Dominic Stone
The humerus is the longest bone in the upper extremity, connecting the shoulder to the elbow. It is a crucial component of the musculoskeletal system, facilitating various upper limb movements and providing stability. The humerus serves as an attachment point for several muscles, including the supraspinatus, infraspinatus, and teres minor. These muscles, along with the shoulder muscles and ligaments, play a vital role in stabilising the shoulder joint and enabling a wide range of motions. The flexion of the humerus, or raising the arm anteriorly, involves the contraction of muscles such as the anterior deltoid, coracobrachialis, pectoralis major, and biceps brachii. Understanding the anatomy of the humerus and its articulations is essential for physiotherapists to enhance patients' range of motion and address functional impairments.
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What You'll Learn
- The pectoralis major muscle helps with flexion, internal rotation, and adduction
- The coracobrachialis muscle assists with flexion and adduction
- The anterior deltoid is one of the shoulder's main flexors
- The subscapularis muscle is involved in internal rotation and abduction
- The biceps brachialis muscle helps with flexion and adduction
The pectoralis major muscle helps with flexion, internal rotation, and adduction
The humerus is a long bone that forms the upper arm. It is the longest bone in the upper extremity and plays a crucial role in the intricate dance of the upper limb's movements. The humerus serves as an attachment to 13 muscles, including the pectoralis major, which contribute to the movements of the hand, elbow, and shoulder, and therefore the function of the upper limb.
The pectoralis major is a large, superficial muscle located on the anterior surface of the thoracic cage. It is the largest and most superior muscle of the anterior chest wall. It is also the largest muscle in the chest area. In males, it is covered by the deep layer of fascia, subcutaneous tissue, and the adjacent skin. In females, it is covered by the breast. The pectoralis major has a broad origin, which is divided into three parts: the clavicular part, the sternocostal part, and the abdominal part. All three parts converge laterally and insert onto the greater tubercle of the humerus.
The pectoralis major plays an important role in flexion, adduction, and internal rotation of the arm. The clavicular part of the muscle helps to flex the humerus up to 90 degrees in a horizontal plane. The sternocostal part of the muscle can produce the antagonistic movement and extend the humerus back to the anatomical position. The pectoralis major also acts as a strong adductor and internal rotator of the humerus at the shoulder joint.
The pectoralis major's size, strength, and anatomical location make it an excellent candidate in transfer surgeries. It is also important in activities such as climbing, as it pulls the trunk forwards or upwards when its humeral attachment is fixed. Additionally, the pectoralis major facilitates the act of inspiration, which is particularly important during forced breathing in physical distress.
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The coracobrachialis muscle assists with flexion and adduction
The humerus is the longest bone in the upper extremity, forming the upper arm. It plays a crucial role in the intricate dance of the upper limb's movements. The coracobrachialis muscle is a slender muscle that originates from the deep surface of the coracoid process of the scapula. The name 'coracobrachialis' refers to its attachment to the coracoid process of the scapula and the shaft of the humerus, the upper arm bone.
The coracobrachialis muscle fibres run inferolaterally towards the humerus and insert onto the anteromedial surface of the humeral shaft, between the brachialis muscle and the medial head of the triceps. The coracobrachialis muscle lies posterior to the pectoralis major muscle and anterior to the tendons of subscapularis, latissimus dorsi, teres major, and the medial head of the triceps. It is located medial to the biceps brachii and brachialis muscles.
The main function of the coracobrachialis muscle is to produce flexion and adduction of the arm at the shoulder joint. It assists in bending the arm and pulling it towards the trunk (adduction). When the arm is abducted and extended, the coracobrachialis acts as an antagonist to the deltoid muscle, contributing to stabilising the head of the humerus in its socket.
The coracobrachialis muscle is not a prime mover, and its overuse can lead to hardening of the muscle. Symptoms of overuse include pain in the arm and shoulder, radiating down to the back of the hand. This can be caused by activities such as bench-pressing with heavy weights or carrying heavy loads with hanging arms.
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The anterior deltoid is one of the shoulder's main flexors
The deltoid muscle is the muscle that forms the rounded contour of the human shoulder. It is also known as the 'common shoulder muscle'. The deltoid muscle is made up of three distinct sets of muscle fibres: the anterior or clavicular part (commonly known as the front deltoid), the posterior or scapular part (commonly known as the rear deltoid), and the intermediate or acromial part (commonly known as the side deltoid). The anterior deltoid is one of the shoulder's main flexors.
