INTRODUCTION TO ANATOMY AND PHYSIOLOGY

Position and Action of Muscles – Arm and Hand

Position and action of the upper arm muscles.

Muscle name

location

action

Coracobrachialis

Anterior aspect deep to biceps (top of humerus)

Flexes and adducts humerus

Biceps

Anterior aspect

Flexes elbow and supinates forearm

Brachialis

Anterior aspect deep to biceps (distal end of humerus)

Flexes elbow joint

Triceps

Posterior aspect

Extends elbow.

Position and action of the lower arm and hand muscles.

The muscles of the hand (skeletal) are responsible for the movement of the hand and fingers – they can be categorised as:

  • Extrinsic – these are the long flexors and extensors, and the muscle belly is located on the forearm.
  • Intrinsic – these are the smaller muscles located within the hand itself.

The muscles of the hand are innervated by the radial, median, andulnar nerves from the brachial plexus.

INTRINSIC

The intrinsic muscle groups are the thenar (thumb) and hypothenar (little finger) muscles; the interossei muscles (four dorsally and three volary) originating between the metacarpal bones; and the lumbrical muscles arising from the deep flexor (and which are special because they have no bony origin) to insert on the dorsal extensor hood mechanism. Palmaris brevis which is a superficial muscle and adductor pollicis are also intrinsic muscles.

EXTRINSIC

The fingers have two long flexors, located on the underside of the forearm. They insert by tendons to the phalanges of the fingers. The deep flexor attaches to the distal phalanx, and the superficial flexor attaches to the middle phalanx. The flexors allow for the actual bending of the fingers. The thumb has one long flexor and a short flexor in the thenar muscle group. The human thumb also has other muscles in the thenar group (opponens and abductor brevis muscle), moving the thumb in opposition, making grasping possible.

The extensors are located on the back of the forearm and are connected in a more complex way than the flexors to the dorsum of the fingers. The tendons unite with the interosseous and lumbrical muscles to form the extensorhood mechanism. The primary function of the extensors is to straighten out the digits. The thumb has two extensors in the forearm: the tendons of these form the anatomical snuff box. Also, the index finger and the little finger have an extra extensor, used, for instance, pointing. The extensors are situated within 6 separate compartments.

 

Muscle name

location

action

Brachioradialis

Connects the humerus to the radius

Flexes the forearm at the elbow

Flexor carpi radialis

Extends along the radial side of the anterior of the forearm, from the medial end of the humerus to the radial side of the forearm and the base of the second and third metacarpals

Flexion of the wrist

Flexor carpi ulnaris

Extends along the ulnar side of the anterior of the forearm, from the medial end of the humerus to the pisiform and hamate carpal bones and the base of the fifth metacarpal

Flexion of the wrist

Extensor carpi radius

Extends along the radial side of the posterior of the forearm, from above the lateral end of the humerus to the posterior of the base of the second metacarpal

Extension of the wrist

Extensor carpi ulnaris

Extends along the ulnar side of the posterior of the forearm, from above the lateral end of the humerus to the ulna and the posterior side of the base of the fifth metacarpal

Extension of the wrist

Extensor digitorum

Extends along the lateral side of the posterior of the forearm, from the lateral end of the humerus to the second and fifth phalanges

Extension of the fingers and wrist

 Thenar eminence (abductor pollicis brevis, flexor pollicis brevis, opponens pollicis)

Soft tissue on the radial side of the palm

Moves the thumb

Hypothernar eminence (abductor digiti minimi manus, flexor digiti minimi manus, opponens digiti minimi)

Soft tissue on the ulnar side of the palm

Moves the little finger and helps you to grip objects.

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