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Learn: Arm
ARM
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Biceps brachii muscle
Origin | Long head: supraglenoid tubercle of scapula Short head: apex of coracoid process |
Insertion | Radial tuberosity |
Innervation | Musculocutaneous nerve |
Artery | Brachial artery (muscular branches) |
Action | Flexes forearm at elbow joint; supinates forearm; accessory flexor of arm at glenohumeral joint |
Brachialis muscle
Origin | Anterior aspect of humerus (medial and lateral surfaces) and adjacent intermuscular septae |
Insertion | Tuberosity of the ulna |
Innervation | Musculocutaneous nerve |
Artery | Brachial artery (muscular branches), recurrent radial artery |
Action | Flexes the forearm at the elbow joint |
Coracobrachialis muscle
Origin | Apex of coracoid process |
Insertion | Middle third of medial surface of humerus |
Innervation | Musculocutaneous nerve |
Artery | Brachial artery (muscular branches) |
Action | Helps in flexion and adduction of arm |
Triceps brachii muscle
Origin | Long head: infraglenoid tubercle Lateral head: posterior surface of humerus Medial head: posterior surface of humerus |
Insertion | Olecranon of ulna |
Innervation | Radial nerve |
Artery | Profunda brachii artery |
Action | Extends forearm at elbow joint. Long head also can extend and adduct the arm at the shoulder joint. |
Anconeus muscle
Origin | Lateral epicondyle of humerus |
Insertion | Olecranon and proximal posterior surface of ulna |
Innervation | Radial nerve |
Artery | Middle collateral branch of deep brachial artery; Recurrent interosseous artery |
Action | Abduction of the ulna in pronation; accessory extensor of the elbow joint |
Nerves
Relatively speaking, there is not that much to know in terms of nerves in the arm. The few nerves that are relevant here include:
- Musculocutaneous nerve
- Comes off of lateral cord of brachial plexus
- Pierces and innervates coracobrachialis muscle
- After piercing the coracobrachialis muscle, it descends in between the biceps brachii and brachialis muscles and provides motor innervation to both of them
- Passes the elbow, pierces deep fascia, and becomes the lateral cutaneous nerve of the forearm (also called lateral antebrachial cutaneous nerve)
- Radial nerve
- Comes off of posterior cord of brachial plexus
- Passes through triangular interval with profunda brachii artery and travels down the posterior compartment of the arm, initially between long and medial heads of triceps brachii muscle and later between medial and lateral heads of triceps brachii muscle, in the radial groove of the humerus
- Provides motor innervation to triceps brachii muscle
- After piercing lateral intermuscular septum of arm, passes anterior to lateral epicondyle of humerus between brachialis and brachioradialis muscles. Enters cubital fossa, where it divides into superior and deep branches.
- Gives off posterior cutaneous nerve of arm, inferior lateral cutaneous nerve of arm, and posterior cutaneous nerve of forearm
- Provides motor innervation to posterior compartment of forearm
- Provides cutaneous innervation to dorsum of hand
- Medial cutaneous nerve of the arm
- Comes from medial cord of brachial plexus
- Cutaneous innervation to anteromedial skin of arm
Arteries
- Brachial artery
- Continuation of the axillary artery after it crosses the inferior border of the teres major muscle
- Branches
- Profunda brachii artery (deep artery of the arm)
- Often forms an anastamosis with the posterior humeral circumflex artery
- Upon termination, divides into middle collateral artery and radial collateral artery
- Superior ulnar collateral artery
- Inferior ulnar collateral artery
- Profunda brachii artery (deep artery of the arm)
- At elbow, divides into radial artery and ulnar artery
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