Pain is the unpleasant and emotional experience associated with or without actual tissue damage. It could be sharp or slow, acute or chronic. It is expressed in terms of injury for example, pain produced by fire is expressed as burning sensation; pain produced by severe sustained contraction of skeletal muscles is expressed as cramps.
Benefits of Pain Sensation
Within the skin is found in 'free nerve ending'- a kind of receptor for pain-an important sensory system. It protective as well as survival benefits are listed below:
1. It gives warning signal about the existence of a problem or threat; it also creates the awareness of injury
2. It prevents further damage by causing reflex withdrawal of the body from the source of injury.
3. It forces the person to rest or to minimize the activities thus enabling the rapid healing of the injured part.
4. It urges the person to take required treatment to prevent major damage.
There are three significant reactions besides the distinct sensation of hurt when a lesion is inflicted on the body.
They are:
1. Motor reactions: pain sensation leads to withdrawal, a reflex which remove part or all the body from the painful stimulus e.g withdrawal reflex.
2. Emotional reactions: pain has an unpleasant effect with reactions seen as those of anxiety, anguish, crying, depression, etc
3. Autonomic reaction: Rise in blood pressure, peripheral vasoconstriction (reduction in the diameter of blood vessel), tachycardia (increase in the heart rate above 100/minute due to emotional response such as anxiety) and sweating.
Subdivisions of Pain
Pain can be subdivided into major types: Acute and Slow pain
1. Acute pain: This type of pain is felt when a needle is struck into the skin or when the skin is cut with a knife. It is usually not fleet in most parts of the deep tissues of the body. It occurs with about 0.2 second when a pain stimulus is applied. Type A delta fibers which are myelinated conduct pain at a rate of 6-30m/s.
2. Slow pain: This type of pain is associated with tissue destruction. It can also lead to prolonged unbearable suffering and can occur both in the skin and in almost any internal tissue or organ of the body. It occurs after a a second or more, and increases slowly over a period of many seconds and sometimes, even in minute. Type ' fibers which are unmyelinated conduct at a rate of about 1m/s.
The receptors of both the components of pain are the same i.e the free nerve endings but the afferent nerve fibers are different. The first pain sensation I'd carried by A delta fibers and slow pain is conducted by C type of nerve fibers.
It is important to note-The non-adapting nature of pain.
Pain receptors adapt very little compare to other sensory receptors which include Meissner's for touch, Merkel's disk (touch), Pacinnian corpuscle (for pressure), Krause's end bulb (cold), Raffinis end organ (warmth).
In some conditions, excitation of pain fibers increase as long as the stimulus persists especially for slow aching pain. This increases in sensitivity is terned hyperalgasia. The importance of this is that it keeps us aware of the tissue damaging stimulus ad long as it is there, prompting us to take action.
Recommendations: You also can consult, Essentials of Medical Physiology by K. Sembuligam also Neurophysiology by Prof E. Osim.
