Hand – Muscles

Muscles of Hand

Intrinsic Muscles of Hand and Their Nerve Supply.

There are total 20 intrinsic muscles of the hand which are grouped into five groups.

1. Thenar muscles:
   • Abductor pollicis brevis
   • Flexor pollicis brevis
   • Opponens pollicis brevisAdductor pollicis ( does not form thenar eminence)
2. Hypothenar muscles:
   • Abductor digiti minimi
   • Flexor digiti minimi
   • Opponens digiti minimi
   • Palmaris brevis
3. Four Lumbricals (one for each digit except thumb)
4. Four Palmar interossei (third digit /middle finger does not have palmar interrossei).
5. Four dorsal interrossei ( thumb and the fifth digit/little finger do not have dorsal interrossei, whereas middle finger has two dorsal interrosei) 

Nerve supply Of Intrinsic Muscles

The intrinsic muscles of the hand are on the palmar aspect and are innervated by  branches of the ulnar and median nerves.

• Five muscles are supplied by the median nerve:
• Muscles forming thenar eminence:
  • Abductor pollicis brevis
  • Flexor pollicis brevis
  • Opponens pollicis brevis and
• 1^st and 2^nd lumbricals
• Fifteen muscles are supplied by ulnar nerve
  • Four hypothenar muscles
  • 3^rd and 4^th lumbricals
  • Four parmar  interrossei
  • Four dorsal interrossei
  • Adductor pollicis   

 Lumbricals

• Arise from the tendons of the flexor digitorum profundus
• Are numbered 1st, 2nd, 3rd and 4th from lateral to medial side.
• Lumbrical 1st and 2nd take origin from lateral side of the tendons of flexor digitorum profundus.
• Lumbricals 3rd and 4th take origin from the adjacent sides of the tendons of flexor digitorum profundus.
• They are inserted into the lateral side of the dorsal digital expansion of  2nd to 5th digits.
• Medial 2 lumbricals are innervated by the ulnar nerve and lateral 2 lumbricals by the median nerve.
• Flex the metacarpophalangeal joints and extend the interphalangeal joints.    

Interrossei muscles

    Four dorsal interossei:

• There is one dorsal interossei for index and ring finger and two dorsal interossei for the middle finger. They are numbered 1-4 from lateral to medial side.
• They are bipennate .
• They take origin from the adjacent sides of the shafts of the metacarpal bones.
• Are inserted into the dorsal digital expansion (DGE) and base of proximal phalanx of the difgits ( 1st and 2nd on the lateral side of DGE and 3rd and 4th on the medial side of DGE.
• They are the abductors  of digits (Dorsal ABduct = DAB).
• All are supplied by deep branch of ulnar nerve.

Three palmar interossei

• There is one palmar interossei for index, ring and little finger. They are numbered 1-3 from lateral to medial side.
• They are unipennate.
• They take origin from  the anterior aspect of metacarpals 2, 4 and 5,
• They are inserted into dorsal digital expansion (DGE) of the difgits ( 1st on the medial side of DGE and  2nd and 3rd on thelateral side of DGE.
• They are the adductors of digits (Palmar ADduct = PAD).
• They  are  innervated by the deep branch of ulnar nerve.

  Extensor expansion/Dorsal digital expansion

• It is a triangular aponeurosis  of extensor dgiitorum longus (EDL) which   coves the metacarpophalangeal joint and the dorsal surface of proximal phalanx.
• The tendons of the  lumbricals and interossei are inserted via it.
• It forms a functional unit to for coordinated action of  EDL, lumbricals and interossei muscles  to perform  extension at the  proximal and distal interphalangeal joints.
• The expansion  divides into three bands at its distal end:
  • Lateral bands pass on either side of the proximal phalanx and are attached to the dorsal surface of the  base of  the distal phalanx.
  • Median band is  attached on the dorsal surface of the  base of the middle phalanx.

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Origin, Insertion, Action and nerve Supply of Thenar Muscles

Origin, Insertion, Action and nerve Supply of Thenar Muscles