Musculoskeletal referred pain

Question 1

Define referred pain in neurological terms?

Answer 1

Pain perceived as occurring in a body region innervated by nerves/branches other than the nerves/branches that innervate the actual source of pain

Question 2

Define referred pain in clinical terms?

Answer 2

Pain perceived as occurring in a region of the body topographically distinct from the region in which the actual source of pain is located

Question 3

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?

Answer 3

Yes, two areas can be distant or contiguous but are still distinguishable as different topographical body regions due to their different nerve supplies

Question 4

In pain transmission, where do third-order neurons project from, and where do they terminate, and why do the neurons terminate here?

Answer 4

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

Question 5

Describe how cutaneous innervation is supplied by spinal nerves?

Answer 5

Nerves at each spinal segmental level supply cutaneous innervation of a specific dermatome, except C1 segment which supplies no dermatome

Question 6

How many pairs spinal segmental level nerves and dermatomes are there, and why are the numbers different?

Answer 6

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

Question 7

Define radicular pain?

Answer 7

Activation of specific nerve root directly causes pain in the area of dermatomal distribution of that nerve root

Question 8

What is the name of the mechanism of referred pain?

Answer 8

Dorsal convergence theory

Question 9

In the dorsal horn convergence theory, what is meant by dorsal horn convergence of sensory neurons?

Answer 9

Afferent primary-order sensory neurons from tissues in different body regions synapse with same second-order dorsal horn neuron

Question 10

In dorsal horn convergence theory, how does the brain locate the source of pain?

Answer 10

Due to convergence of sensory neurons, higher centres in brain can’t locate actual source of dorsal horn activation

Question 11

In dorsal horn convergence theory, how do higher centres in brain determine which body region to project pain to?

Answer 11

Projected to body region with highest density of nociceptors (afferent nociceptive innervation), that converges onto same second-order dorsal horn neuron

Question 12

When considering referred pain, why is it useful to know the innervation of organs/structures?

Answer 12

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

Question 13

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?

Answer 13

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

Question 14

In referred visceral pain, explain what is meant by the viscero-somatic reflex?

Answer 14

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)

Question 15

What are the 2 main ways in which referred visceral pain presents in a patient?

Answer 15

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)

Question 16

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?

Answer 16

Sympathetic neurons

Thoracic, abdominal, pelvic organs

Question 17

What are the 3 nerves of the parasympathetic nervous system that carry visceral afferents to the spinal cord?

Answer 17

Parasympathetic neurons:

9th/IX cranial nerve (glossopharyngeal)

10th/X cranial nerve (vagus)

pelvic splanchnic nerves arising from S2,S3,S4

Question 18

Define myotome, in terms of innervation?

Answer 18

Group of muscles innervated by a single nerve root

Question 19

In referred muscle pain, where is the actual source of pain/nociceptive input and where is the pain referred to?

Answer 19

Nociceptive input from muscle

Referred pain in myotomes, other peripheral tissues such as skin, fascia that correspond to the same segmental level

Question 20

Why does muscle pain project to myotomes as well as peripheral tissues that correspond to the same segmental level?

Answer 20

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

Question 21

Define sclerotome, in terms of innervation?

Answer 21

Area of bone supplied by a single nerve root

Question 22

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?

Answer 22

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

Question 23

Explain Hilton’s law in referred bone and joint pain?

Answer 23

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