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.
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