Auditory system

Question 1

auditory meatus

Answer 1

Opening of the external ear canal.

Question 2

basilar membrane

Answer 2

The membrane that forms the floor of the cochlear duct, on which the cochlear hair cells are located.

Question 3

cochlea

Answer 3

The coiled structure in the inner ear where vibrations caused by sound are transduced into neural impulses.

Question 4

conductive hearing loss

Answer 4

Diminished sense of hearing due to the reduced ability of sounds to be mechanically transmitted to the inner ear. Common causes include occlusion of the ear canal, perforation of the tympanic membrane, and arthritic degeneration of the middle ear ossicles. Contrast with sensorineural hearing loss.

Question 5

endolymph

Answer 5

The potassium-rich fluid filling both the cochlear duct and the membranous labyrinth; bathes the apical end of the hair cells.

Question 6

hair cells

Answer 6

The sensory cells in the inner ear that transduce mech-anical displacement into neural impulses.

Question 7

helicotrema

Answer 7

The opening at the apex of the cochlea that joins the perilymph-filled cavities of the scala vestibuli and scala tympani.

Question 8

inferior colliculi (singular, colliculus)

Answer 8

Paired hillocks on the dorsal surface of the midbrain; concerned with auditory processing.

Question 9

kinocilium

Answer 9

A true ciliary structure which, along with the stereocilia, comprises the hair bundle of vestibular and fetal cochlear hair cells in mammals (it is not present in the adult mammalian cochlear hair cell).

Question 10

lateral superior olive (LSO)

Answer 10

The auditory brainstem structure that processes interaural intensity differences and, in humans, mediates sound localization for stimuli greater than 3 kHz.

Question 11

medial geniculate complex (MGC)

Answer 11

The major thalamic relay for auditory information.

Question 12

medial superior olive (MSO)

Answer 12

The auditory brainstem structure that processes interaural time differences and serves to compute the horizontal location of a sound source.

Question 13

ossicles

Answer 13

The bones of the middle ear.

Question 14

perilymph

Answer 14

The potassium-poor fluid that bathes the basal end of the cochlear hair cells.

Question 15

primary auditory cortex (A1)

Answer 15

The major cortical target of the neurons in the medial geniculate nucleus.

Question 16

sensorineural hearing loss

Answer 16

Diminished sense of hearing due to damage of the inner ear or its related central auditory structures. Contrast with conductive hearing loss.

Question 17

stereocilia

Answer 17

The actin-rich processes that, along with the kinocilium, form the hair bundle extending from the apical surface of the hair cell; site of mechanotransduction.

Question 18

stria vascularis

Answer 18

Specialized epithelium lining the cochlear duct that maintains the high potassium concentration of the endolymph.

Question 19

tectorial membrane

Answer 19

The fibrous sheet overlying the apical surface of the cochlear hair cells; produces a shearing motion of the stereocilia when the basilar membrane is displaced.

Question 20

tonotopy

Answer 20

The topographic mapping of sound frequency across the surface of a structure, which originates in the cochlea and is preserved in ascending auditory structures, including the auditory cortex.

Question 21

tuning curve

Answer 21

A threshold function determined by a common physiological test in which the receptive field properties of neurons are gauged against a varying stimulus such that maximum sensitivity or maximum responsiveness can be defined by the peak of the tuning curve.

Question 22

tympanic membrane

Answer 22

The eardrum.

Question 23

Answer 23

The auditory nerve or eighth cranial nerve is composed of two branches, the cochlear nerve that transmits auditory information away from the cochlea, and the vestibular nerve that carries vestibular information away from the semicircular canals.

Question 24

Answer 24

The coiled structure in the inner ear where vibrations caused by sound are transduced into neural impulses.

Question 25

Answer 25

A component of the external ear.

Question 26

Answer 26

This air-containing space is maintained by the Eustachian tube, which opens intermittently to equalize the intratympanic air pressure with the pressure in the external auditory canal. It also removes secretion and epithelial debris from the middle ear by ciliary motion and gravity.

Question 27

Answer 27

Question 28

Answer 28

The incus or anvil is a bone in the middle ear. The anvil-shaped small bone is one of three ossicles in the middle ear. The incus receives vibrations from the malleus, to which it is connected laterally, and transmits these to the stapes medially.

Question 29

Answer 29

Question 30

Answer 30

The malleus is one of three ossicles in the middle ear which transmit sound from the tympanic membrane (ear drum) to the inner ear. The malleus receives vibrations from the tympanic membrane and transmits this to the incus.

