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Old 03-07-2012
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Question Gray or White rami Communicans?

I've done Neuro through Kaplan Lecture Notes and FA
and now I'm going through it in HY Neuroanatomy as a sort of 'start from scratch' attempt.

I still have no clue what a gray rami communicans or a white rami communicans is, other than one is myelinated and one isn't.

But what the heck are they? What do they do?
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Quote:
Originally Posted by Dr.NickRiviera View Post
I've done Neuro through Kaplan and FA
and now I'm going through it in HY as a sort of 'start from scratch' attempt.

I still have no clue what a gray rami communicans or a white rami communicans is, other than one is myelinated and one isn't.

But what the heck are they? What do they do?

As I know they are pathways of sympathetic NS. white rami are the pre-ganglionic fibers which are myelinated and grey rami are the postganglionic sympathatic fibers which are non-myelinated.

preganglionic fibers ends on ganglion of sympathetic trunk and synapse with the postganglionic nerve in the ganglion of sympathetic trunk.

thats what I know.Hope this helps
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Originally Posted by nadee View Post
As I know they are pathways of sympathetic NS. white rami are the pre-ganglionic fibers which are myelinated and grey rami are the postganglionic sympathatic fibers which are non-myelinated.

preganglionic fibers ends on ganglion of sympathetic trunk and synapse with the postganglionic nerve in the ganglion of sympathetic trunk.

thats what I know.Hope this helps
so since grey rami are postganglionic, does that mean they go straight to the thing they are going to innervate?
as opposed to white rami, which are the preganglionic fibers that will, as you said, synapse with postganglionic fibers.

so why are some pathways grey (1 nerve fiber) and some white (2 fiber pathway)?
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Quote:
Originally Posted by Dr.NickRiviera View Post
so since grey rami are postganglionic, does that mean they go straight to the thing they are going to innervate?
as opposed to white rami, which are the preganglionic fibers that will, as you said, synapse with postganglionic fibers.

so why are some pathways grey (1 nerve fiber) and some white (2 fiber pathway)?

yes, the post ganglionics go straight to the end organ. but the difference is somtimes postganglionics located in the outside of the sympathetic trunk. I will try to explain as I can.

remember ANS are two neuron pathways(when compare to somatic which is one neuron pathway).1st neuron in the CNS, 2nd in the PNS. the sympathetic pre ganglion nerve cell body located in the lateral horns of the spinal cord (cell bodies of motor neurons in somatic NS located in the anterior horn)

so in sympathatic pathway start from the preganglionic from lateral horn of spinal cord-> axon go along with the ventral root->forms spinal nerve-> enter to the white ramus-> sympathetic ganglion(here located 2nd neuron/postganglionic and synapses)->axon of the postganglionic go through grey ramus->forms spinal nerve->enter to the ventral ramus and continue till find the end organ

this is the pathway for organs of body wall structures(ex:sweat glands in skin etc). but remember this pathway of SNS different when innervating internal organ. only difference is their 2nd neuron/post-ganglionic starts in the collateral or para-vertebral ganglia. they are located near to major blood vessels which pass to end organ.
for ex: when innervating stomach smooth m. fibres, post-ganglion located near the celiac trunk. so only when innervating internal organs pre-ganglion fibers pass directly through ventral root to ventral ramus without enter to the white or grey rami then synapses with the post ganglion located at outside near to vessels. so here pre-ganglionic fibres does not synapse at the sympathetic trunk.

I think you should watch the anat vedio lec on this topic if you still have doubts. he is really good in explaining this. Hope this helps

Gray or White rami Communicans?-untitled.jpgGray or White rami Communicans?-untitled2.jpg
click images to enlarge

Last edited by nadee; 03-07-2012 at 03:59 PM.
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Quote:
Originally Posted by nadee View Post
yes, the post ganglionics go straight to the end organ. but the difference is somtimes postganglionics located in the outside of the sympathetic trunk. I will try to explain as I can.

