Musculoskeletal referred pain Flashcards
Define referred pain in neurological terms?
Pain perceived as occurring in a body region innervated by nerves/branches other than the nerves/branches that innervate the actual source of pain
Define referred pain in clinical terms?
Pain perceived as occurring in a region of the body topographically distinct from the region in which the actual source of pain is located
If 2 body regions are contiguous, are they still distinguished as different topological body regions, and so can be each other’s region of referred pain?
Yes, two areas can be distant or contiguous but are still distinguishable as different topographical body regions due to their different nerve supplies
In pain transmission, where do third-order neurons project from, and where do they terminate, and why do the neurons terminate here?
Project from thalamus and terminate in primary somatosensory (S1) cortex
S1 cortex is topological map of all body regions, so area that receives neural input correlates to body region that is painful
Describe how cutaneous innervation is supplied by spinal nerves?
Nerves at each spinal segmental level supply cutaneous innervation of a specific dermatome, except C1 segment which supplies no dermatome
How many pairs spinal segmental level nerves and dermatomes are there, and why are the numbers different?
31 pairs of spinal nerves and 30 dermatomes
Because a pair of nerves at each spinal segmental level supply cutaneous innervation of a specific dermatome, except C1 segment which supplies no dermatome
Define radicular pain?
Activation of specific nerve root directly causes pain in the area of dermatomal distribution of that nerve root
What is the name of the mechanism of referred pain?
Dorsal convergence theory
In the dorsal horn convergence theory, what is meant by dorsal horn convergence of sensory neurons?
Afferent primary-order sensory neurons from tissues in different body regions synapse with same second-order dorsal horn neuron
In dorsal horn convergence theory, how does the brain locate the source of pain?
Due to convergence of sensory neurons, higher centres in brain can’t locate actual source of dorsal horn activation
In dorsal horn convergence theory, how do higher centres in brain determine which body region to project pain to?
Projected to body region with highest density of nociceptors (afferent nociceptive innervation), that converges onto same second-order dorsal horn neuron
When considering referred pain, why is it useful to know the innervation of organs/structures?
You can predict the pattern of referred pain if you know which nerves supply that organ/structure that is the actual source of pain, and what other structures the same nerves innervate
In referred somatic pain, which in the body is the actual source of pain, and where is the pain projected to due to dorsal horn convergence?
Nociceptive input from proximal or axial somatic tissue is projected as pain to a distant somatic tissue that has the same segmental afferent neuron innervation
In referred visceral pain, explain what is meant by the viscero-somatic reflex?
Viscero-somatic reflex: At each segmental level, visceral pain/nociceptive input (from visceral structure/internal organ) is referred to specific body region (distant somatic tissue)
What are the 2 main ways in which referred visceral pain presents in a patient?
Pain in musculoskeletal structures
GI disturbance, pallor, sweating, nausea and changes in blood pressure, temperature, heart rate (because visceral structures are controlled by autonomic nervous system)
Which division of the nervous system supplies visceral afferents (sensations) to the T1-L2 segmental levels of the spinal cord, and which 3 types of organs are supplied by these neurons?
Sympathetic neurons
Thoracic, abdominal, pelvic organs
What are the 3 nerves of the parasympathetic nervous system that carry visceral afferents to the spinal cord?
Parasympathetic neurons:
9th/IX cranial nerve (glossopharyngeal)
10th/X cranial nerve (vagus)
pelvic splanchnic nerves arising from S2,S3,S4
Define myotome, in terms of innervation?
Group of muscles innervated by a single nerve root
In referred muscle pain, where is the actual source of pain/nociceptive input and where is the pain referred to?
Nociceptive input from muscle
Referred pain in myotomes, other peripheral tissues such as skin, fascia that correspond to the same segmental level
Why does muscle pain project to myotomes as well as peripheral tissues that correspond to the same segmental level?
Sensory innervation of a muscle is the same as its motor supply as C-fibres in tendons and muscles contain sensory fibres and run in the motor nerves
This means that any muscle within the myotome and the skin, fascia eg. around that myotome are supplied by single nerve root, so pain can be referred to all of them
Define sclerotome, in terms of innervation?
Area of bone supplied by a single nerve root
In referred bone and joint pain, where is the actual source of pain/nociceptive input and where is the pain projected to, and why does this occur?
Nociceptive input from muscles is projected as pain in sclerotomes near the source muscle
Occurs to due Hilton’s law: innervation of the joint arises from the motor supply of the muscles acting across the joint
Therefore afferent innervation of joint and muscles acting on that joint arise from same segmental level
Explain Hilton’s law in referred bone and joint pain?
Hilton’s law: innervation of the joint arises from the motor supply of the muscles acting across the joint
Therefore the afferent innervation of joint and muscles acting on that joint arise from same segmental level
