Autonomic vs. Somatic

[vicinihil]

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!

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[TexasTriathlete]

We don't get neuro until 3rd term here, but we've glanced over it in histo and GA, so here's my understanding of a few of your questions...

1. Somatic is not just skeletal muscle innervation. There is also sensory. GSA nerves transmit signals from heat/cold receptors, etc.

2. Not all cranial nerves are sensory. CN XI innervates the upper trapezius and I think a few others in the neck. Other cranial nerves control muscles in the eyes. There may be more.

I'm not sure what the significance of the seven different fiber types is. I'm sure we'll hit that in neuro. Or maybe this next week, once we start head and neck in GA.

 

[dienekes88]

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!

We had to read some of this stuff for Gross Anatomy... but I'm no expert on these crazy "nerves." Neural Science and Neuroanatomy is second semester for me.

The Autonomic system is specifically the visceral motor system (General Visceral Efferent), which is distinct from the visceral sensory system.

The somatic system can sense: General Somatic Afferent (pain, temp, touch, and proprioception) and Special Somatic Afferent (vision, hearing, balance).

Can't help you with the Cranial Nerves... haven't learned them yet.

 

[EBI831]

Hey, I don't know of 7 nerve components. just six. hope this helps.

GSE (general somatic efferent)= motor to skeletal muscle: III, IV, VI, (XI), XII
GVA (general visceral afferent) ie chemo/mechano/stretch reception from viscera: IX and X like baroreceptors
SA(special afferent): senses; I (smell), II(sight), VII/IX/X (taste), VIII(hearing)
GSA: (general sensory afferent) ie touch, pain, temp, proprioception: all the cranial nerves with sensory; CN I, II, V, VII, VIII, IX, X
GVE: (general visceral efferents) ie motor to smooth muscles, glands, cardiac muscle:, CNs III, VII, IX, and X [ III= edinger-westphal nucleus, VII: superior salivary nucleus, IX: inferior salivary nucleus, X: dorsal motor nucleus of vagus]
BE (branchial efferents) ie motor to skeletal muscle derived from pharyngeal arches; acts like modified GSE : all the ones with both in the mnemonic ; V, VII, IX, X, and (XI)

 

[wAyRadikull]

Cranial nerves have both, sensory and motor functions. From what i can remember, they only carry parasympathetic fibers as the sympathetic fibers come from the cervical plexus which can kind of "ride along" with certain cranial nerves to their respective destinations.

A useful mneumonic that helped me with the whole sensory/motor thing was:

Some Say Money Matters, But My Brother Says Big Boats Matter Most, (From CN 1-CN 12 respectively)

Where S is sensory, M is motor and B is both.

As for the seven types of fibers:
1) SVA (special visceral afferent)
2) SSA (special sensory afferent)
3) GSE (general sensory efferent)
4) GVE (general visceral efferent)
5) GSA (general sensory afferent)
6) SVE (special visceral efferent)
7) GVA (general visceral afferent)

Hope that helps

 

[TMP-SMX]

To understand neuro you have to see the whole pathway to understand its function starting from the sensory fiber to the efferent fiber. The end result of autonomics is usually contraction/relaxation of smooth muscles that are involuntary. The sensory portions are usually visceral things like taste or homeostasis characteristics carried by the sensory cranial nerves. Pupils (optic), blood gases/chemistry (vagus/glossopharyngeal), taste (facial, glossopharyngeal, vagus). The efferent parasympathetics are as you said carried on the cranial nerves as you said. The ganglia for parasympathetics (craniosacral) are entirely different than the sympathetic ganglia (thoracolumbar) that control the body homeostasis. The sympathetics are separate fibers that are often carried on blood vessels and are controlled through the intermediolateral cell column nuclei in the thoracolumbar region of the spinal cord as said.

The cranial nerves are where it all gets interesting and it will all be much easier after you memorize them.