Question 31

Answer 31

The stapes bone transmits movement to the oval window. As the stapes footplate moves into the oval window, the round window membrane moves out, and this allows movement of the fluid within the cochlea, leading to movement of the cochlear inner hair cells and thus hearing.

Question 32

Answer 32

The auricle (pinna) is the visible portion of the outer ear. It collects sound waves and channels them into the ear canal (external auditory meatus), where the sound is amplified. The sound waves then travel toward a flexible, oval membrane at the end of the ear canal called the eardrum, or tympanic membrane.

Question 33

Answer 33

The round window serves to decompress acoustic energy that enters the cochlea via stapes movement against the oval window. Any inward motion of the oval window via stapes vibration leads to outward motion of the round window.

Question 34

Answer 34

Question 35

Answer 35

The word means “stirrup” in Latin. The two branches of the stapes, known as the inferior and superior crus, convey sound vibrations to the bone’s flat base. From there, the vibrations enter the inner ear, where they are processed into neural data to be transmitted to the brain via the cochlear and the auditory nerve.

Question 36

Answer 36

Its function is to transmit sound from the air to the ossicles inside the middle ear, and then to the oval window in the fluid-filled cochlea. Hence, it ultimately converts and amplifies vibration in air to vibration in cochlear fluid. The malleus bone bridges the gap between the eardrum and the other ossicles.

Question 37

Answer 37

The vestibular nerve is primarily responsible for maintaining body balance and eye movements, while the cochlear nerve is responsible for hearing.

Question 38

Answer 38

Vestibule. The vestibule is the central part of the bony labyrinth. It is separated from the middle ear by the oval window, and communicates anteriorly with the cochlea and posteriorly with the semi-circular canals. Two parts of the membranous labyrinth; the saccule and utricle, are located within the vestibule.

Question 39

What is the function of the middle ear?

Answer 39

Impedance

Protects against infection

Volume Control by the Stapedius Muscle

Question 40

What is the structure of the middle ear?

Answer 40

Malleus (Tensor tympani muscle)

Incus

Stapes (Stapedius muscle)

Question 41

Answer 41

The fluid-filled chamber within the cochlea at the base of which is located the oval window.

Question 42

Answer 42

The fluid-filled chamber within the cochlea that sits on the basilar membrane and that lies between the scala vestibuli and the scala tympani.

Question 43

Answer 43

outer hair cells receive mostly efferent innervation.

Question 44

basilar membrane

Answer 44

The movement of the basilar membrane causes hair cell stereocilia movement. The hair cells are attached to the basilar membrane, and with the moving of the basilar membrane, the tectorial membrane and the hair cells are also moving, with the stereocilia bending with the relative motion of the tectorial membrane.

Question 45

inner hair cells

Answer 45

The hair cells are named for their tufts of stereocilia; inner hair cells receive afferents from cranial nerve VIII

Question 46

Answer 46

The fluid-filled chamber within the cochlea at the base of which is located the round window.

Question 47

Answer 47

The neurons of the spiral ganglion are called bipolar cells because they have two sets of processes, or fibres, that extend from opposite ends of the cell body.

Question 48

Answer 48

A tectorial (roof) membrane is held in place by a hinge-like mechanism on the side of the Organ of Corti and floats above the hair cells. As the basilar and tectorial membranes move up and down with the traveling wave, the hinge mechanism causes the tectorial membrane to move laterally over the hair cells.

Question 49

Describe the hair cell conduction phase

Answer 49

Hair cells normally have a small influx of K+ at rest, so there is some baseline activity in the afferent neurons. Bending the cilia toward the tallest one opens the potassium channels and increases afferent activity. Bending the cilia in the opposite direction closes the channels and decreases afferent activity

Question 50

what characterizes the hair cells in the cochlea?

Answer 50

They are tonotopically organized along the basilar membrane.

K+ ions play a critical role in the transduction process.

Question 51

How frequency is mapped in the basilar membrane?

Answer 51

The points responding to high frequencies are at the base of the basilar membrane, and the points responding to low frequencies are at the apex, giving rise to a topographical mapping of frequency (that is, to tonotopy).

Question 52

The major function of the middle ear is to match low-impedance (low resistance) airborne sounds to the higher-impedance fluid of the inner ear. Most of the energy is reflected when going from low-impedance to high-impedance. However, the middle ear compensates for this loss of energy by two different mechanisms. Name these two processes that result in little loss of energy from the middle ear to the inner ear.

Answer 52

The first is the large size difference between the tympanic membrane and the oval window.

