In this pathophysiology video, we will learn about pain.
The processing of pain by the nervous system is called nociception.
Pain is sensed by free nerve ending called nociceptors.
Impulses from nociceptors follow afferent pathways to the central nervous system for
processing in the brain.
The conversion of pain to electrical impulses is called transduction.
Nociceptors respond to a variety of stimuli including pressure, temperature, and chemicals
such as histamine, bradykinin, prostaglandins, and leukotrienes.
Let’s look at how pain is processed.
Sharp acute pain is carried by A delta nerve fibers to the spinal cord.
Neurons then synapse with other neurons in the spinal cord and travel to the thalamus,
hypothalamus, and limbic system via the spinothalamic tracts.
The thalamus then relays the impulses to the somatosensory cortex for processing.
This part of pain processing is called transmission.
Dull pain follows a similar pathway, but is carried by C fibers.
During transmission, excitatory neurotransmitters are released which can include:
adenosine triphosphate glutamate
calcitonin gene-related peptide bradykinin
nitric oxide substance P
Parts of the brain that process pain include the somatosensory cortex, reticular and limbic
systems.
The somatosensory cortex is involved in the perception of pain including the type of pain,
intensity, and location along with memory.
The reticular system is involved in the motor response to pain, such as pulling away from
a hot object.
The limbic system is involved in the emotional response to pain along with memory.
Pain is also modulated via descending pathways by the following neurotransmitters:
endogenous opioids (enkephalins and endorphins) serotonin (5-HT)
norepinephirine (noradrenalin) gamma-aminobutyric acid (GABA)
neurotensin acetylcholine
oxytocin.
Substance P
These neurotransmitters help to control the severity of pain by inhibiting pain pathways.
The endogenous opioids such as endorphins and enkephalins are produced by the body and
function to decrease pain.
Activities such as aerobic exercise can promote the production of endogenous opioids which
can help reduce pain.
This is why aerobic exercise is sometimes recommended to help manage pain.
Acute pain acts as a protective mechanism and lasts from a few seconds to several months.
Acute pain can be classified as somatic: from skin, muscles, or joints; visceral: from organs;
and referred in which pain pathways are shared in the spinal cord from multiple sources.
Referred pain can be acute or chronic.
Chronic pain is still a bit of a mystery and the mechanism of chronic pain is not well
understood.
It is thought that chronic pain results from long term changes in the nervous system.
Examples of chronic pain include persistent low back pain, pain resulting from surgery,
cancer, damage to nerves, and from surgical removal of a limb (phantom limb)
Neuropathic pain is caused by damage to the nervous system.
Some examples of neuropathic pain include:
trauma, for example, complex regional pain syndrome, chronic post-surgical pain;
infection, for example, post-herpetic neuralgia ischemia, for example, diabetic neuropathy
cancer chemically induced, for example, as a result
of chemotherapy
Neuropathic pain is experienced differently than nociceptive pain.
Some examples include:
burning, dull, aching, tingling, or electric shock-like.
I hope you have learned something about pain and I’ll see you next time.