Logan Steele
The humerus is the longest bone in the upper extremity, consisting of a shaft (diaphysis) and two extremities (epiphysis). It plays a crucial role in the overall movement and stability of the upper limb. The humerus serves as an attachment point for several muscles, including the rotator cuff muscles (supraspinatus, infraspinatus, teres minor, and subscapularis), which support the GH joint and attach the humeral head to the scapula. Other muscles that attach to the humerus include the deltoid, coracobrachialis, biceps brachii, and triceps brachii. These muscles facilitate movements at the shoulder, elbow, and wrist joints, contributing to the overall dexterity and functionality of the upper limb.
| Characteristics | Values |
|---|---|
| Muscles | supraspinatus, infraspinatus, teres minor, subscapularis, deltoid, coracobrachialis, biceps brachii, triceps brachii, teres major, trapezius, rhomboids, levator scapulae, serratus anterior, pectoralis minor, latissimus dorsi, pectoralis major |
| Joint | Glenohumeral Joint |
| Bone | Longest bone in the upper extremity |
| Muscle Functionality | Facilitated by muscle attachments along the humerus, such as the greater and lesser tuberosities |
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What You'll Learn
Rotator cuff muscles
The rotator cuff is a group of four distinct muscles and their tendons that provide stability and facilitate movement in the shoulder complex. The four muscles are supraspinatus, infraspinatus, teres minor, and subscapularis. They are also referred to as the SITS muscle, with reference to the first letter of their names.
The rotator cuff muscles arise from the scapula and connect to the head of the humerus, forming a cuff around the glenohumeral (GH) joint. They are responsible for stabilising the shoulder joint, allowing a wide range of movements while maintaining the stability of the glenohumeral joint. The supraspinatus facilitates abduction, helping to lift the arm out to the side. The infraspinatus and teres minor facilitate external rotation, with the infraspinatus being a powerful lateral rotator and the teres minor being more active towards the end of a rotation or when the arm is raised at a significant angle away from the body. The subscapularis, the largest muscle of the rotator cuff, facilitates internal rotation of the arm at the shoulder.
The rotator cuff muscles are supplied with blood by the suprascapular artery, the subscapular artery, and the posterior circumflex humeral artery. The suprascapular artery supplies the supraspinatus and infraspinatus muscles, while the subscapular artery gives vascular supply to the subscapularis muscle.
Injuries to the rotator cuff are common and can result in pain, shoulder weakness, and decreased function. These injuries can occur at any age and range in type and severity, with tears being the most common upper extremity condition seen by doctors. Tears can occur in the tendons or muscles and are classified based on their size and muscle atrophy.
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Shoulder muscles
The shoulder muscles are a group of muscles that surround the shoulder joint, also known as the glenohumeral joint, and play a crucial role in the movement and stability of the upper limb. These muscles can be divided into two main groups: those that connect the scapula and clavicle to the trunk, and those that connect the clavicle, scapula, and body wall to the proximal (top) end of the humerus.
The first group of shoulder muscles, which connect the scapula and clavicle to the trunk, includes the trapezius, levator scapulae, and rhomboids. These muscles originate from the base of the skull and/or spine, providing stability and movement to the scapula and clavicle.
The second group of shoulder muscles, which connect to the proximal end of the humerus, includes the pectoralis major, pectoralis minor, latissimus dorsi, teres major, and deltoid. These muscles anchor the humerus to the body and facilitate a wide range of movements.
Of particular importance within this group are the four rotator cuff muscles: the subscapularis, supraspinatus, infraspinatus, and teres minor. These muscles not only connect the scapula to the humerus but also provide crucial support to the glenohumeral joint, enabling a wide range of motions at the shoulder.
Additionally, the muscles of the arm that extend into the shoulder complex are classified into anterior (flexor) and posterior (extensor) compartments. This includes muscles such as the biceps brachii, triceps brachii, and coracobrachialis, which contribute to the overall movement and functionality of the upper limb.
The shoulder muscles, along with the humerus bone, work in harmony to enable the intricate dance of the upper limb's movements, showcasing the complexity and importance of the musculoskeletal system in our daily lives.
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Elbow movement
The elbow joint consists of the humerus, radius, and ulna bones. The two primary actions at the elbow are flexion and extension, which facilitate forearm movements. The humerus serves as an attachment to 13 muscles, including the rotator cuff muscles, which contribute to the movement of the hand and elbow, and thus the function of the upper limb.
The four rotator cuff muscles (supraspinatus, infraspinatus, teres minor, and subscapularis) are the main muscles that support the GH joint and attach the humeral head to the scapula. These muscles also play a role in transmitting forces generated by the muscles, acting as a bridge between the shoulder and the forearm.