The second is the mechanical advantage gained by the lever action of the three bones in the middle ear.

Question 53

Humans use at least two different strategies to localize sound in the horizontal plane. Describe these two different strategies and name the region of the brain where these two different strategies take place.

Answer 53

The lateral superior olive detects the intensity level difference between the two ears while the medial superior olive detects the time difference betweenthe two ears.

Question 54

What is the attenuation reflex and what is its significance?

Answer 54

The attenuation reflex results in contraction of middle ear muscles (the tensor tympani muscle and stapedius muscle) in response to loud sounds. This decreases the potential trauma to the small bones of the middle ear.

Question 55

Describe the Organ of Corti.

Answer 55

The organ of Corti is a thickening on the basilar membrane. There is a single row of inner hair cells and a triple row of outer hair cells, each of which are in contact with a gelatinous Called the tectorial membrane. Movement of the basilar membrane will deform the hairs of these hair cells against the tectorial membrane, either opening or closing potassium channels (i.e., depolarizing or hyperpolarizing the cells) depending on which direction the hairs move. Each hair cell contacts the peripheral processes of auditory nerve fibers (although inner hair cells contact multiple axons).

Question 56

Explain the concept of “tonotopy”.

Answer 56

Tonotopy refers to the several places within the auditory system where different frequencies of sound are represented consecutively across structures such as the inferior colliculus and auditory cortex.

Question 57

What does the inferior colliculus do besides relaying sound?

Answer 57

The inferior colliculus is a relay for sound, and creates a spatial map of where sound is arising in the environment. However, it also appears to be important for suppressing internal sounds (such as heartbeat or breathing noises) in order to be able to discriminate outside sounds.

Question 58

Name cortical structures involved in sound perception.

Answer 58

The primary auditory cortex is located on the transverse gyri of Heschl. This is on the superior aspect of the temporal lobe, where it folds into the lateral fissure. The cortex surrounding it is the auditory Association region that provides meaning to the sound. In the dominant hemisphere, this represents the more anterior portions of Wernicke’s area.

Question 59

What elements of sound are most important in speech and language recognition and where does this occur?

Answer 59

Wernicke’s area contains regions that are sensitive to individual phonemes (i.e., sounds that comprise language)and lexemes (sequences of phonemes that make a word). There is evidence that the ability to detect phonemes is established quite early due to exposure to your native language.

Question 60

What are the two general classes of auditory disorders?

Answer 60

Conductive hearing loss results from inability to transfer vibrations in the air into fluid vibrations in the inner ear. This can result from any process that prevents the tympanic membrane from vibrating, the ossicles from moving normally, or the perilymph from being able to vibrate. Sensorineural hearing loss is due to damage of hair cells or the vestibulocochlear nerve.

Question 61

What is Weber’s and Rinne’s test?

Answer 61

These tests are performed following a screening test for hearing loss in order to determine the cause. Weber’s test is placing a tuning fork against the skull in the midline somewhere near the vertex. The patient is asked which side they hear the sound more loudly. Weber’s test will lateralized towards the side of conductive hearing loss, and away from the side of sensorineural hearing loss. Rinne’s test involves placing a tuning fork against the mastoid and asking the patient to tell you when they no longer hear it. At that time the tines of the tuning fork are placed next to the ear. Normally, you can hear the sound for approximately the same amount again of time that the patient reported during the first part of the test. If you cannot, that suggests conductive hearing loss.

Question 62

What type of disorders would produce conductive hearing loss?

Answer 62

Conductive hearing loss will happen due to anything that blocks sound entering the external ear canal, anything that prevents the tympanic membrane from moving (e.g., fluid in the middle ear, or pressure differences on the two sides of the tympanic membrane), anything that prevents the ossicles from moving, or anything that prevents perilymph from vibrating (such as ossification of the membrane of the round window).

Question 63

What type of disorders would produce sensorineural hearing loss?

Answer 63

Sensorineural hearing loss is most often due to damage to hair cells from noise exposure. However, certain drugs can also damage the cells, as can excessive pressure in the inner ear. Meningitis can spread to the inner ear and damage hair cells, as well (worldwide, the most common preventable cause of deafness in younger individuals). This form of deafness can also happen due to damage to the vestibulocochlear nerve, such as by an acoustic neuroma.

Question 64

Why is hearing loss almost never due to damage to the CNS?

Answer 64

Hearing loss due to central nervous system damage is very rare because the auditory pathways necessarily become bilateral immediately after the first synapse in the cochlear nuclei at the medullary-pontine junction.