Pain is a sensation that everyone perceives after an injury has occured to the body. The type of pain that is usually perceived by people has its origin in an organic illness in the body. This is to distinguish it from pain that is perceived due to other causes such as a pain due to pychological reasons which can originate for example due to a psychological conflict that the person can have. This type of pain usually and as far as it is known does not have an organic cause but its causes is largely psychological in nature.
In this article, I will discuss the first type pf pain that has an organic cause only. Pain signals that are transmitted along neuronal system differ than other signals in the nervous system by their ability to sustain strength of quality and magnitude. This character of pain is referred to as nonadaptiveness nature of the pain signals.
This is in contrast to many other signals through the nervous system in which are adaptive that decay in strength and quality such as a stimulus by a neurotransmitter to open voltage gated ion channel. This characteristic pf nonadaptiveness of pain signals in the nervous system is unique among all other signals that are experienced in the nervous system.
Pain is usually preceived due to a damage to body tissues which release in turn chemicals that stimulate pain receptors in the skin and other organs in the body. This stimulation of these free nerve endings is responsible for giving the sensation of pain in the affected individual.
Pain is characterized by two main types. These are: fast pain and slow pain. As the names imply these two types of pain differ by the time it takes for the pain to develop. Fast pain develops quickly after an injury such as occurs after a needle injection or knife cut. On the other hand, slow pain develops over a long period of time and is usually a continuous sensation of pain. Example of such a pain occurs in tissue destruction in the body such as occurs in ulcer of the stomach.
Pain receptors can be influenced by three type of stimuli that pain is triggered by the impact of these external stimuli on the pain receptors. These pain receptors are chemical stimulation and are charecterized by chemical compounds which trigger the pain receptors. Thus causing a sensation of pain. Examples of such chemicals include bradykinin and serotonin in addition to certain proteolytic enzymes. In addition prostaglandins and substance P are two compounds which are known stimulators of pain sensation.
Also there are mechanical receptors for pain which respond to pain sensation by making a mechanical change such as pressing the skin or stretching the capsule of the kidney and liver for example. This type of pain is experienced for example in the stomach after a meal in which the full stomach stretches the receptors of the free nerve endings. Thus causing a sensation of pain which can be ameliorated after emptying the stomach contents.
Also there are receptors that are specialized to sense for changes in temperature. There are usually in the skin nerve receptors which are specialized for the sensation of temperature. High temperature can destroy the tertiary structure of proteins in the skin causing its denaturation. This can induce the free nerve endings giving a stimilus for pain which is preceived in the brain.
Pain in general can be perceived in ischemic state in which the blood supply to a given tissue is interrupted due to ischemia. The affected organ switches to anaerobic respiration due to the deficiency in oxygen supply to that organ. This leads to the formation of lactic acid which is thought to be the main cause to the pain sensation by inducing the pain receptors in the affected organ.
Also muscle spasm is another cause to the sensation of pain. This is thought to be caused by the ischemia that is caused by muscle spasm narrowing the blood arteries which can lead to the sequence of events that were mentioned previously.