Vestibular Apparatus Vestibulospinal Tract Vestibular Apparatus Anatomical location

Vestibular Apparatus Vestibulospinal Tract

Vestibular Apparatus • Anatomical location: Petrous Part of Temporal Bone

Vestibular Apparatus Cochlea (Hearing) -Semicircular -Utricle -Saccule Canals

Membranous Labyrinth showing location of Receptors, Crista Ampullaris & Maculae

Crista Ampullaris & Macula The Functional Receptors of Vestibular Apparatus Specific Gravity of Otolith is 3 times that of Endolymph

Ampullary part of Semicircular canal showing Crista Ampullaris

Hair Cell Main components: • Kinocilium (One Longest) • Stereocilia (50 -110) • Anchoring Filaments(Tip Links)- Join the Top Of Stereocilia Bathed in Endolymph. What is special feature of Endolymph? More K+ ions just like ICF. Source of K+ – stria Vascularis Endolymphatic Potential=+80 mv -70 mv

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

Arrangement of Hair Cells in Utricle & Saccule (Direction of Kinocillia) Utricle. Kinocillium away from the Arbitrary Line Saccule. Kinocillium Towards The arbitrary Line

Functions of Semicircular Canals, Utricle & Scaule • Detects the change in angular velocity in their respective Planes (Acceleration or Deceleration both) Effective stimulus is 0. 2 – 0. 5 degree / Sec 2 acc or deceleration In Horizontal Canals- Kinocilium is directed towards ampula ( Ampulopetal bending will cause Stimulation). In Remaining Two semicircular Canals i. e (Superior. & Posterior) Kinocilium is Directed away from Ampula ( Ampulofugal bending will cause Stimulation)

Functions of utricle & Sacule Utricle & Sacule Detects – - Linear Acceleration or Deceleration or Special Orientation of Head with respect to rest of the body. - Maintains Equilibrium through their CNS connections, particularly the Posture of the Head & Eyes

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 Med. Descend Bilaterally to supply neck & Shoulder girdle muscles Lateral arises from Lat. Vestibular Nucleus (Deiter’s Nucleus). Lateral are mostly uncrossed & descend in the spinal cord Ipsilaterally in the Ant. Funiculus.

Functions of Vestibulo-spinal Tracts 1. 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 ?