Physiology and Pathophysiology of Pain Flashcards
what is pain?
an unpleasant sensory and emotional experience associated with or resembling that associated with actual or potential tissue damage
what is nociception?
physiologic process in which noxious stimulation is communicated through the peripheral and central nervous system and may or may not result in pain
what is pain?
subjective experience, perception occurs in the somatosensory cortex and can be triggered without tissue damage if brain or spinal cord malfunction
what are the neural pathways?
periphery- detection of tissue damage by nociceptors and are transuded to the spinal cord through the 1st order/primary afferent neurones - spinal cord processing and spinal is transmitted to the brain (thalamus) by the 2nd order neurones- brain= various centres receive input- perception, learning and response - modulation= descending tracts - avoid or dampen stimuli
what fibres are involved in nociception?
A delta= lightly myelinated and transmits the fast pain whereas C fibres are unmyelinated and transmit slow pain
what happens to nociception in the spinal cord?
the 1st order neurones synapse in the dorsal horn of the spinal cord and the 2nd order neurones continue as tracts
what ascending tracts carries nociceptive information?
spinothalamic tract which raised in the rexed lamina 1,2 and 5 which is mainly lateral but also small amount anterior - spinoreticular tract in the medulla, spinomesencephalic tract in the brainstem, spinohyopthalamic tract in the hypotahalmus
what is the function of thalamus?
secondary centre which is in the brain - depending on where they project to in the thalamus from the spinal cord, they are divided into the lateral and medial systems
what is the medial system?
VMpo and Mdvc mainly receive primarily lamina I and they project to the insulation and ACC and they are involved in evaluating the pain
what are the descending pathways involved in nociception?
periaquductal grey (PAG) in the midbrain which assimilates the information and is effective via the rostroventral medulla which is noradrenergic system and have on and off cells and usually decreases pain signal (diffuse noxious inhibitory control - DNIC= normal tone) - normally on= inhibitory but if on= more signals sent to the higher centres
what is pain modulation?
at each stage in the nociception pathway can be subject to modulation and can become independent on their own giving rise to chronic pain
how do nociceptors?
to create a signal sodium channels must close to allow the cells to depolarise
how does inflammation influence nociception?
inflammatio will cause most cells, macrophages etc to congregate which will release mediators wg histamine, NGF etc which will influence the sodium channels by either keeping them open for longer or inhibit
what effect with inhibition of sodium channels have?
peripheral sensation -lower intensity of stimulus will give rise to greater pain sensation
what is allodynia?
perception of non-painful stimuli due to decreased threshold for response
what is hyperalgesia?
exaggerated response to normal and supranoraml stimuli
what is spontaneous pain?
spontaneous (without pain) activity in nerve fibres
what is central sensitisation?
response of 2nd order neurones in the CNS to both noxious and non-noxious stimuli and have 3 main components= wind-up, classical and long-term potential
what is wind-up?
involves only the activated synapses- homosynaptic activity dependent on progressive increase in response of the neurones, it manifests over the course of stimuli and terminated with stimuli and the neurotransmitters involved are substance P and CGRP
what is classical?
involves opening up of new synapses (silent nocicpetors), heterosynaptic activity dependent plasticity with intermediate onset with appropriate stimuli and can outlast the initial stimuli duration and can be maintained even at low levels of ongoing stimulus
what is long-term potentiation?
involves mainly the activated synapses and occurs primarily for very intense stimuli
what are the different possible durations of pain?
acute or chronic
what are the different mechanisms of pain?
nociceptive, neuropathic or nopciplastic
what is acute pain?
physiological and needs the presence of noxious stimuli, served protective function and is usually nociceptive
what is chronic pain?
pathological and presence of noxious stimuli is not essential, does not serve any purpose and cab be nociceptive, neuropathic or nociplastic
what is nociceptive pain?
a sensory experience that occurs when specific peripheral sensory neurones (nociceptors) respond to noxious stimuli - painful region is typically localised to the site of injury, usually resolves when the damaged tissue heals
what is neuropathic pain?
pain caused by a lesion or disease of the somato-sensory nervous system - pain occurs in the neurological territory of the affected structure, predominantly a chronic condition and responds poorly to conventional analgesics
what is nociplastic pain?
pain that arises from altered nociception despite no clear evidence of actual or theatened tissue damage causing the activation of peripheral nociceptors or evidence of disease or lesion of the somatosensory system causing pain - pathological pain
