Anatomy & Physiology of the Intrinsic Muscles of the Hand

Pima Medical Institute - Anatomy & Physiology Notes

Intrinsic Muscles of the Hand

The intrinsic muscles of the hand are crucial for fine motor movements and are divided primarily into two groups: the thenar eminence (muscles of the thumb) and the hypothenar eminence (muscles of the little finger). Each muscle has specific origins, insertions, actions, and innervations.

Thenar Eminence Muscles

  1. Opponens Pollicis

    • Origin: The 3 intrinsic muscles of the thenar eminence originate from the carpal bones and the transverse carpal ligament.

    • Insertion: Metacarpal 1

    • Action: Opposition of digit 1 (thumb) to digits 2-5 (fingers)

    • Nerve: Median nerve

  2. Abductor Pollicis Brevis

    • Origin: Same as the Opponens Pollicis.

    • Insertion: Proximal phalanx of digit 1.

    • Action: ABDuction of digit 1 (thumb)

    • Nerve: Median nerve

  3. Flexor Pollicis Brevis

    • Origin: Same as the Opponens Pollicis.

    • Insertion: Proximal phalanx of digit 1.

    • Action: Flexion of digit 1 (thumb) at the metacarpophalangeal joint (MCP).

    • Nerve: Median nerve and ulnar nerve

  4. Adductor Pollicis

    • Origin: Metacarpals 2 & 3.

    • Insertion: Proximal phalanx of digit 1.

    • Action: ADDuction of digit 1 (thumb)

    • Nerve: Ulnar nerve

Hypothenar Eminence Muscles

  1. Abductor Digiti Minimi

    • Origin: The 3 intrinsic muscles of the hypothenar eminence originate from carpal bones and the flexor retinaculum.

    • Insertion: Base of proximal phalanx of digit 5.

    • Action: ABDuction of digit 5 (little finger) and flexion of digit 5 at the MCP joint.

    • Nerve: Ulnar nerve

  2. Flexor Digiti Minimi Brevis

    • Origin: Same as Abductor Digiti Minimi.

    • Insertion: Proximal and middle phalanx of digit 5.

    • Action: Flexion of digit 5 at the MCP and PIP joints.

    • Nerve: Ulnar nerve

  3. Opponens Digiti Minimi

    • Origin: Same as Abductor Digiti Minimi.

    • Insertion: 5th metacarpal.

    • Action: Opposes digit 5 slightly.

    • Nerve: Ulnar nerve

Interosseous Muscles

These muscles can be categorized into palmar and dorsal types:

  1. Palmar Interossei

    • Origin: Metacarpals.

    • Insertion: Proximal phalanx of digits 2, 4, and 5.

    • Action: ADDuction of digits 2, 4, and 5 towards the midline of the hand.

    • Nerve: Ulnar nerve

  2. Dorsal Interossei

    • Origin: Metacarpals.

    • Insertion: Proximal phalanx of digits 2, 3, and 4.

    • Action: ABDuction of digits 2, 3, and 4 away from the midline of the hand.

    • Nerve: Ulnar nerve

  3. Lumbricals

    • Origin: Tendons of the flexor digitorum profundus.

    • Insertion: Tendons of extensor digitorum; digits 2-5.

    • Action: Flexion at the metacarpophalangeal joint (MCP) with extension at the proximal interphalangeal (PIP) and distal interphalangeal (DIP) joints, referred to as the "intrinsic plus" position.

    • Nerve: Median nerve for digits 2 & 3; Ulnar nerve for digits 4 & 5.