The autonomic nervous system has parasympathetic and sympathetic
branches (Figure 1) and most pharmacological discussions
concentrate on the efferent outflows of these two systems. The
autonomic efferent pathway has two neurons that synapse at
ganglia. In the case of the sympathetic nervous system, these
ganglia lie close to the spinal cord in the paravertebral chain and
the postganglionic fibre is long. The ganglia of the parasympathetic
nervous system lie on, or close to, their effector organs, such that
the postganglionic neuron is short.