So I'm having a hard time distinguishing between different aspects of Auto/Som. Nervous Systems.
I know that Autonomic can be summarized to essentially be anything that innervates body cavity viscera and gut organs and involuntary muscle actions. Meanwhile, somatic can be essentially skeletal muscle innervation.
So my questions are:
Can both branches sense? This is in reference to Cranial Nerves that I know do sensory but ONLY carry parasympathetic fibers NOT sympathetic. What's the significance of this latter fact?
Furthermore, Cranial Nerves carry 7 types of fibers. What are they?
Thanks ahead of time!
I think everyone's covered the CN topic pretty well, I'll just say that the "para"sympathetic nervous system is exactly that - the ganglia (or the site where the CNS communicates with the nerves that serve the end-organs) are on either side of the sympathetic system (which is housed in the sympathetic chains on either side of the thoracic spinal cord. Hence, there's a cranial portion and a sacral portion to the PsNS. The cranial portion is carried in the cranial nerves, yes, but not all cranial nerves are PsNS, just 3, 7, 9, & 10. And the sacral portion is the pelvic splanchnic nerves. So the ANS looks like this:
Cranial PsNS: CN III, VII, IX, X
SNS
Sacral PsNS: pelvic splanchnic
And ANS nerves are both sensory & motor, just like somatic nerves. The only difference is that the efferent (motor) nerves that cause things like gut peristalsis or sphincter tone etc., don't pass through the spinal cord (the pelvic splanchnic do, but they don't synapse in the anterior horn either) so they don't synapse in the anterior horn like somatic efferent motor fibers. The afferent (sensory) nerves carry sensation back from the PsNS targets through PsNS nerves just like in the somatic system, and they even synapse in the dorsal root ganglia just like the somatic system. But they come in from all over...and kind of just jump on to an incoming somatic sensory nerve as it's going back into the spinal cord.
They synapse in the DRG just like the pain/temp/vibration/proprioception fibers of the somatic sensory nerves and go back up to the brain, which is why you get "referred" pain, because you may get PsNS sensory nerve fibers jumping on at someplace higher/lower than the anatomical structure actually is (but usually it's close). Like how the upper GI abdominal visera (PsNS sensory) localizes epigastric, small bowel/distal large bowel localizes periumbilical (which is why appendicitis pain is initially periumbilical in appendicitis, because it's being carried by proximal large bowel abdominal visera...or PsNS fibers on their way back), and lower bowel localizes infraumbilical/suprapubic. Sensation carried by somatic sensory fibers localizes to where it is anatomically, because they almost always enter into the DRG right where they're supposed to and the body has a more sophisticated system for detecting somatic pain. An interesting example of an exception to this (in that it's referred somatic pain) is an irritated diaphragm. The diaphragm gets motor innervation from cervical spinal nerves 3,4,5 (somatic). The abdominal side of it is covered with parietal peritoneum, so you get abdominal pain if it's irritated somehow from the abdomen, but since cervical spinal nerves 3,4,5 also carry in somatic sensation from the shoulder, sometimes as the fibers get distributed into phrenic nerve vs. shoulder innervation, the phrenic nerves get a few somatic sensory nerves that were supposed to go to the shoulder. So if the diaphragm gets irritated, you can get shoulder pain because the brain thinks those nerves were sent to the shoulder. As far as the question of "where is the somatic/viseral (PsNS) split" in the abdomen, parietal peritoneum and out is somatic, and visceral peritoneum and in is PsNS. That's why once the appendix ruptures and the parietal peritoneum gets irritated, the pain then localizes to the actual anatomical location of the appendix, because the parietal peritoneum is somatic and thus the pain is better-localized.
Hopefully that made sense. Pretty sure it's mostly correct, feel free anyone to correct me.
