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The muscles in the human body are groups of cells that have the ability to contract and relax. The extremity muscles are those that are located in the upper and lower limbs. The muscles of the upper limb can be divided into six different regions: pectoral, shoulder, upper arm, anterior forearm, posterior forearm, and the hand. The muscles of the forearm, for example, are subdivided into an anterior and posterior compartment. The muscles of the anterior compartment are involved in flexion at the elbow and shoulder joint, while the muscles of the posterior compartment are called extensor muscles, which extend the wrist and digits.
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What You'll Learn
Upper extremity muscles include the biceps, triceps, and deltoid
The human body is made up of different types of muscles, some of which are controlled by the autonomic nervous system, while others, like skeletal muscles, are controlled by the somatic or voluntary nervous system. Muscles are groups of cells that have the ability to contract and relax. Extremity muscles are those that are located in the arms and legs. Upper extremity muscles refer to those located in the upper arms, specifically between the shoulder and elbow joints.
The upper extremity muscles include the biceps, triceps, and deltoid. The biceps, or biceps brachii, is a two-headed muscle that helps rotate the forearm, allowing the palm to be rotated up and down. It also assists in bending the elbow. The biceps brachii is located in the anterior compartment of the upper arm, along with the brachialis and coracobrachialis muscles. These three muscles are all innervated by the musculocutaneous nerve. The biceps brachii is also a flexor, opposing the action of extensors such as the triceps brachii.
The triceps, or triceps brachii, is located in the posterior compartment of the upper arm and has three heads: the long head, the lateral head, and the medial head. The long head of the triceps brachii is attached to the scapula, which allows it to extend the elbow and also move the shoulder joint. The triceps' primary function is to extend the forearm at the elbow joint and stabilize it during fine movements of the forearm and hand, such as writing.
The deltoid muscle is active in most shoulder motions and helps to stabilize the shoulder during activities such as carrying, lifting, and even walking. It is one of the muscles that move the humerus bone of the arm, along with the pectoralis major, latissimus dorsi, subscapularis, supraspinatus, infraspinatus, and teres minor. The deltoid can be built up through exercises such as pullovers, straight-arm pull-downs, and bent-over lateral raises.
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Lower extremity muscles include the quadriceps, hamstrings, and gluteal muscles
Extremity muscles are groups of cells in the body that have the ability to contract and relax. There are different types of extremity muscles, and they can be categorised as either upper or lower extremity muscles.
The hamstrings are the muscles at the back of the thigh that work in tandem with the quadriceps to facilitate leg movement. They are also prone to injury, especially when the leg is suddenly and forcefully straightened, which can cause tears in the muscle fibres.
The gluteal muscles, or glutes, are a group of three muscles that form the buttocks and play an important role in stabilising the pelvis and supporting the spine. They are also involved in hip abduction and external rotation movements.
Overall, the lower extremity muscles are crucial for maintaining balance, posture, and facilitating movement, such as walking, running, and jumping.
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![Extremities [Blu-ray]](https://m.media-amazon.com/images/I/41FxwFzK1qL._AC_UL320_.jpg)
The muscles of the forearm
The forearm is the section of the upper limb between the elbow and the wrist. The forearm contains twenty muscles that act on the elbow and wrist joints, as well as the carpometacarpal, metacarpophalangeal, and interphalangeal joints of the hand. These muscles are divided into two compartments: the anterior (flexor) and posterior (extensor) compartments.
The superficial anterior forearm muscles are a group of five muscles located in the anterior (flexor) compartment of the forearm. These muscles share a common origin on the common flexor tendon that arises from the medial epicondyle of the humerus. The majority of muscles from this group are innervated by the median nerve, except for the flexor carpi ulnaris muscle, which is innervated by the ulnar nerve. All of the muscles in this compartment work together to produce movements of the hand and digits. Specifically, they are in charge of flexion, adduction, and abduction of the hand at the wrist joint, as well as flexion of the fingers at the metacarpophalangeal (MCP) and proximal interphalangeal (PIP) joints.
The pronator teres muscle is the most laterally placed muscle of the superficial anterior forearm muscles. It consists of two heads (humeral and ulnar), each of which originates from a separate site. The humeral head originates from the medial supracondylar ridge of the humerus, while the ulnar head arises from the coronoid process of the ulna. The fibres from both muscle heads converge onto a single tendon that inserts onto the pronator tuberosity on the lateral surface of the radius. The pronator teres muscle is innervated by the median nerve and receives its blood supply from the brachial, radial, and ulnar arteries. Its main action is pronation of the forearm at the proximal radioulnar joint, although it also contributes to the flexion of the forearm at the elbow joint.
The flexor carpi radialis is a muscle situated medially to the pronator teres muscle. It originates from the medial epicondyle of the humerus and extends into a long tendon that passes beneath the flexor retinaculum and inserts onto the bases of the metacarpal bones. Like most muscles in this compartment, it is innervated by the median nerve and vascularized by the branches of the recurrent ulnar and radial arteries. The contraction of the flexor carpi radialis produces movements of the hand at the wrist joint, including wrist flexion and wrist abduction.
The flexor digitorum superficialis is the only muscle of the intermediate compartment. It can sometimes be classified as a superficial muscle, but in most individuals, it lies between the deep and superficial muscle layers. This muscle has two heads, one originating from the medial epicondyle of the humerus and the other from the radius. The muscle splits into four tendons at the wrist, which attach to the base of the middle phalanx of the four digits. The flexor digitorum superficialis flexes the metacarpophalangeal and proximal interphalangeal joints of the four fingers, as well as the wrist.
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The muscles of the hand
The human hand is a complex structure, with a variety of muscles that enable movement and dexterity. These muscles can be categorised as extrinsic or intrinsic. Extrinsic muscles are located in the anterior and posterior compartments of the forearm and are responsible for crude movements and a strong grip. On the other hand, intrinsic muscles are found within the hand itself and facilitate fine motor functions.
The development of hand muscles begins in the early stages of embryonic growth. During week 4, the upper extremity of the embryo appears as a lateral projection, known as the limb bud. As nerves and vasculature enter the developing arm, muscles begin to form. The intrinsic muscles of the hand develop from the deep layers of myogenic progenitor cells.
The thenar and hypothenar muscles are important muscle groups in the hand. The thenar muscles are located at the base of the thumb and consist of three short muscles, producing a bulge known as the thenar eminence. These muscles enable the fine movements of the thumb and are innervated by the median nerve. The hypothenar muscles, on the other hand, form a protrusion on the medial side of the palm, at the base of the little finger. This group also consists of three muscles, similar to the thenar muscles in structure and organisation. The ulnar nerve innervates the hypothenar muscles.
The interossei muscles are another crucial group of hand muscles. There are four dorsal and three palmar interossei muscles, located between the metacarpal bones of the hand. While all interossei bend the MCP joints, the dorsal interossei allow the spreading of fingers, and the palmar interossei pull the fingers together.
The lumbrical muscles are also essential for hand function, allowing the fingers to straighten and assisting in bending the MCP joints. They are named after the Greek word for earthworm. Additionally, the adductor pollicis plays a vital role in pinching by providing power to the first web space between the thumb and index finger.
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The rotator cuff muscles
The rotator cuff is a group of four muscles and their tendons that surround the shoulder joint, providing stability and enabling a wide range of motions. These muscles originate from the scapula (shoulder blade) and attach to the humerus (upper arm bone), forming a cuff or sleeve around the shoulder joint. The four muscles of the rotator cuff are the supraspinatus, infraspinatus, teres minor, and subscapularis. Each muscle has a specific role in rotating and stabilizing the shoulder.
Let's take a closer look at each of these rotator cuff muscles:
- Supraspinatus: This muscle originates from the supraspinatus fossa, which is a shallow depression on the posterior aspect of the scapula (shoulder blade). The supraspinatus tendon runs across the top of the shoulder joint and attaches to the superior aspect of the humeral head (upper arm bone). Its primary function is to initiate abduction of the arm, which means moving the arm away from the body in a lateral direction. A healthy supraspinatus helps to keep the head of the humerus securely in the shoulder socket during arm movements.
- Infraspinatus: The infraspinatus muscle originates from the infraspinatus fossa, which is located below the supraspinatus fossa on the posterior aspect of the scapula. Its tendon attaches to the middle of the greater tubercle of the humerus. The main function of the infraspinatus is external rotation of the shoulder joint, which means turning the arm so that the palm faces forward or backward. This muscle also assists in stabilizing the shoulder joint by holding the head of the humerus in place.
- Teres Minor: This muscle is located below the infraspinatus and originates from the lateral border of the scapula. The teres minor tendon attaches to the lower part of the greater tubercle of the humerus. Similar to the infraspinatus, the teres minor externally rotates the shoulder joint. It also assists in adduction, which is pulling the arm downward and across the body.
- Subscapularis: Unlike the other three muscles, the subscapularis muscle is located on the front of the scapula, in the subscapular fossa. Its tendon attaches to the front of the humeral head. The subscapularis internally rotates the shoulder joint, turning the arm so that the palm faces inward. It is the strongest internal rotator of the shoulder and also helps to stabilize the joint by compressing the humeral head into the socket during overhead activities.
In summary, the rotator cuff muscles play a crucial role in shoulder function and stability. They work in a coordinated manner to provide a full range of motion to the shoulder joint, allowing us to perform various activities that involve reaching, lifting, and throwing. Weakness or injury to any of these muscles can lead to pain and significant limitations in shoulder movement, affecting daily activities and sports performance. Therefore, it is important to maintain the strength and flexibility of the rotator cuff muscles through targeted exercises and physical therapy when needed.
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Frequently asked questions
Extremity muscles are groups of cells in the body that contract and relax to move skeletal bones.
Upper extremity muscles are those in the upper limb, which can be divided into 6 regions: pectoral, shoulder, upper arm, anterior forearm, posterior forearm, and the hand.
The biceps brachii, coracobrachialis, and brachialis are all muscles in the upper arm. The deltoid and latissimus dorsi are muscles in the shoulder.
Lower extremity muscles are those in the lower limb, from the hip to the toes. There are over 40 muscles in each lower extremity, including the quadriceps and hamstrings.
The gluteus maximus (buttocks), gluteus minimus, gluteus medius, and tensor fasciae latae are all hip muscles. The iliopsoas muscles, which include the iliacus and psoas major, help flex the hips.
