d. Membranous Labyrinth. The specific portions of the membranous labyrinth
involved are the two sac-like structures--the sacculus and the utriculus. Each of these
two structures has an area of special hair cells called the macula. In addition, there are
three semi-circular ducts located within the osseous semi-circular canals of the temporal
bone of the skull. Each semi-circular duct has a crista, a little ridge of hair cells across
the axis of the duct.
e. "Body Sense." All of the various sensory inputs related to the maintenance
of equilibrium and posture are integrated within the brain as "body sense." Correct
information is sent to the muscles of the body by means of specific postural reflexes in
order to maintain the proper posture.
5-11. SACCULUS AND UTRICULUS
a. The sacculus and the utriculus are two sac-like portions of the membranous
labyrinth. They are filled with endolymph.
b. On the wall of each sac is a collection of special hair cells known as the
macula, which serves as a receptor organ for static and linear kinetic gravitational
forces. The saccular macula and the utricular macula are oriented at more or less right
angles to each other. For the pair of maculae in the membranous labyrinth of the right
side, there is a corresponding pair in the labyrinth of the left side. Information from all of
these maculae is sent into the brain for continuous sensing of the position of the head in
5-12. SEMICIRCULAR DUCTS
Extending from and opening into the utriculus are three hollow structures called
the semicircular ducts. Since the utriculus completes the circle for each duct, the ducts
act as if they were complete (Figure 5-5).
a. Orientation. Two of the ducts are vertically oriented (one anterior and one
posterior). The third duct is essentially horizontal. The three ducts are all oriented at
right angles to each other. In addition, the three ducts of one membranous labyrinth are
matched or paired by the three ducts of the opposite membranous labyrinth.
b. Ampullae and Cristae. Each semi-circular duct ends with an enlargement
where it opens into the utriculus. This enlargement or swelling is called an ampulla.
The crista is at a right angle to the axis of the duct. Movement of the endolymph within
the duct--caused by movement of the head in space--deforms (bends) the hairs of the
crista in specific directions. These are responses to linear and/or angular kinetic