LEC 19 Ear and hearing part 2

Question 1

Describe the main structural features of the cochlea.

Answer 1

The cochlea has a base and a series of turns terminating at an apex, forming a spiral-shaped osseous labyrinth coiled around a central core known as the modiolus.

Question 2

How does CNVIII enter the inner ear?

Answer 2

CNVIII enters the inner ear via the internal auditory meatus, specifically its cochlear division.

Question 3

Define the role of the cochlear division of CNVIII.

Answer 3

It transmits sound waves from the oval window to the spiral organ of Corti.

Question 4

Identify the two perilymph-filled chambers of the cochlea.

Answer 4

The vestibular duct (scala vestibuli), which starts at the oval window, and the tympanic duct (scala tympani), which ends at the round window.

Question 5

What is located in the middle chamber of the cochlea?

Answer 5

The cochlear duct (scala media), which is filled with endolymph.

Question 6

Where are hair cells situated in the cochlea?

Answer 6

Hair cells are found in the organ of Corti, which sits on the basilar membrane.

Question 7

How are hair cells organized in the cochlea?

Answer 7

They are arranged in 1:3 rows, with inner cells transducing sounds and outer cells providing support and amplifying dim sounds.

Question 8

Describe the role of stereocilia in sound transduction.

Answer 8

Stereocilia contact the overlying tectorial membrane, playing a role in sound transduction.

Question 9

Define the consequence of hair cell loss in the cochlea.

Answer 9

Hair cells do not regenerate; loss of these cells can lead to hearing loss.

Question 10

How is sound stimulation information transmitted to the central nervous system?

Answer 10

Information about the region and intensity of stimulation is relayed via the cochlear branch of CNVIII.

Question 11

Explain the effect of very low frequencies on pressure waves in the cochlea.

Answer 11

Very low frequencies create pressure waves that travel the entire length of the cochlea, from the oval window to the round window, without being heard.

Question 12

How do audible sounds navigate through the cochlea?

Answer 12

Audible sounds take a ‘shortcut’ through the cochlear duct.

Question 13

What function does the round window serve in the cochlea?

Answer 13

The round window acts as a pressure valve, bulging into the middle ear.

Question 14

How do different frequencies influence the displacement of the basilar membrane?

Answer 14

Different frequencies cause maximal displacement of the basilar membrane at different regions along the cochlea; high frequencies displace it at the base, while low frequencies do so at the apex.

Question 15

Describe how sound intensity is determined.

Answer 15

The energy of the sound wave determines the amplitude (intensity) of the sound, while volume perception is based on the displacement of the basilar membrane and the number of stimulated hair cells.

Question 16

Define the two mechanisms through which we hear sounds.

Answer 16

Sounds are heard via air-conducted mechanisms, which involve the tympanic membrane and ossicular chain, and bone-conducted mechanisms, which involve vibrations through bones directly to the cochlea.

Question 17

How can bone conduction be demonstrated in practice?

Answer 17

Bone conduction can be illustrated by Beethoven’s method of hearing through a rod connected to a piano, or by using headphones that allow situational awareness while blocking the ears.

Question 18

Explain why your own voice sounds different when recorded.

Answer 18

Your own voice sounds deeper when recorded because skull conduction emphasizes lower frequencies.

Question 19

Describe bone-conduction hearing loss and its prevalence.

Answer 19

Bone-conduction hearing loss is common in armed forces and noisy industries, occurring despite the use of earplugs or mufflers.

Question 20

What is the function of a bone-anchored hearing aid?

Answer 20

A bone-anchored hearing aid converts sound into electrical signals and mechanical vibrations to send to the cochlea via cranial bones, bypassing the outer and middle ear.

Question 21

Identify the two types of hearing loss.

Answer 21

The two types of hearing loss are conductive hearing loss and sensorineural hearing loss.

Question 22

Describe conductive hearing loss.

Answer 22

Conductive hearing loss is characterized by a blockage of normal vibrations to the inner ear.

Question 23

Define sensorineural hearing loss.

Answer 23

Sensorineural hearing loss involves problems with the cochlea or the nerve pathway.

Question 24

How can conductive hearing loss occur?

Answer 24

Conductive hearing loss can occur due to wax buildup, perforation of the tympanic membrane, immobilization of ossicles, or infections in the middle ear or ossicles.

Question 25

Identify the causes of sensorineural hearing loss.

Answer 25

Sensorineural hearing loss can be caused by noise-induced damage, drug-induced damage to hair cells, bacterial infections, degeneration of the cochlear nerve, or damage to the auditory cortex.

Question 26

Describe the relay nuclei in the auditory pathway.

Answer 26

The auditory pathway includes three relay nuclei: the cochlear nucleus (medulla), superior olivary complex (pons), and inferior colliculus (midbrain).

Question 27

Locate the primary auditory cortex.

Answer 27

The primary auditory cortex is located posteriorly on top of the superior temporal gyri, specifically in the transverse or Heschl’s gyri.

Question 28

What are the subdivisions of the cochlear nucleus?

Answer 28

The cochlear nucleus has three subdivisions: dorsal, anteroventral, and posteroventral.

Question 29

Describe the role of the ventral part of the cochlear nucleus.

Answer 29

It receives sound input from the horizontal plane.

Question 30

How does the superior olivary complex assist in sound localization?

Answer 30

It compares timing differences for low-frequency sounds and stimulus intensity for high-frequency sounds between the left and right ear.