00:01
Now let's take a look at some of the
superficial structures of the neck.
00:06
We'll start with a very, very thin
muscle called the platysma.
00:11
We'll also look at some more
substantial muscles such as
the sternocleidomastoid
and the trapezius.
00:17
On this anterior
review of the platysma,
we can see that it's a very wide
flat and thin sheet of muscle.
00:25
And in fact,
it inserts into the fascia
that covers the areas around the
pectoral muscle, clavicle,
and acromion.
00:32
Rather than a bone
like most muscles.
00:35
More approximately it does attach
to the lower border of the mandible
as well as a little bit of
the orbicularis oris muscle.
00:43
And the platysma is a
muscle of facial expression.
00:45
So it's innervated by the facial
nerve or cranial nerve VII
Because it's a very thin muscle
that really only attaches
into fascia distally
its action is really just to tense
the skin of the lower face and neck.
01:00
Here we see the sternocleidomastoid
which has a sternal head
and a clavicular head
and cleido is another word
for clavicular.
01:11
When we look at the
origins insertions,
we can see how it gets its name.
01:15
The sternal head is attaching
to the manubrium of the sternum
while the clavicular head
is attaching to the
medial third of the clavicle.
01:24
It also attaches superiorly
to the mastoid process
as well as a little bit of
the superior nuchal line,
which is how it gets its name
sternocleidomastoid.
01:36
The sternocleidomastoid
is innervated
by the accessory nerve
or cranial nerve XI.
01:41
And there are some contributions
from the cervical plexus.
01:46
The sternocleidomastoid,
if it's acting unilaterally,
will act to rotate the
head to the opposite side
while tilting the
head to the same side.
01:58
So it has the effect
of looking up and away
from the muscle that's contracting.
02:04
When both work
together bilaterally,
they serve to extend the head.
02:11
Now let's swing around to the
back to find the trapezius
which is a very long muscle.
02:17
It has a descending
part, a transverse part,
and an ascending part.
02:24
Here we see it begins all the way
up at the superior nuchal line.
02:28
And that bump on the
back of the school called
the external occipital
protuberance.
02:32
It runs down the nuchal ligament,
and along the spinous processes
of C7 to T12.
02:40
And then it attaches out laterally
to the lateral third
of the clavicle,
as well as the spine
of the scapula.
02:48
The trapezius like the
sternocleidomastoid
is innervated by the 11th cranial
nerve or the accessory nerve.
02:55
It also has some contributions
from cervical spinal nerves
for proprioception or
sensing where it is in space.
03:03
In terms of the function,
it really depends on which
fibers are contracting.
03:06
If it's the descending part,
or the upper fibers,
it's causing elevation
of the scapula.
03:12
If it's the transverse
part of the middle fibers,
it's causing retraction
of the scapula
bringing it towards the midline.
03:18
And if it's the ascending
part with these lower fibers,
it will cause depression
of the scapula.
03:25
But because of the odd
shape of the scapula,
when the upper and lower
fibers work together,
they also serve to
rotate the scapula.
03:33
We would say, be rotated superiorly
because it will bring the inferior
angle a little bit upward.
03:38
And that's an important
sort of accessory motion
when we talk about
upper limb movements.
The lecture Superficial Structures of the Neck by Darren Salmi, MD, MS is from the course Neck Anatomy.
What is the origin of the platysma?
What innervates the sternocleidomastoid?
What are the functions of the trapezius? Select all that apply.
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