illness processes. Chapter 3 describes the key theoretical approaches to stress and
evaluates the research evidence concerning the links between stressors and illness and
between stressors and health behaviour. Psychological factors such as stress can affect
health directly, through autonomic and neuroendocrine changes but also indirectly,
through changes in health behaviours. The direct effects of stress on health outcomes
are known as psychophysiological pathways, while the indirect effects are known as
behavioural pathways.
The role of the nervous system is to allow us to adapt to changes both within our
body and our environment. It consists of the brain, the spinal cord and billions of
nerves. The brain is the central part of the nervous system and consists of three major
components: the forebrain, the midbrain and the hindbrain. The forebrain is divided
into two main subdivisions: 1) the telencephalon, which comprises the cerebrum and
the limbic system; and 2) the diencephalon, which is composed of the thalamus
and hypothalamus. The midbrain consists of two major parts: the tectum and the
tegmen tum. Similarly, the hindbrain has two major divisions: the metencephalon and
the myelencephalon.
The nervous system is divided into the central nervous system (CNS) and the
peripheral nervous system (PNS). The CNS comprises the brain and spinal cord
whereas the PNS is a network of nerves that connects the brain and spinal cord to the
rest of the body. An important part of the PNS is the autonomic nervous system (ANS)
that has a sympathetic division and a parasympathetic division. The former mobilizes
bodily processes (e.g. increases heart rate), whereas the latter restores the body’s energy
resources.
Two response systems are activated when we experience stress. The first and easiest
to activate is the sympathetic adrenal medullary (SAM) system; the second is the
hypothalamic–pituitary–adrenal (HPA) axis response system. The SAM system leads
to the release of the adrenaline and noradrenaline that put the body on alert; the HPA
axis response system leads to the release of the stress hormone, cortisol. The stress
response has been found to impact negatively on a number of health outcomes such
as cardiovascular disease. Excessive wear and tear of the cardiovascular system through
repeated activation of the stress response may increase the development of athero -
sclerosis and increase the likelihood of myocardial infarction and stroke.
Psychological factors can play a role in the perception of pain. Early theories of pain
were mechanistic and did not account for the influence of cognitive, emotional and
social factors. Gate-control theory, introduced by Melzack and Wall (1965), proposes
that a neural gate in the spinal cord receives signals from pain fibres at the site of injury,
other peripheral fibres and messages descending from the brain. The degree to which
the gate opens (leading to experience of pain) is determined by the combined effects
of these three factors. Gate-control theory was extended by Melzack and is known
as the neuromatrix theory of pain. This theory contends that the pain experience is
governed by the body–self neuromatrix.
The human body has the capacity to mount two types of defence known as cell-
mediated immunity and antibody-mediated immunity. Psychological factors such as
stress have been found to influence these immune functions. A number of researchers
have shown stress to be associated with increased susceptibility to infectious illnesses
and the slowing down of wound healing.
BIOPSYCHOSOCIAL PATHWAYS 37