Dr.Dodson 9.25.96

Autonomic nervous system

Practical aspects.

made of sympathetic and parasympathetic components. there are two 
convenient concepts to recall. all organs of the body have both 
sympathetic and parasympathetic innervation. the nerves tend to go to the 
organs as a mixed nerve, with both symp and parasymp fibers in it. These 
tend to be small unmyelinated nerves.

Sympathetic and parasympathetic differ greatly, though.

Parasympathetic = craniosacral system

Sympathetic = thoracolumbar system

this separation is interesting - the sympathetic system arises in the 
thoracid and lumber region, coming off the spinal cord in each thoracic 
and lumbar segment, in successive segments. You can't destroy the 
sympathetic system, therefore, because there are many segments.

the parasympathetic arises in the head, distributing as cranial nerves, 
and the sacral region, distributing as the pelvic nerve.

So, the sympathetic system needs to get to the head, and the parasymp 
needs to get to the body. how? travel together in the neck as the vagus 
nerve (cranial nerve X)

vagus distributes parasympathetic fibers to heart stomach and gut. There 
is a "switchboard" called the cranial-cervical ganglion which separates 
the vagus and sympathetic systems at the base of the head. Also, middle 
cervical ganglion splits them at the thoracic inlet. 

vagus splits off of trunk, and splits into dorsal and ventral, travelling 
through diaphragm.

sympathetic splits into greater/lesser splanchnic which form a plexus 
(cranial mesenteric plexus, where the fibers of the vagus nerve join, so 
the fibers leaving the plexus are mixed sympathetic/parasympathetic 
nerves, which then distribute to the organs.

note that after the splanchnic nerves come out, the sympathetic trunk 
decreases in size, but it does continue, through to the caudal part of 
the animal. another splanchnic (lumbar splanchnic) nerve splits off in 
the lumbar region, and forms another ganglion called the caudal 
mesenteric ganglion.  after this split the sympathetic trunk dies out, 
but sympathetic fibers are carried into the pelvis via the hypogastric 
nerve, which comes out from the ganglion and travels into the pelvis.
there is yet another plexus (pelvic plexus) in region of vagina/prostate. 
The pelvic and hypogastric nerves run into this plexus, mixing symp and 
parasymp fibers, and then these mixed nerves innervate bladder, rectum, 
etc. So, all pelvic viscera recieve this mixed nerve supply.

the pelvic nerve is dorsal in position, not very conspicuous, hard to 
find in dissection. Easiest thing to do is find caudal mesenteric plexus 
(near caudal mes. artery) and watch hypogastric nerve running caudally 
from it into the pelvis. Key pelvic artery= vaginal or prostatic artery. 
pelvic plexus should be caudal to that artery. If you find the pelvic 
plexus, you might find the pelvic nerve dorsally, leading into the pelvic 
plexus.

it's not one of the great wonders of nature or anything, so don't stress 
out over it. 

Illustration in small millers fig 105 pg 136, fig 143 p 199, fig 150 p 
212. dr.dodson recommends coloring in the pix.