Page 12 - BSAVA Guide to Pain Management in Small Animal Practice

2 | Physiology of pain

VetBooks.ir potent, for example, being able to run from a variety of nociceptive centres in the brain.
life threatening situation with a fractured femur,
igher cortical centres, including the anterior
cingulate, insular and prefrontal cortices, as
which is termed stress induced analgesia .
any descending transmitters are involved well as the amygdala, hippocampus and parts
in modulating dorsal horn responsiveness but of the limbic system, all play a role in the
of particular interest are serotonin pro a ective component of pain in humans
nociceptive and a component of central igure . and all are present in dogs, cats and
sensiti ation and norepinephrine, which is the other mammals.
ma or transmitter involved in descending
inhibition of pain transmission at the spinal level. Location or Function or role
Norepinephrine is released from brainstem structure
nuclei especially the NR and acts Anterior Role in anxiety, anticipation of
predominantly at adrenoceptor spinal cord cingulate pain, attention to pain, and motor
receptors, inhibiting transmitter release from cortex responses
primary a erent neurons and suppressing ring Insular cortex Potential role in the sensory
of pro ection neurons. discriminative and a ective
aspects of pain that contribute to
behavioural aspects of pain must also be the negative emotional responses
and behaviours associated with
considered. Perception refers to the sub ective painful stimuli
experience of pain that results from the
interaction of transduction, transmission, Prefrontal Role in sensory integration,
decision making, memory
cortex
modulation, and the psychological aspects of retrieval, and attention processing
the individual. Although well studied in human in relation to pain
medicine, this is an area that is di cult to Amygdala, Role in the formation and storage
elucidate in veterinary patients due to their hippocampus, of memories associated with
non verbal status. eneral anaesthesia, whilst and other parts emotional events, which a ect
not analgesic per se, acts on perception by of the limbic arousal and attention to pain and
decreasing overall awareness, thereby system learning. he limbic system may
eliminating the sensory component of pain. also be partially responsible for
the fear that accompanies pain
It is recogni ed that fear and anxiety
increase pain perception and that pain can 3 he role of higher cortical centres in the
a ective component of pain Cohen and
cause fear and anxiety. here are many plastic ao, .
connections between pain pathways and
neuro endocrine, limbic pain, pleasure,
autonomic components and withdrawal Additional features of
re exes. In addition, the cortex responds to pain physiology
pain, giving rise to the behavioural component
that can be assessed by validated small animal Visceral pain di ers from somatic pain as pain
pain scales see below . from viscera is poorly locali ed. his is because
Although the degree is not as completely viscera are innervated by very few nociceptors
elucidated in animals as in humans, there is no C bres but with large overlapping receptive
uestion that pain has an a ective component. elds and a graded response to stimulation,
A ective behaviours are generally easily although there are many mechanoreceptors
observed by pet owners and can be assessed present that respond to distension. Referred
uanti ed using uality of life oL scales in pain is common visceral a erents synapse on
dogs, cats and other mammals. his is not a spinal cord segments, which also receive inputs
surprise, in that pain is a multidimensional from speci c somatic areas, a typical human
experience that is not purely physiological. he example being arm pain in angina. his is
a ective components are likely mediated at a termed somato visceral convergence and is

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