Notes taken from Physiology for Nursing Practice (1999) Hinchcliffe, S. Montague, S. Watson, R. 2nd Edition, London; Harcourt Brace and Company Ltd and Pathophysiology The Biologic Basis for Disease in Adults and Children (2010) McCance, K.L., Huether, S. E., Brashers, V., Rote, N. S., Missouri; Mosby Inc
As a protective mechanism pain does have some shortcomings:
Irradiation can cause extensive
tissue damage but is not illicit pain
at the time of stimulation
The pain of sunburn does not serve as a warning
function but occurs after thevent
Pain associated with cancers does
generally not occur until the cancer is very
extensive
The location and intensity of
the pain stimulus will affect the
quality and severity of the
perceived pain
Known as the Specificity Theory, Rene Descartes,
generally correct when applied to certain types of injury
and the acute pain associated with them.
Does not allow for
psychologic
contributions, such as
prior experience of
pain, and emotions.
Pain signals are transmitted in
myelinated A Delta and unmyelinated C
fibres
These are ascending tracts and
carry sensory information from
the periphery to the different
areas of the brain, such as the
cerebral cortext, cerebellum and
brain stem
The ascending sensory pathways can be divided into:
Dorsal column medial lemniscal pathway
Mediate tactile and
kinaesthetic information which
is highly discriminatory and
can be precisely localised
A Delta fibres are
thought to cause
sharp pricking
sensations
Faster conducting
Known as epicritic
Spinothalamic tract
Transmits important
information concerning
pain and temperature
but poor localisation
and poor discrimination
of the stimulus
C Fibres are
thought to
transmit duller
burning or aching
sensation
Slower conducting
Known as protopathic
The thalamic nuclei influence the
conscious appreciation of pain
Substance P is a
neurotransmitter or
neuromodulator identified
in various parts of the NS
including the substantia
gelatinosa of the dorsal
horn
Noxious stimulation causes the
release of substance P from dorsal
root afferents
Other peptides seem to posess
anelgesic properties; these endogenous
substances act similar to morphine,
known as enkephalins and endorphins
Discovered by Hughes et al., 1975
Enkephalins and endorphin
existance goes some way to
explaining the phenomena of
Placebo Response, where an
individual percieves pain relief even
though no anelgesic agent is
administerd
The expectation of pain relief is sufficent to
release psychogenically the endogenous
opiates
These endogenous opiates have been shown to inhibit
prostaglandin formation, prostaglandins are considered
chemical stimuli for pain
Have been shown to inhibit
the actions of a number of
transmitters including
substance P