hi everyone let's talk about the cervical and brachial plexus cities in this video
we'll discuss the spinal nerves that participate in both the cervical and brachial plexuses
will also talk about how these plexuses are organized and what structures they serve so
spinal nerves originate from the spinal cord and they're named for the various levels of which
they exit the spinal cord in association with the vertebrae that they leave the cords adjacent to - there
are seven cervical vertebrae and there are eight cervical spinal nerves c1 are the first cervical
nerve exits above the first cervical vertebra c2 above the second and so on and so forth so
c8 is exiting below the seventh cervical vertebra thereafter each of the spinal nerves exits through
the spinal foramen that's below the Associated lis named vertebra so for instance t1 leaves
below T 1 the second thoracic nerve thanks it's below T 2 and so on and so forth so the cervical
spinal nerves are a little different than the thoracic the lumbar the sacral and the coccygeal
as we'll see so let's erase this and take a look at what we have here so the first four
spinal nerves of the cervical region c1 through C 4 will send their ventral primary Ram eye out
into the lateral neck to form the cervical plexus the 5th through the 7th I'm sorry the
5th through the 8th cervical nerve and then the first thoracic spinal nerve so that's c5 through
t1 central primary Rami will form the brachial plexus the majority of the thorax lacks a plexus
so t2 all the way down through t12 is is going to be plexus free and then beginning below that we'll
have the lumbar and the sacral and coccygeal plexuses but considering this is a had a neck
course we only have to contend with the circle and a brachial plexus ease so let's start with
the cervical plexus and we'll work our way on down the the spinal cord so the cervical plexus
consists of contributions of ventral primary ram i of c1 through c4 the cervical plexus has a couple
of major structures which it serves one of which you're familiar with already from our discussion
of the anterior neck and that happens to be the cutaneous nerves of the neck which originate at
the nerve point or herbs point of the neck that go out to serve the the anterior and the lateral
neck as well as portions of the inferior posterior head as well as up to the the lower face as well
and down over the the clavicle so all of these green branches are cutaneous nerves in terms of
our efferent there are a couple of structures served by the cervical plexus ansa cervicalis
ansa means handle cervicalis of the neck consists of two limbs so the superior limb comes
down that's from c1 and the inferior limb has contributions of c2 and c3 and these loop down
over the carotid sheath so these are serving the the various infrahyoid muscles here also
contributions from c1 that are not of ansa cervicalis go out to serve the geniohyoid
muscle in the thyrohyoid muscle so the thyrohyoid is unique among the infrahyoid and that it's the
only infrahyoid muscles not served by Ansa but rather served by independent fibers from c1 the
the diaphragm is another structure that is served from the cervical plexus both efferently and a
family so there are contributions of the ventral primary rami from c3 c4 and c5 which if you're
keeping track c5 is not of the cervical plexus c5 actually participates in the brachial plexus
which we'll discuss next but so c3 c4 and c5 are going to come together to form the phrenic nerve
this phrenic nerve is going to be featured very prominently in the root of the neck we'll see
its association with the anterior scalene muscle in it dives deep into the end of the thorax where
it continues on it sends some branches out to the the pericardium and then goes down to both
apparently and apparently serve the diaphragm so the mnemonic that we hear is C 3 4 5 keeps
the diaphragm alive there are also some branches from the ventral primary Rami of cervical nerves
that are going to directly innervate some of the scalene muscles the anterior in the middle
in particular but there's some variation here there will also be branches of ventral primary
Rami of lower cervical nerves such as 5 and 6 and beyond which which serve the the scalene muscles
sometimes we conceptualize this as being branches of the cervical plexus sometimes we say that these
are just directly from the vpr of cervical nerves you can conceptualize it however you like I mean
these plexuses themselves are but concepts they are intentionally defined by anatomist so moving
distally along the spinal cord we have the ventral primary Rami of cervical spinal nerves see five
six seven eight and then the first thoracic spinal nerve t1 the way that I remember this
is you know the old dance trope see five six seven eight T1 and so the brachial plexus
is going to be the source of innervation for the upper limb inclusive of the shoulder the brachial
plexus is organized hierarchically so there are roots of the brachial plexus these roots are the
ventral primary rami see five through t1 not to be confused with the spinal roots these come
together variously so see five and six will be a superior trunk c7 will be a middle trunk and
then c8 and t1 will be an inferior trunk and then these trunks will form divisions the the
divisions are either anterior or posterior these divisions are named for their relationship to the
axillary artery which has been cut and removed yeah and then there are chords that that arise
from various anterior and posterior divisions so we can see there's a posterior cord from
the posterior division and then there is both a lateral cord and a medial cord from the anterior
division these cords are also named for their associations to the the axillary artery and then
from you know both ventral primary rami and roots and Trunks and divisions and chords come
the branches the branches are the named nerves that come from plexus and you know some of the
the big named nerves that you may have heard of in your previous studies of anatomy or just
encountered in the world include things like the the musculocutaneous nerve the axillary
nerve the radial nerve the median nerve the ulnar nerve and so on and so forth these roots so VPR's
are emerging posterior to the anterior scalene muscle so they're actually sandwiched between
the anterior scalene as well as the middle and posterior scalene muscles as they emerge laterally
from the neck so big picture here those roots of the brachial plexus see 5 6 7 8 t1 are not true
spinal roots but ventral primary Rami of those spinal nerves those roots are going to coalesce
into trunks so there is our superior trunk from c5 and c6 our middle trunk is just a continuation of
c7 and our inferior trunk from c8 and t1 as they happen alone that's the the sum total of what you
will be held responsible for in in this course the anterior scalene muscle here has been reflected
away we can see some of the the middle and the posterior scalene muscles behind see we have the
left common carotid artery there so there's the else see hey there's the left vagus nerve cranial
nerve 10 right there and coursing along the bottom here is the subclavian artery which round about
there turns into the axillary artery should be a very important artery for the the brachial plexus
in terms of its named terminology if you recall generally arising from the third part of the
subclavian artery but this may arise from the transverse scapular artery or cervical artery
is the dorsal scapular artery the dorsal scapular artery very frequently is going to travel between
or insinuate itself between the superior and middle trunk of the plexus so that's a it's a
really good classic anatomical relationship that you're going to want to hold on to in the in
the memory bank so as usual I'll leave you with a question so that we can assess your understanding
of the the cervical and brachial plexus ease and that question is which features of spinal
nerves form the roots of the brachial plexus so is it the dorsal primary Rami of spinal nerves
C 531 the trunks of the spinal nerves of C 531 the ventral primary rami the ventral roots or the
ventral roots of spinal nerves C 531 so recall when we are talking about plexus ease cervical
and brachial we're talking about ventral primary Ram I of C 5 6 7 81 so the correct answer is C
and just to review your nerve root anatomy here so let's do it any sec 'td spinal cord will do a
little bit of Pia matter within the cord there so there is a dorsal there is ventral so coming
out of the dorsal Horn we have dorsal rootlets these are going to coalesce into a dorsal root
going in to the ventral are the ventral rootlets
either going to coalesce from a ventral root the dorsal root is ganglianated so
there is our dorsal root ganglion our DRG so there is our dorsal root and there is
our ventral root there's our trunk of the spinal cord and then there is our dorsal
primary ramus and this is our ventral primary ramus dorsal root and rootlets
our afferent ventral our efferent trunks are mixed and rami are mixed
and so when we're talking about the portions of the cervical and
brachial plexuses we're talking about ventral primary rami in
cervical c1 through c4 and brachial is C 531 thank you for your time