00:00 okay we're gonna talk about muscles of
00:02 the neck and answer the what questions
00:03 what muscles are found in each plane a
00:05 cervical fascia what are their actions
00:07 and innervation and what's the deal with
00:10 the different layers of muscles hello
00:12 my name is dr. Morton and I'm the noted
00:14 anatomist so my approach for this is
00:18 going to be covering the muscles based
00:19 upon their location in the cervical
00:22 fashio so we see this cross-section
00:24 through the neck and so I'll cover the
00:26 muscles in the superficial and in the
00:29 deep investing and in the pre vertebral
00:31 and in the pre tracheal facist so let's
00:34 start with the superficial fascia and
00:36 the platysma muscle so here's a
00:38 cross-section of the neck around the c6
00:40 vertebra and there in red is the
00:42 platysma muscle which is in the
00:44 superficial fascia or hypodermis and so
00:47 from this lateral view there's our
00:49 platysma muscle and it's going to come
00:51 from the corner of the mouth and the
00:53 angle of the mandible all the way down
00:55 to the sternum and clavicle and that
00:56 fashio over the PEC major in deltoids
00:59 and so the platysma muscle wrinkles the
01:01 skin of the neck and what that means as
01:03 we take a look at this picture and you
01:05 see that action right there BAM and so
01:09 you see those fibers in the arrows are
01:11 showing the platysma muscle that tenses
01:13 and wrinkles the skin of the neck as
01:17 shown in that red diagram where the
01:18 platysma is and the innervation is via
01:22 the facial nerve cranial nerve number
01:24 seven and so there's cranial nerve seven
01:26 right after it comes out the style of
01:28 mastoid framin and it comes down to the
01:30 cervical branch innervates the platysma
01:32 muscle it's the only muscle I think
01:34 really that the cervical branch of the
01:36 facial nerve innervates so we've covered
01:39 the muscle in the superficial fascia now
01:41 the deep investing fashio
01:42 which includes our sternocleidomastoid
01:44 and trapezius muscles
01:46 sternocleidomastoid or SCM and trapezius
01:49 let's start with sternocleidomastoid
01:50 which is named according to its
01:52 attachments and so there we have the
01:54 sternal attachment clavicular attachment
01:57 and clyde o means clavicle and the
02:01 mastoid process hence
02:02 sternocleidomastoid and the
02:05 sternocleidomastoid turns the head to
02:06 the opposite side and it flexes the neck
02:08 on the same side so here we have the
02:10 sternocleidomastoid on the left and when
02:14 it turns the head to the right and so
02:16 the Lester Nalina mastoid causes you to
02:18 look over your right shoulder
02:20 that's one action the also it has is you
02:24 to the sternocleidomastoid flexes the
02:27 neck on the same side so the right
02:28 sternocleidomastoid flexes or bends the
02:31 neck on the right side like that and the
02:35 trapezius muscle this elevates the
02:37 scapula or shrugs the shoulders and so
02:40 there's the trapezius muscle from the
02:41 side and there it is from the front
02:44 superimposed on this model and you see
02:47 the traps elevates the scapula or shrugs
02:50 the shoulder it does other actions but
02:53 that's covered in greater detail in the
02:55 back muscle so the scapula elevation of
02:59 the shoulders and the other big one is
03:01 the extension of the head and neck
03:02 things that you see the head and there
03:04 we have the head that's flexed and the
03:07 trapezius muscle extends the head and
03:10 neck from here to here we're next going
03:12 to talk about the innervation of this
03:15 SCM in the traps which is through
03:17 cranial nerve 11 the spinal accessory
03:18 nerve in this lateral view we see the
03:21 spinal accessory nerve there within the
03:24 posterior triangle of the neck the
03:26 spinal accessory nerve exits through the
03:28 jugular foramen and then gives a nerve
03:30 innervation to the sternocleidomastoid
03:32 courses across a posterior triangle the
03:35 neck and innervates the trapezius muscle
03:37 the deep investing fascia now we're
03:40 going to the pre vertebral fashion
03:41 muscles and so those include the scalene
03:44 muscles the anterior middle and
03:46 posterior neck ssin there's anterior
03:49 middle and posterior leg muscles and
03:51 shing cervical and brachial plexus ease
03:54 exit between these anterior middle
03:56 scalene muscles now let's look at an
