Balance mechanisms

The mechanisms of achieving balance are: Vestibular hair cells respond to changes in movement or position of the head; The semicircular ducts respond to angular acceleration in specific directions; The utricle responds to linear acceleration in all directions; The lateral vestibular nucleus participates in control of posture; The medial and superior vestibular nuclei mediate vestibulo-ocular reflexes;

Factors involved in equilibrium

Visual system

Eyes and eye muscles

Proprioceptive system:

Posterior column Tendons Joints Muscles

Statokinetic system

Ear labyrinth VIII nerve Brain stem Cerebellum Cerebral cortex

These visual, vestibular and statokinetic inputs are integrated in the CNS and modified by input from the extrapyramidal system, reticular formation, cerebellum and cerebral cortex.

Vestibular function testing i

Responses to rotational acceleration in the plane of a semicircular canal: Barany a chair. With abrupt cessation of rotation, the endolymph continues to circulate for a ¡i period of time. ct

Responses to linear acceleration. n

Caloric stimulation: convection currents in the endolymph, with consequent motion of the cupula.

Electronystagmography: based on the corneo-retinal potential difference to allow measurement of eye movement. Galvanic stimulation. Vestibular-evoked responses.

The inferior vestibular nucleus integrates inputs from the vestibular labyrinth and the cerebellum; The vestibulo-collic and vestibulo-spinal reflexes maintain the head vertical with respect to gravity.

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