Hearing & Equilibrium

Question 1

What are the eight structures that sound waves need to traverse from the auricle to reach the inner ear?

Answer 1

1. auricle
2. auditory canal
3. tympanic membrane
4. malleus
5. incus
6. stapes
7. oval window
8. cochlea

Question 2

What three components constitute the external ear?

Answer 2

The auricle, auditory canal, and tympanic membrane (eardrum).

Question 3

Where can cerumen (ear wax) be found, and what role does it serve?

Answer 3

In the auditory canal. It helps to clean and lubricate the ear canal and prevent the entry of bacteria, water and foreign objects.

Question 4

(a) What alternative term is used for the tympanic membrane? (b) How does this membrane contribute to the transmission of sound waves?

Answer 4

a) Eardrum. (b) By vibrating in response to sound waves; movement of the eardrum by these vibrations displaces the auditory ossicles.

Question 5

What are the four components that make up the middle ear?

Answer 5

The auditory ossicles (malleus, incus, and stapes) and the oval window.

Question 6

What is the sequence of ossicles from the outer ear to middle ear?

Answer 6

Malleus, incus, stapes

Question 7

What role do ossicles play in the auditory system? Why do we need to increase the sound wave pressure before reaching the inner ear?

Answer 7

Ossicles amplify the vibrations increasing the sound wave pressure. The inner ear consists of a liquid, so the vibrations must transfer into a liquid – vibrating or moving particles of liquid is much harder than moving particles of air.

Question 8

What are the two muscles associated with the ossicles, and what are their functions?

Answer 8

Tensor tympani and stapedius. They attenuate sound levels by dampening vibration of the ossicles.

Question 9

What are the names of the two labyrinths found in the inner ear, and which one is enclosed within the other?

Answer 9

The membranous labyrinth (1) is enclosed within the bony labyrinth (2).

Question 10

What are the three components of the bony labyrinth, and which ones are associated with equilibrium and hearing respectively?

Answer 10

Semicircular canals (equilibrium), vestibule (equilibrium), and cochlea (hearing)

Question 11

(a) In the context of the inner ear, where is the perilymph located, and where is the endolymph located? (b) Which of these fluids is more similar in composition to cerebrospinal fluid (CSF)?

Answer 11

(a) The perilymph is inside the bony labyrinth, endolymph is inside the membranous labyrinth. (b) The perilymph.

Question 12

What makes up the membranous labyrinth?

Answer 12

The cochlear duct, semi-circular ducts, utricle and the saccule (the last two structures are inside the vestibule).

Question 13

(a) The cochlea consists of how many chambers, and what are their names?

Answer 13

3 chambers: scala vestibuli, scala media (contains endolymph) , and scala tympani

Question 14

The vestibular membrane separates which two fluids?

Answer 14

Perilymph from endolymph

Question 15

What chamber (scala) within the cochlea corresponds to the cochlear duct?

Answer 15

The scala media.

Question 16

(a) What is the organ of corti? (b) Which two membranes surround the organ of corti?

Answer 16

(a) A sensory epithelium - the organ for hearing. (b) Tectorial membrane on the top and basilar membrane (at the base).

Question 17

What are the functions of the cochlear hair cells?

Answer 17

The outer hair cells (OHCs) receive descending inputs from the brain to assist with the modulation of inner hair cells (IHC) function. The IHCs are the responsible for hearing transmission.

Question 18

(a) Which cells are responsible for converting mechanical vibrations produced by sound into electrical signals, and where are these cells located? (b) What is the term for this conversion process?

Answer 18

(a) The inner hair cells (IHCs) in the organ of corti (in the cochlear duct). (b) Transduction, in this specific case: mechanotransduction

Question 19

What leads to the mechanical bending of the hair bundle toward the longer stereocilia in the IHCs?

Answer 19

Upward movement of the basilar membrane which produces the mechanical bending of the hairs with the tectorial membrane

Question 20

What serves as the stimulus for the opening of mechanosenstive channels that allows potassium ions to enter or exit? (b) What is the consequence in terms of membrane potential?

Answer 20

(a) Positive mechanical deformation (=mechanical deformation of the hair bundle toward the longer stereovilli). (b) K+ influx into the cell will cause depolarization of the membrane.

Question 21

(a) What triggers the opening of voltage-sensitive Ca2+ channels in the hair cells, and (b) what is the outcome of the influx of this ion?

Answer 21

(a) The depolarization of the membrane caused by the influx of K+. (b) The release of synaptic vesicles with neurotransmitters with will stimulate the sensory neuron.

Question 22

(a) What induces a negative mechanical bending of the stereocilia in the hair cells? (b) How does this affect the K+ channels? (c) What is the ultimate impact on the membrane potential of these cells?

Answer 22

(a) Downward movement of the basilar membrane. (b) Close K+ channels. (c) Hyperpolarization: no transmission of hearing signal.

Question 23

(a) What cranial nerve is responsible for transmitting auditory signals from the ear to the brain? (b) Can you list the four nuclei associated with the auditory projection pathway in their sequential order?

Answer 23

(a) CN VIII: The vestibulocochlear nerve, that consists of the vestibular and cochlear nerves. (b) Cochlear nucleus, superior olive, inferior colliculus (midbrain), medial geniculate nucleus (MGN, thalamus).

Question 24

What makes up the vestibular apparatus?

Answer 24

3 semicircular ducts, otolith organs (utricle and saccule)

Question 25

What are the sensory receptors for the vestibular system?

Answer 25

Hair cells (in the crista and macula)

Question 26

What are the utrilce and saccule? Where are they located?

Answer 26

Parts of the inner ear (membranous labyrinth) involved in the sense of balance.

Question 27

What is the name of the sensory epithelium found in the utricle and saccule?

Answer 27

Macula

Question 28

(a) What is the crista, and where is it situated? (b) What is located above the receptor cells in the crista ampullaris?

Answer 28

a) The crista, or crista ampullaris, is a sensory epithelium that contains hair cells. (b) A cupula, gelatinous structure primarily composed of glycoproteins.

Question 29

What is the primary function of the hair cells in the macula and crista?

Answer 29

Hair are the sensory receptors of the vestibular system, they monitor head position and movement.

Question 30

What us the function of the vestibular apparatus?

Answer 30

The vestibular apparatus maintains balance & awareness of the body’s spatial orientation.

Question 31

Which structure (s) are responsible for detecting head rotation in different planes?

Answer 31

The semicircular ducts and crista ampullaris.

Question 32

What does the utricle detect? What about the saccule?

Answer 32

The utricle detects linear accelerations and head-tilts in the horizontal plane and the saccule in the vertical plane.

Question 33

How is the tilt of the head detected, and what is the role of otoliths in this process?

Answer 33

Macula utriculi detect the tilt of the head. ex. When you tilt your head down to read a book the heavy gelatinous membrane (containing otoliths) bends the stereocilia, stimulating the hair cells in the macula

Question 34

What type of fluid moves through the ducts during head rotation?

Answer 34

Endolymph