Pain;
pain is defined as an unpleasant and emotional experience associated with or with out actual tissue damage. The pain sensation is described in many ways.
The word unpleasant comprises the whole range of disagreeable feelings from being merely inconvenienced to misery, anguish, anxiety, depression and desperation to ultimate cure of suicide. Pain may acute or chronic. Acute pain is a sharp pain of short duration with easily identified cause often its localize in small area before spreading to neighboring areas. Usually was treated by medication chronic pains. The intermediate or constant pain was different intensities. it last for long periods.
it is somewhat difficult to treat chronic pain and it needs professional expert care.
Pain is produced by real or potential injury to the body. Often its expressed in terms of injury, e.g. pain produced by fire is expressed as burning sensation, pain produced by
Severe sustained contraction of skeletal muscles expressed as cramps.
Phenomenon of pain;
1- Pain can occur without tissue injury or evident disease and can persist after injury has healed.
2- Serious tissue injury can occur without pain
3- Emotion (anxiety, fear, depression) is an inseparable co eminent of pain and can modify bois intensity and the victim’s behavioral response.
4- There is important processing of afferent nociceptive and other impulses in the spinal cord and brain.
appreciation that pain is a both a sensory and an emotional (effective) experienced has allowed clinicians to realize that to meet a complaint of pain automatically with a prescription alone is not appropriate response for there is always more to analgesia than analgesics. Pain that is not the subject of an analysis by the clinicians (and explanation to the patient) may be inadequately relieved because of lake of understanding that doctors do not provide adequate relief of serve pain by bad choice and by over using and also important understanding drugs and by defective relation with their patients has been & still is injustified and shaming criticism.
Components of pain sensation;
A pain stimulus produces two pain sensations
1- Fast pain
2- Slow pain
è Fast pain is the first stimulation when a pain stimulus is applied. Its experienced as an bright sharp and localized pain sensation.
Fast pain fallows show pain which is experienced as dull diffused, and unpleasant pain the receptors for both the components of pain are same i.e. the free none endings.
The relative abundance of various types of receptors differ greatly, e.g. pain receptor are 27 times more abundant then cold receptors, the cold receptors are nearly 10 times more abundant than heat or temperature receptors . The receptors are not distributed evenly over the entire surface of the body e.g. the finger tips have an abundance of touch receptors than skin of back.
The afferent nerve fibers are different, the fast pain sensation is carried by A8 fibers and the slow pain sensation is carried by C types of nerve fibers.
è Glutamate and substance P are the neuro-transmit secreted by the pain nerve endings. The A8 afferent fibers when transmit impulses of fast pain secrete glutamate. C type fibers which transmit impulse of slow pain secrete substance P.
Advantages or Benefits of Pain Sensation;
We know pain is unpleasant sensation but it has same proactive and beneficial or survival effects such as,
1- Pain gives alarming signals about the existence of a problem or threat, it also creates the awareness of injury.
2- Pain prevents further damage by causing reflex withdrawal of the boy from the source of injury.
3- Pain tell the person to acquired treatment to prevent the major damage.
4- It forces the person to rest or to minimize the activities thus enabling the raping healing of the injured part.
Pathways of Pain Sensation;
Pain
Pain sensation from various parts of body is carried to brain by different pathways which are,
1- Pathways from skin and deeper structures
2- Pathways from face
3- Pathways from viscera
4- Pathways from pelvic region
1- Pathways of pain sensation from skin and deeper structure;
Receptors;
The receptors of pain sensation are the face nerve endings which are distributed throughout the body
First order neuron;
First order neurons are the cells in the posterior nerve root ganglia which receive the impulses of pain sensation from the pain receptor through their dendrites. These impulses are transmitted to spinal cord through the axons of there neurons.
Fast pain fibers;
Fast pain sensation is carried by A8 type afferent fibers which synapse with neurons of marginal nucleus in the posterior grey horn.
Slow pain fibers;
Slow pain sensation is carried by C type afferent fibers which synapse its neurons of substentia gelatinosa of reelendo in the posterior grey horn.
Second order neurons;
The neurons of the marginal nucleus and substentia gelatinosa of palando from the second order neurons fibers from these escred in the form of the lateral spin thalamic tract.
