9 junio, 2024

Arm and forearm muscles: description and functions (images)

The arm and forearm of the human body have numerous muscles that work together to move these extremities and allow them to perform all the functions that are characteristic of them such as writing, playing musical instruments, holding different objects and moving them, lifting their own weight, etc.

Human beings have two arms and two forearms, one pair on each side of the body, which are structurally composed of part of the appendicular skeleton and its associated muscles. The arms are formed by the humerus bone and the forearms by the bones called the ulna and radius.

A human’s arm extends from the shoulder to the elbow, and the forearm spans the space between the elbow and the wrist. The shoulder corresponds to the joint between the humerus bone and the clavicle, one of the bones of the shoulder girdle, and the elbow is the joint between the humerus, ulna, and radius; the wrist, meanwhile, is the joint between the ulna, radius and the first bones of the hand.

What movements are allowed by the muscles of the arm?

Thanks to the association of these bones with their respective muscles, the arms are responsible for movements such as:

Flexion: which consists of the approach of two parts of the body to each other, such as the movement we make when we bring the arm and forearm closer when flexing the elbow.
Extension: which has to do with the distance of two parts of the body from each other, as when we extend our arm and straighten our elbow.
Abduction: which is the movement of a part of the body away from the center of the body, such as when we raise the arm out and away from the body.
Adduction: The movement of a part of the body toward the center of the body, as well as when the arm is brought closer to the body.

Likewise, the function of these muscles is controlled directly through the central nervous system, specifically by three nerves (medial, ulnar and radial), belonging to the portion related to the peripheral nervous system known as the brachial plexus.

The blood supply, on the other hand, depends on the brachial artery, which runs along the arm, passes through the elbow and divides into two branches: one radial and one ulnar, which supply the entire forearm and hand.

arm muscles

The arm, which corresponds to the region of the upper extremities corresponding to the structures located between the shoulder and the elbow, has 4 muscles, divided into two regions, one anterior and one posterior.

Anterior face or region

Where are the muscles that correspond to the region of the palm of the hand, that is, the one that is exposed when we extend the limb with the elbow and the nails facing the ground.

biceps brachii muscle: is as long as the distance between the clavicle and the elbow; it is very bulky, has two parts -one short and one long- and participates in the movement of rotation and flexion of the forearm with respect to the elbow.
anterior brachialis muscle: It is smaller than the biceps brachii, it is wide and flat, and it is the most important in the movement of flexion of the forearm on the arm.
coracobrachialis muscle: it is located between the scapula (second bone of the shoulder girdle) and the biceps; facilitates quick movements and raising the arm with the shoulder immobile.

Face or posterior region

Where are the muscles that correspond to the region of the back of the hand, where the knuckles are; the one that is exposed when we extend our arms in front of us with the palms of the hands pointing towards the ground.

Triceps brachii muscle: It is the main anterior muscle of the arm and has three portions, one long, one internal and one external; works on the extension of the forearm with respect to the elbow.

forearm muscles

The forearm contains 20 muscles, which are anatomically located in three regions: one anterior, one posterior, and one lateral. The muscles in the anterior and posterior regions are organized in layers; the anterior region has 4 layers and the posterior region has two, one superficial and one deep.

The anterior region of the forearm is characterized as a «compartment» that participates in flexion movements, while the posterior region participates in extension movements.

Anterior region or face (flexion)

This muscular region of the forearm is made up of 8 muscles in total, distributed in four «layers»: first, second, third and fourth. This shows the muscles that allow the flexion of the fingers of the hand.

First layer

These muscles originate-insert on the humerus, in the medial region of the epicondyle of this bone.

pronator round muscle: its final insertion site is the middle region of the radius bone
flexor carpi radialis muscle: finally inserts into the base of the second metacarpal of the hand.
flexor carpi ulnaris muscle: finally inserts at the base of the fifth metacarpal of the hand.
palmaris longus muscle: Inserts on the palmar fascia and is between the flexor carpi radialis and ulnaris muscles.

Second layer

flexor digitorum superficialis muscle: which facilitates the flexion of all the fingers, except the thumb.

third layer

Deep common flexor muscle of the fingers: which facilitates the flexion of all the fingers, except the thumb; arises in the posterior three-quarters of the ulna.
flexor pollicis longus muscleIt originates from the anterior portion of the radius bone.

fourth layer

pronator quadratus muscle: originates in the antero-medial part of the ulna and inserts in the antero-lateral region of the radius.

Region or posterior face (extension)

8 more muscles form the posterior region of the forearm, which are arranged in two layers: one superficial and one deep. In this region of the forearm are the muscles that allow the extension of the fingers of the hand.

Surface layer

Finger extensor muscle: it is one of the most important in this region, it extends from the elbow to the back of the wrist; participates in the extension of the proximal phalanx of the fingers.

Little finger extensor muscle.
Extensor carpi ulnaris muscle.
anconeus muscle.

deep layer

Abductor pollicis longus muscle.
Short extensor muscle of the thumb.
Long extensor muscle of the thumb.
Extensor muscle of the second finger (the index).

region or side face

This region is made up of four important muscles, which are responsible for the movement of the thumb and other movements related to the forearm and wrist.

Brachioradialis muscle.
Extensor carpi radialis longus muscle.
short extensor carpi radialis muscle.
supinator muscle.

References

Alshammari SM, Bordoni B. Anatomy, Shoulder and Upper Limb, Arm Muscles. [Updated 2020 Jul 31]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2020 Jan-. Available from: ncbi.nlm.nih.gov/books/NBK554420/
Mitchell B, Whited L. Anatomy, Shoulder and Upper Limb, Forearm Muscles. [Updated 2020 Aug 15]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2020 Jan-. Available from: ncbi.nlm.nih.gov/books/NBK536975/
Netter, FH (2014). Atlas of human anatomy, Professional Edition EBook: including NetterReference. com Access with full downloadable image Bank. Elsevier Health Sciences.
Pigeon, P., & Feldman, AG (1996). Moment arms and lengths of human upper limb muscles as functions of joint angles. Journal of biomechanics, 29(10), 1365-1370.
Saladin, KS, & McFarland, RK (2008). Human anatomy (Vol. 2). New York: McGraw-Hill.

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