Logan Steele
The humerus is a long bone that forms the upper arm. It serves as an attachment point for muscles, including the supraspinatus, infraspinatus, and teres minor, which facilitate the movement of the hand and elbow. The deltoid muscle covers the lateral aspect of the greater tubercle, resulting in the normal rounded shape of the shoulder. The deltoid tuberosity is a roughened surface on the lateral surface of the shaft of the humerus and acts as the site of insertion of the deltoid muscle. The greater tubercle is the most lateral bony point of the humerus and serves as an attachment site for three rotator cuff muscles: supraspinatus, infraspinatus, and teres minor. These muscles attach to superior, middle, and inferior facets on the greater tubercle. The crest of the greater tubercle forms the lateral lip of the bicipital groove, and the supraspinatus muscle attaches to the highest point of the greater tubercle.
| Characteristics | Values |
|---|---|
| Description | The humerus is a long bone that forms the upper arm. |
| Parts | The humerus has a head, anatomical neck, surgical neck, tuberosities, and body. |
| Function | The humerus serves as an attachment point for muscles that contribute to the movement of the hand and elbow, and the function of the upper limb. |
| Muscle Attachments | The humerus serves as an attachment site for 13 muscles, including the supraspinatus, infraspinatus, teres minor, coracobrachialis, deltoid, brachialis, brachioradialis, triceps, subscapularis, teres major, latissimus dorsi, pectoralis major, and pronator teres. |
| Facilitation of Forearm Movements | The humerus enables flexion and extension movements of the forearm, contributing to the dexterity of the upper limb. |
| Glenohumeral Joint | The head of the humerus forms the proximal articular surface of the glenohumeral (shoulder) joint, facilitating a wide range of movements. |
| Neurovascular Structures | The humerus is in close proximity to the axillary nerve and the posterior circumflex artery. |
| Fracture Risks | The surgical neck of the humerus is a common site of fracture, which can result in axillary nerve damage and paralysis of the deltoid and teres minor muscles. A mid-shaft fracture can damage the radial nerve and profunda brachii artery. |
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What You'll Learn
Supraspinatus, infraspinatus, and teres minor muscles
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 humerus serves as an attachment point for muscles, including the supraspinatus, infraspinatus, and teres minor muscles. These muscles contribute to the coordinated actions and functionality of the upper limb.
The supraspinatus, infraspinatus, and teres minor muscles are rotator cuff muscles that work together to control the movements of the humeral head and stabilize it within the glenoid cavity of the shoulder joint. The teres minor is a posterior muscle of the shoulder that extends between the scapula and the head of the humerus. It is one of the four muscles of the rotator cuff, along with the supraspinatus, infraspinatus, and subscapularis. These muscles act together to stabilize the shoulder joint and control the movements of the humeral head within the glenoid cavity.
The supraspinatus muscle is one of the rotator cuff muscles that help to stabilize the shoulder joint. It originates from the scapula, specifically from the supraspinous fossa, which is located superior to the infraspinatus muscle. The supraspinatus muscle attaches to the greater tubercle of the humerus, which is located on the lateral side of the humerus bone.
The infraspinatus muscle is also a rotator cuff muscle that works together with the teres minor muscle to externally rotate the arm. It originates from the infraspinous fossa of the scapula, which is located inferior to the spine of the scapula. The infraspinatus muscle also attaches to the greater tubercle of the humerus, similar to the supraspinatus muscle.
The teres minor muscle is the smallest of the two "teres muscles", with the other being the "teres major." It originates superior to the teres major on the superior two-thirds of the lateral border of the scapula. The teres minor muscle inserts into the greater tubercle of the humerus, just like the supraspinatus and infraspinatus muscles. The tendon of the teres minor muscle blends with the glenohumeral joint capsule as it crosses the shoulder joint, providing reinforcement and mechanical support to the joint.
In summary, the supraspinatus, infraspinatus, and teres minor muscles are rotator cuff muscles that play a crucial role in stabilizing the shoulder joint and controlling the movements of the humeral head within the glenoid cavity. They attach to the greater tubercle of the humerus and work together to facilitate the coordinated actions and functionality of the upper limb. Altered activity in these muscles can lead to reduced upper extremity speed, agility, and strength, as well as a decrease in the effectiveness of resistance training for the upper body.
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Teres major muscle
The teres major muscle is a thick but somewhat flattened muscle of the upper limb. It is one of the seven scapulohumeral muscles that act around the glenohumeral joint to facilitate shoulder movement. It is sometimes referred to as "lat's little helper" because of its synergistic action with the latissimus dorsi.
The teres major originates on the dorsal surface of the inferior angle and the lower part of the lateral border of the scapula. The fibres of the teres major insert into the medial lip of the intertubercular sulcus of the humerus. The tendon, at its insertion, lies behind that of the latissimus dorsi, from which it is separated by a bursa. The two tendons are, however, united along their lower borders for a short distance. The teres major is supplied primarily by the lower subscapular nerve and additionally by the thoracodorsal nerve (middle subscapular nerve).
The main function of the teres major is to produce movements of the humerus at the glenohumeral joint. By contracting, it pulls the humerus posteriorly (extension) and rotates it medially towards the trunk (internal rotation). Additionally, it contributes to the stabilisation of the shoulder joint. It assists the latissimus dorsi in drawing the previously raised humerus downwards and backwards (extension, but not hyperextension). It also helps stabilise the humeral head in the glenoid cavity.
