Hand Muscles

Thenar Muscles

These muscles are located at the base of the thumb and collectively make up the thenar eminence. The following are thenar muscles and are responsible for fine movements of the thumb:

  1. Opponens Pollicis

    • This muscle originates from the tubercle of the trapezium and attaches to the lateral margin of the first metacarpal.

    • This muscle acts to oppose the thumb by medially rotating and flexing the metacarpal on the trapezium.

    • This muscle is innervated by the median nerve.

  2. Abductor Pollicis Brevis

    • This muscle originates from the tubercle of the scaphoid and trapezium and attaches to the lateral margin of the proximal phalanx of the thumb.

    • This muscle acts to abduct the thumb.

    • This muscle is innervated by the median nerve.

  3. Flexor Pollicis Brevis

    • This muscle originates from the tubercle of the trapezium and attaches to the proximal phalanx of the thumb.

    • This muscle acts to flex the metacarpophalangeal joint of the thumb.

    • This muscle is innervated by the median nerve.

Hypothenar Muscles

These muscles are located on the medial side of the palm at the base of the little finger collectively make up the hypothenar eminence. The following are hypothenar muscles and are responsible for fine movements of the thumb:

  1. Opponense Digiti Minimi

    • This muscle originates from the hook of hamate and attaches to the medial margin of the fifth metacarpal.

    • This muscle acts to allow for opposition by rotating the metacarpal of the little finger towards the palm.

    • This muscle is innervated by the ulnar nerve.

  2. Abductor Digiti Minimi

    • This muscle originates from pisiform and the tendon of flexor carpi ulnaris muscle and attaches to the proximal phalanx of the little finger.

    • This muscle acts to abduct the little finger.

    • This muscle is innervated by the ulnar nerve.

  3. Flexor Digiti Minimi Brevis

    • This muscle originates from the hook of hamate and attaches to the proximal phalanx of the little finger.

    • This muscle acts to flex the metacarpophalangeal joint of the little finger.

    • This muscle is innervated by the ulnar nerve.

Lumbricals

These muscles are each associated with a digit and there are a total of four lumbricals in each hand. The lumbricals originate from a tendon of the flexor digitorum profundus and attach to the extensor hood of each digit by passing dorsally and laterally around each digit. The lumbricals act to produce flexion at the metacarpophalangeal joint and extension at the interphalangeal joint of each digit. The medial two lumbricals (ring and little fingers) are innervated by the ulnar nerve while the lateral two lumbricals (index and middle fingers) are innervated by the median nerve.

Interossei

These muscles are located between the metacarpals and can be categorized as:

  1. Dorsal Interossei

    • These four muscles are the most superficial and can be palpated on the dorsum of the hand. They each originate from the lateral and medial surfaces of their associated metacarpals and attach to the extensor hood and proximal phalanx of each digit.

    • They act to abduct the digits at the metacarpophalangeal joint.

    • They are innervated by the ulnar nerve.

  2. Palmar Interossei

    • These three muscles are located on the palmar surface of the hand and originate from the medial or lateral surface of an associated metacarpal and attach to the extensor hood and proximal phalanx of the same digit.

    • These muscles act to adduct the digits at the metacarpophalangeal joint.

    • These muscles are innervated by the ulnar nerve.

Palmaris Brevis

This muscle is also located in the palm and it is a small and thin muscle found in the subcutaneous tissue of the hypothenar eminence.

This muscle originates from the palmar aponeurosis and flexor retinaculum and attaches to the dermis of the skin on the medial margin of the hand. It acts to improves grip and is innervated by the ulnar nerve.

Adductor Pollicis

This muscle is triangular in shape with two muscle heads through which the radial artery passes to form the deep palmar arch.

This muscle originates from the third metacarpal (first head) and from capitate and adjacent areas of the second and third metacarpals (second head) and attaches to the base of the proximal phalanx of the thumb. It acts to adduct the thumb and is innervated by the ulnar nerve.