The vestibular apparatus (from the Latin ldquo;a hallwayrdquo;) - is the main organ of balance (Fig 185, 186.). He is placed in the inner ear and

Vestibular system anatomy and sense of balance [apparatus]

The vestibular apparatus (from the Latin “a hallway”) — is the main organ of balance (Fig 185, 186.). He is placed in the inner ear and consists of two functional parts — vestibule and three semicircular canals filled with fluid.

Otolith organs

The vestibule consists of oval and round sacs, where the balance organs are placed, called the otolith apparatus (from the Latin “ear and stone”).

The otolith apparatus has sensory receptor hair cells — mechanoreceptors. Their hairs are immersed in a viscous fluid with calcareous crystals — otoliths, which form the otolith membrane, the density of which is higher than the density of surrounding environment. Therefore, under the effect of gravity or acceleration membrane moves (slides) relatively to receptor cells, which hairs are bent toward the sliding. Cell stimulation occurs. Otolith apparatus is placed vertically in an oval sac and horizontally — in the round. Hence, it controls the body position in space relative to the force of gravity and responds to rectilinear acceleration at the vertical and horizontal movements of the body.

Diagram 185. Location of the vestibular system in the inner ear: 1 — vestibule; 2 — the semicircular canals; 3 — oval sac; 4 — round sac; 5 — ampoule; 6 — the vestibular nerve; 7 — otolith apparatus

Semicircular canal system

The second part of the vestibular apparatus is the three semicircular canals with a diameter of about 2 mm (diagram 185, 187). Each of them communicates with an oval sac and at one end has an expanding — vial in which the middle crest (diagram 186) is pulled out. It is the accumulation of the receptor cells, which hairs are immersed in the viscous mass, forming a dome. The acceleration that occurs during circle movement of the head causes displacement of fluid within the semicircular canals. Crest dome bents with the hairs. The excitement of the receptor cells occurs. The semicircular canals are placed in three mutually perpendicular planes, so that their receptor cells respond to circular and rotational movement of the head and torso (diagram 187).

Diagram 186. The balance receptors and their placement in the vestibular apparatus: a) the sensitive area of the inner ear at rest; b) displacement of the viscous mass during tilting head; c) ampoule crest at rest; d) ampoule crest during the rotation: 1 — endolymph; 2 — viscous mass with otoliths; 3 — hairs of sensory cells; 4 — supporting cells; 5 — fibers of the vestibular nerve

Balance (vestibular) receptors

Almost all human movement, walking, cycling, skating, acrobatics are possible while maintaining body balance. Balance receptors are responsible for this; they continuously supply the brain with information about the location and position of the body in space. Balance receptors are located in the joints, skeletal muscles and the vestibular apparatus of the inner ear. Superior motor centers of the cerebral cortex send commands to the cerebellum, and then — to the muscles and joints. This happens automatically, but, if necessary, superior (cortical) centers of voluntary movement regulation interfere.

Vestibular nerve

From vestibular receptors depart thin sensory nerve fibers which, twining, form the vestibular nerve (diagram 185). Is sends impulses of the body position in space to the medulla oblongata, in particular in the vestibular center, which is connected by neural pathways with the cerebellum, subcortical structures and cerebral cortex (superior balance center) and visual centers. Taken from

Diagram 187. The receptors of the semicircular canals respond to circular and rotational movement of the head

Vestibular disorders

Losing sight, a human for some time loses sense of balance and orientation in space. And when the function of the vestibular apparatus is disrupted, the vision helps to navigate in space.

There are people who have increased excitability of vestibular system. They are afraid of heights, feel bad in the plane, during a sea voyage, swayed in transport; it accompanies by unpleasant sensations: weakness, dizziness, nausea or vomiting, because the vestibular center of the medulla oblongata is placed close to the respiratory centers, circulation, digestion, and due to their excitation such ailments occur.

However, the human vestibular system has a large spare capacity that can be developed by workouts. This is evidenced by the experience of the astronauts and jet aircraft pilots work.

Congenital or acquired disorders of the vestibular apparatus, which cause dizziness or nausea, envisage certain restrictions in the choice of profession (such people cannot work as a drivers or high-altitude installers), sport (climbing, acrobatics and so on).

  • Determine the biological importance of balance sensation.

  • Explain the structure and functions of the vestibular apparatus.

  • Define the structure and functions of the otolith apparatus.

  • What are the nerve centers of balance sensation?

  • Describe the relationship of the nerve centers of balance feeling with other brain formations.