we'll begin our study of the appendicular muscles with the pectoral girdle and shoulder joint and like before here's a quick reminder about the formatting of the arrows and what the different colors and so on meet now when we talk about the pectoral girdle we're basically saying this is the shoulder socket and the pectoral girdle is made of both the scapula and the clavicles but really it's the scapula that provides that glenoid cavity where the head of the humerus sits so if you want to position the pectoral girdle what we're saying is you're trying to tweak or move around the shoulder joint a bit specifically the scapula so all of these muscles if they're going to position the scapula must insert on the scapula so if you can learn that the muscles of the pectoral girdle are the rhomboids PEC minor and the trapezius you should always be able to at least take a guess at the insertion somewhere on the scapula the origins of course are in a lot of different places so that the scapula can move in a lot of different ways first let's look at the rhomboids you have a minor in major and just as with these eigem atticus muscles the minor is superior to the major their origins are both on the spinous processes of the thoracic vertebrae and of course rhomboid minor attaches to different vertebrae than rhomboid major but you're not responsible to know exactly which vertebrae but they both have their origins on those spinous processes in the thoracic region and the insert on the medial border of the scapula so if you think about the actions for these muscles all of them are moving the scapula so again if you're going to take a guess at what these muscles do it will do something to the scapula and if we look at these rhomboids we can see that the muscle fibers are somewhat transverse somewhat across the body so just based on that if you can imagine these muscle fibers contracting and shortening they will pull the scapula towards the midline of the body and just like when I pull my humerus is towards the midline of my body I am add ducting so to is this process the adduction of the scapula but the rhomboids muscle fibers also kind of run from inferior towards the superior at an oblique angle right so the scapula will not just add duct but they will also be elevated so the rhomboids can both add duct and elevate the scapula pectoralis minor has its origin on the ribs and it inserts on the coracoid process of the scapula remember this looks kind of like a corvid like a crow type bird as that little deacon head on it so if we look at the way these muscle fibers run and you can imagine the coracoid process being pulled towards the ribs that will slide the scapula away from the midline of the body it will cause abduction of the scapula will be hold away from the midline and finally we have the trapezius with many origins the external occipital protuberance at the back of the school the spinous processes of both cervical and thoracic vertebrae and there are other regions you can probably tell that we're not even bothering to name so many different origins and the trapezius inserts on the spine of the scapula so like all of these we've talked about their positioning the pectoral girdle meaning they're moving the scapula so how does the trapezius move the scapula well in a lot of ways because look at that trapezius it's got all these fibers that are running in you know different directions so it can do a lot to the scapulae you can just say it can do all the actions like every way that the scapula moves the trapezius can move it except it can't abduct the scapula it can hold the scapula up it can pull it in words it can pull it downwards but only the pectoralis minor on the front of the body can pull the scapula away from the midline so all actions except abduction and finally there is this concept of a reverse action a reverse action means that sometimes you will pull the origin towards the insertion it's kind of rare but you basically use other muscles to fix your insertion and then you're pulling on the origin doing the opposite thing the reverse action and if the trapezius does its reverse action it can pull on the external occipital protuberance it helped you extend your neck so now we're gonna look at the muscles that move the shoulder joint another way you can say this is muscles that move the humerus as so if you took your arm in lock your elbow lock your wrists and your hands we're not moving any of that we're just moving the shoulder joint just the humerus and all the arm stuff beneath that now all these muscles if they're going to move the humerus they must insert somewhere on the humerus so remember all those bumps and structures and grooves on your humerus now we're going to use those and if they're moving the humerus their action must be some change in the position of the humerus so what I'm saying is you really want to make sure before you just start memorizing all these muscles and all these different oh is make sure you kind of embrace the fact that okay it makes sense all of these muscles move the humerus so the must have insertions on the humerus and they must have actions that include a movement of the humerus don't start giving wild guesses on your tests make sure if you have to guess you're guessing within the framework that makes sense for this group of muscles so let's look at