Auditory System

Question 1

Anatomical components of the auditory system

Answer 1

-external ear (pinna)
-external ear canal – up to the tympanic membrane
-middle ear – air filled, auditory ossicles (3x bones): malleus, stapes, incus
-inner ear – cochlea filled with endolymph to detect sound when disturbed

Question 2

How sound reaches brain?

Answer 2

1.vibration through the air
2.hits the tympanic membrane causing it to vibrate
3.tympanic membrane attached to the ossicles
4.ossicles vibrate and amplify the sound wave to therefore amplify auditory signal
5.Results in vibrations (fluid wave) in the perilymph of cochlea
6.Results in vibrations (fluid wave) in the endolymph, passes onto the hair cells in organ of corti secreting NTs
7.Hair cells pass information onto the CN VIII through NTs

Question 3

Distinguishing frequencies

Answer 3

-hair cells lining cochlea innervated by a nerve.
>low frequencies less vibrations, high frequencies more vibrations

Question 4

Locate sound

Answer 4

-can determine where sound is coming from based on sound delay and intensity that sound is collected at based on where it is coming from

Question 5

Detection of sound

Answer 5

1.frequency of sound
2.timing of sound

Question 6

Frequency of sound

Answer 6

-determines which axons will be activated
-combination of frequencies produce complex sounds (ex.talking)
-this information provides the animal with an indication of what the sound is (bark, growl, owner calling them, explosion, predator

Question 7

Timing of sound

Answer 7

-timing of when sound reaches each ear allows the animal to localize where the sound is located

Question 8

Auditory pathway

Answer 8

CN VIII -> medulla (modulate- more or less activation) -> thalamus -> auditory cortex

Question 9

Unilateral deafness lesion type

Answer 9

-always means peripheral lesion (damage in that ear auditory system or the CN VIII)

Question 10

Deafness examination

Answer 10

-not examined in a regular neuro exam because it is not easy to do

Question 11

Most common cause of deafness

Answer 11

-infections are the most common cause of deafness

Question 12

Types of deafness

Answer 12

1.Conduction deafness
2.Sensorineural deafness

Question 13

Conduction deafness

Answer 13

-issue with the external ear/middle ear

Question 14

Sensorineural deafness

Answer 14

-issue with cochlea/CN VIII/damage in brainstem/auditory cortex

Question 15

Deafness over time

Answer 15

-progressive degenerations (loss) of hair cells occurs over the lifespan of an animal
>high frequencies are lost first, as these hair cells are most prone to degeneration/cell death

Question 16

Excessive or chronic stimulation of hair cells

Answer 16

-can result in deafness
-ex. loud environments (ie. hunting dogs, boarding kennels)

Question 17

Drugs

Answer 17

-Aminoglycosides (systemic antibiotics) which have the ability to kill the hair cells

Question 18

Congenital deafness

Answer 18

-typically associated with pigmentation
>white coats, merle, dalmatians (30%)
-organ of corti lacking melanocytes to contribute to the endolymph properly
>often animal will be born able to hear and then hearing loss will occur
-unilateral or bilateral deafness

Question 19

BAER test (brainstem auditory evoked response)

Answer 19

-electrodes are placed in the head around the ear
-earphones placed inside to deliver sound (clicks or various frequencies)
-electrodes are recording brain activity
>should record multiple waves as it hits different parts of the brain (CN VIII, brainstem, midbrain, auditory cortex); when deaf, no waves.