Upper Arm Anatomy Quiz

Upper Arm Anatomy

• The upper arm extends from the shoulder to the elbow.
• The upper arm has three layers:
  • Skin
  • Superficial fascia containing basilic and cephalic veins and fat.
  • Deep fascia, which has two fascial septa, the medial and lateral intermuscular septa, extending from the deep fascia and connecting to the supracondylar ridges of the humerus.

Arm Compartments

• The two fascial septa divide the arm into an anterior (flexor) compartment and a posterior (extensor) compartment.

Anterior (Flexor) Compartment

• Contains the biceps brachii, coracobrachialis, and brachialis muscles.
• Supplied by the musculocutaneous nerve.
• Contains the brachial artery and basilic vein.
• The median, ulnar, and radial nerves pass through the anterior compartment.

Posterior (Extensor) Compartment

• Contains the three heads of the triceps muscle and subanconeus muscle, all supplied by the radial nerve.
• Contains the profunda brachii artery, superior and inferior ulnar collateral arteries.
• Contains the radial and ulnar nerves.

Cutaneous Nerves of the Upper Arm

• Lateral Side:
  • Supraclavicular nerves (C3, C4): supply the upper half of the deltoid.
  • Upper lateral cutaneous nerve of the arm (C5, C6): supply the lower half of the deltoid.
  • Lower lateral cutaneous nerve of the arm (C5, C6): supply the lateral side below the deltoid.
• Medial Side:
  • Intercostobrachial nerve (T2): supply the upper part of the medial side of the arm near the axilla.
  • Medial cutaneous nerve of the arm (C8, T1): supply the medial side of the arm below the axilla.
• Back of the Upper Arm:
  • Posterior cutaneous nerve of the arm (C5, 6, 7, 8):

Muscles of the Upper Arm

• Biceps Brachii:
  • