THE MUSCLES OF THE ARM and HAND

Contents:

  Upper Arm

  Muscles of the forearm

I   Important construction lines on the arm

  The hand

UPPER ARM

All the muscles on the upper arm are superficial to some degree; the entire arm is covered by a fascia which smoothes muscles — the deep segments go to the bone — the fascia divides the flexors from the extensors and impacts the surface form only in a couple of places.

Flexors are on the front of the arm (supine position) and extensors are on the back.

For the entire arm the origins are above, the insertions below.

Descriptions of form and function are based on the arm in supination.

CORACOBRACHIALIS — smallest muscle

origin: coracoid process

insertion: approximately halfway down the medial side of the humerus

action: helps raise the arm forward; helps pull arm to the side (adducts it) and to turn the arm inward

form: mostly covered by other muscles when arm at the side — becomes evident when the arm is raised ("crucifixion muscle")

 

BRACHIALUS ANTICUS

origin: right below insertion of coracobrachialis — covers entire lower half of upper arm and front of arm

insertion: into coronoid process of ulna

function: flexor — in contraction pulls ulna towards humerous

form: does not quite cover the eipicondyles — responsible for outline on lower outside of the upper arm

 

BICEPS — two heads: long and short

long head origin: above glenoid fossa of scapula

long head insertion: tendon passes over head of humerus down through bicipital groove and becomes part of the muscle

short head origin: coracoid process

short head insertion: joins main muscle by single tendon to radial tuberosity

action of biceps: flexor — flexes elbow: since it has its origin on the scapula it can also function as a flexor of the shoulder; it aids in supination — when fully flexed as in supination the biceps are fullest; it is pulled down when the bones rotate in pronation and is elongated

form: forms entire front profile of upper arm — creates entire anterior thickness of arm

 

The back of the upper arm is controlled by one massive muscle:

TRICEPS — three heads, one point of insertion

lateral and medial heads: origin: on humerus: lateral — just below head of humerus on outside

medial — just below head of humerus on inside

insertion: into common tendon — broad flat strap attached to olecranon process; this tendon is the characteristic flattened area on the back of the upper arm above the elbow — the bulge above this area is a characteristic landmark

long head:

origin: on scapula right beneath glenoid fossa: thicker than medial head and gives characteristic bulge high on the arm

insertion: olecranon process

action: long head — adducts arm; draws it backward; three heads together extend forearm

The muscles of the back of the arm create most of the outline of the front of the arm just as the muscles of the back create the outline of the front of the torso. 

ANCONEUS — extensor of the elbow (forearm)

origin: back of lateral epicondyle of humerus

insertion: olecranon process and partly on ulnar ridge

form: helps create characteristic "V" on back of elbow

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 MUSCLES OF THE FOREARM -- numerous and complex — operate not only supination and pronation but also create flexion and extension of wrists and fingers — this outline will consider 9 or 10 muscles.

flexors of the fingers — deep muscles

flexors and extensors of wrist — more superficial

TWO MAJOR GROUPS designated according to function and position

anatomically the division of hand and arm is based on the palm forward position when the arm is supinated

interior-anterior-flexor-pronator group all arise from the inner or medial epicondyle of the humerus

four muscles in the anterior-interior group — responsible for flexing wrist/hand

one of the muscles in the group crosses from the inner epicondyle to the radius - when it contracts it pronates the arm (the pronator teres)

these four muscles create the interior-anterior-flexor-pronator group — they are thick above and thin below

 

external-posterior-extensor-supinator group starts in the back of the arm — they start at the external epicondyle of the humerus and for the most part pass over the wrist to the fingers — the tendons on the back of the hand are part of this group

these muscles extend the hand (extensors)

one of these muscles starts on the lateral epicondylar ridge of the humerus and inserts on the radius — when flexed the arm is fully supinated (the brachioradialis)

 


 
FLEXOR - PRONATOR GROUP OF FOREARM - flexor muscles have short bodies with tendons going the rest of the way to the insertion point