The scapula is stabilized by muscles connecting it to the spine (trapezius, rhomboids, and levator scapulae muscles), to the ribs (serratus anterior and pectoralis minor), and to the neck (omohyoid). The pectoralis major, pectoralis minor, latissimus dorsi, teres major, and deltoid muscles connect to the proximal end of the humerus and anchor it to the body.
The biceps brachii and triceps brachii muscles are also involved in elbow movement. These muscles are part of the anterior (flexor) and posterior (extensor) compartments of the arm, respectively. They work together to facilitate the flexion and extension movements at the elbow joint.
Overall, the complex interplay of these muscles and their attachments to the humerus bone plays a crucial role in enabling the dexterity and functionality of the upper limb.
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Forearm movement
The forearm is the part of the arm between the elbow and the wrist. There are 20 muscles in the forearm that help to move the arms, hands, fingers, and thumbs. These muscles are supported by the two forearm bones, the ulna and radius, which form a joint that rotates to allow the turning of the palm.
The muscles in the forearm allow for both big and small movements. Big movements include swinging a baseball bat, while small, precise movements include writing your name or threading a needle. Forearm muscles also help with grip strength, which is useful for opening jars or holding sports equipment like a pickleball racquet.
The anterior (front) and posterior (rear) compartments of the forearm contain layers of muscles that run from deep inside the arm to its surface. The anterior compartment has three layers of muscle: superficial, intermediate, and deep. The superficial muscles in the anterior compartment are the flexor carpi ulnaris, palmaris longus, flexor carpi radialis, and pronator teres. The flexor carpi radialis helps move the arm away from the body, while the palmaris longus helps flex the wrist. The pronator teres muscle rotates the forearm. The flexor carpi ulnaris moves the wrist back and forth.
The flexor digitorum superficialis is the only muscle in the intermediate layer. It can sometimes be classed as a superficial muscle, but it usually lies between the deep and superficial muscle layers. It flexes the metacarpophalangeal joints and proximal interphalangeal joints at the four fingers, and flexes at the wrist.
There are three muscles in the deep anterior forearm: flexor digitorum profundus, flexor pollicis longus, and pronator quadratus. The flexor digitorum profundus flexes the distal interphalangeal joints of the fingers, the metacarpophalangeal joints, and the wrist. The flexor pollicis longus moves the thumb joint.
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Muscle attachments
The humerus is a long bone that consists of a shaft (diaphysis) and two extremities (epiphysis). It is the longest bone in the upper extremity, playing a crucial role in the intricate movements of the upper limb. The humerus serves as an attachment site for 13 muscles, which facilitate the movement of the hand, elbow, and shoulder, contributing to the overall dexterity and stability of the upper limb.
The proximal region of the humerus articulates with the scapula and clavicle, forming the glenohumeral joint, commonly known as the shoulder joint. This joint enables a wide range of movements in the shoulder. The humerus also articulates with the radius and ulna at the elbow joint, facilitating flexion and extension movements of the forearm.
The muscle attachments along the humerus play a vital role in muscle functionality. The greater and lesser tuberosities, for example, facilitate the function of muscles such as the supraspinatus, infraspinatus, and teres minor. The lateral and medial borders of the distal humerus form the medial and lateral supraepicondylar ridges, with the lateral ridge providing a common origin site for the forearm extensor muscles.
The deltoid muscle attaches to the deltoid tuberosity, which is located on the lateral border of the humerus. The roughened surface of the deltoid tuberosity provides a firm attachment site for the deltoid muscle. The teres major tendon attaches to the medial lip of the intertubercular sulcus, while the tendon of the pectoralis major muscle attaches to the lateral lip, also known as the crest of the greater tubercle.
The anterior surface of the humeral shaft is attached to the coracobrachialis, deltoid, brachialis, and brachioradialis muscles. Conversely, the posterior surface is attached to the medial and lateral heads of the triceps brachii muscle. The radial groove, located on the posterior surface, houses the radial nerve and profunda brachii artery, which are vulnerable to injury in the event of a mid-shaft fracture.
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Frequently asked questions
The humerus is a long bone that consists of a shaft (diaphysis) and two extremities (epiphysis). It is the longest bone in the upper extremity.
The humerus serves as an attachment to 13 muscles which contribute to the movements of the hand and elbow, and therefore the function of the upper limb. These include the supraspinatus, infraspinatus, teres minor, and subscapularis rotator cuff muscles.
The humerus plays a crucial role in transmitting forces generated by the muscles, acting as a bridge between the shoulder and the forearm.
The glenohumeral joint, commonly referred to as the shoulder joint, consists of the attachment of the humerus bone to the scapula. This joint facilitates a wide range of movements.
The muscles of the shoulder either connect the scapula and clavicle to the trunk or connect the clavicle, scapula, and body wall to the proximal (top) end of the humerus. The trapezius, levator scapulae, and rhomboids are examples of muscles that connect the scapula and clavicle to the trunk.
