T19. SPECIAL SENSES III

Question 1

What is hearing?

Answer 1

Hearing is the ability to perceive sound by detecting vibrations.

Question 2

What is equilibrium?

Answer 2

Equilibrium is the sense of motion, body orientation, and balance.

Question 3

Where do the senses of hearing and equilibrium reside?

Answer 3

Both reside in the inner ear, which contains fluid-filled passages and sensory cells that convert motion into action potentials.

Question 4

What causes sensory cells of the inner ear to activate?

Answer 4

Motion of the fluid in the inner ear sets sensory cells in motion, generating informative patterns of action potentials.

Question 5

What is sound?

Answer 5

Sound is any audible vibration of molecules.

Question 6

How do sound vibrations reach the eardrum?

Answer 6

A vibrating object pushes air molecules, which hit the eardrum and cause it to vibrate.

Question 7

What are the two key characteristics of sound?

Answer 7

Frequency (in Hz) and intensity/loudness (in decibels).

Question 8

What is the human hearing frequency range?

Answer 8

20–20,000 Hz.

Question 9

At what intensity level can sound begin to cause damage?

Answer 9

Prolonged exposure to sounds above 90 dB can cause damage.

Question 10

What are the three sections of the ear?

Answer 10

Outer ear, middle ear, and inner ear.

Question 11

What is the role of the outer and middle ear?

Answer 11

They are concerned with transmission of sound to the inner ear.

Question 12

What is the role of the inner ear?

Answer 12

It converts vibrations into nerve signals.

Question 13

What structures make up the outer ear?

Answer 13

The auricle and the external auditory canal.

Question 14

What is the function of the auricle?

Answer 14

It funnels sound waves into the external auditory canal.

Question 15

Where do sound waves go after the auditory canal?

Answer 15

They reach the tympanic membrane (eardrum).

Question 16

What lies between the tympanic membrane and the cochlea?

Answer 16

The middle ear.

Question 17

What bones are found in the middle ear?

Answer 17

Malleus, incus, and stapes (ossicles).

Question 18

What is the function of the ossicles?

Answer 18

They transfer and amplify vibrations to the inner ear.

Question 19

What connects the stapes to the inner ear?

Answer 19

The stapes is attached to the oval window, transferring vibrations into the inner ear.

Question 20

What are the components of the inner ear?

Answer 20

Bony labyrinth, membranous labyrinth, vestibular apparatus, and cochlea.

Question 21

What fluid fills the membranous labyrinth?

Answer 21

Endolymph, which has a high K+ concentration.

Question 22

What fluid surrounds the membranous labyrinth?

Answer 22

Perilymph.

Question 23

What makes up the vestibular apparatus?

Answer 23

The vestibule and three semicircular ducts.

Question 24

What is the function of the vestibular apparatus?

Answer 24

It is responsible for equilibrium.

Question 25

What is the cochlea?

Answer 25

The hearing part of the inner ear.

Question 26

What chambers make up the cochlea?

Answer 26

Scala vestibuli, scala tympani, and scala media (cochlear duct).

Question 27

What fluid fills the scala vestibuli and scala tympani?

Answer 27

Perilymph.

Question 28

What fluid fills the scala media?

Answer 28

Endolymph.

Question 29

What is the organ of Corti?

Answer 29

The spiral organ inside the scala media that converts vibrations into nerve impulses.

Question 30

What types of hair cells are in the organ of Corti?

Answer 30

Inner hair cells (for hearing) and outer hair cells (for adjusting frequency response).

Question 31

What is the function of inner hair cells?

Answer 31

They provide hearing and are each innervated by 10–20 sensory neurons.

Question 32

What is the function of outer hair cells?

Answer 32

They adjust the cochlear response to different frequencies via motor neuron input.

Question 33

What are stereocilia?

Answer 33

Hair-like extensions of sensory hair cells, embedded in the tectorial membrane.

Question 34

What happens when stereocilia bend?

Answer 34

K+ channels open, allowing K+ to enter and depolarize the cell, leading to glutamate release.

Question 35

What is the role of glutamate in the cochlea?

Answer 35

It excites sensory neurons by acting as a neurotransmitter.

Question 36

Describe the path of sound vibrations in the cochlea.

Answer 36

They enter via the oval window, displace perilymph in scala vestibuli, pass through endolymph in scala media, then into perilymph of scala tympani, and exit through the round window.

Question 37

How is sound volume discriminated?

Answer 37

Greater cilia flexion releases more glutamate, generating more frequent action potentials.

Question 38

How is sound frequency discriminated?

Answer 38

High-frequency waves vibrate the stiffer, initial part of the basilar membrane; low-frequency waves vibrate the more flexible end regions.

Question 39

What does tonotopic mean in the auditory cortex?

Answer 39

It means different areas correspond to different sound frequencies.

Question 40

What is the auditory neural pathway?

Answer 40

Cochlear nerve → medulla oblongata → inferior colliculus → thalamus → auditory cortex of temporal lobe.

Question 41

What does the vestibulocochlear nerve do?

Answer 41

It carries auditory and equilibrium signals to the brain.

Question 42

What is static equilibrium?

Answer 42

Perception of head orientation when the body is stationary.

Question 43

What is dynamic equilibrium?

Answer 43

Perception of motion or acceleration.

Question 44

What structures detect linear acceleration?

Answer 44

Utricle (horizontal) and saccule (vertical).

Question 45

What structures detect angular acceleration?

Answer 45

Three semicircular ducts.

Question 46

What do utricle and saccule contain?

Answer 46

Sensory hair cells in a specialized epithelium called the macula.

Question 47

What is the otolithic membrane?

Answer 47

Gelatinous structure that pushes stereocilia in the direction of head tilt.

Question 48

What happens when stereocilia bend toward the kinocilium?

Answer 48

K+ channels open, K+ enters the cell, and neurotransmitters are released to depolarize sensory neurons.

Question 49

What happens when stereocilia bend away from the kinocilium?

Answer 49

The sensory dendrites are hyperpolarized.

Question 50

What are the semicircular canals?

Answer 50

Three fluid-filled ducts in different planes that detect head rotation.

Question 51

What is the crista ampullaris?

Answer 51

A receptor structure in the semicircular canals that contains hair cells embedded in a gelatinous cupula.

Question 52

How does rotation affect the crista ampullaris?

Answer 52

Endolymph pushes the cupula, bending hair cells and sending signals about rotation.

Question 53

What is the equilibrium neural pathway?

Answer 53

Vestibulocochlear nerve → medulla → cerebellum, oculomotor area, spinal cord, reticular formation, and thalamus.

Question 54

What does the cerebellum do in equilibrium?

Answer 54

It integrates vestibular info for head/eye movement, posture, and muscle tone.

Question 55

What does the reticular formation do in equilibrium?

Answer 55

It adjusts blood circulation and breathing to postural changes.

Question 56

What is the role of the thalamus in equilibrium?

Answer 56

It relays vestibular info to the cerebral cortex for awareness of position and motor control.

Question 57

What is nystagmus?

Answer 57

Jerky eye movement caused by post-rotation fluid inertia bending the cupula.

Question 58

What is vertigo?

Answer 58

A loss of equilibrium, often with dizziness, nausea, sweating, and vomiting, usually caused by nystagmus.