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According to the Eaton Electronic Textbook of Hand Surgery, there are 35 muscles controlling the movement of your hands. The 17 muscles originating in the palm of your hand are called "intrinsic," while the remaining 18 "extrinsic" muscles originate in your forearm. These muscles can be further divided into four main groups based on their function: the carpal, intrinsic hand, extrinsic hand and extrinsic thumb muscles.
The carpal muscles originate in the forearm and control your hand's movements at the wrist. The extensor carpi radialis longus and brevis muscles both act to move your hand, at the wrist, toward your thumb and away from your palm. The extensor carpi ulnaris also moves the hand away from the palm, but moves the hand away from your thumb. The flexor carpi radialis muscle bends your hand toward your palm and toward your thumb, while the flexor carpi ulnaris bends your hand away from your thumb and toward your palm. The palmaris longus muscle also helps to move your hand toward your palm and helps you to grip objects.
The intrinsic hand muscles act only on your fingers and thumb, and include six groups of muscles. Your four thenar muscles contribute to your ability to grasp objects, allowing you to move your thumb toward and away from your other fingers. The three hypothenar muscles allow you to move your little finger in a similar manner. The lumbricales are four muscles that help to extend your fingers, but not your thumb, and move them toward your palm. The four dorsal interossei muscles connect the joints in your fingers to your palm, help to move your fingers away from your thumb and contribute to moving them toward your palm. The three palmar interossei muscles serve the same functions, but move the fingers toward your thumb.
The extrinsic hand muscles originate in your forearm and contribute to the movement of your four fingers. The extensor digitorum allows you to move your finger joints, fingers and your hand at the wrist away from your palm. The extensor indicis (proprius) and extensor digit minimi (proprius) muscles work exclusively on your index finger and small fingers, respectively, in the same manner. The flexor digitorum superficialis and profundis muscles work in the opposite direction, helping to move your fingers, finger joints and bend your hand, at the wrist, toward your palm. Together, these muscles are essential to your ability to point, raise and lower your fingers, as is required when playing sports such as basketball, volleyball and football.
Your thumb is unique from your other fingers because it is primarily controlled by four extrinsic muscles, allowing it a greater range of movement in all directions than your other fingers. The flexor pollicis longus muscle helps to move your thumb toward your palm. The extensor pollicis longus and brevis muscles both help to straighten and extend your thumb, moving it away from your palm. The abductor pollicis longus muscle serves three functions, helping to: extend your thumb, flex your hand and rotate your thumb, particularly in the direction of the palm of your hand. The range of motion that these muscles permit allows you to hold onto and manipulate objects of different shapes, like the bats, sticks and balls used in a variety of sports.