Outline
Pain is a very unpleasant sensation which human sense can detect although it is very rare to remember its feelings when it is not being experienced and therefore we do not wish to encounter a painful experience. When a person experiences pain, he/she is in less danger and is able to run away from a possible further harm. Nociceptors are receptors that detect pain caused by noxious stimuli through their nerve ending located below the skin and in tendons including joints. Therefore, nociceptors determine duration of pain and the more they are, the longer the duration that a person experiences pain. If stimulation of nociceptors becomes massive, the victim can die as a result of the effects on the nervous system such as shock which greatly reduces the blood supply to the vital organs.
Introduction
According to (Jackson, 2005), pain is any sensation that create discomfort and serves the purpose of creating awareness to the victim about the dangerous situation he/she is in so that immediate withdrawal can be done. It is evident that, when a person withdraws from the stimuli causing pain, chances of further damage are greatly reduced. Pain also quickens the process of healing because a person tends to protect the injured part of his/her body from further damage in effort to minimize a similar experience. It is therefore important to understand how pain is detected by human body. Nociception is a terminology commonly used to mean perception of pain through receptors known as nociceptors which means receptors for noxious stimuli.
Types of pain
Generally there are two types of pain that are based on the mechanism involved and these are nociceptive and neuropathic pain. Division of the two types of pain is also based on the body’s part affected. This section will dwell much on the nociceptive pain. When doctors classify the pains, they are able to easily choose the right medicine as well as manage pain better.
Nociceptors
Nociceptive pain is also referred to as nociceptors and plays a significant role of receiving sensory neurons found in the skin or internal organs. Whenever these receptors receive activation from a damaging stimulus, the resulting effect is pain. Research has shown that, a particular nociceptor has a capacity to perceive a particular stimulus. For example, thermal nociceptors perceive activation from noxious variation in temperatures while mechanical nociceptors perceive activation from excess pressure as well as deformation. On the other hand, chemical nociceptors notice changes in the chemical substances. (Rose, 1989)
(Aronoff, 1998) found that, the nociceptors are nerve endings with terminus just below the skin that plays the role of detecting cutaneous pain. Nociceptors are also located in the tendons for detection of somatic pain. However, majority of pain receptors are found in the skin and therefore detection of pain is well defined in the skin due to easy localization of pain. Research has also shown that, the length of experienced pain is also largely dependent on the number of nociceptors. For example, cutaneous pain lasts for a short duration of time but when subjected to new impacts, it gets reactivated. On the other hand, visceral and somatic pain lasts for a long period of time. Generally, nearly all body tissues contain nociceptors, a fact which is important as far as warning functions regarding pain are concerned. If one is not able to feel pain, he/she would not look for help when the body is aching and therefore it makes a lot of sense for the body to have several nociceptors in almost every part. Studies have shown that, it is only in brain does not have nociceptors unlike many parts of the body. Therefore, brain cannot experience pain and this is important since any experience that would be strong enough to cause pain in the brain is likely to be fatal. This is explained by the fact that, evolution of species largely depends on the ecological environment and therefore, brain does not need to have nociceptors. However, the membrane that surrounds the brain known as meninges contain nociceptors but the input received by them is relayed to the brain through nerve endings that forms part of neurons.
Pain perception
According to (Lisney, 1996), both psychological and physiological factors greatly influence perception of pain long before a person is conscious about it. Regarding acute pain that is experienced immediately when the tissues are damaged, it can be destructive especially when it persists and it is not possible for one to avoid it. Therefore, a persistence pain can actually be a disease in itself where it becomes chronic if it persists for several weeks or months thereby becoming a source of great suffering.
Physiology regarding pain
Philosophers have for a long time being amazed by issue of pain and have therefore spent a lot of time in studying about it. In ancient Greek, people thought for many years that, pain was just an emotion but latter studies revealed that, it was a sensation that was caused by certain stimuli surrounding a given environment. Medical scientists are today credited for their effort in merging both perceptions of emotions and physical stimuli as the key determinants of pain. There are a variety of behaviors that are associated with pain such as the case of a painful stimulus with a capacity of arousing a person to wake up when pinched (Turk, 1999). Pain therefore has an ability to focus ones attention around the site where injury has occurred. Pain can cue a person in making an effort to run away from the cause as well as immobilizing him/her so as not to suffer further harm. Research has also shown that, heart rate and blood pressure may be to a large extent be influenced by pain. Elevation of stress hormones can also influence the way endocrine system responds by increasing its level. Studies have shown that, for all the responses that are caused by an injury with a capacity to cause pain, there is a pathway in the central nervous system that is unique for that particular response. When pain is being experienced by healthy individuals, it is because some verve endings have been activated. Any process that has a capacity to cause immediate damage to a human body has the ability to activate nociceptors. Most of these nociceptors have a capacity to respond to a number of noxious stimuli such as extreme temperatures and severe mechanical stimulations such as pinching or cutting. It can also include excess tissue acidity as well as many other causes of injury. Various chemical agents that are produced by damaged cells can also activate nociceptors including when they are responding to foreign substances such as bacteria.