Isolated teres major injuries are rare. They are almost exclusively encountered in professional and high-level recreational athletes, such as baseball pitchers. The main symptom of a teres major tear is a sudden sharp pain in the shoulder, upper arm and armpit. This usually arises if the muscle is not rested and no treatment is carried out. Most cases of teres major injuries heal successfully without surgery. Treatment includes a proper warm-up before exercising, strengthening exercises and stretches.
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Deltoid muscle
The deltoid muscle, also known as the 'common shoulder muscle', forms the rounded contour of the human shoulder. It is made up of three distinct sets of muscle fibres: the anterior or clavicular part (commonly known as the front delt), the posterior or scapular part (commonly known as the rear delt), and the intermediate or acromial part (commonly known as the side delt). The deltoid muscle is responsible for elevating the arm in the scapular plane, and its contraction elevates the humeral head.
The deltoid muscle is supplied by the thoracoacromial artery, the circumflex humeral arteries, and the profunda brachii artery. It is innervated by the axillary nerve, which originates from the anterior rami of the cervical nerves C5 and C6. The axillary nerve supplies sensation to the deltoid muscle, and compression or damage to the nerve can occur during surgery, traumatic injury, or overuse of a crutch. Axillary nerve damage can result in paralysis of the deltoid muscle, causing difficulty in performing abduction of the affected limb.
The deltoid muscle functions include arm abduction, flexion, and extension. It helps raise the arm to the front, side, and back. The anterior deltoid is responsible for flexion, internal rotation, and horizontal adduction, while the posterior deltoid is responsible for extension, external rotation, and horizontal abduction. The deltoid muscle also helps stabilise the shoulder joint and prevent dislocations.
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Rotator cuff muscles
The rotator cuff is a group of four distinct muscles and their tendons that provide strength and
The supraspinatus muscle is the only muscle of the rotator cuff that is not a rotator of the humerus. The infraspinatus is a powerful lateral rotator of the humerus. The teres minor is a narrow and long muscle entirely covered by the deltoid, making it hardly differentiated from the infraspinatus. The subscapularis muscle receives its vascular supply from the subscapular artery, which is the largest branch of the axillary artery.
The rotator cuff muscles are deeper muscles that are very active in the neuromuscular control of the shoulder complex during upper extremity movements. They are essential for almost every type of shoulder movement, including flexion, abduction, internal rotation, and external rotation. These muscles allow a wide range of movement while maintaining the stability of the glenohumeral joint. The rotator cuff muscles keep the head of the humerus within the small glenoid fossa of the scapula, enlarging the range of motion in the glenohumeral joint and avoiding mechanical obstruction.
The rotator cuff muscles can be evaluated through specific tests, such as Jobe's test, commonly known as the "empty can" test, which is used to evaluate the supraspinatus muscle. Additionally, imaging methods such as MRI are used to evaluate rotator cuff pathologies, including tears and inflammation, and to establish proper treatment protocols.
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Forearm extensor muscles
The humerus is the longest bone in the upper extremity, and it serves as an attachment point for muscles that contribute to the coordinated actions and overall movement of the upper limb. The humerus also plays a role in transmitting forces generated by the muscles.
The forearm is the section of the upper limb from the elbow to the wrist, and it contains twenty muscles that act on the elbow and wrist joints, as well as the carpometacarpal, metacarpophalangeal, and interphalangeal joints of the hand. These forearm muscles are divided into two compartments: the anterior flexor compartment and the posterior extensor compartment. The posterior extensor compartment contains the forearm extensor muscles, which are responsible for producing movements in the forearm, hand, and fingers.
The forearm extensor muscles are commonly referred to as the extensor muscles and are organised into two layers: deep and superficial. The superficial layer contains seven muscles, four of which (extensor carpi radialis brevis, extensor digitorum, extensor carpi ulnaris, and extensor digiti minimi) share a common tendinous origin at the lateral epicondyle. The extensor digitorum is the main extensor of the fingers, and it originates from the lateral epicondyle, with its tendon inserting into the extensor hood of each finger. The extensor digiti minimi is thought to originate from the extensor digitorum muscle, and it extends the little finger while contributing to wrist extension.
The extensor carpi radialis muscles are situated on the lateral aspect of the posterior forearm and produce abduction and extension at the wrist. The extensor carpi radialis longus is a long muscle that arises from the lateral supracondylar ridge of the humerus and inserts onto the base of the metacarpal bone of the second digit. The extensor carpi radialis brevis is located deep to the extensor carpi radialis longus and arises from the lateral epicondyle of the humerus, with its tendon inserting onto the base of the metacarpal bone of the third digit.
The brachioradialis is a unique muscle that shares characteristics of both extensor and flexor muscles. It arises from the proximal aspect of the lateral supracondylar ridge of the humerus and attaches to the distal end of the radius. It acts as a flexor at the elbow and contributes to supination at the proximal radioulnar joint.
The anconeus is another muscle in the extensor compartment of the forearm, situated proximally and medially. It originates from the lateral epicondyle and attaches to the posterior and lateral part of the olecranon, extending and stabilising the elbow joint.
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Frequently asked questions
The supraspinatus, infraspinatus, and teres minor muscles all attach to the greater tubercle of the humerus.
The humerus is the longest bone in the upper extremity, forming the upper arm.
The lesser tuberosity provides attachment for the subscapularis muscle, the last rotator cuff muscle.
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