, leading to distorted sounds.

Question 8

Describe the structure and function of the tympanic membrane (eardrum).

Answer 8

The tympanic membrane is a thin, translucent connective tissue membrane that vibrates in response to sound and transfers sound energy to the bones of the middle ear.

Question 9

What is the role of the pharyngotympanic (auditory) tube?

Answer 9

The pharyngotympanic tube connects the middle ear to the nasopharynx and helps equalize pressure in the middle ear cavity with external air pressure.

Question 10

How do the auditory ossicles function in hearing?

Answer 10

The auditory ossicles (malleus, incus, stapes) transmit vibratory motion from the eardrum to the oval window, facilitating sound transmission.

Question 11

Describe the role of the tensor tympani and stapedius muscles in hearing.

Answer 11

The tensor tympani and stapedius muscles contract reflexively in response to loud sounds to prevent damage to hearing receptors.

Question 12

Identify the three small bones in the tympanic cavity and their names.

Answer 12

The three small bones in the tympanic cavity are the malleus (hammer), incus (anvil), and stapes (stirrup).

Question 13

Explain the significance of the epitympanic recess in the middle ear.

Answer 13

The epitympanic recess is the superior portion of the middle ear, contributing to the overall structure and function of the tympanic cavity.

Question 14

What is the function of the mastoid antrum?

Answer 14

The mastoid antrum is a canal that allows communication with mastoid air cells in the mastoid process.

Question 15

How does the trigeminal nerve relate to the ear’s function?

Answer 15

Motor input from the trigeminal nerve (V) is involved in the reflexive contraction of the tensor tympani muscle in response to loud sounds.

Question 16

Define the role of the saccule and utricle in the inner ear..

Answer 16

The saccule and utricle are membranous sacs within the bony labyrinth that house equilibrium receptor regions called maculae, which respond to gravity and changes in head position.

Question 17

Explain the function of the membranous labyrinth.

Answer 17

The membranous labyrinth consists of a series of membranous sacs and ducts contained within the bony labyrinth, filled with potassium-rich endolymph. It plays a crucial role in balance and hearing.

Question 17

Describe the bony labyrinth and its components.

Answer 17

The bony labyrinth is a system of tortuous channels and cavities within the bone, divided into three regions: vestibule, semicircular canals, and cochlea. It is filled with perilymph fluid, which is similar to cerebrospinal fluid.

Question 18

How are the semicircular canals oriented in relation to each other?

Answer 18

The three semicircular canals are oriented in three planes of space: the anterior and posterior canals are at right angles to each other, while the lateral canal is horizontal.

Question 19

What is the function of the ampulla in the semicircular canals?

Answer 19

The ampulla is the enlarged area of the ducts of each semicircular canal that houses the equilibrium receptor region called the crista ampullaris, which responds to angular (rotational) movements of the head.

Question 20

Describe the structure and function of the cochlea.

Answer 20

The cochlea is a small spiral, conical, bony chamber that extends from the vestibule and coils around a bony pillar called the modiolus. It contains the cochlear duct, which houses the spiral organ (organ of Corti) responsible for hearing.

Question 21

Explain the significance of the scalae in the cochlea.

Answer 21

The cochlea is divided into three chambers: scala vestibuli, scala media (cochlear duct), and scala tympani. The scala vestibuli and scala tympani contain perilymph, while the scala media contains endolymph, playing essential roles in sound transmission.

Question 22

What is the role of the basilar membrane in sound processing?

Answer 22

The basilar membrane vibrates in response to sound waves, with different areas resonating at specific frequencies. This mechanical processing occurs before signals reach the hair cell receptors.

Question 23

How do hair cells in the cochlea convert mechanical energy into neural signals?

Answer 23

Movement of the basilar membrane deflects the stereocilia of inner hair cells, which project into the potassium-rich endolymph. This mechanical deflection transforms mechanical energy into neural signals.

Question 24

Explain the concept of resonance in the basilar membrane.

Answer 24

Resonance refers to the movement of different areas of the basilar membrane in response to specific sound frequencies, with shorter, stiffer fibers near the oval window resonating with high frequencies and longer, floppier fibers near the apex resonating with lower frequencies.

Question 25

Describe the pathway of sound waves from the tympanic membrane to the cochlea.

Answer 25

Sound waves enter the external acoustic meatus, strike the tympanic membrane causing it to vibrate, and this vibration is transferred through the auditory ossicles to the oval window, creating wave motions in the perilymph of the cochlea.

Question 26

What is the function of the stria vascularis in the cochlear duct?

Answer 26

The stria vascularis is the external wall of the cochlear duct composed of mucosa that secretes endolymph, essential for maintaining the ionic composition of the fluid in the cochlear duct.

Question 27

How does the tympanic membrane contribute to hearing?

Answer 27

The tympanic membrane vibrates when sound waves strike it, and the intensity of the sound affects the degree of vibration, which is then transferred to the auditory ossicles.

Question 28

Define the role of the cochlear branch of nerve VIII.

Answer 28

The cochlear branch of nerve VIII runs from the spiral organ to the brain, transmitting auditory information from the cochlea.

Question 29

What happens to sound waves with frequencies below the threshold of hearing?

Answer 29

Sound waves with frequencies below the threshold of hearing travel through the helicotrema and scala tympani to the round window, where they cause it to bulge outward into the middle ear cavity.

