Muscular System II (Trunk) Flashcards
How many layers can the Back Muscles be divided into?
- can be divided into three layers: superficial layer, intermediate layer and deep layer
- the first two layers (superficial and intermediate) are known as extrinsic muscles so one attachments of the muscle in in the back and the other can be somewhere else (scapula, humerus, skull)
- extrinsic muscles are innervated by ventral rami of spinal nerves - ventral rami come together and make plexuses - directly supplied by ventral rami but usually they are supplies branches of plexuses (all of them are indirectly or directly supplied by ventral rami)
- intrinsic are deep layer muscles so origin and insertion is within back area and they are all innervated by posterior rami of spinal nerves
Trapezius
the most superficially positioned muscle - muscle is originating from occipital bone and it also originates from all cervical and thoracic vertebrae’s spinous processes (big origin)- from that origin muscle fibers are converging laterally and getting to insertion which is spine of scapula and acromion (lateral end of spine) and some fibers also reach to the your clavicle (3 insertions)
◦ function: muscle fibers are directed differently- upper are directly inferiorly and latterly and middle fibers are running horizontally and inferior ones are directly superiorly and laterally- each set of fibers do something else - upper fibers help to shrug you shoulders, elevating your shoulders/scapula
◦ horizontal fibers running horizontally between scapula and vertebrae - retraction or adduction of scapula
◦ inferior fibers do opposite to upper and they can depress your scapula or shoulder (bring it down)
- nerve supply has exceptional nerve supply - not from ventral or dorsal rami rather the accessory nerve (cranial nerve XI)
Levator Scapulae
- levator scapulae (name indicates function) and origin is coming from cervical vertebrae and insertion is on superior angle of scapula - elevates your scapula - nerve supply: brachial plexus
- below LS there are two muscles almost running parallel to each other - rhomboid minor (smaller) and rhomboid major - both arise from lower cervical, upper thoracic vertebrae and insertion for both of them is medial border of scapula - function: run obliquely so they have two different movements: can do a bit of retraction and help in elevation (help in both) - supplied by same branch of brachial plexus
Latissimus dorsi
- huge muscle - latissimus dorsi means broad muscle of the back (testable)
- muscle originates from spinous processes of lower thoracic and all lumbar vertebrae and some attachments to sacrum and iliac crest - from all that big origin lots of fiber originates and the are converging to humerus - these fibers wrap around torso, pass medial to the arm and get inserted into to inter-tubercular groove because the muscle is passing medial to the arm it should pull the arm medially (medial rotation) but the main function is extension of the shoulder - prime mover for extension of shoulder joint (there are a few that muscles can extend the shoulder but this is the most powerful) - emphasize on these prime movers because they are important muscles - supplied by direct branch from brachial plexus
What are the two groups called in the deep muscles of the back?
erector spinae and transversospinalis
What bundles of muscle fibers fall under Erector Spinae?
divided into a few groups - one group is presented here named erector spinae (name of group of muscles - not an individual one) - erect of extend or straighten you back/spine/vertebral column
- band of muscles called iliocostalis (refers to ilium of hip bone and ribs) - running between hip bone and ribs (most lateral one)
- bundle of muscle fibers known as longissimus (middle one) - and the last bundle quite close to midline is spinalis
- comprised of 3 bundles of muscle fibers
What bundles of muscle fibers fall under transversospinalis?
transversospinalis is second group in deep layer - name of this family indicates attachment- run between transverse processes and spinous processes
- small group is called multifidus (quite prominent in the lumbar region) covered by latissimus dorsii and erector spinae but this is most chunky - can feel this as a bulk of muscle on either side of vertebral column in lower back region (muscle mass on either side of lumbar vertrbrae)
- group of muscles known as semispinalis - more prominent in thoracic region and we have last group called rotatores (smallest one) - responsible for rotation of your vertebrae (rotate one vertebrae in relation to the next vertebrae close to them)
- they are running obliquely - so rotation of vertebral column is the main function but both of these big groups provide stability of the vertebral column (common feature of both groups)
What muscles fall under Segmentals (deep muscles)?
- smaller muscles which run between adjacent vertebrae
- interspinales - run between adjacent spinous processes
- intertransversarii - running between adjacent transverse processes
- help maintain stability of vertebral column
- all of them are supplied by directed branches of dorsal rami of spinal nerves
What is an extrinsic muscle in the thorax region and what does it mean to be extrinsic? - most superficial
- extrinsic muscles have attachment outside the thorax and intrinsic muscles have both attachments within the thorax region
- extrinsic muscle: pectoralis major - origin is clavicle and sternum (most important origins are these two) - fibers are converging laterally and they are inserting to lateral lip of intertubercular groove - muscle fiber need to cross the shoulder joint anteriorly so they are passing in front - muscle will perform medial rotation of shoulder because it is in front - if the arm is already abducting it can be help adduct the arm back - muscle can help perform horizontal adduction - can palpate it during that
- this muscle is innervated by a branch of brachial plexus
Serratus Anterior (testable)
- originating from first 9 ribs and then it does something interesting - wraps around your chest and passes between your scapula and ribs - separates scapula from your thoracic wall (ribs)- reaches to its insertion which is medial border of scapula
- function: stabilize your scapula against your thoracic wall - firmly attaches scapula against your thoracic wall - scapula only has one bony attachment to clavicle and that is not much but on other other side it is articulating with the humerus and through the humerus it is transferring or passing the whole weight of your upper limb to the axial skeleton - so scapula only has some muscle attachments to the torso
- the muscles running between scapula and humerus - when they contract they tend to bring origin and insertion closer together
- when the muscles contract, the muscles running between scapula and humerus they have as tendency to move scapula towards humerus so you can prevent it through a stabilizing it - this muscle stabilizes the scapula and allows others muscles to perform their function properly
- lot of muscles depends on this so when you paralyze this muscle you lose a lot of muscles
- stabilize the scapula and it produces protraction or abduction of scapula (to grab something for example)
- this muscle is prime mover for protraction and prime mover for upward rotation of scapula (rotates your scapula upwards) - passing 90 of rotation for scapula
- main stabilizer of scapula to your thorax
- the nerve which supplies this muscle is a branch of the brachial plexus - the nerve is descending on the lateral side of your chest, and as it goes down, it sends numerous branches to supply the serratus anterior
- for breast cancer sometimes the surgeon has to go in and remove the entire breast tissue and they may unintentionally cut the nerve as it is quite close to the breast tissue - mastectomy - they will lose lots of muscle due to this
