Tactual Sensation

Tactual Sensation:

            The skin is composed of several layers. The very top layer is the epidermis and is the layer of skin you can see. It is made of dead skin cells, the epidermis is waterproof and serves as a protective wrap for the underlying skin layers and the rest of the body. It contains melanin, which protects against the sun’s harmful rays and also gives skin its color.. The epidermis also contains very sensitive cells called touch receptors that give the brain a variety of information about the environment the body is in.

The second layer of skin is the dermis. The dermis contains hair follicles, sweat glands, sebaceous (oil) glands, blood vessels, nerve endings, and a variety of touch receptors. Its primary function is to sustain and support the epidermis by diffusing nutrients to it and replacing the skin cells that are shed off the upper layer of the epidermis. New cells are formed at the junction between the dermis and epidermis, and they slowly push their way towards the surface of the skin so that they can replace the dead skin cells that are shed. Oil and sweat glands eliminate waste produced at the dermis level of the skin by opening their pores at the surface of the epidermis and releasing the waste.

The bottom layer is the subcutaneous tissue which is composed of fat and connective tissue. The layer of fat acts as an insulator and helps regulate body temperature. It also acts as a cushion to protect underlying tissue from damage when you bump into things. The connective tissue keeps the skin attached to the muscles and tendons underneath.

The ability to sense touch:

            Our sense of touch is controlled by a huge network of nerve endings and touch receptors in the skin known as the somatosensory system. This system is responsible for all the sensations we feel – cold, hot, smooth, rough, pressure, tickle, itch, pain, vibrations, and more. Within the somatosensory system, there are four main types of receptors: mechanoreceptors, thermoreceptors, pain receptors, and proprioceptors.

Mechanoreceptors: These receptors perceive sensations such as pressure, vibrations, and texture. There are four known types of mechanoreceptors whose only function is to perceive indentions and vibrations of the skin: Merkel’s disc, Meissner’s corpuscles, Ruffini’s corpuscles, and Pacinian corpuscles.

·         Meissner’s corpuscles:

Meissner’s corpuscles are a type of mechanoreceptors. They are a type of nerve ending in the skin that is responsible for sensitivity to light touch. They are rapidly adaptive receptors and have highest sensitivity.

·         Pacinian corpuscles:

Pacinian corpuscles are a type of mechanoreceptors. They are nerve endings in the skin responsible for sensitivity to pain and pressure.

·         Ruffini’s corpuscles:

It is a slowly adapting mechanoreceptors thought to exist only in the glabrous (without hair) dermis and subcutaneous tissue. It is sensitive to skin stretch and contributes to the kinesthetic sense and control of finger position and movement.

·         Merkel’s disc:

Merkel's disk are slow-adapting, unencapsulated nerve endings that respond to light touch; they are present in the upper layers of skin that has hair or is glabrous.

Thermoreceptors: As their name suggests, these receptors perceive sensations related to the temperature of objects the skin feels. They are found in the dermis layer of the skin. There are two basic categories of thermoreceptors: hot and cold receptors.

Cold receptors start to perceive cold sensations when the surface of the skin drops below 95 ° F. They are most stimulated when the surface of the skin is at 77 ° F and are no longer stimulated when the surface of the skin drops below 41 ° F. This is why your feet or hands start to go numb when they are submerged in icy water for a long period of time.

Hot receptors start to perceive hot sensations when the surface of the skin rises above 86 ° F and are most stimulated at 113 ° F. But beyond 113 ° F, pain receptors take over to avoid damage being done to the skin and underlying tissues. Thermoreceptors are found all over the body, but cold receptors are found in greater density than heat receptors. The highest concentration of thermoreceptors can be found in the face and ears.

Pain receptors:  These receptors detect pain or stimuli that can or does cause damage to the skin and other tissues of the body. There are over three million pain receptors throughout the body, found in skin, muscles, bones, blood vessels, and some organs.

They can detect pain that is caused by mechanical stimuli (cut or scrape), thermal stimuli (burn), or chemical stimuli (poison from an insect sting). These receptors cause a feeling of sharp pain to encourage you to quickly move away from a harmful stimulus such as a broken piece of glass or a hot stove stop. They also have receptors that cause a dull pain in an area that has been injured to encourage you not to use or touch that limb or body part until the damaged area has healed. While it is never fun to activate these receptors that cause pain, they play an important part in keeping the body safe from serious injury or damage by sending these early warning signals to the brain.

Proprioceptors: In Latin, the word “proprius” means “one’s own” and is used in the name of these receptors because they sense the position of the different parts of the body in relation to each other and the surrounding environment. Proprioceptors are found in tendons, muscles, and joint capsules. This location in the body allows these special cells to detect changes in muscle length and muscle tension. Without proprioceptors, we would not be able to do fundamental things such as feeding or clothing ourselves.