The wrist and hand are supported by a complex system of muscles, which can be categorized into extrinsic and intrinsic muscles. Here’s a summary of those muscles:
Extrinsic Muscles of the Wrist and Hand
Anterior (Flexor) Muscles
These muscles originate on the medial epicondyle of the humerus and insert into the hand. They primarily function to flex the wrist and fingers. The key muscles include:
- Flexor Carpi Radialis - Flexes and abducts the wrist.
- Flexor Carpi Ulnaris - Flexes and adducts the wrist.
- Flexor Digitorum Superficialis - Flexes the proximal interphalangeal joints and assists in flexing the wrist.
- Palmaris Longus - Assists in flexing the wrist (absent in some individuals).
- Flexor Digitorum Profundus - Flexes the distal interphalangeal joints (note: does not originate from the common flexor tendon).
Posterior (Extensor) Muscles
These muscles originate on the lateral epicondyle of the humerus and insert into the hand. They primarily function to extend the wrist and fingers. The main muscles include:
- Extensor Carpi Radialis Brevis - Extends and abducts the wrist.
- Extensor Digitorum (Communis) - Extends the fingers.
- Extensor Carpi Ulnaris - Extends and adducts the wrist.
- Extensor Digiti Minimi (Proprius) - Extends the little finger.
- Extensor Carpi Radialis Longus - Extends and abducts the wrist.
- Extensor Indicis - Extends the index finger.
Intrinsic Muscles of the Wrist and Hand
The intrinsic muscles originate and insert within the hand itself and are responsible for finer motor control. Notably, the intrinsic muscles can be divided into groups:
Hypothenar Eminence Muscles
These three muscles control movements of the little finger:
- Abductor Digiti Minimi - Abducts the little finger.
- Flexor Digiti Minimi Brevis - Flexes the little finger.
- Opponens Digiti Minimi - Allows opposition of the little finger.
Interosseous Muscles
These muscles operate between the bones of the hand and include:
- Dorsal Interossei - Abduct the fingers away from the midline of the hand.
- Palmar Interossei - Adduct the fingers towards the midline of the hand.
- Lumbricales - Flex the metacarpophalangeal joints while extending the interphalangeal joints.
Muscles of the Thumb
Extrinsic Muscles
The following muscles originate outside of the thumb and facilitate its movement:
- Extensor Pollicis Longus - Extends the thumb.
- Extensor Pollicis Brevis - Extends the proximal phalanx of the thumb.
- Abductor Pollicis Longus - Abducts and extends the thumb.
- Flexor Pollicis Longus - Flexes the thumb.
Intrinsic Muscles
Focusing specifically on the thumb, these muscles originate and insert within the hand:
- Flexor Pollicis Brevis - Flexes the thumb.
- Abductor Pollicis Brevis - Abducts the thumb.
- Opponens Pollicis - Allows opposition of the thumb.
- Adductor Pollicis - Adducts the thumb.
This system of muscles plays crucial roles in various functions, from gross movements like gripping and lifting to precise tasks requiring fine motor control.