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Vestibular Apparatus Vestibulospinal Tract

Vestibular Apparatus Vestibulospinal Tract. Vestibular Apparatus. Anatomical location: Petrous Part of Temporal Bone. Vestibular Apparatus. Cochlea (Hearing) - Semicircular Canals -Utricle -Saccule. Membranous Labyrinth showing location of Receptors, Crista Ampullaris & Maculae.

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Vestibular Apparatus Vestibulospinal Tract

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  1. Vestibular Apparatus Vestibulospinal Tract

  2. Vestibular Apparatus • Anatomical location: Petrous Part of Temporal Bone

  3. VestibularApparatus Cochlea (Hearing) -Semicircular Canals -Utricle -Saccule

  4. Membranous Labyrinth showing location of Receptors,Crista Ampullaris & Maculae

  5. Crista Ampullaris & MaculaThe Functional Receptors of Vestibular Apparatus Specific Gravity of Otolith is 3 times that of Endolymph

  6. Ampullary part of Semicircular canalshowing Crista Ampullaris

  7. 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

  8. 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 anIon Channel

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

  10. Functions of Semicircular Canals, Utricle & Scaule • Detects the change in angular velocity intheirrespective Planes(Acceleration or Deceleration both) Effective stimulus is0.2 – 0.5 degree / Sec2 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)

  11. 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

  12. Termination of First Order N • First order Neurons from 3 SemicircularCanalsrelay onsuperior, Medial & Inferior Vestibular Nuclei. • 2nd 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 3rd. 4th & 6th Cranial nerve Nuclei

  13. 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.

  14. 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

  15. Functions Contd. 4. Ascending fibers control bilateral ocular movements in response to rotation of the head through 3rd, 4th & 6th 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

  16. 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

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

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