Otolith organs

Otolith Organs

Latin	Organum otolithi
Part of	Inner ear
System	Vestibular system

The otolith organs are structures in the inner ear that are part of the vestibular system, responsible for detecting linear accelerations and head tilts. These organs help to maintain balance and spatial orientation. There are two otolith organs in each ear: the saccule and the utricle, which are located in the vestibule of the inner ear, adjacent to the semicircular canals.

Structure

The otolith organs consist of a small, oval, gelatinous layer called the otolithic membrane. Embedded in this membrane are tiny calcium carbonate crystals called otoliths or otoconia. Underneath the otolithic membrane is a layer of sensory hair cells, which are similar to those found in the semicircular canals.

Saccule

The saccule is oriented vertically and responds primarily to vertical accelerations, such as when moving up or down in an elevator.

Utricle

The utricle, in contrast, is oriented horizontally and responds to horizontal movements and head tilts relative to gravity.

Function

When the head moves, the otoliths shift due to inertia, bending the hair cells in the otolithic membrane. This bending alters the rate of neurotransmitter release from the hair cells, thereby changing the firing rates of the vestibular nerve fibers connected to them. The brain interprets these changes in firing rates as motion and orientation of the head.

Clinical significance

Dysfunction of the otolith organs can lead to conditions such as vertigo, balance disorders, and dizziness. Tests such as the ocular tilt reaction can assess the function of the otolith organs.

See also

• Balance disorder
• Vestibular neuronitis
• Meniere's disease