Arm Muscles Anatomy PDF

- Rhomboidus major (Fig. 67): Origin: from the spines of 2nd to 5th thoracic vertebrae and their supraspinous ligaments. Insertion: into the dorsal surface of the medial border of the scapula from the root of the spine to the inferior angle. Nerve supply: dorsal scapular nerve (nerve to rh...

- Rhomboidus major (Fig. 67): Origin: from the spines of 2nd to 5th thoracic vertebrae and their supraspinous ligaments. Insertion: into the dorsal surface of the medial border of the scapula from the root of the spine to the inferior angle. Nerve supply: dorsal scapular nerve (nerve to rhomboidus). Action: retracts the scapula. - Movements of the scapula: The scapula moves on the posterior wall of the thorax in the following order: A. Elevation (upwards): by the levator scapulae and the upper fibers of trapezius. B. Depression (downwards): by the pectoralis minor and the weight of the upper limb. C. Protraction (forwards): by the serratus anterior and the pectoralis minor. D. Retraction (backwards): by the rhomboidus minor and major and the middle fibers of trapezius. E. Lateral rotation: this is the movement which draws the inferior angle of the scapula away from the vertebral column so the glenoid fossa becomes facing upwards. It is done by the upper and the lower fibers of trapezius and the lower five digitations of serratus anterior. F. Medial rotation: this is the movement which draws the inferior angle of the scapula towards the vertebral column so the glenoid fossa becomes facing downwards. It is done by the pectoralis minor, and the rhomboidus minor and major and the middle fibers of trapezius and the weight of the upper limb. 71  The arm - The arm is the region extended from the shoulder to the elbow. - Medial and lateral intermuscular septa extend from the inner surface of the deep fascia to the medial and lateral borders of the humerus respectively. - These septa divide the arm into anterior and posterior compartments (Fig. 68). The anterior compartment - This compartment contains: 1. Three muscles (Fig. 69): the coracobrachialis, brachialis and the biceps brachii. 2. The musculocutaneous, median and ulnar nerves. 3. Brachial artery. 72 - The coracobrachialis (Figs 70 and 71): Origin: from the tip of the coracoid process with the short head of biceps (common origin). Insertion: into the middle of the medial border of the shaft of the humerus. Nerve supply: the musculocutaneous nerve. It pierces the muscle before it gives its nerve supply. Action: flexion of the shoulder joint, and assists in its adduction. 73 - The biceps brachii muscle (Figs 72 and 73): Origin: It takes origin by two heads: 1. Short head: from the tip of the coracoid process with the coracobrachialis. 2. Long head: from the supraglenoid tubercle (Fig. 74) This tendon is intracapsular (lies inside the capsule of the shoulder joint). It passes through the bicipital groove surrounded by a tubular synovial sheath. The transverse humeral ligament bridges over the tendon as it passes through the bicipital groove to prevent its bulge during contraction. - Insertion: into the posterior rough part of the radial tuberosity (Fig. 75). It gives a flat sheath called the bicipital aponeurosis which passes medially and fuses with the deep fascia on the medial side of the front of the forearm. 74 - Nerve supply: the musculocutaneous nerve. - Action: 1. Flexion of the elbow. 2. Supination of the forearm. 3. Flexion of the shoulder. 75 76  - The brachialis muscle (Figs 76 and 77): - Origin: from the anterior surface of the lower half of the shaft of the humerus. - Insertion: into the anterior surface of the coronoid process of the ulna. - Nerve supply: it has a double nerve supply. a. Musculocutaneous nerve (main nerve supply). b. radial nerve. - Action: flexion of the elbow joint. - Notice that: 1. The coracobrachialis muscle crosses the shoulder only (one joint). 2. The brachialis muscle crosses the elbow (one joint). 3. The bicips brachii crosses the shoulder and the elbow (two joints). 4. Long head of triceps muscle crosses two joints (shoulder and elbow joints), its lateral and medial heads crosses one joint (elbow) only. 77  The triceps muscle - Origin: it has three heads (Figs 78 and 79): 1. Long head: from the infra-glenoid tubercle. 2. Lateral head: from an oblique area on the posterior surface of the humerus above the spiral groove. 3. Medial head: from the posterior surface of the lower half of the humerus corresponding to the origin of the brachialis. - Insertion: into the posterior part of the superior surface of the olecranon process of ulna (Fig. 81). - Nerve supply: radial nerve (each head receives a separate branch). - Action: extension of the elbow joint. 