Pain Flashcards by Elizabeth Stevens

What are the different responses to pain?

Autonomic - increased heart rate, pupil dilation
Somatic - eg withdrawal from pain source
Endocrine - eg cortisol from adrenal glands
Emotional

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What is meant by pain being subjective?

It affects thinking and behavioural processes eg response to pain

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What can pain, in general, be modified by?

Experience
Expectation
Immediate context ef playing sport, won’t feel pain as much

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What is the difference between pain threshold and tolerance?

Stimulus threshold is the same in everybody - the amount of sensation required to feel pain

Tolerance is our variable reaction to a pain stimulus

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What can affect pain tolerance?

Environmental situation
Physiological or emotional factors
Age
Ongoing pain
Placebo effect

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What is nociception?

The non-conscious neural traffic originating with trauma or potential trauma to tissue

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What are the stages of nociception?

Transduction - activation of nociceptors by a stimulus

Transmission - relay of action potentials along nociceptive fibres to the CNS

Modulation - by other peripheral nerve or CNS mechanisms

Perception - interpretation of the brain of the sensation as painful

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What are nociceptors?

Specialised receptors for painful stimuli

They are free nerve endings

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What are the types of nociceptors and what do they respond to?

Aδ: mechanical stimuli eg cut to skin

C fibres: respond to mechanical, thermal and chemical stimuli

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What activates a nociceptor?

Cell damage which increases potassium, prostaglandin, serotonin and bradykinin levels to activate the nociceptor

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What happens when a nociceptor is activated?

Depolarises the membrane over the threshold allowing generation of an action potential
Substance P is released by nociceptors

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What does substance P do?

Increases capillary permeability

Contributes to inflammation by causing mast cells to release histamine - makes the receptor even more sensitive to stimuli as a protective mechanism to avoid further damage

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How can analgesics have an effect at the site of injury and give examples

Reduce inflammation

NSAIDs which are COX inhibitors
steroids

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Differences between Aδ and C fibres?

type of pain
localisation
threshold
purpose
velocity

Aδ: sharp and stabbing
C: dull, throbbing

Aδ well localised, C is poorly and often does visceral organ pain

Aδ fibres have lower threshold

Aδ: initiates withdrawal reflex
C: shows that tissue damage is occurring

Aδ: myelinated and small so conduction velocity is quicker

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Which tract does pain travel up?

Lateral spinothalamic tract

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What is analgesia?

The inability to perceive pain when tissue damage is occurring

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How can analgesia be induced?

Drugs
Hypnosis
TENS (transcutaneous electrical nerve stimulation)
Natural childbirth techniques
Placebos

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How does the body naturally ‘close the gate’ in pain?

Descending inhibitory neurones inhibit laminae I and V directly and indirectly (via SG) by using endogenous opioids and other neurotransmitters.

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Name some endogenous analgesics

Enkephalins
Endorphins
Dynorphins
Endomorphins

What are the opiate receptors?

μ mop
δ dop
κ kop
Nociceptin

What are some antagonists of opiate receptors?

Naloxone

What are some agonists of opiate receptors?

Morphine
Codeine
Heroin

How do local anaesthetics work?

Inhibit voltage-dependent sodium channel activity which stops transmission to the CNS
Sit inside sodium channels, stopping transmission of the action potential and stabilising the membrane

What do thalamocortical projections carry?

Information on location, intensity and nature of pain

Via which system is the emotional response to pain?

The limbic system

What does the stress response to pain travel via?

The hypothalamus

Where does the lateral spinothalamic tract decussate? Where does it travel?

At the level of the spinal cord it enters | Up through the midbrain and thalamus to the post-central gyrus of the cerebral cortex

Where do Aδ and C fibres enter the spinal cord?

At the apex of the dorsal horn

Which fibres go through the substantia gelatinosa?

C fibres

What do visceral fibres do when they enter the spinal cord and what is the consequence?

Visceral fibres coverage on the spinal cord second order neurones shared by somatic nociceptive fibres and feel the pain in that dermatome

Which neurotransmitters are involved in the transmission of pain through the spinal cord?

Glutamate and substance P which excite second order neurones

Where are opiate receptors found?

On terminals of the central processes of first-order nociceptive dorsal root ganglion neurones (pre-synaptic opiate receptors) On dendrites of second order spinothalamic neurones (post-synaptic)

What analgesics can be used in morphine-tolerant patients?

Baclofen (GABA) antagonist Anti-depressants Anti-convulsants Somatostatin

What is pain?

An unpleasant sensation and emotional experience associated with actual or potential tissue damage

What is the difference between the direct and indirect pathway of pain?

Direct is the main pain pathway Indirect is the pathway involved in the affective aspect of pain ie the response. It is much slower

What are the four main pathways involved in the indirect pathway?

Spinoreticular: arousal and wakefulness Spinomesencephalic: activation of descending inhibition and emotional Spinotectal: reflexes of eyes, upper body and head Spinohypothalamic: autonomic and endocrine responses

What happens to pain fibres when they enter spinal cord?

Enter laminae I, II and V I and V synapse with second-order neurones Fibres in II (the substantia gelatinosa) will be involved in modulation of the pain stimulus They then decussate to other side

Where do pain fibres of the face go?

They enter the trigeminothalamic system

How is pain modulated by the substantia gelatinosa?

Acts negatively on laminae I and V to inhibit nociceptive impulses

How can the effect of the substantia gelatinosa itself be modulated?

Aδ and C fibres can act on the SG to inhibit its inhibitory signal on I and V, resulting in positive effect of the pain impulse Mechanoreceptors, via Aβ fibres, can increase its inhibitory effect, so rubbing the damaged area can reduce the pain felt

Where do the descending inhibitory neurones arise from? Where do they receive their stimulus from?

Periaqueductal grey matter (PAG) of the brain Stimulated by the cortex and hypothalamus

How does the PAG activate inhibitory neurones?

PAG consists of cells sensitive to opioid neuropeptides and stimulation of this area will have an analgesic effect PAG stimulates the nucleus raphe magnus, sending inhibitory neurones down to laminae I and V

What is a mixed nerve?

Contains a variety of different nerve fibres, which can vary in diameter, myelinated or demyelinated, different modalities

What does a compound action potential show and how?

The different nerves present in a mixed cell by showing the varying conduction speeds Fastest nerves appear in A waves (larger or myelinated or both) C wave is smaller, unmyelinated neurones

What can a compound action potential be used to highlight?

Conditions such as MS where there is demyelination of neurones, affecting their conduction velocities