Upload
gaurav-singh
View
235
Download
0
Embed Size (px)
Citation preview
VESTIBULAR APPRATUS
INTRODUCTION Vestibular apparatus is a complex sense
organ of inner ear Primary organ for equlibrium Is required for- ▪the movement of the eye that
accompany the movement of the head ▪detection of various movements
and positions of the head
Internal ear consists of-
Bony labyrinth- bony structure of inner ear
Membranous labyrinth Cochlea and vestibular apparatus are
situated here
Perilymph- Fluid between bony and
membranous labyrinth
● Endolymph- Fluid within membranous labyrinths
FUNCTIONAL ANATOMY Lie in temporal bone on each side of the
head
It consists of- ▪ three semicircular canal ▪utricle and saccule (the otolith
organ)
SEMICIRCULAR CANAL Are three in numbers- horizontal (lateral) superior (anterior) inferior (posterior)
●All three canals are at right angles to each other
Ampulla- each canal begins as a dilatation called ampulla
All three canals open into the utricle
Utricle opens into the saccule through a duct called Ductus endolymphaticus
Saccule communicates with cochlea
CRISTA AMPULLARIS AND CUPULA Crista is the receptor present in
semicircular canal In the ampulla there is a ridge On ridge are hair cells which give rise to
hairs Cupula- hairs and gelatinous substance
Crista- cupula and hair cells
MACULA Macula is the receptor present in utricle
and saccule In utricle and saccule ridge like structure
hair cells and hair is present Otolith membrane- hairs and gelatinous material
Macula- Otolith membrane and hair cells
HAIR CELLS Kinocilium- ▪present at one end of hair cell ▪large non motile hair
Stereocilia- ▪present in the remaning hair
cells ▪are small with progressive
increase in height
Hair cells are of two types- ▪Type I –flask shaped ▪Type II-most common type
VESTIBULAR PATHWAYNerve fibers from cristae and maculae ↓Form vestibular division of 8th nerve ↓Vestibular ganglion(Scarpa`s ganglion) ↓Central axon proceeds towards the brain
stem ↓Enters brain stem and end in vestibular
nucleus
Efferent fibers from vestibular nucleus terminates in-
1.In the 3rd,4th,6th cranial nerve nuclei via median longitudinal fasciculus
2.Anterior horn of spinal cord via lateral vestibulospinal tract
3. In the cerebellum
4.Nuclei of reticular formation of the brain stem
5.Temporal lobe of opposite side via the opposite thalamus
6.Some fibers go back to the hair cells
MODE OF ACTION OF SEMICIRCULAR CANAL Semicircular canal detects angular
acceleration during rotation of head along three perpendicular axes
Stimulus to each ampulla is rotation of the head
Posterior canal of one side and Anterior canal of other side form a pair
Two horizontal canal of both sides make a pair
Semicircular canal signals changes in acceleration but are insensitive to constant rotatory movement
MODE OF ACTION OF UTRICLE AND SACCULE Saccule and utricle gives information
about linear acceleration and change in head position relative to the
gravity
Saccule → Vertical acceleration
Utricle → Horizontal acceleration
Maculae of the saccule and utricle are stretch receptors
Stimulus for maculae is pull of the gravity on the otolith membrane
The hairs are deformed resulting in stimulation of the nerve fibres
Saccule are affected by lateral tilt of the head
Utricle are affected by nodding the head up and down
Movement of stereocilia towards the kinocilium increases action potential frequency
ROLE OF VESTIBULAR APPARATUS IN REGULATION OF POSTURE It is a sense organ of balance
-Balance is regained by righting reflex
Vestibulo-ocular reflex
- When the head is moving towards a given direction, the eyes move to the opposite side
Otolith reflex-
prevent injuries when a person walks downstairs or jumps from a platfrom
FUNCTIONS
Enable the erect position of the head and the normal posture of the body is maintained
Semicircular canal gives information about movement of the head
Otolith organ gives information about position of the head
VESTIBULAR DYSFUNCTION 1. MOTION SICKNESS-
▪is a syndrome consisting of nausea, vomiting, headache, vertigo
▪ occurs during travelling ▪due to overstimulation of
vestibular apparatus
2. SEA SICKNESS ▪ type of motion sickness occuring
during travelling by sea
▪results from irregular and repetitive motion of the ship
3. MENIERE`S DISEASE
▪Disorder involving vestibular apparatus
▪ Episodes of dizziness (vertigo),tinnitus
and hearing loss ▪ Due to distension of
endolymphatic system
Drug treatment ▪ Bed rest ▪ Vestibular sedative ▪ Vasodilator like histamine
Surgical treatment ▪Decompression of endolymphatic sac ▪Sacculotomy ▪ Section of vestibular nerve
4. DRUG INDUCED DAMAGE -By streptomycin when used in heavy
dose for treatment of tuberculosis
NYSTAGMUS ▪ Involuntary jerky oscillation of eyes ▪ Railwayman`s nystagmus- seen in
normal person ▪Cause of pathological nystagmus -Disease of cerebellum - Vestibular dysfunction - Weakness of extra-ocular
muscles of eyes ( Myasthenia gravis)
LABRYRINTHECTOMY
-Removal of labyrinth
a) Unilateral labrinthectomy - There is derangement of postural
activity -Nystagmus
b) Bilateral labyrinthectomy
- Individual behaves normally ,if allowed to use the vision
- Muscle tone is decreased
TEST FOR VESTIBULAR FUNCTION Romberg`s sign -Test for loss of position sense
Barany`s Caloric test -Diagnostic purpose -Semicircular canal are stimulated -Water is at 30˚ C or 44˚ C - Causes nystagmus ,vertigo and
nausea
Fistula test
- To induce nystagmus by producing pressure changes in the external canal which are then transmitted to the labyrinth
-Normally the test is negative