Editing Upper limb (section)

===Musculoskeletal system===

====Shoulder girdle====
[[File:Pectoral girdle front diagram.svg|thumb|Bones of the shoulder girdle]]
{{Main|Shoulder girdle}}
The shoulder girdle<ref name="Thieme-Atlas-208">{{harvnb|Ross|Lamperti|2006| p=208}}</ref> or pectoral girdle,<ref name="Sellers-1">{{harvnb|Sellers|2002| pp=1–3}}</ref> composed of the [[clavicle]] and the [[scapula]], connects the upper limb to the [[axial skeleton]] through the [[sternoclavicular joint]] (the only joint in the upper limb that directly articulates with the trunk), a ball and socket joint supported by the [[subclavius muscle]] which acts as a dynamic [[ligament]].  While this muscle prevents dislocation in the joint, strong forces tend to break the clavicle instead.  The [[acromioclavicular joint]], the joint between the [[acromion]] process on the scapula and the clavicle, is similarly strengthened by strong ligaments, especially the [[coracoclavicular ligament]] which prevents excessive lateral and medial movements.  Between them these two joints allow a wide range of movements for the shoulder girdle, much because of the lack of a bone-to-bone contact between the scapula and the axial skeleton.  The [[pelvic girdle]] is, in contrast, firmly fixed to the axial skeleton, which increases stability and load-bearing capabilities.
<ref name="Sellers-1" />

The mobility of the shoulder girdle is supported by a large number of muscles.  The most important of these are muscular sheets rather than fusiform or strap-shaped muscles and they thus never act in isolation but with some fibres acting in coordination with fibres in other muscles.<ref name="Sellers-1" />
; Muscles: of shoulder girdle excluding the glenohumeral joint<ref name="Thieme-Atlas-256" />
:; Migrated from head: [[Trapezius]], [[sternocleidomastoideus]], [[omohyoideus]]
:; Posterior: [[Rhomboideus major]], [[rhomboideus minor]], [[levator scapulae]]
:; Anterior: [[Subclavius]], [[pectoralis minor]], [[serratus anterior]]

====Shoulder joint====
[[File:Gray326.png|thumb|Shoulder joint with ligaments]]
The [[glenohumeral joint]] (colloquially called the shoulder joint) is the highly mobile ball and socket joint between the [[glenoid cavity]] of the scapula and the head of the humerus.  Lacking the passive stabilisation offered by ligaments in other joints, the glenohumeral joint is actively stabilised by the [[rotator cuff]], a group of short muscles stretching from the scapula to the humerus.  Little inferior support is available to the joint and dislocation of the shoulder almost exclusively occurs in this direction.
<ref name="Sellers-3">{{harvnb|Sellers|2002| pp=3–5}}</ref>

The large muscles acting at this joint perform multiple actions and seemingly simple movements are often the result of composite antagonist and protagonist actions from several muscles.  For example,  [[pectoralis major]] is the most important arm flexor and [[latissimus dorsi]] the most important extensor at the glenohumeral joint, but, acting together, these two muscles cancel each other's action leaving only their combined medial rotation component.  On the other hand, to achieve pure flexion at the joint the [[Deltoid muscle|deltoid]] and [[supraspinatus]] must cancel the adduction component and the [[teres minor]] and [[infraspinatus]] the medial rotation component of pectoralis major.  Similarly, abduction (moving the arm away from the body) is performed by different muscles at different stages.  The first 10° is performed entirely by the supraspinatus, but beyond that fibres of the much stronger deltoid are in position to take over the work until 90°. To achieve the full 180° range of abduction the arm must be rotated medially and the scapula most be rotated about itself to direct the glenoid cavity upward.
<ref name="Sellers-3" />

; Muscles: of shoulder joint proper<ref name="Thieme-Atlas-256" />
:; Posterior: [[Supraspinatus]], [[infraspinatus]], [[teres minor]], [[subscapularis]], [[deltoideus]], [[latissimus dorsi]], [[teres major]]
:; Anterior: [[Pectoralis major]], [[coracobrachialis]]

====Bones of upper limb====
The bones forming the human upper limb are
* Clavicle
* Scapula
* Humerus
* Radius
* Ulna
* Carpal bones
** Scaphoid
** Lunate
** Triquetral
** Pisiform
** Trapezium
** Trapezoid
** Capitate
** Hamate
* 5 Metacarpal bones
* 14 Phalanges
[[File:Upper Limb Bones with articular cartilage.svg|thumb|Upper limb bones with articular cartilage]]

====Arm====
[[File:Arm muscles front superficial.png|thumb|Superficial muscles of the arm]]
{{Main|Arm}}
The arm proper (''brachium''), sometimes called the upper arm,<ref name="Thieme-Atlas-208" /> the region between the shoulder and the elbow, is composed of the [[humerus]] with the [[Elbow|elbow joint]] at its distal end.

