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Comprehensive Guide to Vestibular Apparatus Anatomy and Function

Explore the structure and function of the vestibular apparatus located in the petrous part of the temporal bone, including the cochlea, semicircular canals, utricle, and saccule. Learn about the receptors, hair cells, and neural pathways involved in maintaining balance and equilibrium. Discover vestibular function tests and their significance.

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Comprehensive Guide to Vestibular Apparatus Anatomy and Function

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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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