Neuroanatomy Draw It To Know It

34 Neuroanatomy: Draw It to Know It

Brachial Plexus (Cont.)

Now, let’s include some of the less oft en clinically tested
brachial plexus structures. First, where the fi ft h and sixth
cervical roots join together, indicate the nerve to the sub-
clavius muscle. Th e subclavius provides clavicle depression.
Next, show that in addition to the biceps brachii, the
musculocutaneous nerve also innervates the brachialis
muscle, which lies deep within the anterior upper arm,
and fl exes the elbow with the forearm in any position;
also show that the musculocutaneous nerve innervates
the coracobrachialis muscle, which assists the clavicular
head of the pectoralis major muscle in shoulder fl exion.
Proximal and distal to the thoracodorsal nerve, respec-
tively, draw the upper subscapular and lower subscapular
nerves. Show that they both innervate the subscapularis
muscle, which assists in shoulder internal rotation. Th en,
show that the lower subscapular nerve also innervates

teres major, which assists in shoulder internal rotation,

as well.

Next, return to the axillary nerve and show that the

more "minor" muscle it innervates is teres minor, which

assists in shoulder external rotation. Th e action of teres

minor is best remembered by its relationship to the

action of the axillary-innervated deltoid muscle, which

provides shoulder abduction.

Lastly, show that if the brachial plexus is shift ed up

one level and receives substantial innervation from C4,

it is called a prefi xed plexus, and if it is shift ed down one

level and receives substantial innervation from T2, it is

called a postfi xed plexus.

Note that we have only listed the major actions of

each muscle — refer to a kinesiolog y textbook for a list-

ing of additional muscle actions.^1 – 6

FIGURE 3-11 Coracobrachialis. FIGURE 3-12 Subscapularis.

FIGURE 3-13 T e r e s m a j o r. FIGURE 3-14 Teres minor.