Somatosensation

Somatosensation

Somatosensation is a mixed sensory category and includes all sensation received from the skin and mucous membranes, as well from as the limbs and joints. Somatosensation is also known as tactile sense, or more familiarly, as the sense of touch. Somatosensation occurs all over the exterior of the body and at some interior locations as well. A variety of receptor types—embedded in the skin, mucous membranes, muscles, joints, internal organs, and cardiovascular system—play a role.

Recall that the epidermis is the outermost layer of skin in mammals. It is relatively thin, is composed of keratin-filled cells, and has no blood supply. The epidermis serves as a barrier to water and to invasion by pathogens. Below this, the much thicker dermis contains blood vessels, sweat glands, hair follicles, lymph vessels, and lipid-secreting sebaceous glands (Figure). Below the epidermis and dermis is the subcutaneous tissue, or hypodermis, the fatty layer that contains blood vessels, connective tissue, and the axons of sensory neurons. The hypodermis, which holds about 50 percent of the body’s fat, attaches the dermis to the bone and muscle, and supplies nerves and blood vessels to the dermis.

Illustration shows a cross section of mammalian skin. The outer epidermis is a thin layer, smooth on the outside, bumpy on the inside. The middle dermis is much thicker than the dermis. Blood, nerve and lymph vessels run along the bottom of it, and smaller capillaries and nerve endings extend to the upper part. One nerve ends in a receptor. Sweat glands extend from the dermis into the epidermis. Hair follicles extend from the base of the dermis to the upper part where they are joined by oil glands. Hairs extend from the follicles, through the epidermis and out of the skin. The hypodermis is a fatty layer beneath the dermis.
Mammalian skin has three layers: an epidermis, a dermis, and a hypodermis. (credit: modification of work by Don Bliss, National Cancer Institute)
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