okay hi folks welcome to lesson 26 we're going to look at the ailla today specifically location and organization of anterior axio appendicular muscles that contribute to formation of the ailla and attachments interation actions of these muscles then we're going to preview the borders of the exilla and then the general overview of um contents within the exilla the exilla as we've mentioned previously is that space um near the armpit so we're going to get to explore that a little further uh by the end of today's lesson you'll be able to identify anterior axio appendicular muscles that contribute to formation of the EXA and describe the organization of these three muscles that we're going to discuss describe the attachments interation and actions and then identify and describe Pathways of nerves that inate these muscles as well then we'll identify and describe the borders of the ailla so the Apex the base and the four walls three of which are muscular and identify structures that pass through the ailla big one being the bracho plexus which we'll discuss further in lesson 2 seven but before we begin let's just recall that some of our extrinsic back muscles are also known as posterior axio appendicular muscles so take a second and just pause the video here list the five posterior axio appendicular muscles we've discussed so far we can see that in this image on the right hand side of the screen here and then I want you to describe the general characteristics of the posterior axio appendicular muscles their location function and innervation okay so our five posterior Axia pendicular muscles we've discussed previously let's look at the left side of this individual here we see most superficial and largest or one of the larger ones we have trapezius present here inferior and deep to trapezius we can identify lisus dorsai and then when we reflect trapezius we're able to identify the three other posterior axio appendicular muscles levator scapula rhomboid minor and then rhomboid major so what are these general characteristics well location their names telling you a little bit about their location axio appendicular posterior aspect of the body they attach to both the axial skeleton and the appendicular skeleton and they're superficial to that deep fascia we've discussed function well since they're originating on the axial skeleton but attaching to the appendicular skeleton specifically the Toral girdle humorous they're going to cause and control movement of the Upper Limb finally inovation with the exception of trapezius inated by anterior Rami of spinal nerves what are the anterior Rami well again we've discussed how the spinal nerves bifurcate into an anterior Ramis and a posterior Ramis the posterior Rami go to inovate those deep muscles of the back but the anteri form all of these um peripheral nerves that then inate these structures so why are we bringing back the posterior a axio appendicular muscles well because they share a lot of the same characteristics with the anterior axio appendicular muscles with the exception of their kind of General location in the body so anterior axio appendicular muscles also attach to the axial and appendicular skeleton except they're not originating from the vertebral column for the most part or actually whatsoever they're originating from the thoracic cage instead um different from the posterior a axio appendicular muscles these muscles are located on the anterior lateral aspect of the body specifically in the pectoral region present here um kind of where your chest is and then the lateral thoracic wall they too cause in control movement of the Upper Limb since they are attaching again to the humoris right or the pectoral girdle and again they're inovated by the anterior Rami of spinal nerves so specifically branch of the brachial plexus again those anterior Rami are going to continue or converge to form all of these peripheral nerves that then go to inate these structures to cause contraction or to bring sensory information back to the central nervous system so we're going to dis discuss three anterior axio appendicular muscles although there are four of them we're only going to look at the ones that contribute to uh borders of the ailla so we're looking at anterior views of the bodies here most superficial we see this very large muscle pectoralis major within the pectoral region hence the name major because it's large when we reflect pectoralis major we'll be able to identify pectoralis minor again when there's a major there's a minor minor just indicating that yes it's in that same region but it's a smaller muscle then on the lateral aspect of the thoracic wall we'll be able to identify seratus anterior so we've come across seratus posterior Superior seratus posterior inferior both having this saw like kind of organization or or look to it but this one located on the more anterior aspect so let's start with pectoralis major it has a broad attachment a broad origin but then tapers in order to insert to its insertion site so because it's so broad it's actually comprised of two heads a clavicular head and a Stern costal head and those names telling you what they're attaching to the clavicular Head originating from the anterior surface of the clavicle specifically that medial half right we know that the more lateral aspect of the clavicle is occupied by trapezius and deltoid the sternal costal head as the name suggests originating from the sternum so manubrium and the body of the sternum as well as the coastal cartilage of ribs 1 through six sometimes we have this