Helmut Segner Fish Nociception and pain A biological perspective

2. Nociception and pain perception in man
ception in fish. The discussion will focus on acute pain, neglecting
other aspects of pain such as chronic pain or the modulation of
pain experience by psychological factors, for instance, individual
attitudes and beliefs.
Pain perception in man is a sensation that results from three major
steps (Figure 1):
• peripheral nociception, that is the sensing of noxious stimuli in
peripheral organs such as skin, viscera, etc.,
• processing of nociceptive information at the spinal cord level,
and transmission to the brain,
• processing of the nociceptive information in the brain.
It is this processing of nociceptive message in the brain that turns
the nociceptive signal into the sensation we perceive as “pain”. Pain
arises from the integration of a sensory-discriminative component,
which records intensity, location, and modality of the noxious stimuli,
with an affective-cognitive component, which associates the
nociceptive input with cognitive properties (e. g., attention, memory)
and with emotional properties (e. g., fear, unpleasantness)
(Millan 1999, Peyron et al. 2000). As formulated by Tracey (2005),
pain is “an interpretation of the nociceptive input influenced by
memories, emotional, pathological and cognitive factors”.
Perceiving pain leads to behavioural pain expression and (protective)
responses. These reactions are governed both by automatic
processes (unintentional/reflexive, for instance, screaming,
vocaling, withdrawal reflex) and controlled processes (intentional/
purposive, for instance, sequences of instrumental motor activity)
(Craig et al. 2010). Neuro-anatomically, these reactions are
anchored in the brainstem (e. g., reticular area, globus pallosa), in
subcortical regions such as thalamus, as well as in the cortex (Rose
2002, Braz et al. 2005).
In the following, the three steps leading from nociception to
pain perception will be discussed with respect to man. This is intended
to provide a basis for discussing nociception and pain per-
ascending
nociceptive
pathways
endogenous
injury
Brain:
nociceptive processing,
pain perception
• cordical
• subcordical
descending
(faciliating/onhibitory)
pathways
Spinal cord:
nociceptive processing
and transmission
nociceptive input
nociceptors
exogenous
noxius stimuli
Figure 1: Schematic overview of key
elements in pain perception:
peripheral nociception, spinal cord
processing and transmission, and
brain processing
14 Fish. Nociception and pain | Contributions to Ethics and Biotechnology
Fish. Nociception and pain | Contributions to Ethics and Biotechnology
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