According to (Chapman, 1979), Nociceptors can be classified into two general types with a clear understanding of the difference. When a person trips and falls, landing hard on his/her knee, the person experiences an acute painful sensation that is well localized in the knee. Shortly after, the person experiences a dull, aching sensation that may last for sometime. The sensations are a representation of a fiber system through which pain travels along the central nervous system. Research has shown that, those fibers that are insulated with myelin are able to conduct pain rapidly. Shortly after, c-fibers are not insulated with myelin but carry the pain signals that are longer lasting consequently resulting to slow conduction of pain. Every nociceptor in the body has a unique responsibility of communicating messages to the spinal cord where the messages are received in specific areas. Each of these areas is connected to the neurons that conduct the sensation of pain to the respective areas in the brain. Messages carrying pain sensations in the head reach similar neurons located in the hindbrain. These specific areas in the brain are unique to receive messages from particular body parts before the information is interpreted for the response to take place. This is supposed to take the shortest time possible. Research has shown that, great damage of tissues especially when it is prolonged can permanently sensitize nociceptors so that they can easily be activated even by the slightest stimuli creating unnecessary pain. Slight sensations even in a shower are likely to produce pain when such damage has occurred. Also, when a person has arthritis or has undergone sports injury, the person becomes familiar with how he/she can be much comfortable when resting but experiences significant pain when attempting to make usual innocuous movements. So, when nociceptors are sensitized, they can produce significant pain and this is applicable to both muscle and tendons.
Studies have shown that, certain chemical in the body can actually cause pain without necessarily activating nociceptors. Such chemicals include prostaglandins caused by tissue inflammation due to infection as well as arthritis (Mailis, 2005). Production of such chemicals can be caused by a variety of factors but studies have shown that such factors can greatly be reduced through use of certain medicines. Such medicines include aspirin and ibuprofen that are particularly effective if the experienced pain is associated with this kind of sensitization. They are more effective for tenderness compared with pain that is prolonged and severe.
Neurons that are responsible for transmission of pain in the central nervous system can as well be sensitized in the same way as primary nociceptors and this explain why when one is injured, there is increased response produced by the activity of nociceptors. This increased experience of pain along pathways usually causes further pain even when there is a consistence in the stimulus that initially caused the pain. (Craig, 2003)
Psychology regarding of pain
According to (Baker, 2005), human brain has a capacity to integrate both physical sensation together with psychological factors whenever there is a stimuli causing pain and this enhances quick response. The most common example of the power in the influence of psychological factors regarding pain is headache that can be caused by even emotional stress. An example is when a person complains of a headache especially after spending many hours doing an involving task in office or on studying difficult concepts that are not flowing easily. In this case, it is the emotions and attitude regarding the task that creates sensation that finally translate to pain. Research has also shown that, certain memories in ones life have the ability to influence their perception on pain through the emotions revived when this occurs. Studies have shown that, there are mechanisms in the central nervous system that are responsible in controlling such memories. Research has shown that, the concerned regions in the forebrain get involved with such emotions and feed into the brain stem through neural circuit. These circuits have a direct control of the pathways followed by pain. The control is able to influence both direction and it can therefore increase pain in the same it can reduce it.
Studies have shown how possible it is for a person to separate the intensity of the sensory nerves from the unpleasantness that arises from the same sensation and depending on his/her particular perception on it; it is possible to quantify each of the two separately. According to the results of the imaging, there are two separate parts in the brain that are involved with the separation. Such measurements are largely dependent on the level of activity going on in the body tissues. On the other hand, unpleasantness is closely linked with activities going on around areas in frontal lobe cortex that is associated with ones emotions. Research has also shown that, there are surgical procedures that are effective in reducing the agony experienced when one is subjected to severe pain and this is possible without interfering with the sensory intensity. By implication it means that, aspects of emotions have a higher capacity of producing significant effects compared to the impact of the physical damage. This is important in determining the extent to which a person can perceive pain expected (Baker, 2005).
Pain disorder during sensory processing
Studies have shown that, conditions of chronic pain are likely to be caused by disorder during sensory processing which occurs in body of a human being and also in the brain. The theory suggests that, nociceptors send signals to the brain and in the process; something goes wrong resulting into pain signals replacing basic information. On the other hand, overly strong signals sent from the body may also cause disorders resulting to pain in the body. Nerve impulses only become pain during tissue damage as in the case of a broken leg. In fact research has shown this to be the confusion with many doctors for a long time when they try to diagnose patients and are not able to see damage in the tissues consequently making an assumption that, the patient could be lying (Baker, 2005).