Fast pain fibers;
Fibers of the fast pain arise from neurons of marginal nucleus. Immediately after taking origin the fibers cross the midline via anterior gray commissure reach the lateral white column of the opposite side and ascend, these fibers from the neospino thalamic fibers in lateral spino thalamic tract. These nerve fibers terminate in ventral posteo lateral nucleus of thalamus some of the fibers terminate in ascending reticular activating system of the brainstem.
Slow pain fibers;
The fibers of slow pain which arise from neurons of substantia gelatinosa cross the mid line and run along the fibers of fast pain as pateospinothalamic fibers in lateral spinothalamic tract. One fifth of these fibers terminate in ventral posteolateral nucleus of thalamus the remaining fibers terminate in any of the fallowing areas.
1- Nuclei of reticular formation in brainstem.
2-Tactum of mid brain
3- Grey matter surrounding aqueduct of sylvius.
Third order neurons:
The third order neurons of pain pathway are the neurons in
1- Thalamic nucleous
2- Reticular formation
3- Tectum
4- Grey matter around aqua duct sylvivs
Axons from these neurons reach the sensory area of cerebral cortex. Some fibers from reticular formation reach hypothalamus.
Center for pain sensation:
The center for pain sensation is in the post central gyrus of parietal cortex. Fibers reaching hypothalamus are concerned with the arousal mechanism due to pain stimuli.
Pathway of pain sensation from face:
Pain from face is carried out by trigeminal nerve. This nerve carries somato sensory information from face, teeth, tissue around teeth, oral cavity, cranial daura matter and major part of scalp to sensory cortex. It also conveys prprioceptive impulses from extrinsic muscles of eye ball.
Pathway of pain sensation from viscera:
The pain sensation from thoracic and abdominal viscera is transmitted by sympathetic nerves. Pain from esophagus, trachea, phyranx is carried by vagus and glassophyrrengial nerves.
Pathways of pain sensation from pelvic region:
Pain sensation from deeper structures of pelvic region is conveyed by sacral parasympathetic nerves.
Visceral pain:
Pain from viscera is un pleasant. It is poorly localized.
Cause f visceral pain:
1-Ischemia
The substance released during ischemic condition like bradykinnin and proteolytic enzymes stimulate the pain receptors of viscera.
2-Chemical stimuli
The chemicals like acidic gastric juice leaks from ruptured ulcers into peritoneal cavity and produce pain.
3-Spasm of hollow organs
Spastic contraction of smooth muscles in GIT and other hollow organs of viscera cause pain by stimulating the force nerve endings.
4-Over distention of hallow organs also cause pain
Referred Pain
It is a pain that is perceived at a site adjuvant to away from the site of origin. The deep and some visceral pain are referred to other areas. But superficial pain is not referred.
Examples :
1-cardiac pain is felt at inner part of left arm and left shoulder.
2-Pain in ovary is referred to umbilicus.
3-pain from testes is referred in abdomen.
4-Pain in diaphragm is referred to right shoulder.
5-Pain in gallbladder is referred to epigastric region.
Mechanism of referred pain:
Dermitomal rule
According to this pain is referred to a structure which is developed from the same dermeterne from which the pain producing structure is developed.
A dermatome includes all the structures or parts of body which are innernated by afferent nerve fibers of one dorsal root. For example the heart, the inner aspect of left arm originates from same dermatome so the pain of heart is referred to left arm.
Gate contract theory:
This theory was proposed in 1965 to explain the pain suppression.
According to them the pain stimuli transmitted by afferent pain fibers are blocked by gate mechanism located at posterior gay horn of spinal cord. If the gate is opened pain is felt but if the gate is closed pain I suppressed.
Mechanism of gate control at spinal level:
1- When pain stimuli is applied on any part of body , besides pain receptors, the receptors of other sensation such as touch are also stimulated.
2- When all the impulses reach the spnal cord through posterior nerve root, the fibers fo touch sensation of apin pathway
3- The impulses of touch sensation passing thorough these collaterals inhibit the release of glutamate and substance P from the pain fibers.
4- This closes the gate nd the pain transmission is blocked.
Headache
Headache originating inside the skull may be due to destention of artries arising from circle of willis, or traction on dura matter.
Headache originating outside the skull is may be due to local stimulated muscle spasm.
Written by Ahmed Abdullah
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