Vestibular Apparatus and Equilibrium

• Vestibular apparatus maintains the body (mainly the head) at equilibrium (at balance) and stabilizing the eyes relative to the environment

• Static equilibrium- maintenance of the position of the body (mainly the head) relative to the force of gravity

• Dynamic equilibrium- maintenance of the position of the body (mainly the head) in response to sudden movements such as rotation, acceleration, and deceleration.

• Consists of 2 parts:

• Otolithic organs

• Utricle and saccule- static equilibrium

• Semicircular canals- dynamic equilibrium

• Bony labyrinth surrounds membranous labyrinth filled with endolymph (like ECF).

• Between bony labyrinth and membrane of membranous labyrinth is perilymph (like CSF)

Otolithic organs

• Utricle and saccule

• Saccule connected to utricle by duct.

• Each sensory area consist of a macule that contains the sensory mechanisms

Utricle

• an irregular, oblong membranous sac located on the medial wall of the vestibule.

• lies horizontally

• More sensitive to horizontal acceleration.

• macula consist of sensory hair cells and supporting cells (sustentacular cells)

• Each sensory hair cell has one kinocilium and many stereocilia

• The stereocilia and kinocilium are embedded in a gelatinous membrane, the otolithic membrane, which sits on top of the sensory cells.

• The membrane is produced by the sustentacular cells.

• On the surface of the otolithic membrane are otoliths (or otoconia), crystals of Ca⁺⁺ carbonate which are composed of calcium carbonate and protein.

• These otoliths sensitive to horizontal movements

Saccule

• a flattened, irregularly-shaped membranous sac also located in the medial wall of the bony vestibule.

• saccular macula, having the same struture as the utricle, lies perpendicular and verticle to the macula of the utricle.

• More sensitive to vertical (saggital plane, up and down forward and back) acceleration.

• has two small openings are present in the saccule.

• One is the opening of a duct, called the endolymphatic duct, that communicates with the utricle.

• The other opening communicates with the duct of the cochlea via the ductus reuniens.

Semicircular Canals

• Provide information about rotational acceleration.

• Project in 3 different planes.

• Each canal contains a semicircular duct. At the base is the crista ampullaris.

• = enlarged swellings at base of each canal communicating with utricles

Endolymph Movement in Canals

Movement of Cupula Relative to Body Movement

Category: Physiology Notes