03:58 anterior view there is our anterior
04:00 scalene our middle scalene and our
04:03 poster scalene muscles and up high you
04:05 can see the phrenic nerve a branch from
04:07 the cervical plexus exiting between
04:09 anterior middle and then there's the
04:12 brachial plexus exiting as well between
04:14 the anterior and middle scalene so this
04:17 term scalene is Greek for uneven because
04:20 the anter middle and posterior scalings
04:22 are all different lengths now
04:25 let's do a small detour the trunk
04:27 consists of the neck the thorax the
04:30 abdomen and the pelvis and then you have
04:32 the head on top and the two limbs upper
04:34 and lower limbs but the trunk are these
04:37 so the abdomen in cross-section we
04:41 notice the following there is the
04:42 external oblique the internal oblique
04:44 the transverse abdominus muscles and
04:47 then the lumbar and intercostal nerves
04:50 course between the internal oblique and
04:53 transverse abdominus now let's take a
04:55 look at a cross-section through the
04:56 thorax there is the external intercostal
04:59 internal intercostal and innermost
05:01 intercostal muscles and look the
05:03 intercostal nerves course between the
05:05 internal and innermost intercostals now
05:08 let's look at a cross-section through
05:09 the neck so the posterior scaling
05:11 there's the middle scalene and there's
05:13 the anterior scalene muscle and the
05:16 cervical and brachial plexus ease exit
05:18 between the anterior middle scalings so
05:21 the take-home point for this is the
05:23 following the anterolateral trunk wall
05:26 has three layers of muscles and the
05:29 nerves and vessels course between layers
05:32 two and three the neck the thorax the
05:35 abdomen and the pelvis all work in that
05:37 way so back to the scalene muscles they
05:41 elevate the first and the second ribs
05:43 and so here we have the scalene muscles
05:46 and you see when they contract they
05:48 elevate that first and second rib that
05:51 helps to increase the diameter of the
05:52 thoracic cavity which increase volume of
05:54 the lungs that helps you inhale then you
05:57 also have lateral flexion of the neck so
05:59 when you look at this view and you see
06:01 there's the posterior triangle the neck
06:03 because it's between the traps and the
06:05 sternocleidomastoid and the muscles that
06:07 form part of the floor are the scalene
06:09 triangle of scalene muscles form part of
06:12 the floor of the posterior triangle and
06:13 they Bend the neck to the same side
06:16 lateral flexion of the neck the scalene
06:19 muscles are innervated by branches from
06:21 the c4 to c8 ventral remise so here's a
06:24 picture of the brachial plexus and
06:27 labeled c5 - t1 I don't have c4 on here
06:30 but branches coming off of the ventral
06:33 Ram I from C 4 5 6 7 & 8 are going to
06:37 then go and innervate the scaling
06:38 muscles levator scapulae elevates a
06:41 scapular shrugs the shoulders and
06:43 there's the levator scapulae in this
06:44 cross-section and there it is here in
06:48 this posterior view again this muscle
06:51 even though we find it in the floor of
06:52 the posterior triangle the neck and it's
06:54 part of this in this pre verbal fashio
06:56 it covers in more detail in the upper
06:59 limb scapular linked scapular sling
07:01 content now the longest capitis and
07:04 longest coleye muscles and here in this
07:06 anterior view there's our longest
07:08 capitis this word longest as its name
07:11 indicates is a long muscle that attaches
07:14 to the head capitis like a baseball cap
07:17 and then there's the longest coleye long
07:19 muscle in the coli which is abbreviation
07:23 e team ology is neck long muscle
07:25 attaches to the head lung muscle it's on
07:27 the neck and it's there in the cross
07:30 section these muscles are important for
07:33 topographical but functionally not as
07:36 much there's some little bit that can be
07:37 done if during whiplash they can get
07:39 injured but for the most part clinically
07:41 it's just nice to know it's good to know
07:43 where they're located
07:44 so muscles in the pre vertebral fashion
07:47 now muscles in the pre tracheal fashion
07:49 this includes the infrahyoid muscles the
07:52 sternohyoid thyroid omohyoid and
07:55 thyrohyoid muscles whew there is our
07:58 sternohyoid our sternal thyroid and our
08:01 omohyoid muscles now let's take a look
