Skin Receptor

Skin Sensors of Damaging Stimuli

Pain receptors are bare sensory nerve termination. They are present throughout the body of mammals. But they are absent in brain and intestines. These nerve endings are also called nociceptors. Nociceptors are stimulated by severe heat, cold, irritating chemicals and strong mechanical stimuli. They send impulse to the brain. It interprets it as pain or itching. However, detail of the structure and physiology of pain receptors is unknown.

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Skin Sensors of Heat And Cold (Thermoreceptors)

Sensors of temperature are also bare sensory nerve endings. Thermoreceptors are present in epidermis or dermis. Mammals have different sensitive areas for cold or warm. These areas are called cold or warm spots. A small area of the skin which gives temperature sensation is called cold or warm spots.

(a) Cold receptors; respond to temperatures below skin temperature. For example a metal is placed on the skin. It absorbs heat and we feel a sense of coldness.

(b) Heat receptors; respond to temperatures above skin temperature. For example wood is placed on the skin. It absorbs less heat. Therefore, we feels it warmer than metal.

Thermoreceptors in Snakes

The rattlesnakes and pit vipers have heat-sensitive pit organs. These organs are present on each side of the face between the eye and nostril. These pits are lined with sensory epithelium. This epithelium contains receptor cells. These cells respond to temperatures different from the surroundings. It is called infrared thermal regulation. Snakes use these pit organs to locate warm-blooded prey.

Skin Sensors Of Mechanical Stimulus

Many animals get information about their environment by mechanical receptors. Mechanical sensory receptors of vertebrates are present in the skin. They detect stimuli. The brain interprets it as light touch, touch-pressure, and vibration. The touching of skin gives light touch. In this case, skin is not strongly deformed. There are following skin receptors.

    1. Bare sensory endings: They are receptors of light touch. Bare sensory nerve endings are the much widely distributed receptors in the vertebrate body. They are involved in pain, thermal stimuli and light touch.

    2. Tactile corpuscles or Meissner's corpuscles: They also receive light tough stimulus.

    3. Bulbs of Krause: They are mechanoreceptors. They are present in the dermis in certain parts of the body. They respond to some physical stimuli like position changes.

    4. Pacinian corpuscles: They detect touch-pressure stimulus.

    5. Organs of Ruffini: They are also receptor of touch-pressure.

    6. Vibrissae: Many mammals have specially adapted sensory hairs called vibrissae. They are present in wrists, snouts and  eyebrows. There is a blood sinus around the base of each vibrissa. Nerves are present at the boarder of sinuses. They carry impulses from several kinds of mechanoreceptors and send them to brain for interpretation.

Internal receptors
Cell-surface receptors
Ion channel-linked receptors
G-protein-coupled receptors
Enzyme-linked receptors
Thermo receptors
Tactile (touch) receptors
Stretch receptor
Photo receptors
Phono receptors
Hygro receptors
Geo receptors

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