Page 10 - BSAVA Guide to Pain Management in Small Animal Practice

2 | Physiology of pain

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ASIC,
Chemical Purinergic,
stimuli Bradykinin,
Adrenaline
transducers
Mechano-
Mechanical sensitive Membrane
stimuli ion channels depolarization Action potential
TRPV,
Thermal TRPM8,
stimuli TRPA1
transducers
Sodium channels
Calcium channels Voltage-gated
channels
Potassium channels
iagram of a nociceptor terminal illustrating various transducers sensitive to noxious stimuli and ion
channels. In ux of calcium and sodium ions in su cient concentration will cause an action potential
along the nerve axon. Potassium ions are usually inhibitory. ASIC acid sending ion channels; RPA transient
receptor potential ankyrin ; RP transient receptor potential cation channel subfamily member ;
RPV transient receptor potential channel subfamily V.
uliane eubner, University of Saskatchewan, Canada

Nociception is a term fre uently used and
can be considered to be physiological pain , To thalamus
which is not necessarily perceived as pain. or
example, anaestheti ed patients with
inade uate analgesia will often show marked
increases in heart rate and respiratory rate
during surgery, yet be unaware of the surgery
because they are anaestheti ed. his represents
activation of the pain pathways without
conscious perception of the pain and steps
should be taken to provide analgesia to avoid
pain perception in recovery.
Transmission is the process by which
impulses are sent via primary a erent nerves to
the dorsal horn of the spinal cord igure . ,
and then along the sensory tracts to the brain. Spinothalamic
he transmission from the dorsal horn to the tract
brain is sometimes termed projection. As iagram of a transverse section of
previously mentioned, there are two ma or the spinal cord, illustrating the central
bres transmitting to the spinal cord. Aδ bres terminals of the rst order A green , Aδ orange
are smaller diameter, thinly myelinated fast and C red neurons within the dorsal horn of the grey
matter. he numerals represent the position of the
transmitting bres carrying thermal terminals in Rexed s laminae of the spinal cord.
mechanical information responsible for the uliane eubner, University of Saskatchewan, Canada
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