Week 7: Vestibular & Auditory Systems

What is vestibular dysfunction

a disturbance in the body's balance system due to an insult to the vestibular system of the inner ear

Two types of vestibular dysfunction

underactive and over-responsive

Functions of the Vestibular System

provide snesnory information about head and body movement

postural control

control of eye movements

Where is the vestibular system located

inner ear

What are the bony labyrinths of the vestibular apparatus

3 semicircular canals & 2 otolithic organs

What are the membranous labyrinths of the vestibular appartus

endolymph and hair cells

What are the otolithic organs

utricle and saccule

What structure is within the utricle and saccule

macula

Within each macula are ____ (receptor)

hair cells

Where are hair cells embedded

otolithic membrane (gelatinous mass) & covered with otoconia (gem stones)

What is the general structure of Macula

supporting cells - hair cells - hair - gelatinous mass - otoconia

What is the function of the otolitchi organs

respond to static head position

respond to linear acceleteration and deceleration & static head tilt

What movement is the utricle responsible for

horizontal movement & static head tilt

Examples of utricle movement

walking, cervical lateral flexion; any linear movement

What movement is the saccule responsible for

vertical movement & static head tilt

Examples of saccule movement

jumping, nodding, going in elevator

Explain the transmission of otolithic organs

in movement, hair cells (receptors) move and get stimulated & perform trasnduction

these signals can be excitatory (depolarization) or inhibitory (repolarization)

What are the semicircular canals

3 hollow rings that detect rotary acceleration and deceleration (rolling down hill, teecup ride, shaking head)

Anatomy of the semicircular canals

3 hollow rings

filled with endolymph

swelling called the ampulla

What does the ampulla contain

supporting cells and hair cells

Describe the transmission of the semicircular canals

when the head is rotated, the force of the endolymph acts against the cupula which displaces the hair cells ; bending of hair cells leads either to depolarization or hyperpolarization

What is the receptor type of the otoliths

mechanoreceptors

What is the receptor type of the semicircular canals

mechanoreceptors

In the otoliths, what is the receptor (raised area) and where is it located

hair cell located in the macula

In the semicircular canals, what is the receptor (raised area) and where is it located

hair cell located in ampulla of semicircula canals

In the otoliths, what kind of stimulation do they respond to

Linear movement

( Horizontal & Vertical )

In the semicircular canals, what kind of stimulation do they respond to

Rotary movement

( Deceleration & Acceleration )

Information from semicircular canals & otolithic organs is transmitted by what nerve

vestibulocochlear nerve

In the vestibular pathways, most information is sent to the

vestibular nuclei

What are the 4 pairs of vestibular nuclei in the pathways

superior

medial

lateral

inferior

Where do the vestibular pathways send information to

nearby structures of the cerebellum and brainstem

What does the lateral vestibular nuclei do

sends signals to spinal cord

descends ipsilaterally to trunk and limbs

supports postural control

What does the medial vestibular nuclei do

sends signals to spinal cord

descends bilaterally to neck & upper trunk

supports control of neck and upper back

What is the vestibular orcular system connection

medial longitundinal fasiculus

Where does the medial longitudinal fasciculus (MLF) project to

extraocular muscle nuclei & superior colliculus on brainstem (midbrain)

What is the function of the medial longitudinal fasciculus (MLF)

activate muscles attached to the eyeball

control eye movements

coordinate movements of the eyes and head

What are the 2 vestibular ocular pathways

vestibular-ocular reflex & vestibular nystagmus

What is the vestibular-ocular reflex (VOR)

the reflex when the head moves in one direction, eyes move in the opposite direction

What is another name for the vestibular-ocular reflex (VOR)

doll's eye reflex

What happens on the VOR during movement

voluntary shifts in gaze are superimposed on the VOR for stable visual field

What is vestibular nystagmus

rapid movement of eyes after rotating movement

How is vesitbular nystagmus induced

by angular acceleartion

The back and forth eye movements are easily observed during rotation is called

perrotary nystagmus

The nystagmus continue after rotation ceases what

postrotary nustagmus

What is the auditory system

system by which we intercept and perceive sound

Explain the transmission of sound to the CNS

sound reaches the cochlear nerve, then goes to the brainstem, then into the medial geniculate body of thalamus, then primary auditory cortex

What are the three structures that process auditory information

primary auditory cortex (temporal lobe)

secondary auditory cortex

auditory association cortex

What happens in the primary auditory cortex (temporal lobe)

sound is head and interpretation begins; maps loudness, modulation of loudness, and modulation of frequency & critical for perception of speech

What happens in the secondary auditory cortex

discimination of location and direction of sound

(eyes can be shut and we will be able to sense where the sound is coming from)

Whay happens in the auditory association cortex

associated with reading and writing; multisensory integration happens here

What is multisensory integration

input is receieved from vestibular and somatosensory systems (tactile, motor, hearing, writing, listening)