Pain physiology

Question 1

Pain

Answer 1

Pain is an unpleasant sensory and emotional experience associated with actual or potential tissue damage or described in terms of such damage.

Question 2

Px types

Answer 2

1. Nociceptive- immediate output
2. Inflammatory- continue stimulation (prostaglandins, histamines, interleukins)
3. Neuropathic- nervous system damaged

Question 3

Nociceptive Px

Answer 3

No nervous system lesion or inflammation
Mechanical, thermal, chemical injury
E.g. Abnormal mechanical forces - OA
E.g. organ injury - angina

Question 4

Inflammatory Px

Answer 4

Active inflammation
Tissue trauma, surgery, joint inflammation e.g. RA

Question 5

Components of the brainstem

Answer 5

Midbrain
Pons
Medulla
Then continues on and becomes the spinal cord

Question 6

Neuropathic

Answer 6

Nervous system lesion or disease
Marked neuroimmune response
E.g. nerve trauma, AIDs, Herpes zoster

Question 7

Structure of the spinal cord

Answer 7

The meninges made up of:
Pia mater
Arachnoid mater
Duramater

White mater (containing axons of nerve cells) surrounded by grey matter (contains body of nerve cells)
Central canal - contains cerebral spinal fluid which nourishes CNS

Question 8

Two fibre types exiting spinal cord

Answer 8

Motor fibres exit the frontal aspect of the spinal cord and carry info out of the spinal cord.
Sensory fibres exit the dorsal aspect of the spinal cord and transmit info into the spinal cord to take it to the brain.

Question 9

Afferent nerve fibres

Answer 9

Carry information from sensory receptors of the skin and other organs to the 2nd order neuron and spinal cord (CNS) .
E.g. Nociceptors/sensory fibres

Question 10

Efferent nerve fibres

Answer 10

Carry motor information away from the CNS to the muscles and glands of the body.
E.g. Motor fibres

Question 11

Nociceptors and types

Answer 11

Special nerve cell endings that initiate the feeling of Px all around the body.
A-beta fibres - detect Touch
A-delta - very small myelinated nerve cells that produce fast, localised sharp Px
C-fibres - Smaller, un-myelinated nerve cells that pick up slow, poorly localised Px - burning/throbbing

Question 12

Spinothalamic tract

Answer 12

A sensory tract that carries nociceptive, temperature, crude touch, and pressure from our skin to the somatosensory area of the thalamus.
It is responsible for our quick withdraw reaction to a painful stimulus such as touching the stove burner.

Question 13

Somatosensory cortex

Answer 13

Area in the cortex (outer part) of the brain associated with sensation.
Contains specific areas related to specific parts of the body.
Location of where Px occurs correlates to area of somatosensory cortex.

Question 14

Ascending pathway

Answer 14

The pathway that goes upward carrying sensory information from the body via the spinal cord towards the brain.
How we sense Px

Question 15

Ascending pathway process:

Answer 15

1) Noxious stimuli occurs e.g. nail penetrates trunk
2) Cytokines (chemicals) released by immune cells stimulate Nociceptors
3) Nociceptors bring Px info in through dorsal horn via 1st order neuron (as sensory fibres are dorsal)
4) Nociceptors then release Px neurotransmitters e.g. Substance P
5) 2nd order neuron receives information and crosses over to opposite side of spinal cord
6) Info travels to brain Via spinothalamic tract
7) 2nd order neuron passes on info to 3rd order neuron which locates the area of Px through the somatosensory cortex.

Question 16

Crossing of info across the spinal cord and brain

Answer 16

2nd order neuron on the right side crosses over to the left side and ascends to the left side of the brain
Px on the right side of the body is processed on the left side of the brain and visa versa.

Question 17

Descending pathway

Answer 17

Responsible for controlling and inhibiting the ascending pathway.

Question 18

Key aspects for the Descending pathway

Answer 18

Periaqueductal grey matter of the midbrain
Nucleus Raphe magnus of the medulla

Question 19

Descending pathway walkthrough

Answer 19

1) When not inhibited neurons from Periaqueductal grey matter travel down to Nucleus Raphe magnus and synapse with the second order neuron (SHT/NA)

2) SHT/NA neuron travels to dorsal horn of spinal cord (area known as substantia gelatinosa)

3) Substance P is the neurotransmitter which allows signal to go from 1st order neuron to 2nd order neuron and so allows signal to go up ascending tract- stopping this neurotransmitter means signal doesn’t go to brain

4) SHT/NA neuron releases serotonin and noradrenal which binds to the receptors on 1st order neuron (presynaptic neuron) and stops release of Substance P.

5)SHT/NA further stimulates another neuron known as the interneuron which when stimulated it releases opioid enkephalin which binds to 1st & 2nd order neuron preventing P substance depolarizing 2nd order neuron