Anterior & posterior arm

Upper arm (or arm) is the area between the shoulder joint & elbow joint. It only has 4 muscles – 3 anterior muscles and 1 in the posterior compartment.

Anterior compartment

An easy way to remember the muscles is the mnemonic BBC – biceps, brachialis and coracobrachialis.

Screenshot 2018-12-21 at 13.22.07.png
Fig 1. Muscles of anterior compartment

Biceps brachii

 

  • Two headed muscle
  • Origin – short head from apex of coracoid process of scapula, long head – supraglenoid tubercle of scapula
  • Insertion – tuberosity of radius and fascia of forearm via bicipital aponeurosis
  • Innervation – musculocutaneous nerve (C5-C7)
  • Action – flexes forearm at elbow, weak arm flexor, supinates flexed forearm
  • Myotome reflex = C5/C6

Brachialis

  • Deep to biceps brachii
  • Origin – distal half of anterior humerus
  • Insertion – coronoid process and tuberosity of ulna
  • Innervation – musculocutaneous nerve (C5-C7)
  • Action – flexes forearm

Coracobrachialis

  • Deep to biceps brachii
  • Origin – coracoid process of scapula
  • Insertion – after passing through the axila, attaches to middle third of medial humerus
  • Innervation – musculocutaneous nerve (C5-C7)
  • Action – flexes & adducts arm at shoulder

Brachial artery & main branches

  • Continuation of axillary artery after the border of teres major
  • Palpated medially to biceps brachii at elbow joint
Screenshot 2018-12-21 at 15.17.43.png
Fig 2. Brachial artery and branches

Profunda brachii

  • 1st and main branch
  • Originates immediately distal to teres major, travels in the radial groove of humerus alongside radial nerve
  • Supplies posterior arm muscle triceps brachii

Muscular

  • Branches come off brachial artery directly to give local supply to the muscles of the upper limb

Nutrient artery

  • Arises from brachial artery at middle level of upper arm before going through the large foramen in the humerus known as the nutrient canal.

Ulnar superior & inferior collateral arteries

  • Arise from the medial surface of brachial artery and course distally towards medial aspect of elbow
  • Supply elbow joint by giving off small branches and anastamosing with recurrent vessels

Brachial artery terminates at the level of the radial neck, below the bicipital aponeurosis and becomes ulnar & radial arteries that continue into the forearm.

Musculocutaneous nerve

  • Terminal branch of the lateral cord of brachial plexus (C5-C7)
  • Leaves axilla by emerging from inferior border of pectoralis minor
  • Pierces coracobrachialis and runs superficial to brachialis but deep to biceps brachii
  • Eventually pierces biceps brachii and emerges laterally as lateral cutaneous nerve, which provides sensory innervation to the lateral forearm
Screenshot 2018-12-21 at 15.48.45.png
Fig 3. Musculocutaneous nerve

 

Posterior arm

Triceps

  • Three-headed muscle
  • Medial head lies deeper than the other two
  • Origin
    • long head – infraglenoid tubercle of scapula
    • medial head – posterior surface pf humerus, inferior to radial groove
    • lateral head – posterior humerus, superior to radial groove
  • Insertion – all heads converge into one tendon, which inserts into the olecranon of ulna
  • Innervation – radial nerve (C6-C8)
  • Action – extends forearm at elbow, steadies head of abducted humerus
Screenshot 2018-12-21 at 15.10.01.png
Fig 4. Triceps brachii

Elbow joint

  • Hinge-type synovial joint
  • 2 separate articulations
    • Anterior – trochlear notch of the ulna and trochlea of humerus
    • Posterior – head of the radius and capitulum of humerus
Screenshot 2018-12-21 at 16.08.22.png
Fig 5. Articulations of elbow joint
  • Strengthened by multiple ligaments
    • radial collateral ligament – from lateral epicondyle and then blends with the annular ligament; posterolateral stability
    • ulnar collateral ligament – from medial epicondyle and attaches to the coronoid process and olecranon of the ulna; strong protector as has anterior, posterior and oblique bands
    • annular ligament – surrounds radial head and radial notch of ulna, keeps radial head in radial notch and allows pronation and supination
Screenshot 2018-12-21 at 16.08.29.png
Fig 6. Elbow ligaments

References

  • Teach Me Anatomy (teachmeanatomy.info)
  • Netter’s anatomy colouring book (2010)
  • Wikipedia.org – Henry Vandyke Carter, Anatomy of the Human Body (1918)
  • radiopaedia.org
  • kenhub.com

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