Posterior Axioappendicular Muscles

00:01 Now, let's have a look at some posterior axio-appendicular muscles which form both superficial and deep layers.

00:09 So, here, we're looking at the posterior aspect of the skeleton.

00:13 We can see a large number of muscles here, both superficially, we have trapezius and we have latissimus dorsi.

00:20 Deep to those two muscles, we have rhomboid major, rhomboid minor, and levator scapulae.

00:27 We will see some of these bony attachments when we introduced the osteology of this region.

00:33 So, let's have a look at those muscles. Here, we have trapezius.

00:36 There's a couple of parts to trapezius. There's a descending part, a transverse part, and finally, an ascending part and these are named over the direction of their muscle fibers coming from their origin.

00:49 So, you see these fibers are descending. These fibers are running transversely across.

00:54 And these fibers are ascending, running upwards. These are named after the origin of the muscle which is coming from the superior nuchal line and the external occipital protuberance.

01:06 They're positioned on the posterior aspect, towards the base of the skull.

01:10 The nuchal ligament continues down to attach to the spinous processes on the vertebral column.

01:15 And here, we can see spinous processes C7 through to T12 is where this muscle attaches from.

01:24 As these muscles either descend or they ascend or they run transversely, they're running to the lateral third of the clavicle which we can see here.

01:34 And as they run to the lateral third of the clavicle, some fibers attached to the spine of the scapula.

01:40 This muscle is unique and it is actually supplied by one of the 12 pairs of cranial nerves.

01:46 And this muscle is supplied by the 11th cranial nerve, also known as the accessory spinal nerve.

01:53 There are some fibers from C3 and C4, spinal nerves, and these carry the proprioception.

01:59 So, the level of contractility that the muscle has undergone, enabling the skeleton in the brain to know where that part of the bony skeleton is in space.

02:09 So, C3, C4 carries proprioceptive fibers from this muscle.

02:15 If we look at the function of trapezius, we can see the descending part is associated with elevating the scapula.

02:21 The traverse part is associated with retraction of the scapula.

02:26 And the ascending part is associated with depression of the scapula.

02:31 So, there's three different roles of the trapezius and depending on which motor units, which muscle fibers are activated, will determine the movement of the scapula.

02:41 Here, we have the descending part and the ascending part and if those both contract at the same time, you get superior rotation of the scapula.

02:51 Now, let's turn our attention to latissimus dorsi.

02:54 Latissimus dorsi is a flat sheet of muscle in the lower aspects on the posterior part of the skeleton.

03:03 Here, we can see its origin is coming from T6 through to T12 spinous processes.

03:08 And also, it's coming from some lumbar vertebrae you can see as well.

03:13 Most inferiorly, it's coming from the iliac crest and the thoracolumbar fascia.

03:18 This muscle is going to sweep around the anterolateral aspect of the chest wall and it goes to sit in the floor of the intertubercular groove.

03:28 You can see how it very small, very small tapering of this muscle as it moves around the anterolateral aspect of the chest wall.

03:38 So, actually sit there in the floor of the intertubercular groove.

03:43 This muscle is supplied by the thoracodorsal nerve.

03:46 And again, we'll come to that when we look at the brachial plexus and how that originates.

03:51 The function of latissimus dorsi is one of extending the shoulder joint. So, here on the screen, we can see anteriorly, we have the chest wall pushing out on the right-hand side of the screen.

04:01 And you can see how latissimus dorsi contracting actually helps to extend the shoulder joint, moving the humerus posteriorly.

04:09 We can also see the contraction of latissimus dorsi helps to adduct the shoulder joint.

04:15 And that is to bring the humerus towards the midline.

04:18 Continued contraction will also lead to medial rotation of the shoulder joint, bringing it towards the midline.

04:26 You can see how the function of latissimus dorsi is incredibly complex.

04:30 Again, depending on the degree in which certain motor units within that muscle contract, are activated.

04:37 Let's have a look at rhomboid major.

04:39 We can see rhomboid major here is running between the scapula and the vertebral column, specifically, the second through the fifth spinous processes of those thoracic vertebrae, all the way down to the medial border of the scapula.

04:53 This muscle is supplied by the dorsal scapular nerve.

04:57 We can see we have two rhomboids, it's a paired muscle, one on either side, also like latissimus dorsi, etc. that we've spoken about previously.

05:05 But the function of these muscles is to help retract the scapula.

05:08 You can see how retraction of the scapula can occur as this muscle contracts around the fixed vertebral column.

05:16 And also, contraction can lead to the inferior rotation of the scapula, allowing your arm to be pulled backwards and downwards.

05:23 Now, let's have a look at rhomboid minor. Rhomboid minor sits above rhomboid major.

05:29 You can see its origin and insertions are here.

05:31 The seventh cervical and the first thoracic spinous processes and you see it runs across again to the medial aspect of the scapula which you can see here.

05:42 There may be some fibers that also come from the nuchal ligament.

05:46 This muscle is also supplied by the dorsal scapular nerve.

05:51 The function of rhomboid minor is very much analogous to rhomboid major and they can work together in retracting the scapula. And also, helping to inferiorly rotate.

06:01 So, these muscles, the rhomboid muscles very much work together. We have the levator scapulae here.

06:08 This muscle is extending all the way from the transverse processes of high cervical vertebrae.

06:14 We can see here, C1 through to C4, extending down to the superior angle of the scapula.

06:21 This muscle is also in the same region as the rhomboids, supplied by the dorsal scapular nerve.

06:27 As the position of this muscle may elude and we have a fixed vertebral column, contraction of this muscle will lead to elevation of the scapula.

06:36 It will also help with inferiorly rotating the scapula.