Histology of the Human Ear I. External ear (Figure ... - Faculty.rmc.edu

(2) Function
(a) When the organism's head moves, the fluid in the semicircular canal tends
to stay in place due to inertia.
(b) The head movement therefore results in the wall of the canal moving past
the fluid.
(c) Movement of the wall relative to the fluid causes the fluid to press on the
"dam" in the ampulla (the cupula) formed by the gelatinous mass attached
to the hair cells.
(d) Bending of the cupula in turn moves the processes of the hair cells.
(e) Movement of the processes on the hair cells changes the frequency of
impulses in the sensory neurons which receive inputs from the hair cells.
(f) The organism experiences stimulation of the ampullae as motion, but the
stimulus is actually acceleration (a change in the rate of motion).
c. Cochlea (Figure 25.1, 25.4, 25.13, 25.14, 25.17, 25.21, Plate 104, Plate 105)
(1) Structure
(a) The cochlea is a tubular structure which is coiled into a snail shell-like
spiral.
(b) Two outer canals run the full length of the cochlea.
- the vestibular canal (scala vestibuli)
- the tympanic canal (scala tympani)
(c) The outer canals are continuous at the tip of the cochlea.
(d) A central canal (the cochlear duct) is located between the two outer
canals and does not connect directly to the two outer canals.
(e) The sensory cells (hair cells) are embedded in the columnar epithelium that
forms the "floor" of the cochlear duct. The complex of hair cells and
supporting cells is called the Organ of Corti.
(f) Two arrays of hair cells (inner and outer) run longitudinally within the organ
of Corti.
(g) The microvilli of the hair cells are embedded in a gelatinous structure (the
tectorial membrane) which runs longitudinally in the organ of Corti.
(h) One edge of the organ of Corti (both tectorial membrane and sensory
epithelium) is anchored to bone (the osseus spiral lamina). The other edge
is much more flexible.
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