NURSING CARE RELATED TO THE SENSORY AND
NEUROLOGICAL SYSTEMS
1-6
1-6. EQUILIBRIUM
a. Equilibrium is the state of balance of the body. Through a variety of sensory inputs and postural reflexes, the body can be maintained in a desired posture. All of the various sensory inputs related to the maintenance of equilibrium and posture are integrated within the brain as "body sense." The internal ear provides one of the input systems for general body sense.
b. A primary sensory input for equilibrium consists of gravitational forces. Gravitational forces are of two types: static, when the body is standing still, and kinetic, when the body is in motion. Kinetic motion may be in a straight line (linear), or in an angular direction (curvilinear).
c. The fluid-filled membranous labyrinth of the inner ear has two sac-like structures called the sacculus and the utriculus. On the wall of each sac is a collection of special hair cells, which serve as receptors for static and linear kinetic gravitational forces.
d. Associated with the utriculus are three tubular structures called the semicircular canals. Two of the semicircular canals are vertically oriented and the third is essentially horizontal. All three semicircular canals are oriented at right angles to each other.
e. Each semicircular canal ends with an enlarged area where it opens into the utriculus. This area is called the ampulla. On the wall of each ampulla, at a right angle to the axis of the canal, is a little ridge of hair cells. The hair cells bend in directional response to the kinetic gravitational forces initiated by movement of the head.
f. All the information from the hair cells of the sacculus, utriculus, and ampullae is transmitted to the brain by the vestibular nerve. The vestibular and auditory nerves are contained within the same fibrous sheath from the inner ear to the brain. Within the brain, the two nerves split into different pathways.
