Neurology of Hearing and Balance

Question 1

Hearing is also known as

Answer 1

audition

Question 2

Main divisions of the ear

Answer 2

• peripheral auditory system
  outer, midd, inner ear and CN 8
• central auditory system
  brain & brainstem

Question 3

Peripheral auditory system of ear

Answer 3

outer ear (pinna)
middle ear
inner ear
cranial nerve VIII

Question 4

Central auditory system of ear

Answer 4

brain
brainstem

Question 5

Middle ear

Answer 5

• acoustic energy hits tympanic membrane
• TM begins to vibrate which indicates an energy change (acoustic to mechanical energy)
• mechanical energy transmitted through ossicles (malleus, incus, stapes)
• footplate of stapes rocks in/out of oval window

Question 6

Inner ear

Answer 6

rocking of stapes creates waves in the cochlear fluids
- energy change: mechanical energy changed into hydraulic energy

Waves disrupt hair cells in organ of corti
- 3rd energy change: hydraulic energy to electrochemical energy

Question 7

Nerve conduction

Answer 7

CN VIII = Vestibulocochlear

• cochlear branch of this nerve connects into hair cells of organ of corti
• this nerve conducts electrochemical impulse to the brainstem

Question 8

Brainstem organization

Answer 8

• CN VIII inputs into the brainstem’s cochlear nuclear complex (CNC) or CN
• Cochlear nucleus lies where the pons and medulla meet at cerebellopontine angle
• vestibular & cochlear branches of CN VIII diverge here

Question 9

Cochlear Nucleus

Answer 9

an area of specialized cells for auditory information

Question 10

What does cochlear nucleus do

Answer 10

processes incoming auditory signals by
- differentiating frequencies
- timing information
which is critical for sound localization

Question 11

Brainstem organization: Lateral Lemniscus

Answer 11

a prominent fiber bundle/tract in the midbrain that plays a crucial role in auditory pathway

INFO GOES ALONG THIS TRACT

Question 12

Stapedius reflex

Answer 12

CN VII (FACIAL) triggers stapedius to contract in response to loud noise - causes stapes to move out of oval window

sound is dampened (45 secs)

Question 13

stapedius reflex is triggered

Answer 13

bilaterally

Question 14

stapedius reflexo is used to

Answer 14

• diagnose sensorineural hearing loss and acoustic neuroma
• help locate lesion lower brainstem
• Facial nerve branches both ears, absence stapediala reflux on one side can indicate a lesion in facial nerve

Question 15

inferior colliculi

Answer 15

auditory center of the midbrain
- maintains tonotopic organization
- important for localization of sound/pitch/discrimination

Question 16

inferior colliculi regulates

Answer 16

acoustic startle reflex
(sudden movement when unexpected sound occurs)

Question 17

Diencephalon organization

Answer 17

Medial Geniculate Body

Question 18

Medial Geniculate Body

Answer 18

the auditory center of the thalamus
- relay station (auditory tracts to auditory parts of cerebral cortex)

Question 19

lateral geniculate body in the

Answer 19

thalamus, is the visual center

Question 20

cerebral cortex organization

Answer 20

PAC = primary auditory cortex

Question 21

primary auditory cortex (PAC)

Answer 21

central auditory pathway ends here
- found on superior temporal gyrus
- area is tonotopically organized
- perceives & discriminates sound

Question 22

Main divisions of balance

Answer 22

Peripheral vestibular system
- semicircular canals
- cranial nerve VIII

Central vestibular system
- brain
- brainstem

Question 23

Peripheral vestibular system of balance

Answer 23

• semicircular canals
• cranial nerve VIII

Question 24

Central vestibular system of balance

Answer 24

• brain
• brainstem

Question 25

Semicircular canals

Answer 25

3 fluid-filled canals that correspond to our 3D world
- anterior canal
- posterior canal
- horizontal canal

Question 26

anterior canal

Answer 26

coronal plane of space

Question 27

posterior canal

Answer 27

sagittal plane of space

Question 28

horizontal canal

Answer 28

transverse plane of space

Question 29

Ampulla

Answer 29

• swelling in semicircular canal
• Crista structures inside each

Question 30

cristas

Answer 30

• inside each ampulla
• have hair cells similar to cochlea
• hair cells sensitive to body movements in different planes of space

Question 31

Utricle and Saccule

Answer 31

within macula are hair cells that have calcium carbonite embedded in gelatinous membrane

Question 32

displacement of crystals impact

Answer 32

balance via impact on cerebellum and eyes

Question 33

generation of neural impulse

Answer 33

• with body movement, fluids move in semicircular canals
• if sterocilia bend towards kinocilia, hair cell depolarizes & signal goes to brain
• if bends away = inhibition (no signal sent)

Question 34

Vestibular nuclei - Cerebellum

Answer 34

• Vestibular nuclei projects fibers to cerebellum
• cerebellum coordinates motor movement
• these connections facilitate coordinated movements necessary to preserve body’s balance

Question 35

Vestibular Nuclei - Eye movements

Answer 35

Vestibulo-ocular reflex
- keeps eyes fixed/stable when moving head
- visual field and retinal image

Question 36

Vestibular related reflexes

Answer 36

• Vestibulo-Ocular Reflex
• Vestibulospinal Reflex
• Vestibulocollic Reflex
• Acoustic Startle Reflex
• Stapedius Reflex

Question 37

Vestibulospinal Reflex

Answer 37

• maintain balance, posture, & stability
• via activating skeletal muscles

(bending over and lifting one leg to balance)

Question 38

Vestibulocollic Reflex

Answer 38

stabilizes head in space when head moves, command is to move head in opposite direction of the current head motion

Question 39

Acoustic Startle Reflex

Answer 39

sudden movement when an unexpected sound occurs

Question 40

Stapedius Reflex

Answer 40

AKA acoustic reflex
- bilateral response triggered by CN VII
- in response to intense noise

• causes stiffening of ossicular chain, pulls stapes away from oval window, dampens sound for 45 seconds