Overview
This lecture covers the anatomy of the hand muscles, detailing their groups, origins, insertions, functions, and innervation, as part of the upper limb myology.
Muscle Groups of the Hand
- Hand muscles are divided into four groups: thenar eminence, hypothenar eminence, lumbricals, and interossei.
- Thenar eminence: muscles related to the thumb (mostly three main muscles, sometimes a fourth mentioned).
- Hypothenar eminence: muscles related to the little finger (three primary, plus the variable palmaris brevis).
- Lumbricals: four muscles attached to flexor tendons of fingers 2-5.
- Interossei: divided into palmar (adduction) and dorsal (abduction) muscles.
Thenar Eminence Muscles
- Contains abductor pollicis brevis, flexor pollicis brevis, and opponens pollicis (form the thenar eminence proper).
- Abductor pollicis brevis: originates from flexor retinaculum, trapezium, and scaphoid; inserts on proximal phalanx and external sesamoid of thumb; abducts thumb.
- Flexor pollicis brevis: originates from flexor retinaculum and trapezium; inserts on proximal phalanx and external sesamoid of thumb; flexes thumb.
- Opponens pollicis: originates from trapezium and flexor retinaculum; inserts on first metacarpal; enables thumb opposition.
- Adductor pollicis: not part of the eminence proper; has transverse (third metacarpal) & oblique (second metacarpal, capitate, trapezoid) heads; inserts on proximal phalanx and internal sesamoid; adducts thumb.
Hypothenar Eminence Muscles
- Includes abductor digiti minimi, flexor digiti minimi brevis, and opponens digiti minimi.
- Palmaris brevis (variable muscle): originates from palmar aponeurosis; inserts into skin; relieves pressure over ulnar artery.
- Abductor digiti minimi: originates from pisiform; inserts on proximal phalanx of little finger; abducts little finger.
- Flexor digiti minimi brevis: originates from hook of hamate; inserts on proximal phalanx of little finger; flexes little finger.
- Opponens digiti minimi: originates from hamate hook; inserts on fifth metacarpal; opposes little finger toward thumb.
Lumbrical Muscles
- Four lumbrical muscles originate from tendons of flexor digitorum profundus (fingers 2-5).
- Insert into extensor expansions of fingers 2-5.
- Flex metacarpophalangeal joints and extend interphalangeal joints (despite originating from flexor tendons).
Interosseous Muscles
- Palmar interossei: four muscles (on 1st, 2nd, 4th, and 5th metacarpals); adduct fingers toward third finger.
- Dorsal interossei: four muscles (between metacarpals); abduct fingers away from third finger.
- Both groups insert into extensor expansions of respective fingers.
Innervation of Hand Muscles
- Thenar muscles (abductor, flexor, opponens pollicis): median nerve.
- Adductor pollicis: deep branch of ulnar nerve.
- Hypothenar muscles and palmaris brevis: superficial branch of ulnar nerve.
- Interossei (palmar and dorsal): deep branch of ulnar nerve.
- Lumbricals: first and second by median nerve; third and fourth by deep branch of ulnar nerve.
Key Terms & Definitions
- Thenar eminence — Muscular bulge at the thumb base, mainly three muscles.
- Hypothenar eminence — Muscular bulge at the little finger base.
- Lumbricals — Four muscles that flex metacarpophalangeal and extend interphalangeal joints.
- Interossei — Muscles between metacarpals; palmar adduct, dorsal abduct fingers.
- Flexor retinaculum — Ligament on the anterior wrist, origin for some hand muscles.
Action Items / Next Steps
- Review related videos on muscles of the forearm, arm, shoulder, and hand bones.
- Study the myology of the upper limb from proximal to distal for better understanding.