Anatomy and Physiology of Pain Flashcards
*Pain Definition
Pain is an unpleasant sensory and emotional experience associated with, or resembling that associated with, actual or potential tissue damage.
Purpose of pain
Immediate -> Withdraw from source of injury
Persisting pain -> immobilize to give best chance of healing
Nociception
Neural processes involved in producing sensation of pain
Acute pain
Pain < 12 weeks duration
Chronic
Continuous pain > 12 weeks
Pain that persist beyond the tissue healing time (chronic non-cancer and chronic cancer pain)
Nociceptive pain
Pain that arises from actual threatened damage to non-neural tissue and is due to the activation of nociceptors
Neuropathic pain
Pain caused by a lesion or disease of the somatosensory nervous system.
Tingling, loss of sensitivity
Nociplastic pain
Pain that arises from altered nociception despite no clear evidence of actual or threatened tissue damage causing the activation of peripheral nociceptors, or evidence for disease or lesion of the somatosensory system causing pain.
Allodynia
Pain due to a stimulus that doesn’t normally provoke pain
Dysesthesia
An unpleasant abnormal sensation, whether spontaneous or evoked
Hyperalgesia
Increased pain from a stimulus that normally provokes pain
Hypoalgesia
Diminished pain in a response to a normally painful stimulus
pathway
Peripheral receptor - detect relevant stimulus
1st order neuron - from the periphery to the ipsilateral spinal cord
2nd order neuron - which crosses to the contralateral cord and ascends to the thalamus, the system’s integrative relay station
3rd order neuron - from thalamus to midbrain and higher cortical centers
Nociceptors
Transduction
Physical stimulus –> action potential
Most are poly-modal (thermal / chemical / mechanical)
Primary Afferent Neurones
Nocireceptors are the free nerve endings of primary afferent neurons.
Cell bodies reside in dorsal root ganglion (body)
Trigeminal ganglion (face / head / neck)
Dorsal root ganglion
Present on dorsal root (sensory)
Can be source of pain pathology
Pseudo-unipolar neurons
Dorsal horn
Posterior aspect of spinal cord, grey matter forms 2 horns.
Spinothalamic Tract (STT)
Sensory pathway that carries pain.
2nd order neurons
Pathway of 2nd order neurons
In dorsal horn
Decussate few levels above site of entry
Cross midline in anterior commissure
Form the Anterolateral tract
Terminates in thalamus
Which gyrus is the cenral cortex in?
Postcentral gyrus
Pain matrix
3rd order neurons make many connection to somatosensory centres and deeper midbrain structures (eg limbic system and anterior cingulate cortex)
Insula
Degree of pain is judged
Subjective aspect of pain perception
May also play role in addiction
Amygdala
Part of limbic system.
Role in learned emotional responses
Emotional-affective dimension of pain
Hyperactivity -> pain-related emotional responses and anxiety-like behaviour
Cingulate cortex
Medial aspect of cerebral hemispheres
Linked with limbic system
Attention and response selection.
An area activated by acupuncture
Peri-aqueductal gray
Grey matter located around cerebral aqueduct
Receives input from cortical and sub-cortical areas
Neurons bear opioid receptors
When stimulated can result in profound analgesia
Cortical reorganisation
Smudging of the homunculus
eg. brail readers have larger somatosensory representation of fingers.
3 overlapping factors contributing to chronic pain
Biological, psychological and sociological
3 ways to treat pain
Stimulate descending inhibitory pathway
Gate control
Pharmacotherapy
