So, that’s the purpose of the plexus.
So, let’s start with the brachial
plexus. Nerve roots, where are they from?
C3, 4, 5, 6, T1.
Try again. C4, 5, 6 and T1?
No, five, six. So C5, C6, C7, C8, and T1.
You mentioned the C4, it can happen. Occasionally,
you can have a pre-fixed brachial plexus but
you can start from C4, C5, C6, C7, C8. Or
you can have a post-fixed plexus where you
have from C5, C6, C7, T1, and T2. But that
happens in approximately 10% of the population.
In about 80% of the population, this is the arrangement.
In 10% you have a pre-fixed plexus, in
10% you have a post-fixed. For the purpose
of your understanding discussion, anatomy
knowledge, this is all you need to know.
So, these nerve roots come from the spinal
cord. So if you can imagine the spinal cord,
cervical root comes from the spinal cord.
Do they come from above the vertebra or below
the vertebra? Below. Below or above? So, the question,
what you can get in your MCQ or EMQ, or syllabus
answer, is if somebody has got cervical spondylosis
in C3, C4, which nerve root is affected, nerve
root three or four?
Four. So, does it come from the below
or above? It comes from above apart
from C8 which comes
from below, and then from there onwards.
Very good. So, one thing to remember
for the exam, the cervical vertebrae from
C1 to C7, all the nerve roots come from above.
I’ll come back to this page in a minute.
So, C1, C2, C3, nerve roots come from above.
So if you have a spondylosis between
C2 and C3, it's the C3 nerve root that is affected.
When it comes to C7, you have one coming from
above and one coming from below. So, that’s
why you have seven vertebrae but eight nerve
roots. So this is C7 and C8.
When it goes to thoracic vertebrae, they all
come from below. So in the thoracic-lumbar
region, they’re all from below. So if you
have a disc prolapse, let’s say between,
that's for discussion, let’s say L1 and L2,
the nerve root that is affected is L1.
So this is how your MCQs will be structured.
If you have a disc prolapse or a cervical
spondylosis, which nerve root is affected?
So this is another thing you need to understand.
Okay. Coming back to here, so they’re all coming
out from the cervical vertebra. The next question,
do they lie in the anterior triangle of the
neck or the posterior triangle?
Posterior triangle. So that’s another MCQ question.
A syllabus MCQ question. They’re always
in the posterior triangle of the neck. So
you have the sternocleidomastoid and you can
imagine the cervical vertebra is deeper and
it comes from the posterior triangle.
The nerve roots come out, and then what happens?
So let’s say the nerve roots come out from
here. What happens after that?
They join together.
To form what? Root will form trunk. Okay.
Whenever you think of a plexus, imagine it’s
like a tree. So you have some roots coming
up first. The roots will join to form the
trunk. So the next is a trunk. So you have the
upper trunk from C5, C6. The middle trunk
coming from C7 on its own. And the lower
trunk is C8, T1. So if you imagine here