Question

how are the parasympathetic and sympathetic divisions of the autonomic nervous system different? (pathways, cells, functions)

Please explain

Answer 1

1) The sympathetic trunk lies lateral to the vertebral bodies for the entire length of the vertebral column. It interacts with the anterior rami of spinal nerves by way of rami communicantes.
Preganglionic sympathetic fibers enters the ganglia through gray ramus communicants whereas postganglionic fibers leave the ganglia through whit ramus communicans.
The sympathetic trunk allows preganglionic fibers of the sympathetic nervous system to ascend to spinal levels superior to T1 and descend to spinal levels inferior to L2.

2)parasympathetic system is also called Craniosacral Outflow tract. (Cranial nerves 3,7,9,10 + S2 S3 and S4).

Cranial nerves involved in parasympathetic divisions are:
- CN III
- CN VII
- CN IX
- CN X

3) Sympathetic fibers after emerging from the spinal cord makes synapse and form sympathetic ganglia just near to the spinal cord. Then from it post ganglionic fibers arise which then supply the organs.
Whereas parasympathetic fibers after emerging from the spinal cord travels and they synapse to form ganglia near to the organ they supply called visceral ganglia. From there, post ganglionic fibers arise which then supply the respective organ.

So in sympathetic fibers, preganglionic fibers are short and postganglionic fibers are long which is in contrast to parasympathetic one in which preganglionic fibers are long and post ganglionic fibers are short.

4) Postganglionic fibers of the sympathetic nervous system releases norepinephrine as neurotransmitter while postganglionic fibers of parasympathetic nervous system release acetylcholine.

5) Sympathetic nervous are excitatory to heart, increasing heartrate, contractility, conduction while parasympathetic are inhibitory resulting in decrease heart rate, conduction etx