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Directed Learning week 3 - Anatomedia/Acland's Anatomy/Kanopy...

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Anatomedia Arm flexor compartment muscles • The arm is located between the shoulder and the elbow • Muscles of the arm can be subdivided into flexor and extensor groups, which exert opposite but complimentary actions at the joints they cross • Flexor muscles are located in the anterior compartment of the arm • Attachments and actions of: o Coracobrachialis • O - scapula • I - humerus • Adductor and weak flexor of the shoulder joint • Due to its attachment to the coracoid process, when the upper limb is fixed it is capable of protracting the scapula o Biceps brachii • Biceps brachii consists of two heads (Long and short). The long head biceps joins with the short head at approximately the mid point of the arm • The short head of biceps runs in parallel with coracobrachialis • O (long head) - scapula, adjacent part of glenoid labrum • O (short head) - scapula (tip of coracoid process) • I - radial tuberosity (posterior aspect), deep fascia or forearm • Powerful flexor at the elbow joint and supinator of the forearm • Both heads are weak flexors at the shoulder joint while the short head may also adduct the arm • Because of its intra capsular origin the primary role of the long head of biceps at the shoulder joint is to maintain the head of humerus centred in the glenoid cavity. This prevents excessive upward migration of the humeral head during elevation, thereby increasing shoulder stability. Because of the long head of biceps medley to ineffective stabilisation of the head of the humerus • Biceps generates maximum force when the elbow is flexed to about 90°. it is less efficient when the elbows extended; most of its force is then translatory, resulting in joint stability. As biceps attach to the mobile radius is flexor Force is affected by the position of the forearm, being greatest in supination or midway between pronation and supination and least in full pronation. Biceps may become actively insufficient when the full flexion at the elbow is attempted at the shoulder in full flexion. o Brachialis • O - humerus , intermuscular septa of arm • I - ulnar tuberosity and coronoid process, capsule of elbow joint • Leverage is determined by the distance of the line of pull from the axis of the joint crossed by the muscle. Brachialis, like biceps, is inserted close to the elbow joint axis and generate its greatest force at about 90° of flexion. However, unlike biceps, brachialis crosses only the elbow joint and attaches to the fixed ulna. Its force of contraction is therefore unaffected by the position of the shoulder or by changes in the position of the forearm brought about by rotation of the radius •

Bicipital tendinitis and rupture o The long head of biceps has intracapsular (tendinous) Origin and is lined by a synovial sheath as it passes through the bicipital groove. Irritation e.g. by unaccustomed or repetitive movement in the synovial sheath may result in inflammation with accumulation of fluid. This may also be associated with inflammation of the tendon itself

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Rupture of the tendon of long head of biceps can occur when suddenly resisting a heavy load. The most common sites are at its attachment to the supraglenoid tubercle or entry into the bicipital groove (particularly if weakened by chronic tendinitis). In the elderly, the tendon can even rupture spontaneously. The shortened muscle belly is evident as prominent lump in the middle of the arm.

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Muscular variants that occur in the arm and their significance o Additional slips or heads on muscular variants that can occur in the upper limb, particularly anterior compartment of the arm o Biceps can have 3 heads. The additional head may arise from the middle third of the humerus, from the bicipital groove or even from adjacent muscles. There appears to be doing functional disadvantage. Variations such as this normally occur in certain primates ever generally curiosities in humans, rather than of clinical significance. However, a third head of biceps tends to be associated with higher division of the brachial artery (a variant involving a neighbouring structure). o Coracobrachialis is normally into parts (split by a musculocutaneous nerve). The third part can be present, attached to the intermuscular septum, to a bony process above the medial epicondyle of the humerus (a supracondylar spur) or even to the medial epicondyle itself. A rudimentary third head of Coracobrachialis can be present as a fibrous band arising from a supracondylar spur. The band may entrap structures passing to the forearm under it (median nerve and sometimes the brachial artery as well). This is analogous to the adductor muscles in the thigh which are also in three component s(with nerves passing between them

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Nerve supply of arm flexor muscles o The muscles of the anterior compartment of the arm are all supplied by the musculocutaneous nerve which passes between the 2 parts of coracobrachialis to reach biceps and brachialis o Coracobrachialis is supplied with C5, 6, 7 fibres, while biceps brachii and brachialis are supplied with C5, 6 fibres o Brachialis also receives a branch from the radial nerve (sensory fibres). Being located on the border between 2 compartments, it tends to receive a dual nerve supply

Arm extensor compartment muscle • Triceps brachii is the only muscle in the posterior compartment of the arm. It is made up of long, lateral and medial heads. The long head of triceps crosses both the shoulder and elbow joints while the large medial head and smaller lateral head arise from the shaft of the humerus and cross only the elbow joint. •

Attachments and actions of triceps brachii o O (long head) - scapula (infraglenoid tubercle), capsule of shoulder joint o O (lateral head) - humerus (posterior surface about radial groove) o O (medial head) - humerus (posterior surface below radial groove) o I - ulna (olecranon process), capsule of elbow joint o The long Head of triceps extends the arm at the shoulder joint. Acting together the three heads powerfully extend the forearm at the elbow joint. The triceps insertion is very strong as is the olecranon process of the ulna and an avulsion fracture of it is rare

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The long head of triceps is most efficient as an extensor at the elbow joint if the shoulder is simultaneously flexed. With elbow extension is attempted with the shoulder in extension the muscle becomes actively insufficient. The medial and lateral heads are unaffected by shoulder position and generate the most powerful for elbow extension. o Triceps act as a synergist for elbow flexion by opposing the flex action of the long-head of biceps (at the shoulder joint). Their roles are reversed for elbow extension. Triceps also acts synergistically with biceps to prevent elbow flexion when biceps is acting as a supinator of the forearm. When bicep acts as a pure supinator (e.g. extracting a cork from a bottle) triceps acts synergistically to prevent elbow flexion Nerve supply of triceps brachii and effect of paralysis o Triceps brachii is supplied with C6, 7, 8 fibres by the radial nerve, which passes through the posterior compartment of the arm between the lateral and medial heads o Paralysis of triceps results in almost complete loss of elbow extensor strength (necessary for all pushing activities). Elbow stability is also diminished

Acland's Bones, ligaments and tendons of the shoulder review • Clavicle • Scapula o Glenoid cavity o Supraglenoid o Infraglenoid o Spine o Supraspinous o Infraspinous o Chromium o Coracoid process o Glenoid labrum o Coracoid ligament • Humerus o Head o Greater tubercle o Lesser tubercle o Bicipital groove o Deltoid tuberosity o Sternoclavicular joint o Acromioclavicular joint - conoid and trapezoid ligament Review of shoulder muscles

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Subscapularis Supraspinatus Infraspinatus Teres minor Teres major Coracobrachialis Serratus anterior Levatus scapulae Major and minor rhomboids Trapezius Pec minor Subclavius Omohyoid Pec major Latissimus dorsi deltoid...