Sensation and Perception
The sense of touch is really a collection of several senses, encompassing pressure, pain, cold, and warmth. The senses of itch and tickle are related to pressure, and burn injuries are related to pain. Touch receptors are stimulated by mechanical, chemical, and thermal energy.
Pressure seems to be the only kind of touch sense that has specific receptors.
The Gate-Control Theory of Pain
Researchers don’t completely understand the mechanics of pain, although they do know that processes in the injured part of the body and processes in the brain both play a role.
In the 1960s, Ronald Melzack and Patrick Wall proposed an important theory about pain called the gate-control theory of pain. Gate-control theory states that pain signals traveling from the body to the brain must go through a gate in the spinal cord. If the gate is closed, pain signals can’t reach the brain. The gate isn’t a physical structure like a fence gate, but rather a pattern of neural activity that either stops pain signals or allows them to pass. Signals from the brain can open or shut the gate. For example, focusing on pain tends to increase it, whereas ignoring the pain tends to decrease it. Other signals from the skin senses can also close the gate. This process explains why massage, ice, and heat relieve pain.