ok so now we're going to take a look at some of the muscles of the thoracic wall so first of all we'll take a look at some of the muscles which attach to the thoracic cage and then we'll look at some of these smaller muscles which lie between the ribs and the intercostal spaces so outside the ribcage we've got three muscles really we've got the serratus anterior which you can see laterally and anteriorly here and then at the back we've got the serratus posterior and we've got a superior and inferior muscle so we'll start with the superior muscle so as you can see here the serratus posterior superior originates on the spinous processes of the vertebra so it originates from the from c7 to t3 on the spinous processes and it inserts on the upper borders of the second to fifth ribs so if I just remove the scapula there and just temporarily remove the serratus antara you can see the insertion point of this muscle on the ribs so this muscle is innervated by the corresponding intercostal nerves so it is it attaches to the second to fifth ribs and it's innovated by the second to fifth intercostal nerves and its function is to elevate the ribs so you can imagine if it contracts the angle of the muscles indicates that it's going to pull the ribcage upwards and elevate the ribs so this assists in inspiration so just taking a look a bit lower down at the serratus posterior inferior and this muscle originates from the spinous processes of T 11 to l2 and it's inserts on me on it on the lower rib so ribs 9 to 12 and again it's innovated by corresponding intercostal nerves so intercostal nerves which come from t9 to t12 and its function is opposite to the superior serratus posterior so it depresses the lower ribs and this helps in forced expiration so coming back around to the and you can see the serratus anterior muscle here on either side and this muscle originates on the upper rib so originates from the first eight to nine ribs and it inserts on the medial border of the scapula on the costal surface medially on the scapula so I've just isolated this muscle on the skeleton here and you can see the medial border of the scapula here and the costal surface of the scapula is the SCAP is the anterior surface of the scapula which lies close to the rib cage so the serratus anterior originates on the medial side of the scapula on its costal surface so this muscle is innervated by the long thoracic nerve and its function is to protract and to stabilize the scapula so it works to pull the scapula forward around the thorax and it also keeps the scapula pressed against the thorax so now we're going to take a look at some of the muscles that lie in the intercostal spaces so you've got three muscles three layers of muscles that lie in this intercostal space so the intercostal spaces are the spaces between the ribs and the three muscles that you have are the external intercostal the internal intercostal and then you've got the innermost intercostal muscle so that's from superficial to deep so it's useful to know the orientation of the muscle fibers of these three layers so the external intercostal muscle has fibers which are oriented in farily and medially so the external oblique fibers run like this so towards the midline and in fairly and what's particularly interesting about this muscle is that anteriorly where it's about to meet the sternum it doesn't continue as muscle but it forms this aponeurosis called the external intercostal membrane and this aponeurosis connects it TV to the sternum so it's got a little sheet of aponeurosis called the external intercostal membrane so underneath the external intercostal muscle you've got the internal intercostal muscle and these fibers are oriented in the opposite direction so they're oriented in superior direction and medial direction so they're like this and this doesn't have the aponeurosis which connects it to the sternum and deep to the internal intercostal muscle when you remove the internal intercostal muscle layer you see the innermost intercostal muscle there and these fibers are oriented in the same direction as the internal intercostal muscles so superiorly and medially so the way to remember the orientation of these fibers is with a simple mnemonic which is the same as the mnemonic I used in the abdominal anterior abdominal wall muscles cheetor so hands in pockets and hands on tits so if I just draw some hands which are in pockets pretty crappy drawing but it's best I can do unfortunately so this is a before arm and this is the hand and this is the sort of angle your forearms would be if they were in your pockets so pockets has the letter e in it so this is the direction the external intercostal muscles would be oriented and if your hands are on your tits so another pair of badly drawn hands then the muscle fibers sorry your forearms would be angled upwards and inwards in the same direction as the internal intercostal so tits has the letter i' in it so the internal intercostal muscles are oriented in the soup arrow medial direction the same as the angle of your forearms so those are the three layers of intercostal muscles and underneath the innermost intercostal muscle you've got the endo thoracic fashio which separates the intercostal muscles from the underlying plural cavity containing the lungs so underneath the end I throw a successor you've got the parietal pleura then the visceral pleura and finally you've got the lung so in terms of the actions of these muscles the external intercostal muscle is important in inspiration whereas the internal intercostal muscle is important in expiration and the innermost intercostal acts with the internal intercostal muscles so remember they have the fibers oriented in the same direction so the muscle actions are similar so they're active during expiration and these three muscles are innervated by the Associated intercostal nerves so the intercostal nerves from T 1 to T so I've removed the muscles from this model and I want to point out something that's quite important so between the internal intercostal muscle and the innermost intercostal muscles you've got a neurovascular bundle so you've got the intercostal vein artery and nerve which lie in the sub costal groove underneath the rib so if I just show you this skeleton model again we're just going to rotate round to the back and if I just zoom in a little bit on this rib cage I can show you the sub costal groove so at the inferior margin of the rib you've got this little groove at this sort of level and you've got this neurovascular bundle which runs in this inter cost in this sub costal groove so the costal groove so in this groove you've got nerves arteries and veins so from superior to inferior you've got the vein at the top the intercostal vein then you've got the intercostal artery and the intercostal nerve so the easy way to remember that is that it spells vang vien from superior to inferior vena r2 nerve so just going returning to this model you can see those structures here so you've got the vein artery nerve but these are shown a little bit out of place as they are mostly covered by the rib and line the costal groove but sometimes the the lowest structure the nerve can be can lie out of the costal groove and be unprotected so these these these newer vascular structures light between the innermost and the internal intercostal muscle so just to give you a quick to give you a better idea of how the structures are organized from superficial to deep I'm just going to draw a little diagram on the side so the first muscle you've got is the external intercostal then underneath that you've got the internal intercostal and then the next muscle down is the innermost intercostal and between these two muscles you've got the the neurovascular structures so at the top you've got the vein and then you've got the artery and then you've got the nerve and then underneath the the innermost intercostal you've got the endo thoracic fashio and then just underneath this you've got the floor so you've got the parietal pleura and then you've got the visceral pleura and then you've got the lung tissue onto that so just coming back to this model again we've got three more muscles that we need to talk about and these are quite minor muscles but I'll just talk about them very quickly so rotation around to the back I've dissected away the serratus posterior and the intern and the intercostal muscles from the right hand side and you can see these twelve small muscles here and these muscles are called the lever Torres costal and muscles and they attach from the transverse processes on to the rib below so for instance the fourth thoracic vertebra attaches to the fifth rib so the transverse process of t4 attaches to the rib five so you've got these on either side so I've just isolated the lever Torres costal muscle on the skeleton and you can see the 12 small muscles so these muscles function to assist in elevation of the thoracic ribcage so the next muscle is this muscle called the sub cost Ali's muscle and as you can see it attaches from one rib to the next below or the one to below so this muscle lies on the internal surface of the ribs and the final muscle I'm going to talk about is this one which also lies internally to the rib cage and this is called the transversus for a kiss muscle so this muscle originates in fear early on the body of the sternum and also on the safeword process and originates on some parts of these costal cartilages and it inserts onto the and it sets internally on ribs 2 to 6 on the costal cartilages of ribs 2 to 6 and its function is to pull up the ribs down so those are the muscles which make up the thoracic wall