Pain in animals Flashcards
Define pain?
An unpleasant sensory and emotional experience associated with actual or potential tissue damage
Define noxious stimulus?
A stimulus that actually or potentially damages tissue, or is of quality or intensity to trigger nociceptive reactions
Define pain threshold?
The least amount of pain that a subject can recognise.
Relatively constant among species and individuals
Define pain tolerance?
Greatest level of pain that a subject will tolerate.
Varies considerably
Define nociception
Neurophysiological term denoting specific activity in nerve pathways.
The transmission mechanism for physiological pain
Characterise acute pain
Arises quickly
Can be severe
Short duration
Often fast and sharp, followed by aching pain
Centralised in one area, before becoming spread out
Responds well to medications
Characterise chronic pain
Pain persisting for longer than is associated with the particular injury.
A constant or intermittent pain that has outlived its purpose
Often more difficult to treat
Often caused by improper treatment of acute pain
Classifications of physical pain
- Cutaneous
- Somatic
- Visceral
- Phantom limb
- Neuropathic
- Central
Describe cutaneous
- Caused by
- Nociceptors
- Aetiology
Caused by injury to skin or superficial tissue
Cutaneoud nociceptors, terminating just below the skin
From things such as paper cuts, first degree burns and lacerations
Describe somatic pain
- Originates from
- Nociceptors
- Aetiology
Originates from ligaments, tendons, bones, blood vessels and nerves
Nociceptors - somatic, causing diffuse and prolonged pain
Aetiology - sprains and broken bones
Describe visceral pain
- Originates from
- Nociceptors
- Aetiology
Originates from organs
Nociceptors - visceral (i.e. within the organs or internal cavities) causing prolonged and diffuse pain
Aetiology - myocardial ischaemia
Describe phantom limb
Sensation of pain from a limb that has been lost. e.g. in amputees
Describe neuropathic pain
Due to injury of the nerve tissue itself.
Causes prolonged burning pain, allodynia, hyperpathia
Often combined with vasomotor dysfunction
Define allodynia
Pain caused by a stimulus that does not normally evoke a response
What causes central pain?
CNS lesions
Physiological processes of pain
- transduction
- transmission
- modulation
- integration
Transduction of pain
When the noxious stimuli is converted into an electrical signal by nociceptors
- alpha-delta
- c-polymodal
- visceral
Transmission of pain
- Afferent sensory fibres
- spinal cord
- synapse with 2nd order neurones
- ascending neurones in thalamus
- brainstem
- somatosensory cortex
Modulation of pain
Using neurotransmitters such as:
- glutamate and asparate
- COX, prostaglandins
Integration of pain
Electrochemical events combined with the unique psychology of the individual
Determines how they perceive the pain
Describe the phenomenon of “wind up”
Repetitive noxious stimulation results in a change of dorsal horn cells.
Reactivity progressively increases, due to a decrease in the response threshold, resulting in hypersensitivity
Variables affecting pain dynamic?
Age of animal
Species
Tissue type
Pre-existance of pain
Physiological changes induced by pain
Hyperventilation Increased cardiac output, blood pressure, and oxygen consumption Increased blood glucose Increased temperature Increased clotting time and platelet aggregation Vasoconstriction - ischaemia Renal failure SHOCK
