What is meant by ‘total pain’?
Pain has 4 dimensions to it.
- Physical: pain, symptoms, fatigue, side effects
- Social: loss of social position, job prestige, role in family, feeling abandoned and isolated
- Spiritual: why am I suffering like this, what’s the point in life, can I be forgiven for actions in life?
- Psychological: anger at delays and treatment which doesn’t work, fear of pain, fear of death
If a patient is in acute pain, what signs will they show?
More of a physical response
Sympathetic response (fight or flight) Pupillary dilation Sweating Tachypnoea Tachycardia Shunting of blood from peripheries to viscera
If a patient is in chronic pain, what signs will they show?
More of a psychological response
Sleep disturbance Anorexia Decreased libido Anhedonia Lethargy Constipation
What are the causes of pain in cancer?
- Cancer itself: soft tissue, visceral and bone damage, compression or damage to nerves
- The treatment: chemotherapy or radiotherapy
- Debility caused by cancer results in constipation, muscle tension, spasm, wasting, ulcers
- Concurrent disorders: arthritis etc.
- Psychological pain
What’s the difference between functional and pathological pain?
Pathological: there is actual damage occurring which is causing the pain
Functional: there is no damage occurring that’s causing the pain
Name and define the two types of pathological pain?
Describe mechanism of action of both types.
Nociceptive: distortion or damage to tissue
Stimulation of sensory nerve endings in tissues
Neuropathic: damage or compression of nerves
Stimulation of nervi nervorum (small nerves that innervate the sheath of larger nerve)
What things might make you think a patient’s pain is neuropathic?
Dermatomal distribution
Type of pain: burning, stinging, deep ache, stabbing
Accompanying sensory loss or paraesthesia
Allodynia: light touch exacerbates pain
Sympathetic component: sweating, cutaneous vasodilation
What is allodynia?
Pain is exacerbated by light touch
What are nervi nervorum?
Nerves of nerves
Small nerve filaments that innervate the sheath of larger nerve
Define pain.
Unpleasant sensory and emotional experience associated with actual or potential tissue damage.
Where are nociceptors found?
Skin Viscera Muscles Joints Meninges Peri-osteum
Describe how nociceptive pain is transmitted to the brain?
Draw it!
Nociceptors are stimulated by the damage to the tissue (be it thermal, mechanical, chemical, inflammatory)
Nociceptors are the free nerve endings of primary afferent nerve fibres (A delta and C fibres)
Which transmit electrical signal to the dorsal horn of spinal cord
Which then goes up the spinothalamic and spinoreticular tract to brain for processing.
Which inflammatory mediators cause pain?
Bradykinin Serotonin Prostaglandins Cytokines H+
Name the nerves which transmit sensation to the spinal cord?
What type of sensation do they transmit?
Primary afferent fibres
3 types
A beta - non-noxious, light touch
A delta - sharp, acute, localised pain
C fibres - chemical, mechanical, thermal pain
Feels like a slow burning pain
What are the differences between the primary afferent nerve fibres?
Size Myelination Speed of conduction Receptor activation thresholds Type of sensation
A beta
- large diameter
- highly myelinated
- fast conduction
- low threshold
- light touch, non-noxious
A delta
- small diameter
- thinly myelinated
- slower speed
- variable thresholds
- rapid, sharp, localised pain
C
- smallest diameter
- unmyelinated
- slowest conduction
- high threshold
- slow, diffuse, dull pain
Which primary afferent nerve fibre…
- is unmyelinated
- has the lowest
- has lowest threshold
- has the slowest conduction velocity
- is thinly myelinated
- transmits sharp pain
- transmits diffuse pain
- transmits light touch
- largely innervates viscera
- C fibres
- A beta
- A beta
- C fibres
- A delta
- A delta
- C fibres
- A beta
- C fibres
Which neurotransmitters do primary afferent nerve fibres use?
Are they excitatory or inhibitory?
Glutamate
Substance P
Excitatory
In which part of the spinal cord do the primary afferent nerve fibres attach?
The dorsal horn
Name some inhibitory neurotransmitters?
GABA (gamma-aminobutyric acid)
Glycine
Name the spinal pathways which carry nociceptive pain signals to the brain?
Where do they each go to in the brain?
What information about the pain do they transmit?
SPINOTHALAMIC
- goes to nuclei in thalamus
- then to somatosensory cortex
- also to peri-aqueductal grey matter
- transmits signals important for pain localisation
SPINORETICULAR
- to nuclei in the thalamus
- then into the cortex
- involved in emotional aspects of pain
Where is the peri-aqueductal gray matter?
What does it do?
It is in the midbrain
It has a role in the inhibition of pain
Known as descending inhibition
What mechanisms are there which inhibit pain transmission to the brain?
Explain them.
Descending inhibition: involving the peraqueductal gray area. Noradrenaline and serotonin pathways inhibit pain transmission
Gate control theory: activation of A beta fibres inhibits signals transmitted by C fibres via inhibitory interneurons in the dorsal horn. (this is why rubbing a painful area helps pain)
Define referred pain?
How can you explain it?
When pain is experienced at a site distant from the source of the pain
Different afferent nerve fibres converge onto the same dorsal horn neurones in the spinal cord.
What is primary sensitisation?
Inflammatory mediators (cytokines, prostaglandins, H+, serotonin etc.) are able to lower the threshold at which nociceptors are activated.
So less stimulation is needed to cause activation and thus cause pain.
