Neuro Chapter 10: Neurology of Hearing and Balance

peripheral auditory system

Outer ear

Middle ear

Inner ear

Central auditory system

Cranial nerve VIII

Brainstem

Brain

When waves in cochlear fluids disrupt hair cells in the ______ __ _____, the hair cells __________ similar to neurons

organ of Corti; depolarize

Stereocilia sway, causing __ channels to open

K+

K+ enters the cell, making it

more positive (depolarizing it)

Depolarization opens __ channels, causing it to flood in

Ca++

After Ca++ floods in, _______ is released

Glutamate

Neuronal transmission continues through

CN VIII and brainstem

Here (in the brainstem) _______ and ______ portions diverge (cochlear nuclear complex (CNC)

vestibular and cochlear

Posterior Cochlear Nucleus (dorsal) is made up of what type of cells

pyramidal cells

Anterior Cochlear Nucleus (ventral) is made up of what type of cells

Spherical bushy cells

Globular bushy cells

Octopus cells

Globular bushy cells

sensitive to specific frequencies

octopus cells

sensitive to wider range of frequencies

CNC fibers project to the ___________ in the pons

superior olivary complex (SOC)

SOC has 2 parts

Medial Superior Olivary Complex

Lateral Superior Olivary Complex

Medial superior olivary complex

specializes in low frequency hearing & binaural hearing

Lateral superior olivary complex

specializes in higher frequency hearing

Both parts of the SOC are involved in (3 things)

sound localization, the stapedius reflex, and sound integration

SOC projects through

lateral lemniscus

lemniscus

white matter pathway

_ tracts through the lateral lemniscus (LL), (2 more are projected directly from CNC)

_ total tracts of the LL travel to inferior colliculus

4; 6

inferior colliculus is called the

auditory center of midbrain

functions of inferior colliculus

Maintains tonographic representation from cochlea

Responsible for startle reflex (hyperacusis)

Medial Geniculate Body

Acts as a relay station; relays auditory tracts to the auditory parts of the cerebral cortex

Primary Auditory Cortex occupies BA 41 and 42, found on the

superior temporal gyrus (Heschl's gyrus)

Primary Auditory Cortex is __________ _________, like the cochlea and the rest of the central auditory system

tonographically organized

Primary Auditory Cortex ________ and ________ sound

perceives and discriminates

Disorders of the Central Auditory System

Sensorineural Hearing Loss

Auditory Processing Disorders

Pure word deafness

Aphasia

Auditory Processing Disorders is called

"dyslexia of the ears"

Pure word deafness is also called

verbal agnosia

pure word deafness

bilateral damage to superior temporal lobes; difficulty distinguishing phonemes and comprehending speech

Aphasia—including a receptive component

Global

Wernicke's

Transcortical sensory

Peripheral vestibular system

Semicircular canals

Central vestibular system

Cranial nerve VIII

Brainstem

Brain

Types of cilia in each hair cells (crista ampullares)

Stereocilia (100)

Kinocilia (1)

When the body moves, fluids move in _______ _______, bending the cilia

semi-circular canals

If stereocilia bend toward kinocilia,

K+ and Ca++ channels open

hair cell depolarizes

Releases glutamate

If stereocilia bends away from kinocilia

hyperpolarization/ inhibition

Vestibular Nuclear Complex consists of 4 nuclei

Superior

Inferior

Medial

Lateral (Deiter's)

______ conducts the electrochemical impulse to the brainstem

CN VIII

VNC projects fibers to the ________

cerebellum

VNC to cerebellum connections facilitate the

coordinated movements necessary to preserve the body's balance

VNC projects fibers to nuclei in brainstem that control

eye movements

Brainstem Nuclei include

Abducens nucleus in pons

Trochlear nucleus in midbrain

Oculomotor nucleus in midbrain

brainstem nuclei keeps eyes

fixed on target while head moves (vestibulo-ocular reflex)

VNC projects to the

reticular formation (RF)

reticular formation coordinates

visceral/autonomic functions

VNC to RF connection involves

motion sickness and possible vomiting

VNC projects to spinal cord as

medial vestibulospinal tracts

vestibulocollic reflex

ability to rotate head in one direction and body in the other

VNC also projects descending fibers as

lateral vestibulospinal tract

vestibulospinal reflex

when bending over, the lifting of one leg to keep oneself balanced

Vestibular schwannoma

slow-growing, unilateral, benign tumor on vestibular branch of CN VIII.

First symptoms are HL in 1 ear, headache, then vertigo and balance issues

Labyrinthitis

infection of the inner ear leading to vertigo, nausea, and vomiting