wonky third head but because it's not um typical it's not textbook we're going to disclude it in our conversations or excluded rather now as I said broad origin tapers inserts on the lateral lip of the intertubercular groove so now we've come across a few muscles that insert to the general area of the intertec groove we'll look at that shortly so let's look at or think about the origin relative to the insertion well the origin is located medial to the insertion therefore when it contracts it's going to cause adduction of the humoris when this contracts because we know that the um glenohumeral joint can permit rotation well this is going to pull that anterior surface of the humorus towards the midline towards that origin and that will cause medial ation of the humorus this um insertion or sorry this origin is also anterior to the um humoris or to its insertion on the humoris so when it contracts it can also contribute to flexion of the humoris and a little bit of a a special um a special action due to the the twisting of these fibers that we see here when the humoris is in a flex position or the arm is in a flexed position pectoral major can also produce extens ition but only from that Flex position now this muscle is inated by branches of the brachial plexus specifically the medial and lateral pectoral nerves these names the pectoral aspect of the name kind of giving you a clue that it's going to inate these pectoralis muscles so we can see one here heading towards pectoralis uh major and another here piercing through pectoralis minor to get to pectoral major now as I mentioned we have our three muscles inserting to the lateral lip the medial lip and the floor of the intertec groove so I want you to remember PLT almost like a BLT sandwich from lateral to medial pectoralis major inserts on the lateral lip of the intertubercular groove latissmus dorsi on the floor of the intertubercular groove and then Terry's major on the medial lip of the intertec groove PLT keep that in mind okay so here we've removed pectoralis major in order to reveal pectoralis minor again within that pectoral region originating from the axial skeleton inserting on the appendicular skeleton smaller in size than Pectus major so this muscle specifically originates from ribs 3 to five and we can confirm that right here's rib one here's rib two 3 4 5 and then it two tapers so it's quite triangular in shape to insert to the coracoid process of the scapula so again multiple muscles inserting to the same attachment site or originating to the same attachment site pectoris M minor we can see right here then when we look at the anterior compartment of the arm short head of biceps break ey and deep to that Coro brachialis also inserting to the same spot now because this muscle inserts to the the scapula it's going to cause movement of the scapula when it contracts towards its origin so it's a shorter muscle it's going to Aid in stabilization of the scapula on that thoracic wall kind of holding it in place but it's also going to produce protraction of the scapula so drawing that scapula kind of Antero uh inferiorly as such think about when you're reaching to something ahead of you or you're going to shake someone's hand pectoralis minor is going to be active in order to draw that scapula forward like pectoralis major also inovated by that medial and lateral pectoral nerves now we're going to look for seratus anterior on the lateral aspect of the thoracic wall again originating from the axial skeleton inserting to the appendicular skeleton specifically this muscle wraps around the lateral thoracic wall in order to get to its insertion site so originates from from ribs 1 through eight and then we can see that kind of serrated orol like edge of the muscle inserting to the medial border of the scapula specifically that anterior aspect along with the superior and inferior angles and let's recall we have a few other muscles also attaching to the medial border of the scapula Lev scapula romboid minor romboid major but they sit more posterior um really on that medial aspect where that seratus anterior is going to insert onto that more anterior aspect now like Pectus minor this muscle is also going to Aid in stabilizing the scapula against the thoracic wall and it too protracts the scapula this muscle is known as the boxers muscle because in boxers where they're constantly punching and protracting um the scapula you can really see this um when you view the surface anatomy of a of a boxer like here like uh trapezius this muscle will also cause upwards rotation of that scapula so enabling that full range of of movement when we abduct the um Upper Limb deltoid and supinatus only getting us to about 90° and then upwards rotation needs to occur in order to extend the arm all the way above our heads this muscle is also inovated by a branch of the bracho plexus a new one here that we're being introduced to the long thoracic nerve named because it's very long and it sits on the thoracic wall you're going to look for this nerve superficial to seratus um directly on that lateral aspect of the thoracic wall so all three of these muscles are going to contribute to um borders of the ailla again this is that space um associated with our armpit or the axillary fossa and it's a passageway um or Distribution Center rather for structures traveling to and from the Upper Limb specifically vasculature So Vein arteries but then also that brachial plexus which is that plexus of nerves contributing to or innervating muscles that will move the Upper Limb so it's pyramidal