Muscles of the Trunk Flashcards
fan-shaped muscle, situated at the chest
action: primarily responsible for movement of the shoulder joint. (flexion of the humerus, as in throwing a ball underhand, and in lifting a child. adducts the humerus, as when flapping the arms. rotates the humerus medially, as occurs when arm-wrestling. responsible for keeping the arm attached to the trunk of the body.)
origin: clavicular head: anterior surface of the medial half of the clavicle.
sternocostal head: anterior surface of the sternum, the superior six costal cartilages, and the aponeurosis of the external oblique muscle
insertion: lateral lip of the bicipital groove of the humerus
(anteromedial proximal humerus)
pectoralis major
“big swing muscle” or “boxer’s muscle”
action: pull the scapula forward around the thorax
origin: fleshy slips from the outer surface of upper 8 or 9 ribs (under arm)
insertion: costal aspect of medial margin of the scapula
(lies deep to the subscapularis)
serratus anterior
largest and the outermost of the three flat muscles (broad, thin, and irregularly quadrilateral)
action: pull the chest downwards and compress the abdominal cavity, which increases the intra-abdominal pressure. same side side-bending and opposite side rotation
origin: ribs 5-12
insertion: xiphoid process, outer lip of the iliac crest, pubic crest, pubic tubercle, linea alba, inguinal ligament, anterior superior iliac spine (ASIS)
external oblique
lies below the external oblique and just above the transverse abdominal muscles.
actions: accessory muscle of respiration. reduce chest cavity during exhalation and pulls lower cavity down to expand volume (antagonist to diaphragm) causes ipsilateral rotation and side-bending (acts with the external oblique muscle of the opposite side)
origin: inguinal ligament, iliac crest and the lumbodorsal fascia.
insertion: linea alba, pectineal line of pubis and ribs 10-12.
internal oblique
“abs” (paired muscle)
runs vertically (long flat muscle, which extends along the whole length of the front of the abdomen)
action: responsible for flexing the lumbar spine, assists with breathing and plays an important role in respiration when forcefully exhaling, and in creating intra-abdominal pressure, such as when exercising or lifting heavy weights, during forceful defecation or parturition (childbirth)
origin: crest of pubis
insertion: costal cartilages of ribs 5-7 xiphoid process of sternum.
rectus abdominus
(so called for the direction of its fibers)(immediately beneath the internal oblique muscle)
action: helps to compress the ribs and viscera, providing thoracic and pelvic stability
origin: iliac crest, inguinal ligament, thoracolumbar fascia, and costal cartilages 7-12
insertion: xiphoid process, linea alba, pubic crest and pecten pubis via conjoint tendon
transversus abdominus
extends across the bottom of the thoracic cavity
action: main muscle of respiration and functions in breathing.
origin: septum transversum, pleuroperitoneal folds, body wall
insertion: N/A
diaphragm
are eleven in number on both sides
action: relax while/contract causing the expansion of the chest cavity and an influx of air into the lungs
origin: lower border of ribs
insertion: upper border of rib below
external and internal intercostals
large paired surface muscle
action: contraction can have two effects: movement of the scapulae when the spinal origins are stable, and movement of the spine when the scapulae are stable. main function is to stabilize and move the scapula.
origin: external occipital protuberance, spinous processes of vertebrae C7-T12, nuchal ligament, occipital bone
insertion: nuchal ligament, medial superior nuchal line, posterior border of the lateral one-third of the clavicle, acromion process, and spine of scapula
(resembles a trapezium or diamond-shaped)
trapezius
action: the prime mover of arm abduction along the frontal plane (an antagonist muscle of the pectoralis major and latissimus dorsi during arm adduction)
origin: the anterior border and upper surface of the lateral third of the clavicle, acromion, spine of the scapula
insertion: deltoid tuberosity of humerus
(is in the shape of the greek capital letter delta (Δ))
deltoid
thin, triangular muscle, situated at the upper part of the chest, beneath the pectoralis major
action: depresses the point of the shoulder, drawing the scapula superior, towards the thorax, and throwing its inferior angle posteriorly
origin: third to fifth ribs, near the costochondral junction
insertion: medial border and superior surface of the coracoid process of the scapula
pectoralis minor
thick but somewhat flattened muscle. positioned above the latissimus dorsi muscle
action: medial rotator and adductor of the humerus and assists the latissimus dorsi in drawing the previously raised humerus downwards and backwards
origin: posterior aspect of the inferior angle of the scapula
insertion: medial lip of the intertubercular sulcus of the humerus
teres major
a large, flat muscle on the back that stretches to the sides, behind the arm, and is partly covered by the trapezius
action: responsible for extension, adduction, transverse extension also known as horizontal abduction, flexion from an extended position, and (medial) internal rotation of the shoulder joint
origin: spinous processes of vertebrae T7-L5, thoracolumbar fascia, iliac crest, inferior 3 or 4 ribs and inferior angle of scapula
insertion: floor of intertubercular groove of the humerus
latissimus dorsi
relatively small muscle
action: performs abduction of the arm, and pulls the head of the humerus medially towards the glenoid cavity
origin: supraspinous fossa of scapula
insertion: superior facet of greater tubercle of humerus
supraspinatus
thick triangular muscle
action: main external rotator of the shoulder
origin: infraspinous fossa of the scapula
insertion: middle facet of greater tubercle of the humerus
infraspinatus
