Page 63 - Human anatomy COMPLETELY DONE1

sensitivity (the zone of skin sensitivity). It is the area of the posterior central gyrus of
the cerebral cortex. The brain analyzes these signals and builds a picture of the
environment.
A person has the most tactile receptors on the tongue, fingers and palms.
According to the nature of the analyzed information, skin receptors can be
divided into nociceptors (nociceptors), mechanoreceptors, thermoreceptors.
A nociceptor is a pain receptor, a type of sensory neuron termination. It is
activated when an irritant damages or only tries to damage the tissues of the body.
Although there are most nociceptors in the skin, they are present in the internal organs
(visceral nociceptors). Pain sensitivity is provided by such type of receptors as free
nerve endings.
Mechanoreceptors include not only receptors located in the skin. They also
include baroreceptors, proprioreceptors, vestibuloreceptors. As for the skin (tactile)
mechanoreceptors, they respond to touch, mechanical pressure, stretching of the skin.
There are several types of such receptors – Merkel corpuscles, Meissner, Ruffini, etc.
Free nerve endings (figure 41) are not encapsulated and do not have complex
sensory structures. They are the most common type of nerve endings and are most
commonly found in the skin. They pass through the dermis and end in the granular layer
of the epidermis. They also penetrate into the middle layers of the dermis and surround
the hair follicles.

Figure 41. Free nerve endings

Free nerve endings can detect temperature, mechanical stimuli (touch, pressure,
stretching) or danger (nociception). Thus, various free nerve endings work as
thermoreceptors, skin mechanoreceptors and nociceptors. In other words, they differ in
their purpose, that is, they have polymodality.
The receptors of the hair follicles are nerve plexuses at the roots of the hair, they
perceive a change in the position of the hair.
The Meissner's body, or tactile body (figure 42), is an encapsulated nerve ending,
localized in the dermis of the skin immediately under the epidermis, perceives light

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