General Review
General Terms of Description
The
Muscles of the Trunk (anterior)
The
Muscles of the Trunk (posterior)
HUMAN ANATOMY FOR THE ARTIST
CONTENTS:
G
eneral review:
In dealing with the human body the whole is greater than the sum of the parts. The human skeleton combines two opposites: STABILITY - from the front the skeleton is balanced BI-symmetrically: ACTION - from the side balance is achieved by movement around a center of gravity.
The skeleton is the ARCHITECTURAL aspect of the body, the mechanical design. The individual parts can be separated from the rest without destroying the whole. The division between the parts is clearly defined. The proportions and actions of the figure are determined by the skeleton.
The muscles are the ORGANIC aspect of the body. They imbricate or lace together the bony structure. All joints but one (the iliac crest) are crossed by muscles. The muscular system cannot be taken apart as can the skeletal without damaging the integrity of the system.
The skeleton can be clearly seen in the living figure. Where bone is near the surface it is said to be
SUBCUTANEOUS.
The single most important influence on the skeleton is the backbone. While the backbone is never seen in its entirety in the living body its influence is always felt.
The skeletal divisions of the trunk of the body are: the thorax (ribcage), the lumbar region (section between the ribcage and pelvis), and the pelvis.
anterior - front posterior - back
superior - upper, towards top inferior - lower, towards bottom
internal - inside external - outside
medial - nearer mid line lateral - further from mid line
supine - forearm and hand, turned prone - forearm and hand, turned palm-side
palm-side upward downward
dorsal - refers to back; also the back of the
hand and top of the foot
TERMS OF DESCRIPTION: THE MUSCULAR SYSTEM
origin - relatively fixed point of muscle attachment
insertion - relatively moveable point of muscle attachment
PARTS:
ligament - fibrous tissue binding bone together or lashing tendons or muscles in place
body or belly of muscle - fleshy part that contracts and changes form as fiber contract and relax
tendon - fibrous end of muscle that attaches to bone (tendons do not change form but do become more visible in action
aponeurosis - expanded tendon for attachment of flat muscle
fascia - fibrous envelope covering groups of muscles
TYPES:
long - long body with cord-like tendons (arm and legs)
broad - wide, thin body with aponeurotic tendons (trunk)
short - sometimes without tend, making direct connection with bone (face, hands, feet)
SITUATION:
superficial - principally on external form
deep - fill depression of skeleton; lie under superficial muscles and influence form indirectly
MUSCLES ARE NAMED ACCORDING TO:
region - as in pectoral (breast), temporalis (temporal region of skull)
direction - as in external oblique (direction of fibers)
dimension - as in supinator longus
form or shape - as in trapezius, rhomboid
structure - as in semitendinosus or number of heads - triceps, biceps
function - as in erector spinae, extensor digitorium longus
attachments - as in sternomastoid (sternocleidomastoid)
NAMES DESCRIBING ACTION:
