(2) Organ of Corti. Located upon the basilar membrane is the organ of
Corti. The organ of Corti is made up of hair cells. When the basilar membrane vibrates,
the hair cells are mechanically deformed so that the associated neuron is stimulated.
13-14. NERVOUS PATHWAYS FOR HEARING
The neuron (associated with the hair cells of the organ of Corti) then carries the
sound stimulus to the hindbrainstem. Via a special series of connections, the signal
ultimately reaches Brodmann's area number 41, on the upper surface of the temporal
lobe (see para 12-36). Here, the stimulus is perceived as the special sense of sound. It
is interesting to note that speech in humans is primarily localized in the left cerebral
hemisphere, while musical (rhythmic) sounds tend to be located in the right cerebral
Section IV. THE SPECIAL SENSE OF EQUILIBRIUM, THE GENERAL BODY
SENSE, AND POSTURAL REFLEXES
a. The human body is composed of a series of linkages, block on top of block.
These blocks can be arranged in a multitude of patterns called postures. In order to
produce and control these postures, the human brain utilizes a great number of
continuous inputs telling the brain the instantaneous condition of the body posture.
Overall, we refer to this process as the general body sense.
b. The internal ear provides one of the input systems for the general body
sense. The internal ear responds to gravitational forces, of which there are two
kinds--static and kinetic (in motion). Of the kinetic stimuli, the motion may be in a
straight line (linear) or angular (curvilinear).
13-16. THE MACULAE
The membranous labyrinth of the internal ear has two sac-like parts--the
sacculus and the utriculus. On the wall of each of these sacs is a collection of hair cells
known as the macula (plural: maculae). The hairs of these hair cells move in response
to gravitational forces, both static and linear kinetic. The maculae are particularly
sensitive to small changes in the orientation of the head from an upright position. Thus,
the maculae are very important in maintaining a standing or upright position.
13-17. THE SEMICIRCULAR DUCTS
a. In addition, three tubular structures are associated with the utriculus. The
circle of each of these semicircular ducts is completed by the cavity of the utriculus. At