(Craig, 2003) found that, a permanent change in pain transmission can result from various factors and any of such factors can cause chronic pain that reduces the body’s mechanism to defend itself against pain. Such conditions include Fibromyalgia which may not necessarily destroy the pathways followed by pain as other conditions do. This condition can lead to chronic changes along the central nervous system and when this happens, one experiences pain in the skin as well as in muscles and other parts that commonly participate in the transmission of pain. The resultant effect of this condition of abnormal changes is a general amplification of pain that consequently results into generalized severe pain. Excellent information has been presented by researchers on why Fibromyalgia hurts. Today, there are emerging concepts regarding neurobiology of pain especially the chronic one. If it is possible to trace pain signals from nociceptors through different parts of pain pathways in people with this condition, it is possible to find a number of abnormalities a long the path.
Nociceptors are the origins of pain
(Bove, 2008) found that, the condition can easily arise when a person is experiencing trauma or tissue injury in the muscles that the key activators of the nociceptors. Other researches have also suggested the occurrence of microscopic injury in specific areas of the muscles. The terms that are used to refer to these conditions include muscle spindle and calcium pumps. Studies have indicated that, there is a certain protein that is activated through a localized injury resulting to pain due to inflamation. Similar to trauma are autoimmune factors that activate pain nerves through creation of compounds with characteristics of irritants. Autoimmune factors chronically activate nociceptors to an extent where the nociceptors are permanently sensitized as well as irritated. As a result, most chemical and hormones in the body undergoes a great change that interferes with most of the mechanism in the body responsible in supply of essentials such as oxygen and glucose. The flow of blood is interfered with and therefore less energy is produced due to low production of hormone in the cells. When there is a faulty condition in the nociceptors, there is imbalance of neurological as well as electrical hormones creating abnormality while the nociceptors suffer more and more activations. Every time nociceptors receive activation; there is a release of neurotransmitters causing pain in areas such as skin and around muscles. The interpretation of these pain signals that are persistently experienced can be taken as itching, swelling or burning on one hand or as knife stabbing on the other hand. Some nociceptors have the ability to sense different forms of pain and sensations depending on the kind of irritation from the stimulus. For such nociceptors, the intensity of the pain increases with the level of irritation. It is possible for such changes to become permanent and result to a level where nociceptors are easily activated to cause sensation of pain even when there is no noxious stimulus. It is therefore possible for a spontaneous occurrence of signals that cause persistent pain sent from peripheral nerve ending passing the same effects through the rest of the pathway followed by pain. This enhances transmission of pain through the nociceptors even when there is no stimulus as it would happen under ordinary circumstances. The effects of the spontaneous pain are the common complain observed from majority of victims of pain.
Reaction by the nerves
According to (Jackson, 2005), when sensory nerves are bombarded, they “try to make out what is happening” when they receive signals from nociceptors and therefore initially they make effort to reduce the painful signals significantly through use of mechanisms of accommodation and gating. When the sensory nerves are exposed to the signals for a relatively ling time none stop, they begin the process of sensitization. The process continues till the sensory nerves are hyper sensitized to a point where they react with a response that is exaggerated rather than a normal and a diminishing process commonly referred to as accommodation. This contributes to more pain and the person experiences numbness and swelling of tissues. He/she gets a feeling of burning and other increased sensations. Research has shown that, nerve growth factor may mediate hyper sensitization in some cases as in the case of higher levels of Fibromyalgia. Studies have indicated that, when the nerves start regenerating or being repaired, such growth can arise. This process interferes with the normal functioning of the body by breaking the ordinary mechanisms. The resulting effects are due to the fact that, nerve growth factor has the role of promoting the capacity of the nerves to transmit pain through the spinal cord and consequently increased pain results.
Conclusion
The key responsibility of the nociceptors is to receive pain and transmit it as signals through the central nervous system along the spinal cord. These signals reaches hypothalamus region located in the brain where perception of pain occurs. The signals then leave hypothalamus and are transmitted to the brain making the victim of pain to sense pain. Managing of pain is important because it continually suppresses it and enhances quality of life of the patient through gaining of autonomy as well as participation in work and social life.
References
- Jackson P. (2005): How we perceive the pain: Elsevier pp. 65-69
- Rose M. (1989): Evidence for Pain and Suffering in Other human beings: Palgrave Macmillan pp. 34-38
- Aronoff G. (1998): Evaluation and Treatment of Chronic Pain: Lippincott Williams & Wilkins pp. 24-27
- Lisney S. (1996): Properties of regenerated nociceptor afferents: Neurobiology of Nociceptors, Oxford University Press pp. 25-30
- Turk D. (1999): The role of psychological factors in chronic pain: Blackwell Synergy pp. 76-81
- Chapman C. (1979): Electrical Stimulation to the Understanding of Pain Mechanisms and Pain Relief: Raven Pr pp. 38-43
- Mailis A. (2005): Beyond Pain: Making the Mind-Body Connection: Michigan Press
- Craig A. (2003): A new view of pain as a homeostatic emotion: Elsevier
- Baker K. (2005): Recent advances in the neurophysiology of chronic pain: Blackwell Synergy pp. 89-94
- Bove G. (2008): Epi-perineurial anatomy, innervations, and axonal nociceptive mechanisms: Elsevier pp. 37-41