CC is correct.
Independent of the location of the SOMA, any axon in the CNS( central branch forming the dorsal column in this case) is myelinated by oligodendrocytes and any axon in the PNS( central branch in the dorsal roots and peripheral branch in the dorsal and ventral rami of the spinal nerve in this case) is myelinated by schwann cells.
Actually the answer is B and C. Between the muscle or skin and the cord, the dorsal roots are myelinated by Schwann cells. Once inside the cord in the dorsal columns, they are myelinated by oligodendrocytes.
@suture, you might not like the way i phrased the question but the concept is correct. Let me take you step by step.
In the dorsal root ganglia, there are pseudounipolar neurons that have a central branch and a peripheral branch.
The PERIPHERAL branch extends from the neuron up to the target organ and is myelinated by SCHWANN cells and runs in the ventral and dorsal rami & peripheral nerves.
The CENTRAL branch has 2 parts:
-the first part runs in the dorsal roots and is myelinated by SCHWANN cells
-the second part enters the spinal cord (dorsal column in the above case) and is myelinated by OLIGODENDROCYTES
in the picture below, the blue part is myelinated by oligodendrocytes, the rest is myelinated by schwann cells.
http://i.imgur.com/TkL4n6j.png
@medicus, which part is confusing you?
@miracoli, The picture you posted is very helpful. Now the explanations make sense.
So I thought that the first order neurons ( Dorsal column in this case) were myelinated by shwann cells. and second order onwards are myelinated by oligo (ML in this case)
But I was wrong
so now i think
Anything in the cns is myelinated by oligo and outside the cns by shwann
so fibres from DRG to spinal cord should be by oligo
Please correct me if I am wrong.
Thanks a lot.
Yes correct except the last sentence "so fibres from DRG to spinal cord should be by oligo "
Fibers from the DRG to the spinal cord form the DORSAL ROOTs and are myelinated by schwann cells.
check this picture
http://i.imgur.com/PU8gFS4.png
a pseudounipolar neuron in the DRG has two branches:
-the peripheral branch(indicated num 3 in the pic) which is myelinated by schwann cells
-the central branch(indicated num 1&2 in the pic)
-the first part of the central branch(indicated num 1 in the pic) forms the dorsal root and is myelinated by schwann cells
-the second part of the central branch(indicated num 2 in the pic) forms the dorsal column in the spinal cord and is myelinated by oligodendrocytes.
Clear now?
So here is a q for you, based on my painting skills, do you think i can be like Leonardo da vinci?
Be sincere!
Thanx for the question and very neat explaination...
Wow that is like crystal clear in my mind now. Beautiful explanation! You should plan a gallery exhibition. Great art
@swamy, my pleasure!
@medicus, cool. you are invited to my upcoming renaissance usmle art gallery exhibition alla Leonardo
Thanks for the invitation. It will be an honor.
