Superficial Structures of the Neck

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.