The elbow joint is a complex of three joints&nbsp;— the [[humeroradial joint|humeroradial]], [[humeroulnar joint|humeroulnar]], and [[superior radioulnar joint]]s&nbsp;— the former two allowing flexion and extension whilst the latter, together with its [[Inferior radioulnar joint|inferior namesake]], allows supination and pronation at the wrist.  [[Triceps brachii|Triceps]] is the major extensor and [[brachialis]] and [[Biceps brachii|biceps]] the major flexors.  Biceps is, however, the major supinator and while performing this action it ceases to be an effective flexor at the elbow.
<ref name="Sellers-5">{{harvnb|Sellers|2002| p=5}}</ref>

; Muscles: of the arm<ref name="Thieme-Atlas-256" />
:; Posterior: [[Triceps brachii]], [[anconeus]]
:; Anterior: [[Brachialis]], [[biceps brachii]]

====Forearm====
[[File:Gray414.png|thumb|90px|Ventral superficial muscles of the forearm]]
{{Main|Forearm}}
The forearm ({{langx|la|antebrachium}}),<ref name="Thieme-Atlas-208" /> composed of the [[Radius (bone)|radius]] and [[ulna]]; the latter is the main distal part of the elbow joint, while the former composes the main proximal part of the wrist joint.

Most of the large number of muscles in the forearm are divided into the wrist, hand, and finger extensors on the dorsal side (back of hand) and the ditto flexors in the superficial layers on the ventral side (side of palm).  These muscles are attached to either the [[Lateral epicondyle of the humerus|lateral]] or [[Medial epicondyle of the humerus|medial epicondyle]] of the humerus.  They thus act on the elbow, but, because their origins are located close to the centre of rotation of the elbow, they mainly act distally at the wrist and hand.  Exceptions to this simple division are [[brachioradialis]]&nbsp;— a strong elbow flexor&nbsp;— and [[palmaris longus]]&nbsp;— a weak wrist flexor which mainly acts to tense the [[palmar aponeurosis]].  The deeper flexor muscles are extrinsic hand muscles; strong flexors at the finger joints used to produce the important power grip of the hand, whilst forced extension is less useful and the corresponding extensor thus are much weaker.
<ref name="Sellers-6">{{harvnb|Sellers|2002| pp=6–7}}</ref>

Biceps is the major supinator (drive a screw in with the right arm) and [[pronator teres]] and [[pronator quadratus]] the major pronators (unscrewing)&nbsp;— the latter two role the radius around the ulna (hence the name of the first bone) and the former reverses this action assisted by [[supinator]].  Because biceps is much stronger than its opponents, supination is a stronger action than pronation (hence the direction of screws).
<ref name="Sellers-6" />

; Muscles: of the forearm<ref name="Thieme-Atlas-256" />
:; Posterior: (Superficial) [[extensor digitorum]], [[extensor digiti minimi]], [[extensor carpi ulnaris]], (deep) [[supinator]], [[abductor pollicis longus]], [[extensor pollicis brevis]], [[extensor pollicis longus]], [[extensor indicis]]
:; Anterior: (Superficial) [[pronator teres]], [[flexor digitorum superficialis]], [[flexor carpi radialis]], [[flexor carpi ulnaris]], [[palmaris longus]], (deep) [[flexor digitorum profundus]], [[flexor pollicis longus]], [[pronator quadratus]]
:; Radial: [[Brachioradialis]], [[extensor carpi radialis longus]], [[extensor carpi radialis brevis]]

