The International Association for the Study of Pain defines it as: "An unpleasant sensory and emotional experience associated with actual or potential tissue damage or described in terms of such damage." Subjectively it could denote any form of unpleasant sensation with varying degrees of intensity. Pain is distinguished based on two basic types identified as acute and chronic. Acute pain results from a disease process whereby there is inflammation or injury to tissues occurring rather suddenly after trauma or surgery and may be accompanied by anxiety or emotional distress. Usually certain medications serve to diminish the intensity of Acute Pain. Chronic Pain however, persists over a longer period than acute pain and is resistant to most medical treatments. Several factors may serve to heighten its perception and frequency thereby causing discomfort to patients in varying degrees.
Pain follows a certain train of events before it is detected and proclaimed by a patient. Luckmann and Sorensen traced it to "the nerve receptors, named as nociceptors which differs from the complex receptors of vision and other senses". These nociceptors are simply free nerve endings in almost all types of tissues which react to change and require a high level of stimulation to elicit a response. However once their threshold is exceeded they communicate the presence of the painful stimulus. At times they become so over sensitized that long after the stimulus is removed, pain still persists. Once these nociceptors are stimulated, they discharge an impulse that travels in the form of an electrical activity to the spinal cord and on to the brain.
The spinal cord is informed on the activity of the body through nerve fibers carrying somatosensory information. The spinothalamic tract then carries the painful information to the brain via the thalamus by passing through the somatosensory cortex which serves to localize and identify the quality of pain before it is diffused to the many areas of the brain including the reticular formation, medulla, hypothalamus and limbic structures. As a response, the brain sends to the receptors a complex response to the painful stimuli. It dictates the receptors to identify the degree, the character and intensity of the pain; its location and how to behave to reduce or avoid it in the future.
"Pain can be inhibited if its pathways are blocked", as presented in the Gate-Control Theory of Melzack and Wall. The "gate" in their report is controlled by a dynamic function of cells that can facilitate or inhibit the transmission of pain signals. The fibers bringing pain information from the tissues are found in layers known as laminae. A certain Laminae II which is different from the rest of the layers and also called the Substantia Gelatinosa(SG) is proposed as the location of the "gate". This serves as the convergence point of all pain information, whether stimulus coming in from the tissues or identification from the brain. A spinal cord transmission cell also known as the t-cell either opens the gate thereby facilitating pain transmission or closing the gate. A variety of sources may close or open the gate but only the brain can manipulate the "gate" to inhibit or