11-36. SEMICIRCULAR DUCTS (FIGURE 11-15)
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 circles.
Figure 11-15. Diagram of semicircular duct orientation.
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 semicircular 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