Download Interactive Shoulder Part 2

Interactive Shoulder Part 2
Muscle Structure
By Primal Pictures
EDITOR’S NOTE: The following is a small sample of the Interactive
Shoulder CD in the ground breaking Primal Pictures 3-D Anatomy CD ROM
series
DELTOIDS
Proximal Attachments
The deltoid is a thick, powerful muscle which
covers the shoulder joint and upper
humerus ( Slide 1, Slide 2). It arises from
the anterior border of lateral third of clavicle,
the lateral border of acromion and the lower
lip of scapular spine, as well as from the
fascia over infraspinatus muscle.
Distal Attachments
It inserts on the V shaped deltoid tuberosity half way down the lateral
aspect of the shaft of humerus.
Nerve Supply
Deltoid is innervated by the axillary nerve (C 5 ,6).
Actions
It is a powerful abductor of the humerus. Abduction is, however, initiated
by supraspinatus. The anterior portion of deltoid contributes to flexion of
the humerus ( Movie 1, Movie 2), with the posterior portion to extension (
Movie 1, Movie 2). When supraspinatus is torn, the upward pull of deltoid
results in superior subluxation of the humeral head.
The acromial part of the deltoid is multipennate. Tendinous septa arising
from the acromion and the deltoid tuberosity interdigitate, with short
muscle fibers extending between the septa. This gives the muscle a
short but powerful pull.
LATISSIMUS DORSI
Latissimus dorsi is a large flat muscle which
passes between trunk and humerus, acting
on both the shoulder joint and shoulder
girdle.
Proximal Attachments
It arises from spines and supraspinous
ligaments of the lower six thoracic vertebrae
deep to trapezius, and from thoracolumbar
fascia, by which it is attached to the spines
of all lumbar and sacral vertebrae. In addition, it arises from posterior
iliac crest and the lower three or four ribs. It passes upwards and
laterally, gaining a small slip from the inferior angle of scapula.
Distal Attachment
The muscle converges to form a flat 'strap like' tendon, which winds
around the inferior border of teres major to reach its humeral attachment
in the floor of the intertubercular groove of the humerus. The lower
border of the tendon unites with the tendon of teres major for a short
distance. A bursa lies between the two.
Nerve Supply
The thoracodorsal nerve (C 6 , 7 ,8).
Actions
Latissimus dorsi retracts the shoulder girdle, and is a powerful extensor
of the flexed humerus (for example, climbing). It also adducts and
internally rotates the humerus. It is an accessory muscle of respiration,
particularly violent expiration.
Latissimus dorsi and teres major form the posterior fold of the axilla.
TRAPEZIUS
The trapezius is a broad flat triangular
muscle which lies superficially at the back of
neck and upper trunk, the pair forming the 'trapezium' from which it
derives its name.
Proximal Attachments
It arises from the superior nuchal line of occipital bone, the external
occipital protuberance, ligamentum nuchae, the spines of seventh
cervical and all thoracic vertebrae and the intervening supraspinous
ligaments.
Distal Attachments
The upper fibers pass down and laterally to insert in the posterior aspect
of lateral clavicle. The middle fibers pass horizontally to the medial
border of acromion and upper lip of scapula spine. The lower fibers
ascend to the tubercle of scapula spine. The upper fibers form the
posterior border of the posterior triangle of the neck.
Nerve Supply
Trapezius receives motor innervation from the spinal accessory nerve,
which enters from the posterior triangle. Fibers from the ventral rami of
C3 and C4 are thought to be sensory.
Actions
The upper fibers elevate the scapula, ( Slide 1, Slide 2 ) for example
when carrying a weight. The middle fibers produce bracing of the
shoulder girdle. The lower fibers depress the medial aspect of the
scapula and shoulder, for example using the hands to rise from sitting.
The action of upper and lower fibers together tend to rotate the scapula
so that the glenoid fossa points upwards and forwards.
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