Hearing & Balance

Question 1

What is the difference between perilymph and endolymph?

Answer 1

The perilymph fills the bony labrynth, which contains the membranous labryinth. Endolymph is found within the membranous labrynth.

Perilymph is continuous with the arachnoid

Question 2

What are the mechanoreceptors of the ear?

Answer 2

Hair cells

Question 3

Describe the how hair cells transmit to the brain.

Answer 3

Sound creates a wave of perilymph that deforms the basilar membrane activating each hair cell. Afferent fibers to the spiral ganglion of CNVIII contain frequency, intensity and timing information.

Question 4

What fluid movement stimulates hair cells?

Answer 4

Endolymphatic flow toward the kinocilium is excitatory. Away from the kinocilium is inhibitory.

Question 5

What is the functional difference between inner and outer hair cells?

Answer 5

Inner hair cells are responsible for transmitting hearing sense. Outer hair cells are responsible for amplification and frequency selection.

Question 6

What brainstem nuclei are associated with CN VIII?

Answer 6

Dorsal cochlear nucleus and ventral cochlear nucleus found on the lateral side of the inferior cerebellar peduncle

Question 7

Describe the auditory pathway from ear to auditory cortex

Answer 7

Hair cell –> Spiral ganglion –> Cohlear nucleus (bilateral) –> Superior olivary nucleus –> inferior colliculus –> medial geniculate –> auditory cortex

Question 8

What role does the vestibular system play with eye movement?

Answer 8

Stabilization of gaze when head moves via extraocular muscles (Vestibuloocular reflex)

Question 9

What is the otolithic membrane?

Answer 9

A gelatinous membrane that is found within the utricle and saccule. Hair cells are imbedded within these calcium carbonate containing structures that help give a sense of gravity, linear motion.

Question 10

What are the major vestibulospinal tracts?

Answer 10

Lateral vestibulospinal tract: from lateral nucleus, uncrossed, acts on proximal limb muscles to maintain balance
Medial vestibulospinal tract: from medial nucleus, bilateral, acts on neck muscles to maintain head erect

Question 11

What eye muscles are stimulated when the head rotates to the right?

Answer 11

Head rotates right causing the left 6th nucleus to activate the left lateral rectus and the right 3rd nucleus to activate the right medial rectus

Question 12

What is nystagmus?

Answer 12

Rhythmic back and forth movement of the eyes

Slow in one direction and fast in the other

Question 13

What is the Weber test?

Answer 13

Tuning fork placed on top of skull. If louder on one side, there is an ipsilateral conductive deafness or contralateral nerve deficit.

Question 14

What is the Rinne test?

Answer 14

Tuning fork on mastoid bone, compared with tuning fork next to ear. Air conduction usually better than bone.

Question 15

What tones are difficult to hear for a patient with a conductive hearing loss?

Answer 15

Low tones are lost from impaired air conduction of sound stimuli

Question 16

What tones are difficult to hear for a patient with a sensorineural hearing loss?

Answer 16

High tones are lost from degeneration of hair cells or the auditory nerve

Question 17

What is the Nylen-Barany maneuver?

Answer 17

Test of vestibular function, positional vertigo.
Patients head is turned and tilted 45 degrees below the plane of the exam table. If rotatory nystagmus is produces, the posterior semicircular canal on the lowered side is overly sensitive.

Question 18

What is benign positional vertigo?

Answer 18

Usually in elderly patients, degenerated otoliths become oversensitive. Minor movements of the head create impulses in the vestibular system.

Question 19

What is acute labyrinthitis?

Answer 19

Viral infection or inflammation of the inner ear labyrinth causes asymmetrical nystagmus, unilateral hearing loss and gait ataxia. Will resolve in days-weeks.

Question 20

What is Meniere’s disease?

Answer 20

Swelling/rupture of the membranous labyrinth leads to mixing of endolymph and perilymph which impairs the receptors. Can lead to permanent deafness.