anatomy and physiology of pain

Question 1

nociceptive

Answer 1

damage to non-neural tissue – activation of nociceptors

Question 2

neuropathic

Answer 2

lesion or disease of the somatosensory nervous system

Question 3

nociplastic

Answer 3

arises from altered nociception 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 the pain

Question 4

allodynia

Answer 4

pain due to a stimulus that does not normally provoke pain

Question 5

dysesthesia

Answer 5

unpleasant abnormal sensation, whether spontaneous or evoked

Question 6

hyperalgesia

Answer 6

increased pain from a stimulus that normally provokes pain

Question 7

hypoesthesia

Answer 7

decreased sensitivity to stimulation, excluding the special senses

Question 8

acute pain

Answer 8

less then 12 weeks

Question 9

chronic pain

Answer 9

continuous more than 12 weeks, pain that persists beyond the tissue healing time – split into cancer and non cancer

Question 10

first order/ primary afferent neurone

Answer 10

• Enters the spinal cord through a spinal nerve, or the brainstem through the trigeminal nerve, on the same side of the body (ipsilaterally) as the peripheral receptor is located
• Remains ipsilateral and synapses with a second order neurone within the CNS

Question 11

second order neurone

Answer 11

• Cell body is located in the spinal cord/brainstem (exact location depends where sensory receptor is e.g. brain stem if face)
• Its axons cross over (decussates) to the other side of the CNS and ascends to the thalamus where it terminates

Question 12

third order neurone

Answer 12

• Cell body is located within the thalamus and its axon projects to the somatosensory cortex – located in the post central gyrus of the parietal lobe of the cerebral hemisphere

Question 13

nociceptors

Answer 13

• Sensory neurons found in any area of body that can sense pain
• Nociception – perception of pain
• External e.g skin, mucosa, cornea
• Internal e.g. viscera, joints, muscles and connective tissue ect.
• Cell bodies of neurons reside in either dorsal root ganglia or trigeminal ganglion
• Most are polymodal (thermal, chemical, mechanical)
• Where there is tissue damage, bradykinin & prostaglandin E2 – these substances both reduce the nociceptive action potential threshold thereby increasing their sensitivity to stimuli – known as hyperalgesia

Question 14

afferent fibres: alpha delta fibres

Answer 14

o Thinly myelinated
o Carried: touch, temperature & fast pain information
o Small diameter (1-5 micrometers)
o Conduction speed is medium (5-40m/s)

Question 15

afferent fibres: C fibre

Answer 15

o Unmyelinated
o Carried: slow pain, temperature, touch, pressure, itch, postganglionic autonomic fires information
o Smallest diameter (0.2-1.5 micrometers)
o Conduction speed is slowest (0.5-2m/s)

Question 16

what do nociceptors synapse with

Answer 16

• Nociceptors (A delta and C fibres – first order neurones) synapse with the secondary afferent neurones (second order) in the grey matter of the dorsal horn of the spinal cord (which is divided up into Rexed laminae)
• The A delta (primary afferent neurone) terminals release glutamate (fast acting) as their neurotransmitter
• C fibres (primary afferent neurone) terminals release glutamate and substance P (slow acting – involved in the mediation of dull aching pain) as their neurotransmitters
• First order/ primary afferent neurones transmit information into the dorsal root ganglion where they synapse with second order neurones at the substantia gelatinosa

Question 17

second order neurones transmit pain impulses up the::

Answer 17

o Spinothalamic tract (carries pain, temp and crude touch information from the body) – enters the spinal cord at Lissauer’s fasciculus
o Trigemino-thalamic tract (carries pain, temperature and crude touch information from face/head/ neck)

Question 18

where to first order neurones enter

Answer 18

 First order neurones enter at the pons and then descend to the medulla forming the spinal trigeminal tract
 Receives contributions from the trigeminal, facial, vagus and glossopharyngeal nerves

Question 19

where do the spinothalamic and trigemino-thalamic tracts terminate

Answer 19

terminate at the thalamus (ventral posterior lateral nucleus)

Question 20

what can the spinothalamic tract be divided into

Answer 20

can be divided into the anterolateral tract which consists of:
o Lateral spinothalamic tract (pain & temperature)
o Anterior spinothalamic tract (crude touch)

Question 21

where do third order neurones ascend

Answer 21

• Third order neurones then ascend from the thalamus to terminate in the somatosensory cortex on the post-central gyrus of the parietal lobe

Question 22

thalamus

Answer 22

• Midline, paired symmetrical structure in the brain
• All sensation (except olfactory) relay/pass through it
• Contains multiple nuclei: relay function, association function

Question 23

insula

Answer 23

• Lies within the brain via the sylvian fissure
• Where the degree of pain is judged
• Contributes to the subjective aspect of pain perception

Question 24

cingulate gyrus

Answer 24

• Located on the medial aspect of the cerebral hemispheres
• Linked with the limbic system which is associated with emotion formation and processing learning and memory
• Involved in the emotional response to pain

Question 25

periaqueductal grey

Answer 25

• Located in the midbrain – grey matter around cerebral aqueduct
• Receives input from the somatosensory cortex
• Part of descending pain pathway
• Contains high concentration of opioid receptors & endogenous opioids
• Under situations of extreme stress this pathway can be activated
• Resulting in the modulation of afferent noxious transmission
• It projects to the dorsal horn

Question 26

periaqueductal grey and opioids

Answer 26

• Once activated, opioid receptors are activated resulting in a reduction in pre-synaptic neuronal sensitivity (thereby reducing substance P release) which in turn results in reduced pain sensation
• Meaning less impulses travel up the first, second and third order neurons to the somatosensory cortex – meaning less pain is felt
• Opioids such as morphine, methadone, codeine & oxycodone mimic this effect by binding to the opioid receptors in the periaqueductal grey thereby conferring profound analgesia

Question 27

analgesia

Answer 27

the selective suppression of pain with-out effects on consciousness or other sensations

Question 28

anaesthesia

Answer 28

the uniform suppression of pain – no pain is felt at all, and sometimes consciousness is lost (general anaesthesia)

Question 29

melzack-wall pain gate

Answer 29

states that non-painful input closes the gate to painful input, thereby preventing pain sensation from travelling to the somatosensory cortex to be perceived and thus felt

Question 30

treatments for pain

Answer 30

• Analgesics
• Acupuncture
• Exercise
• Hypnotherapy

Question 31

substance P

Answer 31

• Peptide neurotransmitter involved in pain transmission
• Also a vasodilator
• Remains bound to receptors for longer time thereby transmitting long-lasting pain