flexor - causes bending or angulation
extensor - straightens
levatator - raises
abductor - draws away from mid line
adductor - draws toward mid line
tensor - draws tight
rotator - causes to revolve
supinator - turns palm of hand upward or forward
pronator - turns palm of hand downward or backward
***Students are NOT responsible for information in red.
MUSCLES OF THE TRUNK (ANTERIOR)
PECTORALIS MINOR: deep muscle - helps fill out side of chest
origin: ribs 3, 4, 5
insertion: corocoid process of scapula
form: helps fill out armpit area
action: helps pull scapula and clavicle down and lower the margin of the scapula medially
SERRATUS MAGNUS: greater part of the muscle is hidden by pectorals and lattisimus
origin: upper 8 ribs - each segment wraps around a rib
insertion: in back - medial border of scapula on interior surface
form: can see lower 3 segments when arm is at the side; 4 when arm is raised - often mistaken for ribs
action: pulls scapula tight against ribs
PECTORALIS MAJOR: entirely superficial
origin: inner half or third of clavicle; entire length of sternum; upper six ribs
insertion: bicipital groove
form: fills in upper part of chest, creates anterior margin of armpit
action: draws arm forward and inward; rotates arm inward (with teres major); lowers raised arm
EXTERNAL OBLIQUE:
origin: extends from lower 8 ribs to anterior half of iliac crest; more a muscle of the side interdigitates with the serratus magnus; broad, flat aponerosis from base of pectoralis major to anterior superior iliac spines and pubic bone
insertion: anterior third of iliac crest - thickest part just above the iliac crest
form: fills space between base of ribcage and pelvic crest
action: with fixed pelvis - draws ribcage downward; rotates torso side to side and pulls ribcage down in side bends; with fixed ribcage - elevates the pelvis (os coxae)
RECTUS ABDOMINIS:
origin: pubic crest
insertion: 5, 6, 7th ribs right above thoracic arch and below pectoralis major - divided into four groups
form: converts thoracic arch from V-shape to a more rounded shape
action: to flex trunk: NOTE: rectus folds at the base of the ribs and at the navel
SURFACE LANDMARKS OF THE TRUNK:
above the clavicle - triangular hollow made by sterno-mastoid and trapezius: supra clavicular depression
below the clavicle - smaller triangular hollow; infra clavicular depression - between the deltoid and the pectoralis major
DEEP MUSCLES:
ERECTOR SPINAE GROUP (Infraspinatus muscles) - partly superficial, partly deep - run on either side of the spine; common mass is inferior end of backbone and spreads into 3 separate groups
origin: dorsal surface of sacrum; spinous processes of all lumbar vertebrae and 2 or 3 lowest thoracic vertebrae
insertion: inserts into ribs at angle of the ribs and to various points of the spine
action: connects lower spine to upper - braces spine, keeps body upright (when standing erect muscles do little work but come into play as body begins to bend forward, backward or sideways)
form: helps create rounded forms on either side of backbone in lumbar region
SPLENIUS - another deep muscle - important in moving neck (sometimes considered part of the erector spinae group)
origin: lower part of nuchal ligament down to 7th cervical; another part drops down to the about to about mid-thoracic vertebra (6th)
insertion: both mastoid processes
action: strengthens neck - helps hold neck erect - helps pull head around (from back)
form: helps fill out upper back of the neck
RHOMBOIDS – Rhomboidus
origin: lower 6th and 7th cervical spinous processes and spinous process of thoracic vertebrae 1 through
insertion: upper and lower vertical margins of scapulae
action: to draw shoulder blades together
form: great fullness in center of back becoming a bulge when shoulder blades are drawn together
ELEVATOR OF THE SCAPULA -
thin set of muscles
origin: upper transverse pines (3 or 4) of cervical vertebrae
insertion: upper medial angle of the scapula
action: helps raise shoulder blades
form: helps fill out sides of neck at back
SUPERFICIAL MUSCLES (posterior)
LATISSIMUS DORSI - largest muscle in the body in terms of covering square inches - flat muscle
origin - lower 6 thoracic vertebrae; all lumbar vertebrae; region of the sacral triangle; posterior third of the iliac crest. The lower part of the latissimus is a diamond-shaped tendonous sheath which covers the rector spinae muscles
insertion - extends upwards, curves around side of body and becomes much thinner (a strap) and inserts in the bicipital groove of the humerus
action - pulls arms down and back (called the "swimmer’s muscle")
form - muscle thickest on lateral margin of the trunk - it shows most clearly here
TRAPEZIUS - fills upper back
origin - extends from the occipital protuberance of skull down nuchal ligament and spinous processes of thoracic vertebrae to #12
insertion - outer half to third of the clavicle, all the way around to the acromion process to the upper margin of the spine of the scapula and then to the inner margin of the scapula
action - can raise shoulders, help turn head if one side is contracted and the other relaxed; can pull down the shoulders from the lower fibers
form - fills out shoulders, adds fullness to upper center back
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