Pain Mechanisms - Acute Flashcards
What is pain?
Unpleasant or emotional experience originating in real or potential damaged tissue
What are the 3 systems that interact to produce pain?
Sensory
Motivational
Cognitive
What is somatogenic pain?
Pain with a cause localised in the body tissue
What are the 2 types of somatogenic pain?
Nociceptive pain - stimulation -eg. sunburn
Neuropathic pain - associated with activation of nerves
What is psychogenic pain?
Pain for which there is no known physical cause but processing of info in the CNS is disturbed
What is an example of phychogenic pain?
Headache
Back pain
What is acute pain?
Protective mechanism that alerts the individual that something is causing them harm
What is the time scale for acute pain?
Up to 3 months
What can be the response to acute pain?
Body changes
Increased HR
Increased respiratory rate
Elevated BP
Pallor or flushing
Dilated pupils
What is chronic pain?
Lasts longer than 3 months and extends beyond an acute illness/injury
Cause is unknown
What is an example of acute pain?
Skin abrasions
Deep/soft tissue injury
Bone fractures
Superficial burn
What is an example of chronic pain?
Inflammatory
Neuropathic
Cancer
Migraine
When is pain tolerance decreased?
Repeated exposure
Fatigue, anger, boredom
Sleep deprivation
When is pain tolerance increased?
Alcohol consumption
Medication
Faith
What is the Gate Theory?
Pain is a balance between info travelling into the spinal cord through small nerve fibres and info travelling though large nerve fibres
What does large nerve fibres carry?
Non-nociceptive info
What does small nerve fibres carry?
Nociceptive info
Describe the production pain via the gate theory
Nociceptive impulses travel through C fibres + A-delta to spinal cord
Create synapses, which function as a gate
Stimulation of larger fibre (A-beta) = close the gate
Decreases stimulation of T cells
Decreases transmission of impulses
Decrease pain perception
What are nociceptors?
Free nerve endings
Stimulated by mechanical, chemical + thermal noxae
Where are nociceptors localised?
Muscle, skin + viscera
What are the different fibre types?
A- beta
A- delta
C
Describe C fibres
Smallest
Non-myelinated
Slow transmission
Transmission of dull + diffuse sensations
Describe A-delta
Middle
Myelinated
Pain + touch
Middle transmission
Describe A-beta
Biggest
Myelinated
Touch
Fastest = feel pain straight away
What are the different classes of nociceptors?
TRP - thermal sensitivity
TREK - K+ channel with TRPs
MDEG - Na+ channel
ASICS + DRASICS - H+
Describe simple physiology of pain
Nociceptors are free nerve endings
Signals are transmitted along afferent nerves (part of peripheral NS) to spinal cord
Fibres (C+A)
Travel to CNS in spinal cord
Then to the brain (thalamus + cortex) = pain perceived
Summary of nociceptive transduction
Acute pain = depolarisation of DH neurons
Excitation via glutamate (AMPA) + SP (NK1R) receptors
What are the 3 neuronal types in the superficial dorsal horn?
Projection neurons
Excitatory interneurons
Inhibitory interneurons
What can each neuron in the SDH receive?
Inputs from A-delta + C fibres
What happens from the spinal cord?
2nd afferent neurons transmit impulse from SG to other side of cord
Through ventral + lateral horn
Impulse carried to spinothalamic tract to the brain
Describe the mechanism of the efferent analgesic system
Pain afferents stimulate neurons in periaqueductal gray (PAG)
= activation of efferent anti-nociceptive pathway
Impulse transmitted to dorsal horn
= block transmission of nociceptive signals
What is the afferent portion composed of?
Nociceptors
Afferent nerve fibres
Spinal cord network
Terminate in dorsal horn
What does the 2nd afferent neuron create?
Spinal part of afferent system
What is the portion of CNS involved?
Limbic signal
Reticular formation
Thalamus
Hypothalamus
Cortex
