This document describes the anatomy of muscles in the posterior forearm compartment. It lists 12 muscles including their origin, insertion, nerve supply, and action. The muscles described extend and abduct the hand, fingers, and thumb. They also supinate the forearm. All are supplied by the deep branch of the radial nerve and have nerve roots of C7 and C8, except for the anconeus and supinator which also have additional nerve roots.

2.  ANATOMY
MUSCLE OF POSTERIOR FOREARM
OSSEOFASCIAL COMPARTMENT:

3. MUSCLES:
ORIGIN.
INSERTION.
NERVE SUPPLY.
NERVE ROOT.
ACTION.

4. EXTENSOR CARPI
RADIALIS BREVIS:
ORIGIN:
lateral epicondyle of humerus.
INSERTION:
Posterior surface of base of
third metacarpal bone.
ACTION:
Extends and abducts hand at
wrist joint.
NERVE ROOT:
C7,C8
NERVE SUPPLY:
Deep branch of radial nerve.

5. EXTENSOR DIGITORUM:
ORIGIN:
Lateral epicondyle of humerus.
INSERTION:
Middle and distal phalanges of medial four
fingers.
ACTION:
Extends fingers and hand.
NERVE SUPPLY:
Deep branch of radial nerve.
NERVE ROOT:
C7,C8

6. EXTENSOR DIGITI
MINIMI:
ORIGIN:
Lateral epicondyle of humerus.
INSERTION:
Extensor expansion of little finger.
Action:
Extends the metacarpal phalangeal joint of
little finger.
NERVE SUPPY:
Deep branch of radial nerve.
NERVE ROOT:
C7,C8

7. EXTENSOR CARPI
ULNARIS:
ORIGIN:
Lateral epicondyle of humerus.
INSERTION:
Base of fifth metacarpal bone.
ACTION:
Extends and adducts hand at wrist joint.
NERVE SUPPLY:
Deep branch of radial nerve.
NERVE ROOT:
C7,C8

8. ANCONEUS:
ORIGIN:
Lateral epicondyle of humerus.
INSERTION:
Lateral surface of olecranon process
of ulna.
ACTION:
Extends elbow joint.
NERVE SUPPLY:
Radial nerve.
NERVE ROOT:
C7,C8; T1

9. SUPINATOR:
ORIGIN:
Lateral epicondyle of humerus,anular
ligament of proximal radioulnar joint,and
ulna.
INSERTION:
Neck and shaft of radius.
ACTION:
Supination of forearm.
NERVE SUPPLY:
Deep barnch of radial nerve.
NERVE ROOT:
C5,C6

10. ABDUCTOR POLLICIS
LONGUS:
ORIGIN:
Posterior surface of shaft of radius and
ulna.
INSERTION:
Base of first metacarpal bone.
ACTION:
Abducts and extends thumb.
NERVE SUPPLY:
Deep branch of radial nerve.
NERVE ROOT:
C7,C8

11. EXTENSOR POLLICIS
BREVIS:
ORIGIN:
Posterior surface of shaft of radius.
INSERTION:
Base of proximal phalanx of thumb.
ACTION:
Extends metacarpophalangeal joints of
thumb.
NERVE SUPPLY:
Deep branch of radial nerve.
NERVE ROOT:
C7,C8.

12. EXTENSOR POLLICIS
LONGUS:
ORIGIN:
Posterior surface of shaft of ulna.
INSERTION:
Base of distal phalanx of thumb.
ACTION:
Extends distal phalanx of thumb.
NERVE SUPPY:
Deep branch of radial nerve.
NERVE ROOT:
C7,C8

13. EXTENSOR INDICIS:
ORIGIN:
Posterior surface of shaft of ulna.
INSERTION:
Extensor expansion of index finger.
ACTION:
Extends metacarpophalangeal joint of
index finger.
NERVE SUPPLY:
Deep branch of radial nerve.
NERVE ROOT:
C7,C8.

14. 
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