PHYSICS

Hair I •
shaft
Meissner's 1\ ~~,
shaft ..
Sebaceous I~id .,
glands "
Pacinian I I
corpuscles
•
­
I Pores
...
I Epidermis
.. Nerve
~·~~~~~;i
,----_/.1: I
~&.llJ
corpuscle
Muscle
\ I Hair
~ folicle
~Sweat
I gland
Blood
vessels
Fig. 5.3. The hair receptor cell
If the head of an animal is
bent at an angle, the semicircular
canals alter their orientation,
while the endolymph remains
at the same place due to
inertia. The deflection of the
otoliths by gravity results in the
transmission of action potentials
by the hair cells to the brain at
about 100 spikes/second. I nterpretation
of the bending by the
brain occurs through the analysis
of changes in the frequency
of the action potentials.
Otoliths
Fig. 5.1. Diagram of the various types of mechanoreceptors in the skin
Fig. 5.2. The vestibular
system in the inner ear which
contains three semicircular
canals, ampullae, an utricle,
and a saccule
Temporal bone of skull
Semicircular ~t
canals
Ampulla
Ampullae
Utricle
Cochlear
"" "duct
Saccule
The utricle is supplied with receptors called hair cells (fig. 5.3).
The cells have several hair-like projections into the endolymph
and are inserted at its base to a gelatinous mass which contains
calcium carbonate crystals called otoliths (fig. 5.4).
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Fig. 5.4. The receptor
hairs of the utricle and
saccule are clustered in
the region called the
macula; their gelatinous
masses contain calcium
carbonate crystals
called otoliths
Macula
5.1.3. Proprioception
Hair cells
Basement
membrane
Proprioception indicates the relative positions of various parts
of the body without having to use the eyes. There are two important
receptor systems in the skeletal muscles of mammals: the
muscle spindle and the Golgi tendom organ.
The muscle spindles are arranged in parallel to the contracting
skeletal muscle fibers. The spindles respond to the relative elongation
of the muscle (fig. 5.5). Elongation is transferred by the
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