the list pectoralis major a very large muscle remember this has a convergent fascicle arrangement so the muscles are broad at the origin and then they all tighten up at a small insertion so the origin includes the ribs sternum and clavicle but it inserts such as one space that we can't see the greater tubercle of the humerus that kind of makes sense to me this is a great big muscle so it needs the biggest largest bump on the humerus to attach to the greater tubercle and when the PEC major pulls on the humerus it can do a lot of different things because again this is a big broad muscle so the fibers can run in a lot of different directions therefore the shoulder joint can be flexed the shoulder joint can be medially rotated and adducted and it will help if you try to walk through these and think about why this muscle can cause all those changes based on the way that it's laid out okay then we have the widest muscle of the back latissimus dorsi you know lateral is like latitude like the width of the planet and dorsi means of the dorsum the dorsal region so this is the widest or most lateral really muscle of the back and the origin we have listed as iliac crest obviously its origin also includes spinous processes and other parts but we just simplify that we said iliac crest and it inserts on the intertubercular groove let's look also at Ares Major while we're here teres major is just like rhomboid major and just like zygomaticus major it's below inferior to the minor so teres major is below teres minor but I want to talk about it now because look it has the same insertion on the intertubercular groove and it results in the same types of actions so what can these two muscles do together they can extend the shoulder which kind of makes sense these muscles are in the back so when they tug on the intertubercular groove the arms should be moving more towards the back so they can extend the shoulder and medially rotate it one difference between these two muscles is their origin with the teres major inserting or having an origin on the lateral border of the scapula well now let's do the next pair of muscles because they also will have the same insertion and they will also contribute to the same actions so we'll do teres minor next along with infraspinatus this kind of makes sense these muscles are right next to each other they both insert on the greater tubercle hey that's a great big chunk of bone so not only will the big PEC major attach there but even more muscles can attach there and they will laterally rotate the shoulder so this kind of makes sense because they're in the back and so they'll pull the muscle backwards whereas the previous muscles lat Tiz miss door C and teres major like how do they medially rotate the shoulder if they're in the back well it's because the muscle comes from the back foot it sneaks up towards the front medially rotates it there's you'll see that in a video it's a little bit more clear when you can see that in a three-dimensional video but anyways so these last two muscles they attach to the greater tubercle they laterally rotate the shoulder but they have different origins the teres minors origin is the same as teres major it's on that lateral border of the scapula and infraspinatus of course because of its name has its origin on the infraspinous fossa of the scapula remember under the scapular spine here's the scapular spine so under that is a dish leg shape or groove called the infraspinous fossa so that's where the infraspinatus attaches onto the next side we can do next the supraspinatus well of course it's origin must be the supraspinous fossa and it attaches to the greater tubercle that's a big chunk of bone we got a whole bunch of muscles attaching to it when this muscle contracts it will abduct the shoulder remember when the aliens lift up your arms that's abduction of the shoulder joint and hopefully that makes sense that this muscle is very high up on the back so when it contracts it's pulling the arm up subscapularis we can't see on the image so I just show where it's hidden deep behind these other muscles as the name implies the origin of the subscapularis is the subscapular fossa it inserts on the lesser tubercle finally we're doing the lesser tubercle and it causes medial rotation of the shoulder we finished with the deltoid and I had a mnemonic device for the origin here I think it was successful students always attend class yeah and that's for the spine of the scapula successful students always is the acromion process of the scapula and clavicle always attend class is the clavicle so hopefully you can make that out those are all origins of the deltoid but where do they insert this is the freebie deltoid tuberosity it's named after the muscle makes perfect sense and deltoid is one of these wide wide muscles just like PEC major just like trapezius it can cause a lot of different movements of the shoulder joint in fact it's one of those cases where you can say it can move the shoulder joint in every way possible save for one except for adduction if you wanted to pull the arm back down to the body you really need to be pulling from below but the deltoid is up high you know it goes towards your back it goes towards your front but it's it's very high up on the body so the deltoid can perform all actions of the shoulder joint except for adduction