The arm, or brachial region, contains the humerus and is located between the shoulder and elbow. The humerus articulates with the forearm (antebrachium) at the elbow complex, which consists of three bones: humerus, ulna, and radius. The articulations of these bones result in three separate joints that share a common synovial cavity, enabling the forearm to flex, extend, pronate, and supinate on the humerus.
ACTIONS OF THE ELBOW COMPLEX
The elbow complex consists of the joints and actions (Figure 31-1A–C):
Humeroulnar joint. Articulation between the humerus (trochlea) and ulna (trochlear notch).
Humeroradial joint. Articulation between the humerus (capitulum) and radius (head).
Flexion. Bending of the elbow (i.e., biceps brachii and brachialis muscles; musculocutaneous nerve).
Extension. Straightening of the elbow (i.e., triceps brachii muscle; radial nerve).
Proximal radioulnar joint. Articulation between the radius (head) and ulna (radial notch).
Pronation. Pivoting the elbow (forearm) into the prone position (palms down) (i.e., pronator teres muscle; median nerve).
Supination. Pivoting the elbow (forearm) into the supine position (palms up) (biceps brachii muscle; musculocutaneous nerve).
A. Lateral view of the elbow demonstrating bony landmarks and articulations. Radioulnar joint during supination (B) and pronation (C). Anterior (D) and posterior (E) views of the brachial muscles.
The muscles of the arm are divided by their fascial compartments (anterior and posterior), and primarily act on the elbow. Identifying the joints that the muscles cross provides useful insight into the actions of these muscles (Table 31-1).
TABLE 31-1.Muscles of the Arm |Favorite Table|Download (.pdf) TABLE 31-1. Muscles of the Arm
|Muscle ||Proximal Attachment ||Distal Attachment ||Action ||Innervation |
|Anterior compartment of the arm |
|Biceps brachii || ||Radial tuberosity ||Flexion of shoulder; flexion and supination of elbow ||Musculocutaneous n. (C5–C6) |
|Brachialis || ||Coronoid process and tuberosity of ulna ||Flexion of the elbow ||Musculocutaneous n. (C5–C6) |
|Coracobrachialis || ||Medial, midshaft surface of humerus ||Flexion of shoulder ||Musculocutaneous n. (C5–C7) |
|Posterior compartment of the arm |
|Triceps brachii || |
Long head: infraglenoid tubercle
Lateral head: posterior humerus
Medial head: posterior humerus
|Olecranon process of ulna ||Extension of shoulder and elbow ||Radial n. (C6–C8) |
MUSCLES OF THE ANTERIOR COMPARTMENT OF THE ARM
The muscles in the anterior compartment of the arm have the following in common:
The following muscles are within the anterior compartment of the arm (Figure 31-1D):