Muscles of the Back
Muscles in the Thoracic Region that Help You Breathe
Muscles That Move the Knee and Ankle

The Intrinsic Muscles of the Wrist and Hand

Moving your hands, fingers and thumbs, requires a lot of muscles. So you have some longer (extrinsic) muscles that run from the forearm and lots of little hand and finger muscles (the intrinsic muscles).

The thenar muscles

The thenar muscles are intrinsic muscles contained within the thenar compartment, which is separated from other compartments by fascia. These four muscles move the thumb:

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  • Abductor pollicis brevis: This muscle originates at the flexor retinaculum and the tubercles on the scaphoid and trapezium bones. It inserts on the lateral side of the base of the proximal phalanx of the thumb. It abducts the thumb and is innervated by the median nerve.

  • Flexor pollicis brevis: This muscle originates and inserts close to the abductor pollicis brevis; however, it flexes the thumb. It’s innervated by the median nerve.

  • Opponens pollicis: This muscle originates near the two brevis muscles, but it inserts on the lateral side of the first metacarpal. It helps to oppose the thumb (the movement you make when touching the thumb to the pinkie). It’s innervated by the median nerve.

  • Adductor pollicis: This muscle has two heads that insert on the medial side of the proximal phalanx of the thumb. The adductor pollicis adducts the thumb (pulls it in next to the fingers) and is innervated by the ulnar nerve.

    • The oblique head originates at the bases of the second and third metacarpals and associated carpal bones.

    • The transverse head originates at the anterior part of the third metacarpal shaft.

The thenar muscles form the thenar eminence, which is that mound of muscle you can see at the base of the thumb.

The hypothenar muscles

The hypothenar muscles are intrinsic muscles found in the hypothenar compartment and form the hypothenar eminence on the medial side of the palm of the hand. They’re all innervated by the deep branch of the ulnar nerve, and they move the pinkie finger.

  • Abductor digiti minimi: This muscle originates at the pisiform and inserts on the medial side of the base of the proximal phalanx of the little finger. It abducts the little finger.

  • Flexor digiti minimi: Originating at the hook of the hamate, this muscle inserts near the abductor digiti minimi. It flexes the proximal phalanx of the little finger.

  • Opponens digiti minimi: This muscle originates at the hook of the hamate and inserts onto the medial border of the fifth metacarpal. It pulls the fifth metacarpal forward and rotates it to oppose the thumb.

The interosseous muscles and the lumbricals

The third group of intrinsic muscles are the interosseous muscles and the lumbricals; they’re found in the hand, and they move the fingers.

  • Interosseous muscles: These seven muscles are innervated by the deep branch of the ulnar nerve. They’re divided into two groups:

    • Four dorsal interosseous muscles run between the metacarpals and abduct the fingers. They also flex the metacarpophalangeal joints and extend the interphalangeal joints.

    • Three palmar interosseus muscles are located on the palmar portion of the second, fourth, and fifth metacarpals. They adduct the fingers. They also flex the metacarpophalangeal joints and extend the interphalangeal joints.

  • Lumbricals: The lumbricals are located between the metacarpals. The first and second lumbricals are innervated by the median nerve, and the third and fourth lumbricals are innervated by the deep branch of the ulnar nerve. They flex the fingers at the metacarpophalangeal joints and extend the interphalangeal joints.

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