Muscles of the Hand
By Justin Carmel, PT, DPT
What are the Muscles of the Hand
The muscles of the hand are the skeletal muscles responsible for the movement of the hand and fingers. These muscles can be subdivided into two groups:
The extrinsic muscle groups are the long flexors and extensors. They are called extrinsic because the muscle belly is located on the forearm. The intrinsic group is the smaller muscles located within the hand itself. The hand muscles are innervated by the radial, median, and ulnar nerves from the brachial plexus.
What are the Intrinsic Muscles of the Hand?
The intrinsic muscles are those muscles that are responsible for position grip. The muscles that originate in the forearm and insert onto the hand are responsible for power grip. The muscles that originate in the hand and are responsible for position grip are the intrinsic muscles. On the thumb side, you’ve got the thenar eminence is this eminence here on the thumb side. You can see this bulge on the hand of the thumb muscles. This is the thenar eminence. You’ve got the hypothenar eminence on the little finger side. Between the hypothenar and thenar muscles, you’ve got this fibrous band of connective tissue, which arches over the carpal bones. This is called the flexor retinaculum. This blends with the muscles of the thenar and the hypothenar muscles.
Beneath the flexor retinaculum, you’ve got flexor tendons and the median nerves that pass through. This is the carpal tunnel. The carpal tunnel is the space between the carpal bones and the flexor retinaculum, and you’ve got these flexor tendons and the median nerve which pass through. In the hand’s intrinsic muscles, you’ve got the hypothenar muscles, the thenar muscles, lumbricals, interosseous muscles, the palmaris brevis, and the adductor pollicis.
Next, we’ve got the lumbrical muscles. These muscles flex the metacarpophalangeal joints. You have four lumbrical muscles, and they originate on the tendons of the flexor digitorum profundus. These hand muscles originate on the sides of these tendons, and they insert onto the extensor hoods of the four fingers – so the index, middle, ring, and little fingers. They flex the metacarpophalangeal joints while extending the interphalangeal joints.
What are the Extrinsic Muscles of the Hand?
In the extrinsic muscles, the fingers have two long flexors located on the underside of the forearm. They insert by tendons to the phalanges of the fingers. The deep flexor attaches to the distal phalanx, and the superficial flexor attaches to the middle phalanx. The flexors allow for the actual bending of the fingers. The thumb has one long flexor and a short flexor in the thenar muscle group. The human thumb also has other muscles in the thenar group (opponens and adductor brevis muscle), moving the thumb in opposition, making grasping possible.
The extensor muscles are located on the back of the forearm and are connected in a more complex way than the flexors to the fingers’ dorsum. The tendons unite with the interosseous and lumbrical muscles of the hand to form the extensor hood mechanism. The primary function of the extensors is to straighten out the digits. The thumb has two extensors in the forearm; the tendons of these form the anatomical snuff box. The index finger and the little finger have an extra extensor, used, for instance, pointing. The extensors are situated within 6 separate compartments. The first four compartments are located in the grooves present on the dorsum of the radius’s inferior side, while the 5th compartment is in between the radius and ulna. The 6th compartment is in the groove on the dorsum of the inferior side of the ulna.
What Nerves Supply the Hand?
The nerves of the hand are the radial, median, and ulnar nerves. The radial nerve innervates the finger extensors and the thumb abductor; that is, the muscles that extend at the wrist and metacarpophalangeal joints (knuckles) and abduct and extend the thumb. The median nerve innervates the wrist and digits’ flexors, the abductors and opens of the thumb, the first and second lumbrical. The ulnar nerve innervates the remaining intrinsic muscles.
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