Nociceptive sensation. Anti-nociceptive system
Physiological importance of pain According to modern notion, pain is subjective perception of systemic processes, which include information about tissue damage. Activation of pain receptors leads to starting different protective reflexes to avoid tissue damage. However, pain is unpleasant sense and involve to pain reaction wide net of regulative and homeostatic systems of human organism. The important specialty in reaction to pain in human is participation of brain cortex and limbic system, which leads to severe emotional experience and autonomic reactions.
Changes in human organism following pain Nociceptive reactions are accompanied by motion reactions of entire body towards avoidance the pain. In human organism such motion reactions for the some part presented by unconditioned reflexes with short reflector arc formed by neurons of spinal cord and brain stem. But majority of that are behavioral and emotional reactions, which based on conditional reflexes. That is why reflector arc includes besides neurons of spinal cord and brain stem structures of limbic-reticular complex and brain cortex.
Also different changes in human organism followed by pain are observed: increase of muscle tone, accelerated heartbeat, increase of blood pressure, intensification of sweating, dilatation of pupils and elevation of glucose and cuprum level in plasma, activation of hemostasis. It considered to cause the majority of both visceral and biochemical reactions by excitation of sympathetic nervous system, which is presented by neurons of hypothalamus, hypophisis and cells in medullar substance of adrenal glands.
Pain and stress reaction In fact tissue damage and pain triggers the stress reaction - common reaction of an organism, which leads to stimulation all the functions, especially motion and that is why blood circulation due to cardiovascular system, metabolism, transport of gases due to activation of breathing. Stimulation of pituitary-adrenal axis increases secretion of adrenocorticotropic hormone from the anterior pituitary, and thus there is increased secretion of glucocorticoides from the adrenal cortex. That is why functions of organism activate to defend one. But long lasting stress reaction is rather dangerous for organism. Adrenalin in high concentration may produce decreasing of blood supply in visceral organs, which leads to metabolic disorders and disturbances of its function. Besides that nociceptive nerve endings in damaged tissues produce a lot of nervous impulses, which spreading into central nervous system activates wide net of nervous cells. This considerable excitation leads to disturbances in nervous regulation of all functions in human organism.
Pain and diagnosing Pain gives useful information about cause of tissue damage. When determining the origin of pain it is important to special fiches of pain. It is necessary pay attention for location, character, duration, motion and visceral reactions and subjective sensations, following the pain. It is considered, after diagnosing pain must be removed.
Ranks of pain According to location of pain: somatic and visceral. According to time of appearance of pain after tissue damage: early and late pain. According to subjective sensation (or character): acute or burning, dull or spread. According to duration: sort or prolonged pain attacks. Subjective sensations in pain may be presented emotional experience as terror, worry, visual hallucination, dizziness, which appears before of followed the pain.
Reflected pain Reflected pain is caused by irritation of visceral organs. Such events as strong constriction of smooth muscles; disorders of blood supply; tension of vessels, stomach, intestines result in pain in certain parts of body. It is determined sensor neurons to connect through interneurons with autonomic and motor neurons in spinal cord. In such a way, viscerosomatic autonomic reflexes are realized. Due to mentioned intracellular contacts, human capable to locate nociceptive sensation. These zones of human body where impulses from certain visceral organs are reflected called as Zacharjin-Ged zones. For example, in stomach disorders a human fells pain around navel. Acute pain caused by blood supply disorders in heart muscle reflected to the left shoulder, left shoulder blade and left epigastria.
Pain reception Damage stimuli perception created by the brain from electrochemical nerve impulses delivered to it from sensory receptors. These receptors transfuse (or change) different influences of both internal processes in organism and surrounding environment into the electric impulses. Pain receptors are specific. Pain does not appear in hyperstimulation of improper receptors. On other hand, adequate stimuli are not so specific as for other sensations. That is why pain receptors maybe stimulated by different kind of irritations. Pain receptors may react also to electric, mechanic and especially chemical energy.