remember ANS are two neuron pathways(when compare to somatic which is one neuron pathway).1st neuron in the CNS, 2nd in the PNS. the sympathetic pre ganglion nerve cell body located in the lateral horns of the spinal cord (cell bodies of motor neurons in somatic NS located in the anterior horn)

so in sympathatic pathway start from the preganglionic from lateral horn of spinal cord-> axon go along with the ventral root->forms spinal nerve-> enter to the white ramus-> sympathetic ganglion(here located 2nd neuron/postganglionic and synapses)->axon of the postganglionic go through grey ramus->forms spinal nerve->enter to the ventral ramus and continue till find the end organ

this is the pathway for organs of body wall structures(ex:sweat glands in skin etc). but remember this pathway of SNS different when innervating internal organ. only difference is their 2nd neuron/post-ganglionic starts in the collateral or para-vertebral ganglia. they are located near to major blood vessels which pass to end organ.
for ex: when innervating stomach smooth m. fibres, post-ganglion located near the celiac trunk. so only when innervating internal organs pre-ganglion fibers pass directly through ventral root to ventral ramus without enter to the white or grey rami then synapses with the post ganglion located at outside near to vessels.so here pre-ganglionic fibres does not synapse at the sympathetic trunk.

I think you should watch the anat vedio lec on this topic if you still have doubts.he is really good in explaining this. Hope this helps
thanks for the detailed response
i understand ANS vs Somatic NS, and 2 neurons vs 1
but i just dont understand when the signal passes through the rami.
i mean, on that picture of the cross section of a vertebrae, the signal goes out from the spinal cord, along that dark black line that comes out of the ventral root.
but the rami part is randomly just coming off it on the side.
and if white rami are preganglionic, i dont understand why the postganglionic rami are right beside it, almost as if its a loop. :S
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so why are some pathways grey (1 nerve fiber) and some white (2 fiber pathway)?[/QUOTE]

as I said before nerve fibres in white rami are myelinated and in grey rami are not. sorry I do not know the reason for that.
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ok your pic is a little different than the one in my black and white kaplan book.
what i meant by thick black line was the green one in your pic
so the signal comes out of the ventral root, then goes to the sympathetic chain ganglion via the presynaptic white ramus, and then back to the spinal cord?
i guess i dont understand why the grey ramus is back in the direction of the spinal nerve.
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Quote:
Originally Posted by Dr.NickRiviera View Post
ok your pic is a little different than the one in my black and white kaplan book.
what i meant by thick black line was the green one in your pic
so the signal comes out of the ventral root, then goes to the sympathetic chain ganglion via the presynaptic white ramus, and then back to the spinal cord?
i guess i dont understand why the grey ramus is back in the direction of the spinal nerve.
u wrote right, but final part that post ganglionic fibre not goes to spinal cord, I mean it enters to the spinal nerve(all nerve fibres pass in between the inter-vertebral foramen together called "spinal nerve"). and remember this can enter to the ventral ramus as I said before (shows in a dots line in the pic) and it can enter to dorsal ramus if it is innervating posteriorly located organ(in pic draws as black line).

Sorry I do not know why they going like this. almost like a circle
But I think that¬s the way it is

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Originally Posted by nadee View Post
u wrote right, but final part that post ganglionic fibre not goes to spinal cord, I mean it enters to the spinal nerve(all nerve fibres pass in between the inter-vertebral foramen together called "spinal nerve"). and remember this can enter to the ventral ramus as I said before (shows in a dots line in the pic) and it can enter to dorsal ramus if it is innervating posteriorly located organ(in pic draws as black line).

Sorry I do not know why they going like this. almost like a circle
But I think that¬s the way it is

ok i think i get it
it seems like a backwards way of going about it, like the body sends it out and then back and then through the motor fibers, but im sure its the result of some evolutionary change over our history.

Thanks alot nadee, i really appreciate the effort you put into your responses.
thanks a bunch!
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Originally Posted by Dr.NickRiviera View Post
ok i think i get it
it seems like a backwards way of going about it, like the body sends it out and then back and then through the motor fibers, but im sure its the result of some evolutionary change over our history.

Thanks alot nadee, i really appreciate the effort you put into your responses.
thanks a bunch!
u r wellcome!!!!!!!
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check this out
White Ramus Vz Grey Ramus
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