Introduction
The muscles of the hand and fingers are divided into three groups: All muscles are innervated by the median nerve or the ulnar nerve and serve mainly for fine motor skills.
- The muscles of the ball of the thumb (Thenar muscles),
- The muscles of the metacarpus and
- The muscles of the ball of the little finger (hypothenary group).
Function
The hand musculature is particularly important for fine motor skills and thus for all everyday movements of the fingers. For this reason, the muscles of the hand are numerous, but relatively small, in order to control the finest possible movements. The general movements of the hand muscles include flexion and extension, adduction and abduction, and the opposition movements of thumb and little finger. This means these two fingers can be moved to the palm of the hand.
Musculature of the ball of the thumb (Thenar muscles)
The group of the ball of the thumb comprises four muscles that are located in the area of the thumb and thus exercise the thumb movements.
- The abductor pollicis brevis muscle originates from one of the carpal bones (Os scaphoideum) and attaches to the distal limb of the thumb (proximal phalanx). It essentially forms the ball of the thumb and causes a spreader in the thumb saddle joint as well as an opposition movement, i.e. the movement of the thumb to the palm of the hand.
In the metacarpophalangeal joint of the thumb, the thumb is flexed; in the metacarpo-phalangeal joint, the thumb is stretched. Innervation is performed by the median nerve. This also innervates
- The Musculus opponens pollicis.
It originates from a carpal bone and attaches to the base joint of the thumb on the radial side (spoke side). As the name suggests, this muscle serves primarily for oppositional movement.
- The muscle flexor pollicis brevis is separated into two muscle bellies. The superficial part (caput superficiale) originates from the retinaculum flexorum and is innervated by the median nerve.
The deep part (caput profundum) originates at three carpal bones and is controlled by the ulnar nerve. Both parts together attach to the base phalanx of the thumb. The superficial part spreads the thumb apart (abduction), the deep part pulls it in again (adduction).
Both parts are also involved in the oppositional movement of the thumb.
- The adductor pollicis muscle also has two heads, which originate from different carpal bones. They are attached to the ulnar (medial) sesamoid bone of the thumb and are mainly responsible for the adduction of the thumb to the hand. This muscle is also supplied by the ulnar nerve.
The muscles of the metacarpus are further divided into three larger muscle groups, each of which has the same function and course, but on different fingers.
- The Musculi (Mm.) lumbricales originate at the 2nd to 5th tendon of the Musculus flexor digitorum profundus. Together they radiate into the dorsal aponeurosis of the 2nd to 5th finger on the extension side.
They all bend the fingers 2 (index finger) to 5 (little finger) in the base joint and stretch them in the middle and end joint. The lumbrical muscles of fingers 2 and 3 (index finger and middle finger) are innervated by the median nerve, fingers 4 and 5 (ring finger and little finger) by the ulnar nerve.
- The dorsal interosseous muscles originate on the sides of the 1st to 4th metacarpals facing each other and are located at the dorsal aponeurosis of fingers 2 to 5. They bend and spread the fingers in the metacarpophalangeal joint and stretch them in the middle joints.
These muscles are innervated by the ulnar nerve.
- The interosseous palmar muscles are a group of three muscles that originate from the metacarpals of fingers 2, 4 and 5 and are attached to the dorsal aponeurosis of the corresponding finger. They bend and close (adduction) the fingers in the metacarpophalangeal joint and stretch them in the middle finger joints. This muscle group is also controlled by the ulnar nerve.
All four muscles of this group are innervated by the ulnar nerve.
- The abductor digiti minimi muscle originates from the pea bone (Os pisiforme) of the carpal bones and attaches to the lateral base of the base joint 5. It spreads the little finger apart.
- The flexor digiti minimi muscle also originates from a carpal bone (Hamulus ossis hamati) and is located on the side of the base joint of the little finger.In the base joint it leads to the flexion of the little finger, in the middle and end joint it stretches the little finger.
- The musculus opponens digiti minimi also originates from the hamulus ossis hamati and attaches to the metacarpal bone of the 5th finger. It causes an opposition movement of the little finger, thus moving it to the palm of the hand.
- The Musculus palmaris brevis serves less for movement than for tightening and tensioning the skin over the ball of the little finger. It originates from the aponeurosis of the palm of the hand and attaches to the ball of the little finger.