Pain

Despite the advances made in the study of pain over the past 50 years and the evolution of several pain theories—such as the specificity, pattern, and gate-control theories—many questions remain about the physiological and psychological components of this enigmatic but common experience. Most scientists agree, however, that the physiology of pain is a complex biochemical process that begins with pain receptors on nerve fibers that lie beneath the skin. An outside stimulus, such as intense heat, a cut, or even an exceptionally strong handshake, causes biochemicals on the nerve endings to produce a series of electrical nerve impulses. These impulses pass a "pain message" through the spinal cord to the brain's thalamus, which is located on top of the brain stem and processes the signals to the cerebral cortex. It is the cerebral cortex that interprets the feeling of pain and produces the appropriate reaction, such as pulling the hand away from a hot surface.

A number of biochemicals are involved in the experience of pain. Prostaglandins are biochemicals that are released where the injury occurs. These prostaglandins increase blood circulation in the injured area in order to battle infection and promote healing by increasing the supply of white blood cells, antibodies, and oxygen. Prostaglandins also work in concert with other biochemicals, like bradykinin, to increase nerve ending sensitivity and transmit electrical impulses to the brain. The speed at which these electrical impulses travel will vary according to the type of pain. For example, a pin prick may cause only a slight pain, but the impulse it triggers travels at the astonishing rate of 98 ft/sec (30 m/sec). In contrast, the pain impulse of a slight burn or ache travels at approximately 6.5 ft/sec (2 m/sec). As a result, some types of pain may cause immediate flinching whereas other kinds of pain produce a delayed response.

As scientists continue to study pain, they are uncovering more detailed information concerning its physiological intricacies. For example, they have identified certain receptors in the brain's neurons, called the NMDA receptors, that may amplify pain messages in the spinal cord, causing an individual to feel pain after touching an area that has been burned. Scientists are also locating with increased precision the areas of the brain that process pain information. One study has indicated that three specific structures in the cerebral cortex interpret pain messages, including where the pain is located. One structure, the anterior cingulate gyrus (which is thought to control emotions), may also play a crucial role in an individual's response to pain. Another group of researchers have found that a complex network of nerves in the brain may control the various responses that different people will have to the identical amount of pain.