Afferent nociceptive impulses are collected into central nervous system by two kinds of nervous fibers: quick a-delta myelinated nerve fibers and C-fibers without myelin. The ascending fibers are included in spinothalamic tract, which passes through the spinal cord and reach medulla oblongata. Here there are second order sensory neurons of spinomesencephalic tract. Fibers of spinothalamic tract synapse with third-order neurons in the thalamus, which in turn project to the postcentral gyrus of the contralateral cerebral hemisphere.
Nociceptive structures in central nervous system Information about the pain from head, face and mouth cavity ascend to central nervous system by sensory fibers of cranial nerves, for instance facial, glossopharyngeal, vagus and trigeminus nerves. Central nociceptive neurons lay in nucleus of thalamus, hypothalamus, midencephalon central gray substance, reticular formation and somatosensoric fields of brain cortex.
Anti-nociceptive system To antinociceptive neuro-endocrine system belong nervous structures, which are concentrated, obviously, in brain stem. High intensity of pain stimuli permits activation of these structures, which contain neurons capable to release endogenous opioids. To such structure belong, for instance, prefrontal cortex, hypothalamus, central gray substance, medial thalamic nuclei and limbic system.
Role of opioid peptides In brain and digestive tract are located receptors, which bind to morphine. Investigation endogenous ligands of these receptors give ability to reveal two similar pentapeptides, called encephalines, which bind to opioid receptors: met-encephalin and ley-encepfalin. Such chemicals are known as opioid peptides. Encephalines are containing in nerve endings of digestive tract and many parts in brain. It function as neurotransmitters. These peptides are present in gelatinous substance. In injecting into brain stem, opioid peptides manifestate analgetic effect. Encephalines also may slow down intestines peristaltic.
Analgesia with drugs Drugs may influence in different levels. It is known local analgesia by inactivation of nociceptors using chloraethil or by injection of analgesic in tissues adjacent to nervous fibers. Novocain, analgin and other medicines may prevent generation and spreading of nervous impulses by temporarily inactivation of ion gates. Some drugs may be injected in the lumbal space. In this case spreading impulses through ascendant conduction is obtained. In using common analgesia braking activity of central neurons leads to both analgesia and unconsciousness, which cold surgical sleep. There are some drugs, capable modulate activity of limbic system and cause sedative effect.
Electrostimulation for analgesia Electrostimulation through skin or incorporated electrodes into sensory tracts and nucleus is used for analgesia. Acupuncture, electro puncture and other methods of reflex therapy are also effective approaches to analgesia. It considered causing analgesic effect by beta-endorphin secretion stimulation in hypotalamo-hypophisal system, which may block nociceptive impulses in the way to higher nervous centers. Last time artificial hypothermia or hybernacia, which is cold analgesia, is used.
Psychological methods reliving pain Every people can use psychological methods reliving pain by switching attention over pain for instance. In long duration of chronicle pain, sensation becomes blunt. Today psychological therapy of pain is more spread. For this purpose, biological reverse connection may be used. This method proposed to relive chronicle pain, migraine attack for instance
Cutting off nociceptive conduction bundles To surgical methods of treatment in connection with pain belongs cutting off corresponding sensory nerve upper the origin place of pain. It is used peripheral neurotomia, cutting off nociceptive conduction bundles in spinal cord (lobotomy, comissurotomy or bulbar tractotomy). Special place engaged by operations on the brain. The main purpose of such operations is breaking connections between the brain cortex and thalamus, because it determined the brain cortex to bi responsible for subjective pain sensation formation. To such operations belongs stereotaxic operation on thalamus nuclei (thalamaectomy), splitting of nervous fibers in the depth of frontal part of brain, which connect it with thalamus (frontal lobaectimy), cortex removal in gyrus postcentralis and adjacent parts of parietal lobe, temporal cortex and lover parts of frontal lobe. It is necessary to point attention to use last group of analgesic methods in extreme situations only. When other methods will not be effective, patient may be operated. However, field of operations in pain manifestation is considerably wider and is not limited by operations on nervous system.