njit-etd2003-081 - New Jersey Institute of Technology

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The sympathetic nerve fibers leave the central nervous system from the thoracic
and lumbar sections of the spinal cord. The parasympathetic nerve fibers leave the
central nervous system from the brain through cranial nerves III, V, VII, IX, and X and
the second and third sacral spinal nerves. Cranial nerve X is also called the vagus nerve.
The parasympathetic innervation of much of the thorax and abdomen, and especially the
heart, is done by the nerve fibers, which leave from the brain through cranial nerve X.
Therefore, parasympathetic activity related to the heart is often called vagal activity.
Figure 2.5 illustrates the anatomic difference between the sympathetic nervous system
and parasympathetic nervous system as well as some of their respective effector organs.
The second anatomical difference between the sympathetic and parasympathetic
nervous systems has to do with the location of the ganglia. Each connection of the
autonomic nervous system between the central nervous system and the effector cell
consists of two-neuron chains connected by a synapse. Most, but not all, of the
sympathetic ganglia are located close to the spinal cord and form two chains of ganglia,
one on each side of the spinal cord, called the sympathetic trunk. Conversely, the
parasympathetic ganglia lie within the organs innervated by the postganglionic neurons.
Physiologically, the sympathetic and parasympathetic nervous systems are also
different [5]. One common physiological characteristic is that the major
neurotransmitter released between the pre- and post-ganglionic fibers is acetylcholine.
However, in the sympathetic division, the major neurotransmitter between the
postganglionic fiber and the target cell is usually norepinephrine, a neurotransmitter that
activates excitatory receptors, but in some cases can inhibit certain organs. In the
parasympathetic division, the major neurotransmitter between the postganglionic fiber