[Music] the muscles of the back are numerous complex and frequently neglected during your anatomy studies however they play a vitally important role in posture stabilization of the vertebral column respiration movements of the shoulder and much more in this two-part series we're going to cover the muscles of the back divided anatomically into their deep or intrinsic intermediate and superficial layers we'll begin with the deepest layer i'm dr connor boylan and welcome to more than skin deep [Music] first let's re-familiarize ourselves with the bony anatomy of the vertebral column as that's where most of these back muscles will originate from or insert into the vertebral column consists of 26 individual bones which mostly articulate with one another via fibrocartilaginous intervertebral discs the bony subunits of this column are known as the vertebrae there are seven in the cervical or neck spine 12 in the thoracic or chest spine and five in the lumbar spine inferior to this are five fused vertebrae forming the sacrum and lastly the small triangular coccyx from the thoracic spine come the 12 paired ribs which curve around anteriorly and inferiorly to form part of the rib cage there are subtle differences between the vertebrae of each spinal level but today let's just look at the features essential to understand the deep back muscles projecting posteriorly from almost every vertebra is a central protrusion known as the spinous process projecting outwards posterior laterally are the paired transverse processes projecting upwards of the paired superior articular processes and downwards are the inferior articular processes and the broad flatter section that all of these processes connect to is known as the lamina the last bits of bony anatomy in the back that we need to know are the two paired scapulae or shoulder blades which we covered in much more detail in a previous video and the posterior elements of the skull namely the occiput the superior nuchal lines the inferior nuclear lines and the mastoid process i'll also add in the bony pelvis and the proximal parts of the humerus and femur to help contextualize the rest of the anatomy okay that's a lot of bony anatomy but don't worry about memorizing it all now we'll be recapping it all periodically as we learn about the muscles of the back the deepest layer of the back muscles is known appropriately as the deep muscle layer it consists of eight main muscles with a few additional minor muscles that play a less significant role now to confuse things a little the deep back muscles can actually be subdivided again into three more layers in order of depth let's start with the deepest muscles of them all the transverso spinalas these three muscles get their collective name as they are associated mostly with the transverse and spinous processes of the vertebral column present along the entirety of the vertebral column the best developed in the thoracic region are the numerous rotatory muscles these short muscles originate from the transverse processes of the vertebral bodies and insert into the inferior parts of the spinous processes and laminate of the vertebrae immediately above they are named after their primary function which is to assist in rotation of the trunk they also add little in proprioception and stabilization of the spine the next of the transverso spinalei muscles is the huge well-developed multifidus muscle this broad muscle gets its name from the latin origins maltus meaning many and fidus meaning split or cleft you can correctly assume from this that the multifidus has several finger-like origins from the sacrum superior articular processes of the lumbar vertebrae transverse processes of the thoracic vertebrae and articular processes of the cervical vertebrae these fingers group together into one large muscle which inserts at multiple points into the spinous processes of every single lumbar thoracic and cervical vertebra the action of multifidus is first to stabilize the vertebral column and second to extend the neck and trunk when it contracts the third and final transverso spinale muscle is the semi-spinalis this is often further split into the semi-spinalis cavitis associated with the skull the semi-spinalis cholis associated with the neck and the semi-spinalis thoracis associated with the thorax we'll consider them today as one big muscle the semispinalis muscle originates from the superior articular process of c4 to c7 and the transverse processes of t1 to t11 they each ascend four to six spinal levels and insert into the spinous processes of t6 to c2 and the occipital bone at an area between the superior and inferior nuchal lines the purpose of the semi-spinalis muscle is to assist in extension and rotation of the head neck and trunk okay that's the first group of deep back muscles covered if you're feeling a bit overwhelmed now might be a good place to take a quick break and recap what we've covered so far okay now you're ready let's move on to the next deep back muscle group the erector spinae this is probably the most famous group of deep back muscles and together their function is to both extend and flex the vertebral column depending on whether they're contracting unilaterally or bilaterally respectively all of the erector spinae muscles share a large common tendinous origin which connects them to parts of the lumbar and thoracic vertebrae the sacrum and a couple of the large ligaments in the pelvis the first and most medial of the erector spinae muscles is the spinalis this is often split again into its neck part the spinalis cholus and its trunk part the spinalis thoracis the muscle is simply named as it both originates and inserts into the spinous processes of the vertebral column the thoracic part originates from the common tendinous origin and the spinous processes of t11 to l3 and inserts into the spinous processes of t2 to t8 whilst the collis part originates from the spinous processes of c2 to t10 and inserts into the spinous processes of c2 to c4 lateral to the spinalis is the large lungismus muscle which can again be divided into capitis cholis and thoracis parts this originates from the common tenderness origin and the transverse processes of c4 to t6 to insert into the transverse processes of c2 to c7 all of the transverse processes of the thoracic and lumbar spine the second to twelfth ribs and the mastoid process of the skull the third and final erector spinae muscle is the lateral iliocostalis this broad flat muscle can be split into cholus thoracis and lumborum parts and its function is again to both flex and extend the back aleocostalis originates from the common tendency origin the spinous processes of l1 to l5 and the angles of the third to 12th ribs and inserts into the transverse processes of l1 to l4 the angles of the first to 12th ribs and the transverse processes of c4 to c6 the last two major deep muscles of the back are both located in the posterior lateral neck and are known together as the spino transversalis the first of these is the splenius capitis muscle this originates from the nuchal ligament and the spinous processes of c7 to t3 and inserts into the mastoid processes of the temporal bone as well as the lateral part of the superior nuchal line of the occipital bone splenius cavitis acts solely to extend and rotate the head then there's the very similar spenius cholis which originates from the spinous processes of t3 to t6 and inserts into the transverse processes of c1 to c3 its function is similarly to extend and rotate the neck here's an overview of what all these major muscles look like together see how they're arranged into layers of deep deeper and deepest muscles and see how they form this sort of tube-like band of muscle that runs the entire length of the spine it's these muscles that we have to thank for stabilizing our vertebral column and providing most of the extension and rotation movements we take for granted okay as promised let's finish by covering the last very small muscles of the back these are all relatively minor muscles but let's at least familiarize ourselves with them for completeness between the spinous processes of almost every vertebra is a small vertically oriented muscle known as an interspinalis these muscles are best developed in the cervical and lumbar regions and act primarily to stabilize the vertebral column then we have the really similar intratransversary muscles these go between the transverse processes mainly of the cervical and lumbar vertebrae and stabilize the spine and lastly we have the levatorys castorum which originate from the transverse processes of c7 to t11 and insert into the superior borders of the ribs as their name suggests these numerous small muscles help to lift the ribs at their costo vertebral joints and there we go that's every muscle that can be found in the deep back if you're interested in learning about the rest of the back muscles including the famous latissimus dorsi and trapezius muscles check out our next video releasing soon that will be covering both the intermediate and superficial muscles of the back that's all from me for now i hope you learned something and have a great day