Physiology of Pain

Physiology Of Pain Made Easy

Pain is the most common symptom that causes people to seek out healthcare. Pain is unpleasant, uncomfortable and usually means that there is tissue damage and causes a person to become determined to remove the cause or seek after relief of the pain. If not managed properly pain affects a person's quality of life by not being able to complete simple tasks that at one time were easy such as preparing meals, doing the laundry, and hygiene to name a few. The Joint Commission on the Accreditation of Healthcare Organizations stressed the importance of pain by implementing valuable assessment of each person and treating them as an individual. This is because each person perceives pain differently.

Bradykinin in the physiology of pain

Prostaglandins in the physiology of pain

Chemicals involved in the physiology of pain.

As stated before pain occurs when tissue damage activates the free nerve endings called pain receptors or the more scientific name nociceptors. These receptors are located on all peripheral nerves. Pain receptors are concentrated in the skin, soft tissue, muscle, joint surface, artery walls, and periosteum. Pain receptors are limited on most internal organs like the lungs and uterus. Tissue damage can occur physically, with heat, cold, pressure, stretch, spasm, or when blood supply is restricted to certain tissue areas causing damage known as ischemia. The body also releases substances caused by cell damage like bradykinin and prostaglandins. Bradykinin is one of the strongest pain producing substances and it quickly breaks down for this reason it is found mainly in acute pain. Other chemicals involved in the physiology of pain include acetylcholine, adenosine triphosphate, histamine, leukotienes, potassium, serotonin, and substance P. To avoid a confusing, eye glazing, high school lecture, these chemicals become the negotiators by producing pain by stimulating the peripheral pain receptors or stimulating the release of pain-producing substances.

Spinal cord in physiology of pain

Perspectives of physiology of pain Part 1

A-delta and C-fibers in the physiology of pain

In order for a person to actually feel the pain though becomes a completely different story. The signal from the pain receptors in the peripheral tissues must then be transmitted to the spinal cord, from there the pain message is sent to the hypothalamus and cerebral cortex of the brain.  To backtrack a bit, the pain signal is carried to the spinal cord by two types of peripheral nerve cells, they are called A-delta fibers and C-fibers.  A-delta fibers are myelinated (allows a current to flow better) and found mainly in the skin and muscle. A-delta fibers transmit fast, sharp pain signals. A-delta fibers release glutamate and aspartate, "what?", I might as well have said glue and asphalt.  Glutamate and aspartate are excitatory amino acid neurotransmitters and they are released at synapses in the spinal cord.  C fibers on the other hand are unmyelinated (no insulation)  and are located in muscle, mesentery (a membrane that supports an organ or body part), abdominal viscera (organs), and periosteum (tissue around bones). C-fibers conduct a pain signal slowly because they are unmyelinated the pain is described as dull or burning.  To recap, tissue damage resulting from an acute (brief, severe, and quickly comes to a crisis) injury produces an initial sharp pain sent out by the A-delta fibers followed by a dull ache/burning sensation produced by the C-fibers.

Dorsal horn of spinal cord

Perspectives of physiology of pain part 2

Physiology of pain: Relay Station

The dorsal (situated on the back of the body or in this case back of spinal cord) horn of the spinal cord is the managing center or relay station for the pain signal from the A-delta and C nerve fibers, for local frequency of pain impulse, and for interpretations sent down from the higher centers in the central nervous system (CNS, like attention, emotion, memory). At the dorsal horn pain nerve fibers synapse (junction between two nerve cells) with non-nociceptive nerve fibers (nerve cells that carry other information besides pain). The brain also has powerful descending pathways that alter pain input. Some brain nuclei serotonergic (nerves that are capable of releasing serotonin) and project to the dorsal horn of the spinal cord, where they stifle pain transmission. Another major inhibitory pathway from the brain is the noragrenergic and it begins in the pons, which is a whitish band of nerve fibers on the surface of the brainstem between the medulla oblongata and midbrain. Consequently, increasing the concentration of norepinephrine (raises blood pressure to keep blood flow to vital organs) and serotonin (constricts blood vessels at injury sites) in the synapse interrupts or inhibits transmission of nerve impulses that carry pain signals to the brain and spinal cord. Tricyclic antidepressants (TCAs), drugs that increase the amounts of serotonin and norepinephrine which is thought to account for the pain-relieving effects of tricyclic antidepressants. In the brain, the thalamus is a relay station for incoming sensory stimuli, including pain. Awareness of the pain is a primitive awareness in the thalamus and the feeling is not interpreted fully until it sent on to the cerebral cortex. Once at the cerebral cortex the pain signal is perceived more specifically and analyzed to determine the action that is needed.