shaped um we can see that it has an apex and a base in this schematic here and then it has four walls an anterior wall a posterior wall a medial wall and a lateral wall in this image here we have removed um a portion of pectoralis major in order to view the axilla and the contents of the axilla and identify some of those boundaries so specifically highlighted in this green color we can identify a portion of the posterior wall highlighted in purple the medial wall in blue the lateral wall and then in red we can highlight the um anterior wall the base has been removed and the Apex is not visible so the base is um comprised of the skin and fascia of the armpit or of that axillary fossa so in the laboratory for the most part the base will be removed because we've dissected in order to actually access the ailla the Apex is also known as the cervical axillary Canal now break down that name we know that these structures are passing from the region of the neck into the axilla or vice versa and the vertebrae that are present within the neck are those cervical vertebrae hence the cervical aspect of this um name so this is the opening for structures to pass through and it's bounded by the clavicle anteriorly rib one medially and then the superior border of the scapula posterior laterally of course we would have muscles present here too trapezius um for instance which would keep these structures in place the lateral wall is comprised of the humoris so it's the only wall um that's is comprised of seratus anterior so that muscle we were just introduced to on the lateral aspect of the thoracic wall as well as the um osteology of the thoracic cage so those ribs and then those muscles that span those intercostal spaces the anterior wall is comprised of both pectoralis major superficially and here we've removed a little portion to see the other portion pis minor um deep to petalis Major so in the lab in order to actually explore the ailla you need to reflect pectoralis major and minor out of the way in order to access it and then explore its contents these based on their location so subscapularis is going to form the more Superior aspect of the posterior wall inferior to that you can identify teres major and then inferior to teres major you'll be able to identify latissmus dorsi so these three muscles uh contributing to that posterior wall now what's contained within this we're going to explore um the axillary artery just due to its relative positioning uh with the bracho plexus we're definitely going to look at the bracho plexus specifically the cords and the branches contained within this region the axillary vein is also present here um in the laboratory it'll most likely be removed actually it will be removed in order for you to explore the BP and the axillary artery there's also a lot of lymphatic vessels and lymph nodes present in this region and adapost tissue a ton of adapost tissue um which serve to kind of protect and insulate all of these really important structures we can see in this image here pectoris major and minor are still in place but we can see these structures as they enter or exit the axilla from the um region of the neck through that Apex or cervical axillary Canal travel through the axela and then travel into the Upper Limb here we're looking at a superior view of a transverse section so a crosssection um at about this region here this is anterior and this is posterior this is lateral and this is medial I want you to take a second to identify the um structures that are tagged in this region contributing to the formation of the exilla or the boundaries of the exilla and then maybe you can identify some of these contents as well based on their location relative to the structures you're about to identify so again take a second pause the video and then I will reveal the answers okay so let's start anteriorly we see the anterior wall of the exilla present here and we know most superficial and largest is pectoralis major and deep to pectoralis major pectoris minor which means these two structures these nerves arise from um components of the bracho plexus must be the medial and lateral pectoral nerves going to inate these structures pector major heading to insert to this bone right here specifically the lateral lip of the intertec groove well this must be the humoris forming that lateral wall of the ailla forming the medial wall this muscle spanning from the thoracic cage to that anterior aspect of the medial border of the scapula serus anterior and we know that the nerve that's superficial to serus anterior on the lateral aspect must be the long thoracic nerve and then forming the posterior wall well we know there are multiple muscles that form this wall but this muscle specifically is originating from that subscapular fossa and inserting to the lesser tubric of the humoris so this must be subscapularis you can really view that kind of triangular or Pam midal shape of the ailla present here axillary artery axillary vein cords of the bracho plexus and then some of those branches arising from cords as well there's a summary sheet for you so take some time to read through it and I have a couple activities um for you to complete first identifying these structures on the schematics prior to entering the laboratory here you can list the structures that contribute to the Apex based medial lateral anterior wall and posterior wall and then finally I want you to get used to identifying the origin and insertion sites on osteology because you can definitely expect that in your upcoming laboratory exam