I: Olfactory sensory
II: Optic sensory
III: Oculomotor motor (many of the muscles in the eye and out)
IV: Trochlear motor (superior oblique muscle of eye)
V: Trigeminal both (Huge nerve) (sensory to face/teeth and motor to muscles of mastication)
VI: Abducens motor (lateral rectus muscle of eye)
VII: Facial both (sensory to anterior 2/3 tongue and motor to muscles of facial expression)
VIII: Vestibulocochlear sensory (Hearing and balance)
IX: Glossopharyngeal both (minor muscle innervation and sensory to post 1/3 tongue, carotid body/chemoreceptors, and efferent to parotid salivary gland)
X: Vagus both (many muscles for speech, swallowing, and the uvula, GI and other visceral organs, heart rate, sensory to aortic arch receptors for pressure, sensation and some lovely reflexes if you start poking around in the back of the throat, taste for rest of throat/uvula not innervated by the glossopharyngeal nerve)
XI: Accessory motor (trapezius and sternocleidomastoid)
XII: Hypoglossal motor (tongue)

 

[dienekes88]

Cranial nerves have both, sensory and motor functions. From what i can remember, they only carry parasympathetic fibers as the sympathetic fibers come from the cervical plexus which can kind of "ride along" with certain cranial nerves to their respective destinations.

A useful mneumonic that helped me with the whole sensory/motor thing was:

Some Say Money Matters, But My Brother Says Big Boats Matter Most, (From CN 1-CN 12 respectively)

Where S is sensory, M is motor and B is both.

As for the seven types of fibers:
1) SVA (special visceral afferent)
2) SSA (special sensory afferent)
3) GSE (general sensory efferent)
4) GVE (general visceral efferent)
5) GSA (general sensory afferent)
6) SVE (special visceral efferent)
7) GVA (general visceral afferent)

Hope that helps

Nice acronym! I haven't learned that yet, but I'll make sure to come back to this page when I do.

Do you mean "somatic" instead of "sensory" for the fiber types?

 

[TexasTriathlete]

I think that mnemonic is in First Aid. I've been in school for a month, and have already found it to be a useful resource for stuff like that. Only a few things so far, but it will only get more relevant.

And yeah he means somatic.

 

[Slide]

http://www.medicalmnemonics.com/

That'll carry you through a lot of anatomy tests.

 

[87138]

Some Say Money Matters, But My Brother Says Big Boats Matter Most, (From CN 1-CN 12 respectively)

It's "Breasts", not "Boats".

 

[anon-y-mouse]

http://www.medicalmnemonics.com/

That'll carry you through a lot of anatomy tests.

+1. Strangely the only thing I remember from there is the stupidest mnemonic for the branches of the aortic arch... ABC's => Brachiocephalic, Carotid, Subclavian. I know, pretty basic, but when you forget all your anatomy and are getting pimped in surgery, you remember these things.

and Boats => Boobs (in that previous mnemonic) and it will be much more memorable.

however, that whole SSA/GVA/etc. doesn't really matter and is largely insignificant and archaic in the grand scheme of things. if you remember the sensory modalities that are 'special' you can pretty much reason out where they should belong.

"she tastes like sweet apple pie" is good too for that axillary artery...
and "some anatomists like ****ing, others prefer s&m", etc.

 

[wAyRadikull]

It's "Breasts", not "Boats".

It's whatever you want it to be:

If you're a breast man: pick breasts,
If you're an ass man: pick butts, booty..
If you're you love to splurge: pick boats

Whatever you floats your boat.. i was just trying to keep it kosher!

 

[JeffLebowski]

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.

 

[TMP-SMX]

Totally unrelated, but one mnemonic I still remember is for branches of the external carotid artery.

Some Angry Lady Figured Out PMS.

Superior thyroid, Ascending pharyngeal, Lingual, Facial, Occipital, Posterior auricular, Maxillary, Superficial temporal