Posterior Axioappendicular Muscles – Anatomy of the Shoulder

00:01 If we now look at the posterior axio-appendicular muscles, we can split these into two groups, a superficial and a deep group. Here we can see on this side of the screen, the two superficial muscles. I want to talk about trapezius and latissimus dorsi. We can see trapezius here as above the superior or descending part. We have trapezius here forming a transverse or horizontal part and we have trapezius here forming an ascending or a more inferior portion.

00:39 Three parts of trapezius, the superior, we have got a middle and then inferior portion of trapezius. We see it's running from the midline, from the spinous processes of the vertebrae and also from a structure called the nuchal ligament that is coming from the occipital bone. We can see it is passing towards the spine of the scapula as we'll see. If we move over we can see another superficial muscle and this is latissimus dorsi, a large flat muscle. That again it's coming from the spinous processes of the vertebrae by thoracic and lumbar vertebrae and also this white membrane here which is the thoracolumbar fascia.

01:21 This muscle passes up towards the intertubercular sulcus. It also attaches to the intertubercular sulcus of the humerus. We can see it passing up in this direction. So these are the superficial muscles. We can see we have got a descending, transverse and ascending part of trapezius or a superior, middle, inferior part and here we can see that specific origins. The nuchal line and external occipital protuberance for the descending part, the nuchal ligament for the transverse part, and the spinous processes of these vertebrae here. And we can see that the external occipital protuberance, the nuchal ligament and the spinous processes and they are passing towards the spine of the clavicle. Attaching to the lateral third of the clavicle and the spine of the scapula so these are attaching to this region. The nerve supply is quite unique. It is coming from a cranial nerve, the spinal accessory nerve is cranial nerve number 11. So damage to the cranial nerve 11, the accessory nerve inability to elevate the scapula. It also receives innervations from spinal nerves C3 and C4 and this is mostly to be for proprioception which is that positional sense. So these nerves carry information about the level of contraction within the muscle tendon and Golgi organ of the muscle, allowing the central nervous system to know how much that muscle has contracted and therefore where it is in space. The function of these parts of trapezius so the descending part helps to elevate the scapula. The transverse part helps to retract, pull the scapula backwards. And the ascending part helps to depress the scapula. So important movements of the scapula. Working together the descending and ascending parts help to rotate the scapula superiorly. Latissimus dorsi - We can see it's coming from those bony regions that I mentioned and is passing to the intertubercular groove specifically the floor. It is innervated by the thoracodorsal nerve and this originates from spinal cord segments C6 and C7. It is important in extending, adducting and medially rotating the shoulder joint. So latissimus dorsi is important in extending, adducting and medially rotating the shoulder joint. If we then look to the deeper muscles, we can see we have got two, rhomboid muscles, minor and major, and levator scapulae. I will just go back to the previous slide to see these. Here we can see rhomboid muscles running from the spinous processes of the cervical and thoracic vertebrae and they pass towards the medial border of the scapula.

04:27 We can see we have got two parts of the rhomboid muscles. We have rhomboid minor which lies most superiorly and we have rhomboid major which lies inferiorly and sometimes you can make out a separation of these muscles. But in most cadavers the separation is actually quite difficult to see but you have rhomboid minor and rhomboid major. Here we can see passing upwards towards the skull we have levator scapulae and that is important in helping to, as its name suggests, elevate the scapula. So we can see rhomboid minor and rhomboid major. We have the minor coming from the nuchal ligament and really the spinous processes of those vertebrae. And major coming from inferiorly, so coming from the spinous processes of the thoracic vertebrae inferior to C7- T1, coming from T2 - T5. But really these run as one block of muscle. The minor one inserts to the superior aspect of the medial border and the major one inserts into the inferior aspect of the medial border of the scapula.

05:42 Both of these muscles are supplied by the dorsal scapula nerve coming from C5 and it is important in being able to retract the scapula. So pull the scapula backwards and also rotate it inferiorly. So rotate the scapula inferiorly which serves to depress the glenoid cavity. Levator scapulae is running from the transverse process of C1- C4 as well as it is coming from and it runs down to the superior angle of the scapula. So that when this muscle contracts we can see its origin here. When it contracts, this distance is going to be shorter. This is going to stay where it is. It is going to remain stable which results in the scapula moving upwards. So innovating when elevating the scapula. It runs to the superior angle of the scapula and is innervated via the dorsal scapula which comes from the fifth cervical spinal cord segment. It elevates the scapula and is also involved in rotating the scapula inferiorly, again depressing the glenoid cavity. So this muscles can work together in that sense.