Page 53 Acute Pain Management
P. 53






(ie
the
site
and
type
of
painful
stimulus).
The
spinoreticular
(spinoparabrachial)
and

spinomesencephalic
tracts
project
to
the
medulla
and
brainstem
and
are
important
for

integrating
nociceptive
information
with
arousal,
homeostatic
and
autonomic
responses
as

well
as
projecting
to
central
areas
mediating
the
emotional
or
affective
component
of
pain.

The
spinoparabrachial
pathway
originates
from
superficial
dorsal
horn
lamina
I
neurons
that

express
the
NK 1
receptor
and
projects
to
the
ventromedial
hypothalamus
and
central
nucleus

of
the
amygdala.
Multiple
further
connections
include
those
with
cortical
areas
involved
in
the

affective
and
motivational
components
of
pain
(eg
anterior
cingulate
cortex,
insular
and

prefrontal
cortex),
projections
back
to
the
periaqueductal
grey
(PAG)
region
of
the
midbrain

and
rostroventromedial
medulla
(RVM),
which
are
crucial
for
fight
or
flight
responses
and

stress‐induced
analgesia,
and
projections
to
the
reticular
formation,
which
are
important
for

the
regulation
of
descending
pathways
to
the
spinal
cord
(see
Figure
1.1)
(Hunt
&
Mantyh,
2001;

Tracey
&
Mantyh,
2007;
Tracey,
2008).


Figure
1.1
 The
main
ascending
and
descending
spinal
pain
pathways
 CHAPTER
1


ASCENDING DESCENDING
PATHWAYS PATHWAYS
cc cc
Hip Hip
Po Po
ic ic
VPM/VPL VPM/VPL
Ce VMH Ce VMH


PAG BRAINSTEM
opioids
clonidine
A7 N 2O
A TCA
5
PB
bc LC
V RVM
PERIPHERY
NSAIDs NERVE CONDUCTION
Py
opioids local anaesthetics
SPINAL CORD
opioids
clonidine
DRG
ketamine
TCA
NSAIDs


Notes:
 (a)
There
are
2
primary
ascending
nociceptive
pathways.
The
spinoparabrachial
pathway
(red)
originates

from
the
superficial
dorsal
horn
and
feeds
areas
of
the
brain
concerned
with
affect.
The
spinothalamic

pathway
(blue)
originates
from
deeper
in
the
dorsal
horn
(lamina
V)
after
receiving
input
from
the

superficial
dorsal
horn
and
predominantly
distributes
nociceptive
information
to
areas
of
the
cortex

concerned
with
discrimination.


 (b)
The
descending
pathway
highlighted
originates
from
the
amygdala
and
hypothalamus
and
terminates
in

the
PAG.
Neurons
project
from
here
to
the
lower
brainstem
and
control
many
of
the
antinociceptive
and

autonomic
responses
that
follow
noxious
stimulation.


 Other
less
prominent
pathways
are
not
illustrated.


 The
site
of
action
of
some
commonly
utilised
analgesics
are
included.

Legend
 A:
adrenergic
nucleus;
bc:
brachium
conjunctivum;
cc:
corpus
collosum;
Ce:
central
nucleus
of
the

amygdala;
DRG:
dorsal
root
ganglion;
Hip:
hippocampus;
ic:
internal
capsule;
LC:
locus
coeruleus;
PAG:

periaqueductal
grey;
PB:
parabrachial
area;
Po:
posterior
group
of
thalamic
nuclei;
Py:
pyramidal
tract;

RVM:
rostroventrmedial
medulla;
V:
ventricle;
VMH:
ventral
medial
nucleus
of
the
hypothalamus;
VPL:

ventral
posterolateral
nucleus
of
the
thalamus;
VPM:
ventral
posteromedial
nucleus
of
the
thalamus

Source:
 Modified
from
Hunt
(Hunt
&
Mantyh,
2001).



 Acute
pain
management:
scientific
evidence
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