What are the three key anatomical differences between the sympathetic and parasympathetic divisions of the autonomic nervous system?

The sympathetic and parasympathetic divisions differ in (1) sites of origin: sympathetic fibers are thoracolumbar, while parasympathetic fibers are craniosacral; (2) relative fiber lengths: sympathetic preganglionic fibers are short and postganglionic fibers are long, whereas parasympathetic preganglionic fibers are long and postganglionic fibers are short; and (3) location of ganglia: sympathetic ganglia lie close to the spinal cord, while parasympathetic ganglia lie within or near the visceral effector organs.

These three anatomical differences are summarized in Figure 14.3 of the text. First, the sympathetic division originates from the thoracic and lumbar regions of the spinal cord (thoracolumbar), whereas the parasympathetic division originates from the brain stem and sacral spinal cord (craniosacral). Second, in the sympathetic division the preganglionic fibers are short and the postganglionic fibers are long; the parasympathetic division has the opposite arrangement, with long preganglionic fibers and short postganglionic fibers. Third, sympathetic ganglia are located close to the spinal cord, either alongside the vertebral column or anterior to it, while parasympathetic terminal ganglia are located within or near the visceral effector organs they innervate.