Vestibular Apparatus Vestibulospinal Tract Vestibular Function Tests Hair

Vestibular Apparatus Vestibulospinal Tract Vestibular Function Tests

Hair Cell Main components: • Kinocillium • Stereocillia • Tip links -Anchoring Filaments Bathed in Endolymph. What is special feature of Endolymph? More K+ ions just like ICF Ist. Order Neuron

Role of Tip links in the Responses of Hair Cells • When a stereocillium is pushed towards a Taller adjacent stereocillium, the Tip link is stretched & opens an Ion Channel

Termination of First Order N • First order Neurons from 3 Semicircular Canals relay on superior, Medial & Inferior Vestibular Nuclei. • 2 nd order neurons from Vestibular Nuclei may form – 1. Vestibulospinal Tracts 2. Vestibulo-cerebellar ( to floculo-nodular Lobe) 3. Vestibulo-Nuclear Tracts - via ( medial longitudinal fasciculus to 3 rd. 4 th & 6 th Cranial nerve Nuclei

Vestibulospinal Tract Origin. Two Types – 1. Medial (Ventral) – 2. Lateral Medial arises from Medial / Inf. Vestibular nucleus Lateral arises from Lat. Vestibular Nucleus (Deiter’s Nucleus). Med. Descend Bilaterally to supply neck & Shoulder girdle muscles Lateral are mostly uncrossed & descend in the spinal cord Ipsilaterally in the Ant. Funiculus.

Functions of Vestibulo-spinal Tracts Function. Mainly facilitatory to α- Motor N & selectively to Gamma Motor Neuron of Extensors & inhibitory to Flexors 2. Primarily concerned with maintaining the position of the Head in space. 3. Maintains Head on neck & Head on body position. 4. Equilibrium through Floculo- nodular lobe. 5. Control Muscle tone specially antigravity muscles & Posture

Functions Contd. • 4. Ascending fibers control bilateral ocular movements in response to rotation of the head through 3 rd, 4 th & 6 th cranial nerve nuclei. (vestibulo-ocular Reflex) - - Advantage? While reading book move Book left or right at a rate of once /second. Can you read it ? Ans. NO Keep book stationary and then move your head at the same rate - - - See

Vestibular function Tests • Nystagmus - Jerky movements of the eyes observed at the start & at the end of Rotation is called Nystagmus. Advantage: It is actually a Reflex which maintains visual fixation on stationary Objects while the body Rotates. - RAILWAY Nystagmus Two Components – 1. Slow. Initiated by impulses from Labyrinth 2. Fast - Trigerred by centre in Brain stem

Vestibular function Tests • Caloric Test – – > Convection Currents in the Endolymph -> motion of Cupula. – May cause- Nystagmus, Vertigo & Nausea. CO WS – MOTION Sickness ?