Physiology and Pathophysiology of Pain Flashcards by Robbie Pollock

What is pain?

Pain is an unpleasant sensory and emotional experience which we primarily associate with tissue damage or describe in terms of such damage or both

Is not a stimulus

Final product of complex-information processing network

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What are the steps in the pain pathway?

Step 1. Periphery

Detection
Transmission to spinal cord (first order neurons)

Step 2. Spinal cord

Processing
Transmission to brain (Thalamus) (second order neurons)

Step 3. Brain

• Perception, learning, response

Step 4. Modulation

• Descending tracts

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What does the thalamus do?

Recieves all sensory information then sends it to all different parts of the brain

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What is nociception?

The detection of tissue damage by specialized transducers connected to A-delta and C fibers

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What are nociceptors and what do they respond to?

Free nerve endings of A delta and C-fibres

Respond to thermal, chemical, mechanical noxious stimuli

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Where is the cell body of primary afferents/1st order neurons located and where do they synapse?

Cell body in Dorsal root ganglion

First order neurons

Synapse at spinal cord

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Describe the features of the different types of fibres

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Are C fibres myleinated and therefroe do they conduct fast or slow?

non-myelinated

conduct slowly

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What do axons entering the spinal dorsal horn continue as?

tracts

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What is the spinothalamic tract?

Major ascending tract for nociception

Arises in Rexed Lamina 2 & 5

Forms the lateral spinothalamic tract

Ends in:

Ventroposterior thalamic nuclei

Medial thalamus

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Thalamus is the second ___________

Thalamus is the second relay station

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Where does the thalamus have connections with?

cortex

limbic system

brain stem

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Where is the main area in the thalamus that spinothalamic tracts go?

Ventroposterior thalamic nuclei

Medial thalamus

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Pain perception occurs in ________________

Pain perception occurs in somatosensory cortex

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Why does the thalamus send information about pain to the limbic system?

to help form memories, learning and emotion

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Descending pathways come form the brain to ______

dorsal horn

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What do the descending pathways do to the pain signal

usually decrease it

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What is allodynia?

Allodynia refers to central pain sensitization (increased response of neurons) following normally non-painful, often repetitive, stimulation. Allodynia can lead to the triggering of a pain response from stimuli which do not normally provoke pain

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What is A?

Defnition of Allodynia

Decreased threshold for response

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What is B?

Definition of Hyperalgesia

Exaggerated response to normal and supranormal stimuli

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What is C?

Definition of Spontaneous Pain

Spontaneous activity in nerve fibres

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What is Central sensitization?

Central sensitization is a condition of the nervous system that is associated with the development and maintenance of chronic pain

It is the response of second order neurons in the CNS to normal input both noxious & non-noxious

What are the 3 main components of Central sensitization?

wind-up

classical

long-term potentiation

What is wind up central sensitisation?

Involves only activated synapses

Homosynaptic activity dependent progressive increase in response of the neurons

Manifests over the course of stimuli & terminates with stimuli

Wind-up is literally winding up the response to the input. So the wind-up happens only in neurons taking part in the synapses with primary afferent input. It is activity dependent; progressively increases the response of the neurons

What is classic central sensitisation?

Involves opening up of new synapses (silent nociceptors) the new synapses, which were silent till then, will start to receive input and record the nociception Heterosynaptic activity dependent plasticity Immediate onset with appropriate stimuli Outlast the initial stimuli duration Can be maintained even at low levels of ongoing stimuli

What is long-term potentiation central sensitisation?

Involves mainly the activated synapses Occurs primarily for very intense stimuli a persistent strengthening of synapses based on recent patterns of activity. These are patterns of synaptic activity that produce a long-lasting increase in signal transmission between two neurons

What are the features of acute pain?

\<1 month Usually obvious tissue damage Increased nervous system activity Pain resolves upon healing Serves a protective function

What are the features of chronic pain?

\>3-6 months Pain for 3–6 months or more Pain beyond expected period of healing Usually has no protective function Degrades health and function

Differences between acute and chronic pain: pathological or physiological?

acute - physiological chronic - pathological

Differences between acute and chronic pain: presence of noxious stimuli or not

acute - Presence of noxious stimuli chronic - Presence of noxious stimuli is not essential

Differences between acute and chronic pain: what is the purpose?

acute - Serves protective function chronic - Does not serve any purpose

Differences between acute and chronic pain: what controls it?

acute - Usually nociceptive chronic - Nociceptive, neuropathic or mixed

What is nociceptive pain?

A sensory experience that occurs when specific peripheral sensory neurones (nociceptors) respond to noxious stimuli

Painful region is typically localised at the _______ -often described as throbbing, aching or stiffness

site of injury

Nociceptive pain is usually ______ limited and resolves when ___________ heals (e.g. bone fractures, burns and bruises) Can also be _______ (e.g. osteoarthritis)

Usually **_time_** limited and resolves when **_damaged tissue_** heals (e.g. bone fractures, burns and bruises) Can also be **_chronic_** (e.g. osteoarthritis)

What does nociceptive pain tend to respond to?

Tends to respond to conventional analgesics

What is neuropathic pain?

Pain initiated or caused by a primary lesion or dysfunction in the somato-sensory nervous system

Where is neuropathetic pain felt?

The painful region may not necessarily be the same as the site of injury - pain occurs in the neurological territory of the affected structure (nerve, root, spinal cord, brain)

Does neuropathic pain tend to be a chronic or an acute condition?

Almost always a chronic condition (e.g. postherpetic neuralgia [PHN], poststroke pain)

How does neuropathic pain respond to conventional analgesics?

Responds poorly to conventional analgesics

What is nociplastic pain?

Pain that arises form altered nociception despite no clear evidence of actual or threated tissue damage causing the activation of peripheral nociceptors or evidence for disease or lesion of the somatosensory system causing the pain

Does nociplastic pain depend on a stimulus?

no stimulus independent

In nociplastic pain is there any injury or structural neuronal damage?

No inflammation/injury No structural neuronal damage

What is nociplastic pain due to?

due to central plasticity - Neural plasticity refers to the ability of neurons to change in form and function in response to alterations in their environment

Does nociplastic pain have any function?

serves no protective or adaptive function

Is nociplastic pain pathological or physiologic pain?

pathological

What can be used in the management of transduction of pain?

NSAIDs Ice Rest LA blocks Nerve blocks Drugs e.g. opioids Surgery

What is the gate control theory?

The gate control theory of pain asserts that non-painful input closes the nerve "gates" to painful input, which prevents pain sensation from traveling to the central nervous system. Gate Control Theory of Pain describes how non-painful sensations can override and reduce painful sensations

What is used in the management of perception of pain?

Education Cognitive behavioural therapy Distraction Relaxation Graded motor imagery Mirror box therapy - helps allivate phantom limb pain a box with a mirror down the center, patient places the good limb into one side and the residual limb into the other and patient then looks into the mirror on the side with the good limb and makes "mirror symmetric" movements. Because the subject is seeing the reflected image of the good hand moving, it appears as if the phantom limb is also moving

What can be used in the management of descending modulation in pain? (if the input of pain cant be contorlled then this is how pain would be contorlled)

Placebos Drugs - Opioids, Antidepressants Surgery - Spinal cord stimulation

Pain is a _________ phenomena while nociception is the _________ process

Pain is a **_subjective_** phenomena while nociception is the **_physiologic_** process

Pain is subjected to \_\_\_\_\_\_\_\_\_\_\_at every stage of transmission (this can be used to our advantage)

Pain is subjected to **_modulation_** at every stage of transmission (this can be used to our advantage)

Does chronic pain serve any protective function?