Helmut Segner Fish Nociception and pain A biological perspective

archi- and palaeo cortex. In humans, the neocortex is involved in
higher functions such as sensory perception (including pain), generation
of purposive motor commands, spatial reasoning, conscious
thought and language. The neocortex is folded to accomodate its
increasing volume. The folds are called gyri, and the grooves in
between are designated as sulci. The cortex is anatomically subdivided
into frontal, temporal, parietal and occipital lobes, and it
contains many subregions with distinct functions, e. g., the cingulate
cortex which is located close to the corpus callosum, or the
primary somatosensory cortex in the frontal lobe.
The diencephalon includes (i) the ventral hypothalamus, with a
number of neurosecretory functions and intimate relationship to
the hypophysis or pituitary land, (ii) the dorsal epithalamus, with
the pineal gland which secretes melatonin, and (iii), the thalamus,
which basically represents the lateral walls of the diencephalons.
The diencephalon also houses the chiasma opticum.
The metencephalon contains as a prominent structure the
cerebellum. This brain part is important for equilibrium, and it
processes information pertaining to touch, vision, hearing, proprioreception
and motor information from higher centres. The
cerebellum modifies, refines and monitors motor activity, but it
does not initiate it. An important pathway of information exchange
between cortex and cerebellum is the pons. Often, the midbrain
structures cerebellum and pons, together with the medulla, are
designated as brainstem; the brainstem connects the cerebellum
with the spinal cord, and it controls autonomic functions of the
peripheral nervous system.
The myelencephalon contains the nuclei of a number of cranial
nerves, and the medulla oblongata, which operates primarily at the
reflex level. Information arriving via ascendent projections is partly
processed in the medulla, and, vice versa, efferent output to adjust
visceral or reflexive motor activity is initiated here.
A brain component that is frequently mentioned in the context
of pain perception is the limbic system. It is not an anatomically
discrete region but represents a functional association between several
cortical and subcortical centers. There is no generally accepted
definition which brain structures constitute the limbic system but
most frequently the following structures are included: insular and
cingulate cortex, thalamus, hypothalamus, hippocampus, amygda-
Figure 3: Schematic of ascending
pathways, subcortical structures,
and cerebral cortical structures
involved in pain perception.
(Modified from Price, 2000)
PAG periaque ductal gray,
PB parabrachial nucleus of the
dorsolateral pons,
VMpo ventromedial part
of the posterior nuclear complex
of the thalamus,
MDvc ventrocaudal part of the
medial dorsal nucleus of the thalamus,
VPL ventroposterior lateral
nucleus of the thalamus,
ACC anterior cingulate cortex,
PCC posterior cingulate cortex,
HT hypothalamus,
S1 and S2 primary and secondary
somatosensory cortical areas,
PPC posterior parietal complex,
SMA supplementary motor area,
AMYG amygdala,
PF prefrontal cortex.
22 Fish. Nociception and pain | Contributions to Ethics and Biotechnology
Fish. Nociception and pain | Contributions to Ethics and Biotechnology
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