Vestibular system

Lore & Background

The vestibular system contains three semicircular canals in each labyrinth, approximately orthogonal to each other: horizontal, anterior, and posterior. These canals detect rotational movements; for example, the horizontal canal corresponds to head rotation around a vertical axis, while the anterior and posterior canals detect rotations in the sagittal and frontal planes. The canals are arranged in push-pull pairs, where stimulation of one canal inhibits its counterpart on the opposite side, enabling sensing of all rotation directions.

Reader's Guide

The vestibular system sends signals primarily to neural structures controlling eye movement, forming the vestibulo-ocular reflex (VOR), which stabilizes images on the retina during head movement by producing eye movements opposite to head movement. This reflex works even in total darkness. Signals also go to muscles that keep an animal upright and control posture. The brain integrates vestibular information with proprioception to understand body dynamics and kinematics, though how these sources are integrated is unknown. The system's mechanics are described by a damped oscillator, with cupula deflection proportional to head velocity for typical movements. Central processing involves projections to the cerebellum, cranial nerves III, IV, and VI, reticular formation, spinal cord, and thalamus, enabling reflex reactions and conscious body position awareness.

Did You Know?

• The semicircular canals are approximately orthogonal to each other and include horizontal, anterior, and posterior canals.
• The vestibulo-ocular reflex stabilizes vision by moving the eyes opposite to head movement, even in total darkness.
• The otolithic organs, utricle and saccule, sense linear accelerations using hair cells embedded in an otolithic membrane weighted with otoconia.
• The cupula has a Young's modulus of 5.4 Pa and the time constants T1 and T2 for humans are about 5 ms and 20 s, respectively.