Emotional processing and cognitive abilities develop over time,
which may infuence pain coping mechanisms
Infants and young children have not yet developed these
coping strategies and therefore they express pain differently
• The spinal cord is the link between the brain and other organs of the body.
• The peripheral nervous system consists of all the sensory and motor nerve networks
that link the central nervous system with the periphery, for example, the skin, muscles,
glands and organs.
The two cell types unique to the nervous system are the neurone (nerve cell) and the
dendrite (glial cell), which support the functions of neurones. The neurone has a highly
specialised structure that enables information to be received from sensory receptors and
transmitted to effector organs such as muscles. Neurones consist of a cell body from
which several processes appear (Figure 2.1). Dendrites receive information, which is
transmitted to the cell body. The axon or nerve ?bre carries information away from the
cell body to the effector organ.
There are three types of neurones:
1. Afferent or sensory neurones transmit nerve impulses from peripheral receptors to the
central nervous system.
2. Efferent or motor neurones transmit nerve impulses away from the spinal cord to the
effector organs.
3. Interneurones integrate information within the central nervous system.
The most important feature of a neurone is the ability to generate and conduct nerve
impulses, which enables information to travel around the central nervous system. Before
a sensory signal can be relayed to the nervous system it must be converted into a nerve
impulse in an axon. This involves a process of opening ion channels in the neurone's cell
membrane in response to stimuli. The disruption of the ion concentration outside and
inside the cell membrane causes an ionic current ?ow, creating a nerve impulse (Waugh
and Grant 2006; Longstaff 2005; Swenson 2006).
Once activated, the speed of a nerve impulse is independent of the stimulus strength
and is determined by the presence or absence of myelin, the diameter of the nerve ?bre
and body temperature. Myelin is a fatty substance that wraps round the axons of cer-
tain neurones and speeds up the nerve impulse. Nerve myelination begins from about
22 weeks of gestation in the spinal cord and slightly later in the brain. The process
continues postnatally and is thought not to be complete until adult life (Padgett 2006).
There are two types of nociceptive ?bres: A-delta ?bres and C ?bres, which are primarily
responsible for pain transmission:
• A-delta ?bres have a large diameter, are myelinated, have fast impulse speeds
and pro-duce sensations that are well localised and sharp.
• C ?bres have a smaller diameter, are unmyelinated, have slower impulse speeds and
produce sensations that are poorly localised, diffuse, aching and dull.
A series of actions occur when a neurone receives a painful stimuli, which are outlined
in Box 2.1.