What are the main parts of the autonomic nervous system? What are the structural differences between the parts? Describe the structure of each part of the autonomic system.
The autonomic nervous system has two main parts, the sympathetic and the parasympathetic systems, which differ both structurally and functionally from each other. Structurally, the two systems differ as to where the cell bodies of the first motor neurons are located within the spinal chord and as to what distance from the spinal chord the first motor neurons synapse with the second motor neurons. The cell bodies of the sympathetic system's first motor neurons lie in the thoracic and lumbar sections of the spinal chord. These motor neurons synapse with dendrites of the second motor neurons in ganglia located just exterior to the ventral side of the chord. Thus, the second motor neurons have to have very long axons to reach their target organs. The cell bodies of the parasympathetic system's first motor neurons lie in the medulla of the brain and in the sacral section of the spinal chord. The first motor neurons have very long axons and synapse with the second motor neurons in the near vicinity of the target organs. As a consequence, the axons of the second motor neurons are relatively short.
