Anatomy of the Arm: Upper Limb Muscles and Functions

Study Notes

The Arm: Structure and Functions

The arm, also known as the upper limb, is the external appendage of the upper torso in vertebrates, consisting of two parts: the upper arm and the forearm. It plays a crucial role in providing support, maintaining balance, and performing various tasks such as grasping objects, manipulating tools, and engaging in activities of daily living.

Upper Arm

The upper arm is situated between the shoulder joint and the elbow joint. It contains four muscles, each residing in one of its two compartments. The anterior compartment houses three muscles: biceps brachii, coracobrachialis, and brachialis, whereas the posterior compartment contains the triceps brachii muscle.

Biceps Brachii

The two-headed biceps brachii muscle is primarily responsible for flexing the elbow and the shoulder, as well as supinating the forearm. Its primary attachment sites include the supraglenoid tubercle of the scapula and the coracoid process of the scapula, while its distal attachment is made via the bicipital aponeurosis into the radial tuberosity and the fascia of the forearm.

Coracobrachialis

The coracobrachialis muscle lies deep within the arm, originating from the coracoid process of the scapula. It passes through the axilla and attaches to the medial side of the humeral shaft, just below the deltoid tubercle. This muscle contributes to flexion at the shoulder joint and weak adduction of the upper limb.

Brachialis

The brachialis muscle, located deeper than the other muscles in the anterior compartment, is responsible for flexing the elbow joint. It originates from the medial and lateral surfaces of the humeral shaft and inserts onto the ulnar tuberosity, right next to the elbow joint.

Posterior Compartment

The posterior compartment of the arm houses the triceps brachii muscle, which consists of three heads: long head, lateral head, and medial head. The long and lateral heads originate from their respective attachments on the scapula and humerus, while the medial head is attached to the inferior aspect of the humeral shaft. These heads converge towards the elbow joint, where they insert onto the olecranon of the ulna, allowing extension of the elbow.

Description

Explore the structure and functions of the upper limb muscles in the arm, including the biceps brachii, coracobrachialis, brachialis, and triceps brachii. Learn about their origins, insertions, and roles in flexing, extending, and stabilizing the shoulder and elbow joints.