78 79  The musculocutaneous nerve - It is a branch from the lateral cord of the brachial plexus (C5, 6, 7). - At its origin, it lies lateral to the third part of the axillary artery. - It passes downwards and laterally and pierces the coracobrachialis muscle. - It emerges from the coracobrachialis and passes downwards and laterally between the brachialis and the bicips brachii. - Then it emerges from undercover of the lower part of the lateral border of the bicips muscle (Fig. 82). 80 - It continues into the forearm as the lateral cutaneous nerve of the forearm. - Branches (Fig. 83): 1. Muscular branches to the coracobrahialis, the bicips brachii and the brachialis muscles. 2. Articular branches to the elbow joint. 3. Coetaneous: It terminates as the lateral coetaneous nerve of the forearm which supplies the skin of lateral side of the front and back of the forearm. 81  The ulnar nerve in the arm - It is a branch from the medial cord of the brachial plexus. - At its origin it lies on the medial side of the third part of the axillary artery. - It descends on the medial side of the upper half of the brachial artery down to the level of the middle of the arm (the level of insertion of coracobrachialis). - It pierces the medial intermuscular septum accompanied by the superior ulnar collateral artery to enter the posterior compartment of the arm where both are covered by the medial head of triceps (Figs 84 and 85). - Then it descends down to the back of the medial epicondyle and lies on the medial ligament of the elbow joint. - It enters the forearm by passing between the two heads of the flexor carpi ulnaris muscle. - It has no branches in the arm. - At the cubital fossa it gives an articular branch to the elbow joint. 82  The median nerve in the arm - It takes origin on the lateral side of the 3rd part of axillary artery by two roots: a. Lateral root from the lateral cord of the brachial plexus. b. Medial root from the medial cord of the brachial plexus. - The medial root crosses in front of the third part of the axillary artery to join the lateral root on the lateral side of the artery (Fig. 86). - It descends on the lateral side of the upper half of the brachial artery down to the middle of the arm (level of insertion of coracobrachialis). - It crosses in front of the brachial artery from lateral to medial and descends on the medial side of the lower half of the brachial artery down to the cubital fossa. - In the cubital fossa it lies on the medial side of the brachial artery and where they are covered and protected by the bicipital aponeurosis. 83 - The nerve leaves the cubital fossa and enters the forearm by passing between the two heads of the pronator teres muscle. The deep head of pronator teres separates the nerve from the ulnar artery. - The median nerve has no branches in the arm except for small vasomotor branches to the brachial artery. 84  The radial nerve in the arm - It takes origin from the posterior cord in the axilla. - It is the largest branch of the brachial plexus. - At its origin it lies behind the third part of the axillary artery (Fig. 87). - Then it passes through the lower triangular space accompanied by the profunda brachii vessels. - Then it winds through the spiral groove on the back of the humerus where it is directly related to the bone (Fig. 88). - About 5 cm above the elbow it pierces the lateral intermuscular septum and enters the anterior compartment of the arm where it lies in the groove between the brachialis and the brachioradialis muscles. - It enters the forearm by passing deep to the brachioradialis muscle. - Branches: A. In the axilla: it gives the following branches: 1. Muscular branches to the long and the lateral heads of triceps. 2. Posterior cutaneous nerve of the arm to the skin on the middle of the back of the arm. 85 B. In the spiral groove: it gives the following branches: 1. Muscular branches to the lateral and the medial heads of triceps. 2. Muscular branch to the anconeus muscle. 3. Lower lateral cutaneous nerve of the arm: supplies the skin of the lateral and anterior aspects of the lower part of the arm. 4. Posterior cutaneous nerve of the forearm: runs along the middle of the back of the forearm down to the wrist joint. C. In the groove between the brachialis and brachioradialis: It gives branches to both muscles and the extensor carpi radialis longus. D. In the cubital fossa: it gives articular branches to the elbow joint (Fig. 89). 86  - It ends in the cubital fossa at the level of the neck of the radius by dividing into the radial and the ulnar arteries. - Relations: 88