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PROTECTING, SENSING, REPAIRING |
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Nerves near the surface of the skin
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Schematic representation of Meissner's corpuscles.
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The skin has a battery of sensory receptors which respond to different stimuli such as touch, contact, temperature variation or pain. The density of these receptors varies greatly from one area to another. The face and the extremities are richly innervated.... There are 2,500 receptors per cm2 just on the fingertips.
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Schematic representation of Ruffini's corpuscles.
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Schematic representation of Pacinian corpuscles.
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Vibration, pressure, touch...so many stimulations which the skin receptors detect and transmit via a network of fibres to the brain as a stream of nerve impulses. Impulses will result in a sensation.
Cutaneous receptors take the form of encapsulated nerve endings such as Meissner, Pacini and Ruffini corpuscles or free nerve endings some of which, associated with Merkel cells, go as far as the epidermis.
At the base of the epidermis, Merkel cells
respond to gentle localised pressure. This response is maintained throughout the stimulus which allows these cells to distinguish two points of relief which are close together. Particularly abundant on the palmar surface of the fingers, they are used in the reading of Braille script.
Meissner corpuscles
are situated immediately below the epidermis and are particularly well represented on the palmar surfaces of the fingers. They are particularly sensitive to light touch and to the speed of the stimulus. This characteristic explains why we are no longer conscious of our clothes a few minutes after having put them on.
Ruffini's corpuscles
, situated in the dermis and articulations, are receptors sensitive to vibrations and stretching of the skin and tendons.
Pacinian corpuscles
are mechanoreceptors present deep in the dermis and in the hypodermis, sensitive only to rapid variations of deformation.
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The skin also has pain receptors called nociceptors Pain is a subjective perception of an unpleasant sensation which originates in a specific region of the body. Nociceptors
are thus alarm systems. A burn causes the removal of the hand from the source of heat which avoids aggravating the degree of burn.
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