ear, nose, and throat disorders
Dizziness and Vertigo
Pathophysiology of Dizziness and Vertigo
Thevestibular systemis the main neurologic system involved in balance. This system includes The vestibular apparatus of the inner ear The 8th (vestibulocochlear) cranial nerve, which conducts signals from the vestibular apparatus to the central components of the system The vestibular nuclei in the brain stem and cerebellum Disorders of the inner ear and 8th cranial nerve are considered peripheral disorders. Those of the vestibular nuclei and their pathways in the brain stem and cerebellum are considered central disorders. The sense of balance also incorporates visual input from the eyes and proprioceptive input from the peripheral nerves (via the spinal cord). The cerebral cortex receives output from the lower centers and integrates the information to produce the perception of motion. Perception of stability, motion, and orientation to gravity originates in the vestibular apparatus, which consists of The 3 semicircular canals The 2 otolith organs—the saccule and utricle Rotary motion causes flow of endolymph in the semicircular canal oriented in the plane of motion. Depending on the direction of flow, endolymph movement either stimulates or inhibits neuronal output from hair cells lining the canal. Similar hair cells in the saccule and utricle are embedded in a matrix ofcalcium carbonatecrystals (otoliths). Deflection of the otoliths by gravity stimulates or inhibits neuronal output from the attached hair cells. 