Muscles of the Arms

Presentation

Muscles of the Arms

6. Forearm Muscles (deep)

5. Forearm Muscles (intermediate)

4. Forearm Muscles (superficial)

3. Posterior Arm Muscles

2. Anterior Arm Muscles

1. Sección

ÍNDICE

Why Study Arm Muscles?

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The upper arm is located between the shoulder joint and elbow joint. It contains four muscles – three in the anterior compartment (biceps brachii, brachialis, coracobrachialis), and one in the posterior compartment (triceps brachii).

Anterior Arm Muscles

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Triceps brachii is a large muscle found in the posterior (extensor) compartment of the arm. It consists of three distinct muscle bellies (heads) each of which has a different origin but share the same insertion point.

Posterior Arm Muscles

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The muscles in the anterior compartment of the forearm are organised into three layers:

• Superficial: flexor carpi ulnaris, palmaris longus, flexor carpi radialis, pronator teres.

• Intermediate: flexor digitorum superficialis.

• Deep: flexor pollicis longus, flexor digitorum profundus and pronator quadratus.

Forearm Muscles

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The flexor digitorum superficialis is the only muscle of the intermediate compartment. It can sometimes be classed as a superficial muscle, but in most individuals, it lies between the deep and superficial muscle layers.

Intermediate Compartment

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Deep Compartment

Attachments: Originates from the anterior surface of the ulna and attaches to the anterior surface of the radius.Actions: Pronates the forearm.Innervation: Median nerve (anterior interosseous branch).

• Attachments: Originates from the medial and lateral surfaces of the humeral shaft and inserts into the ulnar tuberosity, just distal to the elbow joint.

• Function: Flexion at the elbow.

• Innervation: Musculocutaneous nerve, with contributions from the radial nerve.

The lateral head originates from a narrow, linear ridge on the posterior surface of the humerus, just superior to the radial groove. A portion of the muscle fibers also arise from the lateral intermuscular septum.

Attachments: The flexor carpi ulnaris has two origins. The humeral head originates from the medial epicondyle of the humerus with the other superficial flexors, whilst the ulnar head originates from the olecranon of the ulna. The muscle tendon passes into the wrist and attaches to the pisiform bone, hook of hamate, and base of the 5th metacarpal Actions: Flexion and adduction at the wrist. Innervation: Ulnar nerve.

• Attachments: Originates from the coracoid process of the scapula. The muscle passes through the axilla, and attaches the medial side of the humeral shaft, at the level of the deltoid tubercle.

• Function: Flexion of the arm at the shoulder, and weak adduction.

• Innervation: Musculocutaneous nerve.

Attachments: Originates from the ulna and associated interosseous membrane. At the wrist, it splits into four tendons, that pass through the carpal tunnel and attach to the distal phalanges of the four fingers.Actions: It is the only muscle that can flex the distal interphalangeal joints of the fingers. It also flexes at metacarpophalangeal joints and at the wrist. Innervation: The medial half (acts on the little and ring fingers) is innervated by the ulnar nerve. The lateral half (acts on the middle and index fingers) is innervated by the anterior interosseous branch of the median nerve.

Attachments: It has two heads – one originates from the medial epicondyle of the humerus, the other from the radius. The muscle splits into four tendons at the wrist, which travel through the carpal tunnel, and attach to the base of the middle phalanx of the four digits. Actions: Flexes the metacarpophalangeal joints and proximal interphalangeal joints at the 4 fingers, and flexes at the wrist. Innervation: Median nerve.

The short head of the biceps brachii muscle primarily functions as a flexor of the elbow. This means it helps to bend your elbow, bringing your forearm closer to your upper arm. While it also contributes to a small degree of supination (turning your palm upward), its main role is in elbow flexion.

The long head arises from the infraglenoid tubercle of scapula, which is a rough area at the inferior margin of the glenoid fossa. Its attachment extends slightly above to the adjacent glenoid labrum and blends with the glenohumeral capsule of the shoulder joint, contributing to its stability.

Attachments: It has two origins, one from the medial epicondyle, and the other from the coronoid process of the ulna. It attaches laterally to the mid-shaft of the radius. Actions: Pronation of the forearm. Innervation: Median nerve.

The medial head is overlapped by the long and lateral head of the triceps. It has a broad origin along the entire posterior surface of the humerus inferior to the radial groove. More specifically, its attachment extends over an elongated triangular area on the humerus. The apex of the triangle is located on the medial border of the humerus above the insertion of teres major, while the base is the line that connects the medial and lateral epicondyles of the humerus. The medial head has an additional attachment to the posterior aspect of the medial and lateral intermuscular septum.

• Elbow Flexion: This is the most well-known function. When you bend your elbow, the long head of the biceps contracts to bring your forearm closer to your upper arm.

• Shoulder Flexion: The long head also contributes to shoulder flexion, which is the movement of raising your arm in front of your body. This is especially important for activities like lifting objects or reaching overhead.

• Supination: This is the movement that turns your palm upward. The long head of the biceps helps to rotate your forearm so that your palm faces upward.

• Humeral Adduction: This is a less common function where the long head helps to bring your arm closer to your body at the shoulder joint.

Attachments: Originates from the anterior surface of the radius and surrounding interosseous membrane. Attaches to the base of the distal phalanx of the thumb.Actions: Flexes the interphalangeal joint and metacarpophalangeal joint of the thumb. Innervation: Median nerve (anterior interosseous branch).