Physiology - Fractures and Dislocation Flashcards by Jasmine Sappor

Nociceptors

Peripheral receptors of pain (noxious stimuli)

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Types of nociceptors

Mechanical nociceptors
Polymodal nociceptors
Thermal nociceptors

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Mechanical nociceptors

Stimulated by intense pressure

Have fast conducting myelination - give rise to sharp fast (1st) pain (localised)

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Polymodal nociceptors

Respond to multiple stimuli

Afferents are C fibres

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C fibres

Slower than A delta fibres - unmyelinated
Result in slow (2nd) pain - aching or burning natures
High threshold thermo, mechano and chemical receptors

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Thermal nociceptors

C fibre afferents

Respond to extremes of hot and cold

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Primary hyperalgesia

Occurs within areas of damaged tissue

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Secondary hyperalgesia

Occurs ~ 20mins after an injury, tissues surrounding a damaged area may become supersensitive

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What is pain proportionate to

Nociceptive input

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Pain pathways

A delta and C fibres enter dorsal horn and interact w/ projection neurons
Ascension via spinothalamic tract to thalamus
3rd order neurons project and terminate in the 1’ somatosensory centre - determine which region of body is experiencing pain

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Limbic cortex

Emotional centre

Tells us pain is unpleasant and concerning

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Molecular sensor for noxious heat stimuli

TRPV1 (capsaicin - chilli)

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Molecular sensor for noxious mechanical stimuli

TRPA1
TRPV4
Piezo

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Molecular sensor for noxious chemical stimuli

ASIC
TRPA1
TRPV1

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Molecular sensors for noxious cold stimuli

TRPM8 (menthol)

TRPA1

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Molecular sensor for ATP

ATP comes from damaged tissue

P2X3

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What happens when molecular sensor channels have been opened

Triggers an influx of Na+ —-> causing an action potential

Mediated by Na channels (1.8 and 1.9)

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Where do projection neurons cross to

Cross to diagonal side of dorsal horn (ventral aspect)

Anatomy of pain pathways

Transduction
Transmission
Modulation
Perception

Transduction

Conversion of noxious stimuli into electrical energy

Transmission

Electrical stimulus is sent to the dorsal horn of the spinal cord and synapse at the 2nd order neuron

Modulation

Inhibition vs amplification of signal (facilitated by EAA)

Inflammatory soup

ATP
Bradykinin
PGE2
Serotonin
Histamines
COX-2 activation
Substance P

PGE2

Prostaglandins

NGF

Nerve growth factor

What happens during transduction

Afferent fibres enter into dorsal horn and transmit signal to WDR neurons at diff laminae

WDR neurons

Wide Dynamic Range neurones Receive stimulation from both small diameter and big diameter fibres Found in lamina V

EAA

Excitatory Amino Acids

Endogenous relievers of pain

Opioids Gate theory (TENS) NSAIDs Local anaesthetic

How do opioids work as an endogenous relievers of pain

Produce analgesia via binding and acting on opioid receptors causing body to produce endorphins - inhibit ascending pathway

Types of pain

Physiological (nociceptive) pain Pathological (neuropathic) pain Psychogenic pain

Pathological pain

Caused by damage of nerve pathway

Psychogenic pathway

In depression and anxiety

Main pain gates

Spinal gate Brain stem gate Thalamic gate

Gate control theory

Concurrent activity in large-diameter (Aβ) primary afferents reduces the transmission of pain signals in small-diameter (Aδ and C) afferents due to inhibitory neuron at lamina II Explains why rubbing skin (exciting tactile and pressure receptors) relieves pain

Spinoreticular pathway

Ascension tract for pain detected by C fibres

Where do pain pathways pass before reaching thalamus

Medulla, pons and midbrain | Spinothalamic and spinoreticular pathways cross at diff levels

A- alpha fibres

Motor neurones

A-beta fibres

Large diameter fibres | Transmit info about touch and pressure - mechanoceptor

When is infl soup released

In response to injury form leaky blood vessels and damaged tissues Directly excites nociceptors or makes them more sensitive to other agents

NSAIDs pain relieving mechanisms

Inhibit COX enzymes - no PGE2 or leukotrienes produced

Local anaesthetic pain relieving mechanism

Reversibly blocks the conduction of action potentials by blocking Na+ channels on axon

Stimulation of inhibitory interneuron at lamina II

Stimulated by A-beta fibres