Nervous System III
The ear of a young person with normal hearing can
detect sound waves with frequencies varying from about
20 to 20,000 or more vibrations per second. The range of
greatest sensitivity is between 2,000 and 3,000 vibrations
and release neurotransmitter to the outside. The neu-
rotransmitter stimulates the ends of nearby sensory nerve
bers, and in response, they transmit nerve impulses along
the cochlear branch of the vestibulocochlear nerve (cranial
nerve VIII) to the brain.
Spiral organ. (
) A micrograph of the spiral
organ and the tectorial membrane (300×). (
) A scanning electron
micrograph of hair cells in the spiral organ, looking down on the “hairs”
(bright yellow) (6,700×).
Scala vestibuli (perilymph)
Scala tympani (perilymph)
Receptors in regions of the cochlear duct sense
erent frequencies of vibration, expressed in cycles per second (cps).