Parasympathetic Nervous System Anatomy

General Anatomy:

The preganglionic neurons of the parasympathetic nervous system lie either in the brain or in the sacral spinal cord. Obviously, in the sacral spinal cord, these preganglionic neurons send their axons out the sacral spinal nerves toward the parasympathetic ganglia. How do the preganglionic neurons in the brain send out their axons?

If you think about this, you will realize that the preganglionic neurons in the brain can only send their axons out any peripheral nerves from the brain-- those are called cranial nerves. Remember them? Oh, oh, oh, to touch and feel and grab Vegas' slot handles.

So, parasympathetic preganglionic neurons send their axons out either a cranial nerve or a sacral spinal nerve. From there, the preganglionic axons run all the way out to their target areas. They synapse on postganglionic neurons in the parasympathetic ganglia. Remember, these parasympathetic ganglia lie on or adjacent to their target tissue. For example, a parasympathetic ganglion lies on the bladder; therefore, a sacral preganglionic neuron runs all the way out to synapse within this ganglion. The postsynaptic neuron does not have to send its axon far to affect its target.

Wow. Wasn't that easy?! It is so much simpler to describe than the sympathetic nervous system because it doesn't have any sort of special anatomical positioning.

Which cranial nerves?

The following cranial nerves contain preganglionic axons, and the parasympathetic targets are noted for each:

	oculomotor: pupillary reflex
	facial: tear and salivary gland control
	glossopharyngeal: salivary gland control
	vagus: all thoracic and most abdominal parasympathetic innervation (heart, lungs, stomach, small intestines, etc...)

So, what does the sacral portion of the parasympathetic nervous system do?

Simply, it innervates all pelvic targets.

For a more detailed view of the targets of the parasympathetic nervous system, take a look at Figure 11.40 of your textbook.