Flexion, extension, pronation, and supination of the hand
The muscles which carry the greatest amount of responsibility as applied to motion of the wrist, hand, or fingers originate if not completely positioned along the forearm. Many of these muscles carry a dual load, causing action on the wrist as well as the elbow while others are dedicated to motion of the hand or fingers. There are specific muscles designed to carry the load of creating rotational movements of the radioulnar joint.
The hand and the fingers are capable of 4 basic types of motion. These include flexion, extension, pronation, and supination. The hand is capable of two additional movement types, adduction and abduction.
SUPINATION AND PRONATION
Supination of the hand in part occurs via the supinator muscle, which is found swirling around upper posterior region of the radius. With cohesive synergy applied with the biceps brachii, supination can occur. Pronation works similarly, with different muscles. The pronator teres and the pronator quadrus are responsible for cohesive synergetic contraction that leads to pronation. The upper medial region of the forearm hosts the pronator teres. Based anterior and deep the pronator teres is the prontator quadrus. The prontator quadrus can be found along the distal quarter, extending down in between the ulna bone and the radius. When these two muscles contract in cohesive synergy, the palm of the hand rotates posteriorly and the thumb aligns itself with the medial region of the forearm.
Image: Flexion Of The Hand
There are 6 muscles involved in the action of flexion as applied to the wrist, the hand, and the fingers. Most often these muscles can be determined with the least effort when described from the lateral to medial positions and from the superficial to the deep locations. 4 of these muscles originate from the medial epicondyle of the humerus but have little to no effect on the motions associated with the elbow. The brachioradialis is an easy reference muscle when determining position and location of these flexion muscles.
Crossing diagonally over the anterior portion of the forearm, the flexor carpi radialis muscle relies on its main tendon for attachment, which runs across the wrist underneath the flexor retinaculum. When finding the position of the radial artery, this muscle is an easy landmark for faster location. The radial artery, of course, is an excellent site for taking a manual pulse.
Superficially located along the anterior portion of the forearm one can find the Palmaris longus muscle. The exceptionally long and thin tendon that assists in the process of wrist flexion attaches to the palmar aponeurosis.
Along the medial anterior portion of the forearm, the flexor carpi ulnaris muscle is found. This muscle plays a role in flexion of the wrist as well as adduction of the hand.
Just under these three muscles, the flexor digitorum superficialis runs superficially from its rather extensive origins. This broad muscle begins along the humerus, the ulna, and the radius. The distal portion of this flexor initially attaches across the wrist only to diverge and attach in various segments to the middle phalanx of digits II, III, IV, and V.
Lying deep to the superficial digital flexor muscle rests the deep digital flexor muscle, which is also known as the flexor digitorum profundus. The insertion points of this muscle run along the distal phalanges numbers II through V. Both of these muscles are responsible for flexion as applied to the hand and the wrist as well as the 2nd through the 5th fingers.
Flexing the joints that are found in the thumb is the deep forearm lateral muscle, the flexor pollicis longus muscle. This muscle is a primary functional unit in allowing the grasping action of the human hand. When a hand grasps tightly into a fist, the tendons of the muscles related to hand flexing can be seen through the skin. These tendons are secured through their attachment to the retinaculum, which can be found transversely running through the wrist.
The posterior region of the forearm hosts the various muscles which are responsible for extension of the hand. Lying medially to the brachioradialis muscle is the long and tapered extensor muscle named carpi radialis longus. This muscle is primarily responsible for extensions of the carpal joint and abducting the hand at the wrist joint.
Just medially positioned to the carpi radialis longus lies the extensor carpi radialis brevis. This muscle is responsible for nearly identical functions as the counterpoint muscle, the carpi radialis longus. The greatest variation between these two muscles is their origination points.
Along the posterior region in the middle of the forearm the extensor digitorum communis muscle originates along the lateral epicondyle of the humerus. Just under the extensor retinaculum the tendon insertions splits into 4 distinctive sections at the wrist. Each of these tendons then attaches to the tip of the medial phalanges numbering II through V.
The long skinny muscle that runs along the ulna side of the extensor digitorum is the extensor digiti minimi. While the tendon insertion of this muscle initially fuses with tendon belonging to the digitorum communis, it then leads to the fifth finger.
Along the posterior region of the forearm, the muscle in the most medial position is the extensor carpi ulnaris. Its main function is to adduct and extend the joints found within the hand. It accomplishes this by inserting along the base of the fifth metacarpal bone.
The distal phalanx of the thumb is the insertion point for the extensor pollicis longus muscle. This muscle originates along the middle of the ulna and runs transverse across the lower segment of the forearm. Its main responsibility includes abduction of the hand and extension of the thumb joints.
The base of the proximal phalanx of the thumb serves as the insertion point for the extensor pollicis brevis. Originating from the lower mid section of the radius, this muscle is nearly identical in both design and function when compared to the pollicis longus.
The abductor pollicis longus muscle is rather aptly named, as its main responsibility is the abduction of the joints involving the thumb and the hand. Its origination point runs along the interosseous ligament which is found directly in between the radius and the ulna. Its insertion point runs along the base of the first metacarpal bone.