DIFFERENCE BETWEEN THE SYMPATHETIC (THORACO-LUMBER OUTFLOW) AND THE PARASYMPATHETIC (CRANIO-SACCRAL OUTFLOW)

 

1.  The sympathetic PREGANGLIONIC CELLBODIES are located in the intermedio-lateral grey horn of the spinal cord at level T1-L2. The parasympathetic PREGANGLIONIC CELLBODIES are located in the cranial nerve nucleus (grey matter of brain) 3, 7, 9, and 10 AND the intermediate grey horn of the spinal cord at level S2-S4. Some may also be seen in the splanchnic nerves.

2.  The sympathetic PREGANGLIONIC AXONS are found in spinal nerves T1-L2 and can also be seen crossing the sympathetic (paravertibral) trunk without synapsing.  The parasympathetic PREGANGLIONIC AXONS are found in cranial nerves 3, 7, 9 and 10 AND sacral nerves of spinal cord S2-S4. They leave their anterior ramus to form PELVIC SPLANCHNIC NERVES. All preganglionic axons are myelinated forming bundles of axons called white rami comunicantes.

3.  The sympathetic POSTGANGLIONIC CELLBODIES are found in either the sympathetic (paravertibral) trunk or the prevertibral plexus (adjacent to the aorta). The parasympathetic POSTGANGLIONIC CELLBODIES are found in the ganglions in the head and neck, cranial nerve autonomic ganglions, and the hypogastric plexus. The pelvic splanchnic nerves innervate the hypogastric plexus.

4.  The POSTGANGLIONIC AXONS of both sympathetic and parasympathetic go to different viscera of the body. Note: the hair follicles are only innervated by the sympathetic postganglionic axons, since they are only contracted, as part of sympathetic response. Bundles of postganglionic axons form the grey rami comunicantes because these axons are non-myelinated.

5.  The primary neurotransmitters released by both sympathetic and parasympathetic preganglionic axons are acetylcholine. The primary neurotransmitter released by postganglionic parasympathetic is also acetylcholine but the ones released by postganglionic sympathetic is NOREPINEPHRINE to all target organs except for the sweat glands to which acetylcholine is released.

Note: acetylcholine released in the synaptic cleft after used is hydrolyzed to acetic acid and choline by enzyme ACETYLCHOLINESTERASE.

6. The sympathetic preganglionic to postganglionic are in the ratio 1:10 while parasympathetic preganglionic to postganglionic are in the ratio of 1:3.

7. The sympathetic postganglionic fibers are longer than the parasympathetic postganglionic because the latter originate from plexus and ganglia around the viscera

 

Note: the preganglionic axons are myelinated, longer and slow conducting B fibers while the post ganglionic fibers are unmyelinated, shorter and slower conducting C fibers.