The anterior deltoid helps to move the arm forward and connects to the clavicle. You use your front deltoids when you reach for an object on a shelf. The deltoid muscles work alongside other shoulder muscles, such as the rotator cuff muscles, to help perform a variety of movements. The deltoid muscle functions include arm abduction, flexion, and extension. Flexion involves moving the arm forward, toward an overhead position. The shoulder's main flexors are the anterior deltoid, coracobrachialis, and pectoralis major. The biceps brachii weakly assist in this action.
The deltoid muscles cover the front, side, and back of the shoulder joint. They help to lift the arm to the front, side, and back. The deltoid muscles are superficial, meaning they are close to the surface of the skin. The deltoid muscle is important for preventing the dislocation of the humeral head when a person carries heavy loads. The humerus is the longest bone in the upper extremity and serves as an attachment point for various muscles, including the deltoid. The humerus plays a crucial role in transmitting forces generated by the muscles.
The humerus serves as an attachment point for 13 muscles, which contribute to the movement of the hand and elbow, and the function of the upper limb. The humerus consists of a shaft and two extremities. It has a unique structure, including a head, anatomical neck, surgical neck, tuberosities, and body. The humerus forms the proximal articular surface, articulating with the glenoid fossa of the scapula, facilitating a wide range of movements at the glenohumeral joint.
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The subscapularis muscle is involved in internal rotation and abduction
The subscapularis muscle is a large, powerful, and triangle-shaped muscle that fills the subscapular fossa of the scapula. It is the only medial (internal) rotator among all the rotator cuff muscles. The subscapularis muscle's primary function is internal rotation, but it can also aid in adduction and abduction of the humerus.
The subscapularis muscle is innervated by the upper and lower subscapular nerves (C5-C6), which stem from the superior and posterior cords of the brachial plexus, respectively. The blood supply to the subscapularis muscle comes from a series of branches of the subclavian artery, including the axillary artery, subscapular artery, and suprascapular artery.
The subscapularis muscle is an important stabilizer of the shoulder joint, particularly during overhead movements of the arm, such as throwing or pulling downwards. It helps to prevent upward shoulder dislocation by providing stability to the glenohumeral joint. The subscapularis muscle also promotes coordination between the movements of the glenohumeral and scapulothoracic joints.
The subscapularis muscle can be examined using special tests such as the Gerber or lift-off test, the abdominal compression or belly-press test, and the bear hug test. These tests help to identify any weakness or pain in the subscapularis muscle, which can result in internal rotation weakness and instability at the glenohumeral joint.
In summary, the subscapularis muscle is involved in internal rotation and abduction of the humerus. It plays a crucial role in stabilizing the shoulder joint and coordinating the movements of the glenohumeral and scapulothoracic joints. The subscapularis muscle is susceptible to tears and injuries, particularly during overhead motions, and its weakness can lead to instability at the glenohumeral joint.
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The biceps brachialis muscle helps with flexion and adduction
The humerus is the longest bone in the upper extremity, and it serves as an attachment point for 13 muscles, including the biceps brachialis, which is responsible for flexion and adduction.
The biceps brachii muscle is one of the chief muscles of the arm, consisting of two heads that merge into one unique distal body. The long head originates at the supraglenoid tubercle of the scapula, while the short head arises from the coracoid process of the scapula.
At the shoulder level, the biceps brachialis facilitates flexion and adduction on a horizontal plane. When the muscle contracts, it pulls the arm towards the body (adduction) and bends the arm (flexion). This movement is particularly important for tasks like lifting heavy weights when the arm is extended downward.
The biceps brachii also plays a role in elbow flexion. It bends the forearm and rotates it outward (supination). The supination is most powerful when the elbow is flexed.
Additionally, the biceps brachii supports the humeral head within the shoulder joint, providing stability to the joint. It is involved in various physical activities, such as lifting, throwing, and racket sports, making it susceptible to tendinopathy and other injuries.
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Frequently asked questions
The muscles that flex the humerus include the anterior deltoid, coracobrachialis, and pectoralis major. The biceps brachii also assists in this action.
The humerus is a long bone that forms the upper arm. It is the longest bone in the upper extremity and plays a crucial role in the movement and stability of the upper limb.
The muscles that extend the humerus are the posterior deltoid, latissimus dorsi, teres major, and pectoralis major (sternocostal fibers). The long head of the triceps brachii is also involved in this movement.
