Bitumen battles – the phenomenon of road rage
Box 1| Hormonal hotheads – stress and the human nervous system
We can’t consciously control everything our bodies do. An example of this is our heart – luckily for us, it keeps on beating without us thinking about it. Moreover, it speeds up when our body needs extra blood (such as when we are exercising) and slows down when we are at rest.
Bodily functions such as this are regulated by what is known as the autonomic nervous system, which is part of the peripheral nervous system.
The autonomic nervous system is subdivided into the parasympathetic nervous system and the sympathetic nervous system. One of the roles of the sympathetic nervous system is to stimulate the release of stress hormones when we are faced with an imminent threat. These hormones prepare us for what has been dubbed the ‘flight or fight’ response – should we run away from the danger, or should we confront it? Either way, the sympathetic nervous system ensures that our bodies can flee as fast or fight as hard as humanly possible.
Effects of stress hormones
How does our nervous system do this? First, the danger must be recognised. In prehistoric times threats might have been posed by a hungry man-eating animal or by an attack from a rival tribe. These days it might be, for example, a negligent driver on the road who is perceived to threaten our wellbeing or status. We see the danger and our brain (subconsciously) triggers a chemical chain reaction.
The limbic system, a network of neurons in the brain, is involved with emotions such as fear and rage. One part of the limbic system, the amygdala, appears to be responsible for interpreting sensory information (eg, seeing a negligent driver) and sending appropriate messages to the hypothalamus. The hypothalamus releases neurotransmitters that stimulate the adrenal medullae – parts of the adrenal glands situated at the top of the kidneys – to release the hormones adrenaline and noradrenaline into the bloodstream. Collectively, these hormones have the effect of:
- making the heart beat faster (thereby supplying more blood and thus more energy and
oxygen to the cells);
- raising blood pressure by constricting blood vessels (except those in the heart, lungs
and some other key parts of the body);
- dilating (widening) the pupils, thereby increasing the amount of incoming visual
information;
- dilating the trachea and bronchial muscle, allowing more air to be sucked in (and thus
more oxygen to be supplied to muscles and other tissues);
- stimulating the conversion of glycogen to glucose in the liver, allowing the delivery of
more energy to the muscles;
- redirecting blood away from the skin and digestive system to the skeletal muscles, brain
and heart;
- inhibiting the contraction of the sphincter muscles;
- inhibiting the production of saliva and mucus and the secretion of urine from the kidneys; and
- suppressing other normal bodily functions, including the immune system.
Very soon the body is primed for action – for flight or fight. Some scientists also suggest that a chronic deficit of a neurotransmitter called serotonin, which is thought to act as an inhibitor to violent impulses, may also play a role in sudden outbursts of rage.
Effects of stress
The effects caused by stress hormones are useful for some kinds of short crisis periods but are harmful if maintained. High blood pressure, for example, can lead to heart failure, and the over-production of glucose can lead to diabetes. Thus, people who are highly stressed are more vulnerable to long-term health problems.
Related sites
The human nervous system (Nova: Science in the news, Australian Academy of Science)
The autonomic nervous system (Neuroscience for Kids, University of Washington, USA)
Violent brains (Brain Briefings April 2001, Society for Neuroscience, USA)
Posted May 2002.