08:03 at them from an anterior perspective and
08:06 you do that this is you're looking at
08:07 someone in their chin door looking up at
08:10 there's the hyoid bone there's thyroid
08:13 cartilage or your laryngeal prominence
08:14 and there is the sternum and so when you
08:18 look at the muscle the arrow and you
08:20 think what's the name of that muscle and
08:21 Adam is said well it goes from the
08:22 sternum to the hyoid let's call it the
08:25 sternohyoid muscle but wait what about
08:26 this muscle well let's going from the
08:28 sternum to the thyroid cartilage we'll
08:30 call it the sternal thyroid muscle but
08:32 what about this one it's going from the
08:35 scapula or shoulder which is the
08:37 abbreviation omo to the hyoid bone we
08:40 call it the omohyoid shoulder to hyoid
08:43 muscle and what about this one that's
08:45 going from thyroid cartilage to hyoid
08:47 thyrohyoid muscles and so the actions
08:51 these muscles is simply not simply what
08:53 they help depress and support the high
08:55 weight bone so when you swallow in the
08:57 hyoid bone goes up it helps to bring it
09:00 back down these are postural muscles
09:03 with the hyoid in to the extent the
09:05 laryngeal prominence that thyroid
09:06 cartilage clinically it's not like
09:09 you're going to be testing these muscles
09:11 they're innervated by the cervical
09:13 plexus specifically the ance of cervical
09:15 oh so here's the cervical plexus from c1
09:17 to c5 and in yellow is the answer
09:20 cervical that has a superior limb that
09:22 comes from c1 and an inferior limb that
09:24 comes from c2 and c3 ventral Ramah and
09:27 so what happens as we see off the
09:29 superior limb there's a nerve to the
09:31 thyrohyoid and the genial hyoid it's
09:34 above the high weight bone a nerve to
09:36 the omohyoid to the superior belly a
09:39 nerve to the sternal thyroid the nerve
09:41 to the sternohyoid and then a nerve to
09:43 the omohyoid the inferior belly
09:45 basically I shown them all here but
09:48 really if you know that these infrahyoid
09:50 muscles are innervated by the answer
09:52 server callus clinically that's
09:54 sufficient okay there we have it so why
09:59 are both somatic body wall muscles and
10:01 brain Kia large muscles found in the
10:03 neck so here in this cross-section take
10:06 a look there is our somatic body wall
10:08 muscles and what I mean by that they're
10:09 derived from the somites so there's
10:11 sternohyoid sternothyroid or normal
10:13 hyoid and then there's our scalenes
10:15 levator scapulae and also the abaxial
10:17 muscles the paraspinal muscles and the
10:19 brain key large muscles like the
10:21 platysma from branchial arch number two
10:23 in the sternocleidomastoid and traps
10:25 from the hind arches so what's the deal
10:28 why do we have this well they answer
10:30 this question we say the head and neck
10:32 are like an orange on a toothpick mm-hmm
10:34 funny movie so there's an orange and
10:36 there's a toothpick so watch what
10:38 happens it doesn't look very stable and
10:40 thump that's what would happen okay
10:42 would just drop so even if we go let's
10:44 push this back up and you let go it
10:46 drops so you push this back up and it
10:48 drops so what do you do to stabilize
10:50 this orange well let's put some tennis
10:52 or maybe some bungee cords on the back
10:54 like this and tighten them see that you
10:57 tighten and it goes up well the head
10:59 neck are like an orange on a toothpick
11:01 you have an orange and you have a
11:04 so then it falls over you put some
11:06 bungee cords we call them the
11:07 sternocleidomastoid in the traps and
11:09 they do this they bring the head up
11:12 because the sternocleidomastoid and the
11:14 trapezius are both hind arches that are
11:17 basically coming from the head and they
11:18 migrate down and so what happens is
11:20 you've got these semitic muscles here
11:22 like those infrahyoid and the scalenes
11:25 those muscles for the most part attach
11:28 to and from within the neck they don't
11:31 go to the head so the head would flop
11:33 forward so that we have these branchial
11:35 arch muscles like sternocleidomastoid
11:37 and traps that migrated down to the
11:39 shoulder and to the back to help
11:42 stabilize this orange the head on the
11:46 toothpick the neck and that my friends
11:49 are the muscles of the neck in a
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