 

PRONATOR TERES - all have their origin on inner epicondyle of humerus

origin: inner epicondyle of humerus

insertion: halfway down radius on the lateral side

action: pronates and flexes forearm

 

FLEXOR CARPI RADIALIS

origin: inner epicondyle of humerus

insertion: base of metacarpal of first and second finger

action: pronates arm; flexes and abducts hand

 

PALMARIS LONGUS

origin: inner epicondyle of humerus

insertion: tendon spreads out into fascia of palm (palmar aponeurosis)

action: pronates forearm, flexes hand

 

FLEXOR CARPI ULNARIS — largest of the group

origin: inner epicondyle of humerus

insertion: wraps around to back of the arm and follows ulnar crest down to the carpal mass on the little finger side

action: flexes and adducts hand

 


 

EXTENSOR-SUPINATOR GROUP OF THE FOREARM - extensors longer, thinner

EXTENSOR CARPI ULNARIS

origin: lateral epicondyle, passes over the anconeous slightly

insertion: base of metacarpa 5 (little finger)

action: adducts hand, extends it somewhat

 

EXTENSOR DIGITORIUM (COMMUNIS)

origin: lateral epicondyle

insertion: phalanges of fingers (dorsal surface)

action: extends hand and fingers, spreads fingers apart

 

EXTENSOR CARPI RADIALIS BREVIS

origin: lateral epicondyle of humerus

insertion: base of metacarpal of middle finger

action: extends and abducts hand

 

The next two muscles create a strong visual and physical link between the upper and lower arm — both originate on the condyloid ridge of the humerus.

EXTENSOR CARPI RADIALUS LONGUS

origin: condyloid ridge of humerus

insertion: base of the metacarpal of the index (second) finger

action: flexes forearm; supinates forearm in extension; pronates arm in flexion; abducts and extends the hand

form: along with the brachioradialis, creates a visual link between the upper arm and the forearm

 

BRACHIORADIALIS (supinator longus)

origin: lateral epicondylar ridge of humerus, between triceps and brachialis

insertion: styloid process of the radius

action: flexes forearm; supinates forearm in extension; pronates it in flexion

form: along with the extensor carpi radialus longus creates a visual link between the upper arm and the forearm

 

IMPORTANT CONSTRUCTION POINTS AND LINES ON ARM:

  • the fossa or depression at the head of the radius (when arm extended)
  • the inner or medial epicondyle of the humerus
  • the olecranon process
  • the ulnar furrow

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THE HAND

There are two groups of interosseus muscles — between the metacarpals and the outside of the little finger; one set is on the dorsal side, one on the palmar side.

The biggest muscles are between the metacarpal of the thumb and finger — triangular shape which bulges when the thumb is adducted.

The other group is on the little finger side — they partly account for the padding there — they do not cover the carpal mass but rather leave the carpal mass subcutaneous.

There are no muscles on the back of the hand (only tendons) — on the palm side there is padding and muscle:

 

THE EXTENSORS OF THE THUMB — these continue the spiral effect of the posterior forearm

origin: about halfway up the radius and the ulna

insertion: base of the thumb

action: extend and abduct thumb

form: some softening effect on harsh line of the radius (two muscles): one muscle has the tendon which creates a depression when the thumb is flexed: this depression is called the "snuff box" (tabatiere)

 

THENAR EMINENCE — largest

origin: carpals of the thumb and metacarpal 3 (covers about half of the palm)

insertion: base of the first phalanx of the thumb

action: pulls thumb in across palm

form: very rounded on inside of palm

 

HYPOTHENAR EMINENCE — on little finger side — longer and flatter; rises from a little higher on the carpal mass than the thenar eminence; blends with the interosseus muscle on the little finger to create padding on medial edge of hand

The webbing between the fingers, on the palm side, extends about halfway down the first phalanx. Hence fingers look longer when viewed on the dorsal side of hand.

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