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