The biceps brachii, commonly known as the biceps, is a prominent muscle in the upper arm that plays a key role in the movement of the shoulder and elbow. This muscle is known for its distinctive two-headed (bicephalous) structure, comprising a long head and a short head, which give it its name. The biceps brachii is involved in the flexion and supination (rotational movement) of the forearm and is one of the most recognizable muscles due to its prominent appearance on the front side of the upper arm.
Location
The biceps brachii is located in the anterior (front) compartment of the upper arm. The long head originates from the supraglenoid tubercle of the scapula, while the short head originates from the coracoid process of the scapula. Both heads converge into a single muscle belly and insert into the radial tuberosity in the forearm and the bicipital aponeurosis, which extends to the fascia of the medial part of the forearm.
Anatomy
The biceps brachii is a crucial muscle of the upper limb with distinct anatomical features enabling its varied functions. Here’s an in-depth look at its anatomy:
Origin
The biceps brachii has two heads, each with its own origin:
- Long Head: Originates from the supraglenoid tubercle of the scapula, which is located at the top of the shoulder socket. This head travels through the shoulder joint via the bicipital groove of the humerus and is covered by the shoulder’s joint capsule, making it susceptible to injuries.
- Short Head: Originates from the tip of the coracoid process of the scapula, sharing this origin point with another muscle, the coracobrachialis.
Insertion
The two heads merge into a single muscle belly as they travel down the upper arm. The muscle then inserts onto the radial tuberosity on the radius bone in the forearm. Additionally, there is an extension from the insertion point known as the bicipital aponeurosis, which fans out to merge with the fascia on the medial side of the forearm.
Muscle Belly
The main portion of the biceps brachii is its large, bulging muscle belly, which is most visible when the muscle is contracted. This is the part that is commonly associated with the muscle’s strength and size.
Blood Supply
The brachial artery primarily supplies the biceps brachii. This major blood vessel runs alongside the muscle, providing it with essential nutrients and oxygen.
Innervation
The muscle receives innervation from the musculocutaneous nerve, which originates from the brachial plexus. This nerve provides the stimuli necessary for muscle contraction.
Relations
- Anteriorly (front): The biceps brachii is covered by skin and subcutaneous tissue and is superficial compared to most other arm muscles.
- Posteriorly (back): It lies on the brachialis muscle, which also contributes to elbow flexion.
- Laterally: The biceps brachii is related to the brachioradialis, a muscle of the forearm.
- Medially: It is near the median nerve and the brachial artery.
Functional Aspects
- The long head of the biceps brachii also contributes to the stability of the shoulder joint due to its origin within the joint capsule.
- The muscle’s location and long tendon allow it to act across two joints: the shoulder and the elbow.
Function
The biceps brachii muscle performs several important functions due to its unique anatomical structure and location:
- Elbow Flexion: The primary function of the biceps brachii is to flex the elbow, bringing the forearm towards the shoulder. This action is utilized in everyday activities such as lifting objects or performing a bicep curl.
- Forearm Supination: The biceps brachii is responsible for supination of the forearm, which is the rotation of the forearm that turns the palm upward or forward. This function is crucial for actions like opening a bottle or turning a doorknob.
- Shoulder Flexion: Although not its primary role, the biceps brachii assists in flexing the shoulder, contributing to movements that raise the arm forward and upward.
- Shoulder Joint Stabilization: The long head of the biceps brachii helps stabilize the top of the arm bone (humerus) within the shoulder socket during various activities, preventing dislocation or excessive movement within the joint.
Clinical Significance
The biceps brachii muscle holds significant clinical relevance due to its role in upper limb function and its susceptibility to injury:
Tendonitis and Tendon Ruptures: The biceps brachii is prone to tendonitis, particularly at the long head tendon, often due to repetitive strain or overuse. Tendon ruptures, noticeable by a “Popeye” bulge in the arm, can result from acute injuries or degenerative changes, affecting the muscle’s function and aesthetics.
Bicipital Tendinopathy: Chronic inflammation or degeneration of the biceps tendon, especially where the long head passes through the bicipital groove, can lead to pain and weakness, significantly impacting arm movements.
Impingement Syndrome: The long head of the biceps can be involved in shoulder impingement syndrome, where the tendon is compressed during shoulder movements, leading to pain and restricted motion.
Diagnostic Imaging: The biceps brachii is often examined using MRI or ultrasound in cases of shoulder pain or injury to diagnose conditions like tears, tendinitis, or other abnormalities.
Rehabilitation and Physical Therapy: Understanding the anatomy and function of the biceps brachii is crucial for designing effective rehabilitation programs for upper limb injuries. Strengthening and stretching exercises targeting this muscle are common components of recovery to restore function and prevent future injuries.