Physiology of pain: Acute pain

Physiology of pain: Chronic Pain

Physiology of pain: Somatic pain

Physiology of pain: Visceral pain

Physiology of pain: Neuropathic pain

Physiology of pain: Types of Pain

Physiology of pain includes a few different pain types acute, chronic, cancer, somatic, visceral, and neuropathic pain.  Acute pain is caused by injury, trauma, spasm, disease processes, and treatment or diagnostic procedures.  Acute pain is often described as sharp, lancing, or cutting.  Acute pain is sometimes called fast pain because it is felt 0.1 second after a pain stimulus is applied.  After that, glutamate (remember it enhances pain perception) is released into the synapse of the spinal cord by the A-delta fibers but it only last a few milliseconds. Chronic pain is pain lasting 6 months or longer and it demands attention less urgently that acute pain this is because the cause of chronic pain is already known, whereas acute pain could be a sign of the beginning of a new underlying disease or condition.  Chronic pain is often not characterized by visible signs of trauma and is accompanied by emotional stress, increased irritability, depression, loss of libido, and disturbed sleep patterns to name a few.  Chronic pain is also known as slow pain which begins after at least 1 second of exposure.  Slow, chronic pain is transmitted by type C nerve fibers to the spinal cord and brain.  Substance P is the neurotransmitter of type C nerve endings, it is released slowly and accumulates over seconds to minutes.  Cancer pain has characteristics of both acute and chronic pain and it can be constant or intermittent.  Chronic cancer pain is caused mainly by tumor spreading into pain-sensitive tissues (bone, nerves, soft tissue, viscera) and results in tissue destruction. Cancer pain usually becomes worse as the disease progresses and can be severe and unbearable.  Somatic pain is a result of pain receptors being stimulated in structural tissues such as skin, bone, muscle, and soft tissue).  Somatic pain is well localized and is a sharp, burning, aching, or cramping pain.  A broken femur is an example of somatic pain.  Somatic pain of low to moderate intensity may activate the sympathetic nervous system and increase blood pressure, pulse, and respirations.  Somatic pain can also increase skeletal muscle tension such as a rigid posture or fist clenching.  Visceral pain is the result of many pain receptors being stimulated at the same time in the abdomen or chest organs and their surrounding structural tissues.  This kind of pain is normally connected to pancreatitis, uterine, and ovarian disorders as well as liver disease.  Visceral pain is diffuse and not pin pointed to one location because it is transmitted through the C-fibers discussed earlier and therefore can only transmit the aching chronic type of pain.  This pain can also be felt in areas not evolved, such as, pain in the liver can be felt in the right shoulder area.  Neuropathic pain is a result of direct injury of the peripheral pain receptors, nerves, or the central nervous system.  It is mostly a common cause of chronic pain and can be described as severe, shooting, burning, or stabbing pain.  Examples of neuropathic pain are diabetic neuropathy, herpes zoster infections, nerve injuries, and some types of cancer or cancer treatments.  Neuropathic pain is difficult to treat with standard pain relief medicine because they are less effective with this type of pain.  Tricyclic antidepressants, anticonvulsants, and corticosteroids are often used along with pain relief medication.

Comments

hiit on June 07, 2012:

Really fantastic hub. "We must learn our limits. We are all something, but none of us are everything." by Blaise Pascal.

Ron from Fitness http://www.intervalstraining.net

hatry on September 28, 2011:

why pain increases heart rate?

FoFo on March 07, 2011:

what's the difference between referred pain and radiating pain?

manu on November 01, 2010:

hi...

In general, In acute pain incidence cases, In practical what is distribution of cases means how many suffers from visceral, somatic and neuropathic pain in Percentage (%)

If you have any information on this thing please send me on nipermanoj@rediffmail.com

Levi (author) from New Mexico on July 10, 2010:

Please feel free to ask any question that you may have.....or give me a thumbs up or down. Physiology of pain is the subject studied in order to treat pain. Questions, or comments definitely welcome.