Question 30

Describe the role of otoliths in the vestibular system.

Answer 30

Otoliths increase the weight and inertia of the membrane, helping to detect changes in head position.

Question 31

Explain the anatomy of a macula.

Answer 31

Each macula is a flat epithelial patch containing hair cells and supporting cells, with hair cells featuring stereocilia and a true stereocilium called kinocilium.

Question 32

Describe the role of outer hair cells in the auditory system.

Answer 32

Outer hair cells can contract and stretch, changing the stiffness of the basilar membrane, which increases the responsiveness of inner hair cells and protects them from loud noises.

Question 33

Explain how the ascending auditory pathway functions.

Answer 33

The ascending auditory pathway transmits auditory information primarily from cochlear receptors (inner hair cells) to the cerebral cortex, with some nerve fibers crossing over to the other side of the brain.

Question 34

Define the perception of pitch in relation to hair cells.

Answer 34

The perception of pitch is based on impulses from hair cells in different positions along the basilar membrane, which the brain interprets as specific pitches.

Question 35

How is loudness detected by the brain?

Answer 35

Loudness is detected by the brain as an increase in the number of action potentials (frequency) that result when hair cells experience larger deflections.

Question 36

Describe the factors that contribute to sound localization.

Answer 36

Sound localization depends on the relative intensity and timing of sound waves reaching both ears; if timing is increased on one side, the brain interprets the sound as coming from that side.

Question 37

Explain the function of the vestibular apparatus.

Answer 37

The vestibular apparatus contains equilibrium receptors in the semicircular canals and vestibule, which help maintain balance and spatial orientation.

Question 38

How do stereocilia contribute to the function of maculae?

Answer 38

Stereocilia are embedded in the otolith membrane, a jelly-like mass that responds to changes in head position and linear acceleration.

Question 39

Describe the relationship between frequency of action potentials and loudness.

Answer 39

The frequency of action potentials correlates with loudness, where a higher frequency indicates a louder sound measured in decibels (dB).

Question 40

What is the difference between static and dynamic equilibrium?

Answer 40

Static equilibrium is monitored by vestibular receptors that detect the position of the head in space, while dynamic equilibrium is monitored by semicircular canal receptors that respond to head movements.

Question 41

Define maculae and their role in equilibrium.

Answer 41

Maculae are sensory receptor organs located in the saccule and utricle walls that monitor static equilibrium and respond to linear acceleration forces.

Question 42

How do utricle maculae respond to head movements?

Answer 42

Utricle maculae are horizontal with vertical hairs and respond to changes along a horizontal plane, such as tilting the head.

Question 43

What stimulates the utricle maculae?

Answer 43

Forward and backward movements stimulate the utricle.

Question 44

Describe the orientation and function of saccule maculae.

Answer 44

Saccule maculae are vertical with horizontal hairs and respond to changes along a vertical plane, such as up and down movements.

Question 45

How do hair cells communicate with the vestibular nerve?

Answer 45

Hair cells release neurotransmitters continuously, and changes in acceleration or deceleration affect the amount released, altering the action potential frequency sent to the brain.

Question 46

Explain the mechanism of hair cell activation in a macula.

Answer 46

When hair cells bend towards the kinocilia, they depolarize, increasing neurotransmitter release and impulse generation to the brain.

Question 47

What happens when hair cells bend away from kinocilia?

Answer 47

Bending away from kinocilia hyperpolarizes the receptors, reducing neurotransmitter release and decreasing impulse generation.

Question 48

Define the crista ampullaris and its function.

Answer 48

Crista ampullaris is a receptor for rotational acceleration located in the ampulla of each semicircular canal, excited by head acceleration and deceleration.

Question 49

How do semicircular canals contribute to balance?

Answer 49

Semicircular canals detect rotational movements of the head, with cristae responding to changes in velocity.

Question 50

What is the role of the ampullary cupula in the vestibular system?

Answer 50

The ampullary cupula is a gel-like mass that hair cells extend into, and it helps detect changes in head rotation by bending hair cells.

Question 51

Explain the process of depolarization in cristae during head rotation.

Answer 51

Inertia in the ampullary cupula causes endolymph to move opposite to the body's rotation, bending hair cells and leading to depolarization.

Question 52

What is the significance of complementary semicircular ducts?

Answer 52

The axes of hair cells in complementary semicircular ducts are opposite, allowing one ear to depolarize while the other hyperpolarizes during head rotation.

Question 53

How does the brain process equilibrium information?

Answer 53

Equilibrium information is sent to reflex centers in the brain stem, allowing for fast, reflexive responses to maintain balance.

Question 54

What are the three modes of input for balance and orientation?

Answer 54

The three modes of input are vestibular receptors, visual receptors, and somatic receptors.

Question 55

Describe sensorineural deafness and its treatment.

Answer 55

Sensorineural deafness can be treated with cochlear implants that convert sound energy into electrical signals, effective for congenital or age/noise-related cochlear damage.

Question 56

How are cochlear implants inserted?

Answer 56

Cochlear implants are inserted into a drilled recess in the temporal bone.

Question 57

What is the outcome of cochlear implants for deaf children?

Answer 57

Cochlear implants are so effective that deaf children can learn to speak.