MEDICAL BIOLOGY, HUMAN ANATOMY, PHYSIOLOGY AND PATHOLOGY - Ya.I. Fedonyuk 2010

ANATOMY, PHYSIOLOGY, PATHOLOGY

SECTION 3. ANATOMICAL AND PHYSIOLOGICAL ASPECTS OF BODY FUNCTION SELF-REGULATION

GENERAL ISSUES IN THE ANATOMY AND PHYSIOLOGY OF SENSORY SYSTEMS

3. SENSATION OF BODY POSITION AND MOVEMENT (EQUILIBRIUM ANALYZER)

In humans, spatial orientation is accomplished by the vestibular sensory system, the visual analyzer, as well as the proprioceptive and tactile sensitivity systems. The vestibular analyzer plays a leading role in spatial orientation because it perceives information regarding the acceleration or deceleration of linear or rotational movement, as well as changes in HEAD position in space. This triggers reflex Muscle contractions that help straighten the body and maintain posture. The peripheral part of the vestibular analyzer is the vestibular organ, which consists of the otolith apparatus and three semicircular canals. Destruction of the vestibular organ leads to a loss of the sense of balance.

Ciliated receptor Cells of the vestibular organ are located in the ampullae of the semicircular canals and the maculae of the utricle and saccule of the Inner ear. Changes in movement speed or head tilting generate a receptor potential in the ciliated cells, which is transformed into a Nerve Impulse and travels along the vestibular nerve. The adequate stimulus for the receptors of the semicircular canals is angular acceleration during rotation in three mutually perpendicular planes.

Vestibular nerve fibers project to the Medulla Oblongata. Subsequently, the nerve impulse propagates to the Brainstem structures, the Cerebellum, and the Spinal Cord, which house the centers for REFLEX REGULATION OF body position, posture maintenance, and balance. The connection between the vestibular nuclei and the oculomotor nuclei causes nystagmus (a rhythmic eye movement followed by a corrective return saccade). The occurrence of ocular nystagmus is an important indicator of the vestibular system's functional state and is widely used in aviation, marine medicine, and clinical practice.

Intense stimulation of the vestibular centers produces vestibulo-vegetative reactions (changes in Heart rate, vasoconstriction and vasodilation, increased sweating, nausea, dizziness). Excessive loads on the vestibular apparatus lead to a pathological symptom complex known as motion sickness.