d. Fluid vibrations of the perilymph are converted to nerve impulses when the
hair cell receptors within the cochlea are stimulated by the fluid vibrations. The nerve
impulses are carried to the brain where they are interpreted as sound.
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
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
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.
Section II. ASSESSMENT
EXAMINATION OF THE EYE
An examination of the eye includes an external examination, examination by
ophthalmoscope, and an assessment of the functions of the eye.
a. External Examination. The anterior segment of the eyes and their
appendages can be examined by visual inspection.