====Wrist====
{{Main|Wrist}}
The [[wrist]] ({{langx|la|carpus}}),<ref name="Thieme-Atlas-208" /> composed of the [[carpal bones]], articulates at the wrist joint (or [[radiocarpal joint]]) proximally and the [[carpometacarpal joint]] distally.  The wrist can be divided into two components separated by the [[midcarpal joint]]s.  The small movements of the eight carpal bones during composite movements at the wrist are complex to describe, but flexion mainly occurs in the midcarpal joint whilst extension mainly occurs in the radiocarpal joint; the latter joint also providing most of adduction and abduction at the wrist.
<ref name="Sellers-8">{{harvnb|Sellers|2002| pp=8–9}}</ref>
[[File:3D Medical Animation Human Wrist.jpg|alt=3D Medical Animation still shot of Human Wrist|thumb|228x228px|3D medical animation still shot of human wrist]]
How muscles act on the wrist is complex to describe.  The five muscles acting on the wrist directly&nbsp;— [[flexor carpi radialis]], [[flexor carpi ulnaris]], [[extensor carpi radialis longus muscle|extensor carpi radialis]], [[extensor carpi ulnaris]], and [[palmaris longus]]&nbsp;— are accompanied by the tendons of the extrinsic hand muscles (i.e. the muscles acting on the fingers).  Thus, every movement at the wrist is the work of a group of muscles; because the four primary wrist muscles (FCR, FCU, ECR, and ECU) are attached to the four corners of the wrist, they also produce a secondary movement (i.e. ulnar or radial deviation).  To produce pure flexion or extension at the wrist, these muscle therefore must act in pairs to cancel out each other's secondary action.  On the other hand, finger movements without the corresponding wrist movements require the wrist muscles to cancel out the contribution from the extrinsic hand muscles at the wrist.
<ref name="Sellers-8" />

====Hand====
[[File:Scheme human hand bones-en.svg|thumb|Bones of the hand]]
{{Main|Hand}}
The hand ({{langx|la|manus}}),<ref name="Thieme-Atlas-208" /> the [[Metacarpus|metacarpals]] (in the hand proper) and the [[Phalanx bones|phalanges]] of the fingers, form the [[metacarpophalangeal joint]]s (MCP, including the [[knuckle]]s) and [[interphalangeal articulations of hand|interphalangeal joints]] (IP).

Of the joints between the carpus and metacarpus, the [[carpometacarpal joint]]s, only the saddle-shaped joint of the thumb offers a high degree of mobility while the opposite is true for the metacarpophalangeal joints.  The joints of the fingers are simple hinge joints.
<ref name="Sellers-8" />

The primary role of the hand itself is grasping and manipulation; tasks for which the hand has been adapted to two main grips&nbsp;— power grip and precision grip.  In a power grip an object is held against the palm and in a precision grip an object is held with the fingers, both grips are performed by intrinsic and extrinsic hand muscles together.  Most importantly, the relatively strong thenar muscles of the thumb and the thumb's flexible first joint allow the special opposition movement that brings the distal thumb pad in direct contact with the distal pads of the other four digits.  Opposition is a complex combination of thumb flexion and abduction that also requires the thumb to be rotated 90° about its own axis.  Without this complex movement, humans would not be able to perform a precision grip.
<ref name="Sellers-10">{{harvnb|Sellers|2002| pp=10–11}}</ref>

In addition, the central group of intrinsic hand muscles give important contributions to human dexterity.  The palmar and dorsal interossei adduct and abduct at the MCP joints and are important in pinching.  The lumbricals, attached to the tendons of the [[flexor digitorum profundus]] (FDP) and [[extensor digitorum communis]] (FDC), flex the MCP joints while extending the IP joints and allow a smooth transfer of forces between these two muscles while extending and flexing the fingers.
<ref name="Sellers-10" />

; Muscles: of the hand<ref name="Thieme-Atlas-256" />
:; Metacarpal: [[Lumbricals of the hand|Lumbricals]], [[Palmar interossei muscles|palmar introssei]], [[Dorsal interossei of the hand|dorsal interossei]]
:; [[Thenar]]: [[Abductor pollicis brevis]], [[adductor pollicis]], [[flexor pollicis brevis]], [[opponens pollicis]]
:; [[Hypothenar]]: [[Abductor digiti minimi muscle of hand|Abductor digiti minimi]], [[Flexor digiti minimi brevis (hand)|flexor digiti minimi]], [[opponens digiti minimi]], [[palmaris brevis]]