PHYSICS

Sensory nerve
to eNS
Intrafusal muscle fiber
(muscle spindle)
------­.... , I _Tendom
j
Extrafusal muscle fiber
Goldi tendom
organ capsule
Tendon inserts
into bone
Fig. 5.5. Muscle spindle which is in parallel
with the extrafusal muscle fibers
Fig. 5.6. The Goldgi tendom organ ­
a stretch receptor located in the
tendom of skeletal muscle
Tendom
spindle sensory (afferent)
nerve as action potentials to
the brain. The frequency of
the potentials depends on
lengthening of the middle
part of the skeletal muscle.
The Golgi tendom organ
is presented as a slender
capsule within the tendom.
It is connected with 15 ­
20 skeletal muscle fibers
(fig. 5.6) and supplies information
to the brain through
the action potentials, the
frequency of which depends
on the tension developed by
the muscle.
5.1.4. System of Mechanoreception in a Fish
Mechanoreception found in many fish and amphibian species,
utilizes a lateral line system located along each side of their body
(fig. 5.7). The lateral line system contains as series of channels at
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Sensory
hair cells
Fig. 5.7. Lateral line canals
along the fish's body
and in the head region
certain intervals which open to
the surrounding water. The channels
in fish consist of viscous gelatinous
structures (cupulae) with
the hairs connected to receptor
cells (neuromasts). Water, flowing
through the channels, results in
a deformation of the hairs, creating
an electric potential which
is transmitted to the nervous system.
The lateral line system makes
it possible to access a minimal displacement
of water, the direction
of water flows, and the presence
of turbulent fluids created by predators.
5.1.5. The Insect's System of Mechanoreception
Mechanoreceptors in bees react to mechanical deformation of
part of the receptor. It may respond to touch, vibration of substrate,
or an air current. The sensitive elements of a mechanoreceptor
are the sensila trichodea, sensila scolopophora, sensila campanijormia,
and sensila schaetica.
Most insects have "ears" in their legs. The mechanical stimuli
provoke nerve impulses in the receptor cells, which are conveyed
to the central nervous system. This allows insects, such as the
sand scorpion, spiders and whirligig beetles, to detect vibrations
in the substrate with their legs.
5.2. EFFECT OF MECHANICAL FACTORS
ON LIVING ORGANISMS
5.2.1. Gravitation and Living Organisms
Gravitational Orientation in Higher Plants. Plants orient their
roots downward and their shoot upward. The ability of plants to
orient the direction of organ growth relative to the gravitational
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