Anatomy and Physiology of Balance


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Anatomy and Physiology of Balance : 

Anatomy and Physiology of Balance Mohamed Shabana,MD Prof. of Audiology Faculty of medicine Cairo University

Vestibular Hair Cells : 

Vestibular Hair Cells Type I (aka inner) Type II (aka outer) With Kinocilium

The Semicircular Canals : 

The Semicircular Canals posterior canal shares plane with contralateral anterior canal. horizontal canals share plane.

Responses of the Cristae : 

Responses of the Cristae All kinocilia are oriented in the same direction Crista in each pair of canals respond inversely to each other

Stimulated by Angular Acceleration : 

Stimulated by Angular Acceleration greatest when fulcrum is within head induces relative motion of endolymph crista is displaced by fluid motion

The Otolithic Organs : 

The Otolithic Organs Saccule: roughly vertical orientation, responds to acceleration components within saggital plane Utricle: horizontal (+ 30 deg.) orientation

Excitation Patterns in the Utricle : 

Excitation Patterns in the Utricle STRIOLA Posterior Anterior Medial

Cranial Nerve VIII : 

Cranial Nerve VIII

Vestibular Portion of C.N. VIII : 

Vestibular Portion of C.N. VIII superior division: utricle, anterior part of saccule, and horiz & anterior canals inferior division: posterior part of saccule, and posterior canal to vestibular nuclei to cerebellum

Vestibulocochlear Nerve : 

Vestibulocochlear Nerve Exits temporal bone near its medial edge. Enters lateral face of brainstem at the level of the lower pons. Synapsing in (Cochlear and) Vestibular Nuclei

Responses of Vestibular Neurons: : 

Responses of Vestibular Neurons: To changes in acceleration, but onset and fade slowly For most normal head movements firing rates are in phase with head VELOCITY.

Other inputs to vestibular nuclei: : 

Other inputs to vestibular nuclei: Cerebellum: primarily inhibitory Spinal cord Pontine reticular formation Contralateral vestibular nuclei

From the Vestibular Nuclei: : 

From the Vestibular Nuclei: Vestibulo-Oculomotor Pathways: Direct: to oculomotor nuclei. Indirect: via reticular formation to oculomotor nuclei (III IV and VI) Vestibulo-Spinal Pathways: Lateral V-S-throughout spinal cord Medial V-S-cervical & thoracic Reticulospinal tract-via brainstem reticular formation

Median Longitudinal Fasciculus : 

Median Longitudinal Fasciculus A tract linking Vest. Nuclei to nuclei of CN III, IV, & VI; Supports conjugate eye movement during movement of the head. Continuous with the medial vestibulospinal tract. The mlf runs near midline ventral to ventricle IV and the periaqueductal gray matter of the midbrain

In the brainstem : 

In the brainstem Vestibular inputs undergo integration Integrated signal is combined with original (velocity driven) signal Processing to reset spatial map for eye musculature

The VOR : 


Central Nervous System Will Adapt to Peripheral Damage : 

Central Nervous System Will Adapt to Peripheral Damage

Eye Movements : 

Eye Movements Saccades—rapid shift in gaze Pursuit—stabilize image of moving object Fixation—stabilize image of still object VOR—stabilize image during head motion OKN—backup for when VOR decays to cont’d head rotation Vergent movements—change depth of focus

Saccades : 

Pause cells inhibit Burst Neurons which stimulate: III & VI (horizontal) or III & IV (vertical) Saccades

Slide 40: 

Visual System Vestibular System Somato- Sensation Compare, Select & Combine Senses SENSORY INPUTSVisionVestibularSomatosensory

Slide 41: 

Somato- Sensation Compare, Select & Combine Senses SOMATOSENSORY RECEPTORS JointsPositionKinesthesia MusclesLengthTension SkinTouchPressure

Slide 42: 

Visual System Compare, Select & Combine Senses CentralOrientation Navigation PeripheralMotion-sensitive Body-sway VISUAL RECEPTORS

Slide 43: 

Vestibular System Compare, Select & Combine Senses Semi-circular canalsOrientation Navigation Utricle & SacculeHorizontal & vertical acceleration & deceleration VESTIBULAR RECEPTORS

Slide 44: 

Selection based on Availability Accuracy Value for the task at hand Processing of inputs from the periphery SENSORY ORGANIZATION Compare, Select & Combine Senses Determination of Body Position Visual Vestibular Somatosensory

Slide 46: 


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