V.6.2. Static and dynamic vestibular system

Static vestibular system:  The ampulla and the vestibule which are part of the fluid-filled labyrinth, bounded by the membranous wall, give information of the spatial position of the head. The pressure and movement of the hair cells which are covered with crystals of calcium carbonate (CaCo3) are sensed by the epithelial cells. These crystals put pressure on the under lying hair cells. If the head’s spatial position changes, the particles are stimulated by other cells, in other directions.

Dynamic vestibular system: the rotation and swivel movements of the head are sensed by the three semi-circular canals. The semi-circular canals are positioned in three planes of space, at a right angle to each other and are half-curved pipes, filled with liquid.  When the head turns, the liquid in the semi-circular canal in the plane of the direction of the movement flows in the opposite direction because of inertia.

The flowing liquid twists the hair cells of the receptors, situated at the end of the canal which creates the stimulus.

The receptor cells of the position sensing are the hair cells. The hair cells are situated in the inner ear, in the cochlea. This is called the organ of Corti. The high frequency sounds arouse impulses at the base of the cochlea.

Cochlea: a bony, snail shaped route which contains the auditory receptors. The cochlea can be divided into three parts: Scala Vestibuli, where the oval window is located. This is linked to the footplate of the stirrup. The impulse spreads through to the cochlea. The organ of Corti can be found in the Scala Media and the round window is in the Scala tympani. The cochlea contains nerve fibers.

The connection between balance and the nervous system is created by the impulses delivered from the position sensing organ to the mid-brain via the pons into the brainstem by the axons of the two stem neurons (the VIII. Cranial nerve).

The nucleus of the mid-brain is connected to the skeletal muscles, eyes and cerebellum through the spinal cord. This makes it possible to maintain balance and level eye and head movements. The information travels from the thalamus to the front bottom part of the parietal lobe of the cerebral cortex (Abrahams, 2012).

Figure 5. The allocation of balance (Hirtz, Hotz, Gudrun, 2004)