VESTIBULAR SYSTEM v Function of the vestibular system

VESTIBULAR SYSTEM

v Function of the vestibular system is to maintain equilibrium or balance by detecting angular and linear accelerations of the head

Psychology 355 THE VESTIBULAR SYSTEM Head Rotation Head Angle Linear Acceleration 3

THE VESTIBULAR ORGAN The Semicircular Canals Function: Detect angular or rotational acceleration of the head. Structure Ampulla: Bulge along canal, contains crista Cilia: Project into gelatinous cupula Semicircular canals: Filled with endolymph 4

Movement of fluid within the horizontal semicircular canal corresponds to rotation of the head around a vertical axis (i. e. the neck). • The anterior and posterior semicircular canals detect rotations of the head in the sagittal plane (as when nodding), and in the frontal plane, � The movement of fluid pushes on cupula, which contains hair cells that transduct the mechanical movement to electrical signals •

THE VESTIBULAR SYSTEM Psychology 355 7

PUSH-PULL SYSTEMS � The canals are arranged in such a way that each canal on the left side has an almost parallel counterpart on the right side. Each of these three pairs works in apush-pull fashion: when one canal is stimulated, its corresponding partner on the other side is inhibited, and vice versa.

� This push-pull system allows us to sense all directions of rotation: while the right horizontal canal gets stimulated during head rotations to the right , the left horizontal canal gets stimulated by head rotations to the left.

OTOLITH ORGANS � The otolith organs sense gravity and linear accelerations. We have two on each side, one called utricle, the other saccule. They are heavier than their surroundings. Therefore they get displaced during linear acceleration, which in turn deflects the ciliary bundles of the hair cells and thus produces a sensory signal

� The utricle is sensitive to a change in horizontal movement, and the saccule gives information about vertical acceleration (such as when in an elevator).

Psychology 355 The Otolith Organs 13

. Most of the utricular signals elicit eye movements, while the majority of the saccular signals projects to muscles that control our posture.

VESTIBULO-OCULAR REFLEXS � The vestibulo-ocular reflex (VOR) is a eye movement reflex that stabilizes images on the retina during head movement by producing an eye movement in the direction opposite to head movement, thus preserving the image on the center of the visual field.