The Skin!

Sensations that we feel on our skin are called somesthetic perceptions. Pain, heat, cold, and also body position are all somesthetic perceptions. Our skin is composed of three layers. The epidermis is the outermost of these layers. It is a thin layer of dead skin cells. Underneath the epidermid is the dermis. The dermid contains sensory receptors and is responsible for manufacturing the cells that for the epidermis. The subcutaneous tissue is the deepest layer of our skin. It contains connective tissue and fat globules. We can feel a wide variety of skin perceptions, from light touch to pain, or from hot to cold. How do we feel thse different senses? Why does every skin perception feel different? To explain these questions, researchers developed the specificity theory. This theory states that there are many different kinds of receptors, each sensitive to a different stimulus. However, it has been subsequently observed that a single type of receptor can sense many different touch sensations. Therefore, the specificity theory could not hold true. To account for this, researchers have proposed the pattern theory, which states that a skin sensation is determined by a pattern of of neural activity across a large group of neurons. The pattern theory more accurately describes the touch sensations.

Pain

Pain is a unique form of skin sensations. One unusual aspect of pain is that it can affect different people very differently. Some people have a much higher threshold for pain then others. To account for this, Melzack & Wall (1965) proposed the gate control theory. This theory states that there is a "gate" in the spinal cord that determines whether a pain signal is allowed to go on to the brain. Researchers have stated that it may be possible to close this gate by activating other skin receptors in the area of the wound(ie. rubbing).

Position and Balance

Another function of skin sensation is in keeping our balance and being aware of our bodily position. Two sensory systems are responsible for this, the kinesthetic system, and the vestibular system. The kinesthetic system is made up of receptors in our joints and ligaments.

This system makes us aware of our bodily movements and aids in motor coordination. The vestibular system is located in the inner ear. Fluid within the semicircular canals in the ear (see diagram in hearing) flows from side if we tilt one way or the other. The motion of the fluid stimulates hair cells in the semicircular canals, and makes us aware of our balance.