The musculature of the arm is simple because it moves one joint. The arm is divided into two compartments: anterior and posterior, separated from one another by the humerus and the medial and lateral intramuscular septa. Large flexor and extensor muscles occupy them. Between these muscles, the brachial artery accompanied by the median nerve and ulnar nerve approaches the elbow in the anterior compartment on the medial side of the arm. Neither nerve gives off any branches in the arm; both innervate only the forearm and hand. Emerging from the axilla, the musculocutaneous and radial nerves course through the flexor and extensor compartments, respectively (Fig. 8-16).
Nearly 20 muscles are contained in the forearm. The forearm, which also consists of anterior (flexor) and posterior (extensor) compartments, is much more complex than the arm because it contains the prime movers for several joints. These muscles are packed into layers in each compartment. After entering the forearm, the radial, median, and ulnar nerves pass down to the hand beneath the superficial muscles of the anterior compartment (Table 8-3). They give off most of their branches to the superficial muscles in the region of the elbow. A deep branch of the median nerve, the anterior interosseous nerve, innervates the deep muscles anteriorly. The deep branch of the radial nerve and its posterior interosseous branch supply the remaining muscles in the back of the forearm. The radial and ulnar nerves descend to the wrist, accompanied by the arteries to the wrist in the anterior compartment.
The upper limb has six primary homeostatic ARPs: the lateral pectoral nerve on the chest, the dorsal scapular and suprascapular nerves on the shoulder, the lateral antebrachial cutaneous and
The Five Important Nerves in the Arm
Radial nerve Extension of entire arm, forearm, wrist, and finger joints below the shoulder Forearm supination Thumb abduction in plane of the palm
Flexion of digits 2 and 3 Wrist flexion and abduction Forearm pronation Finger adduction and abduction other than the thumb Thumb adduction Flexion of digits 4 and 5 Wrist flexion and adduction Axillary nerve Abduction of arm at shoulder beyond the first 15 degrees Musculocutaneous Flexion of arm at elbow nerve Supination of forearm
Ulnar nerve deep radial nerve on the forearm, and the superficial radial nerve on the hand.
As emphasized previously, each ARP contains a main peripheral nerve that is responsible for the dynamic physiology of the point. In addition, different nerves also innervate different tissues at different layers of the same point. Only the major nerves that affect the physiology of the primary homeo-static ARPs are discussed as follows.
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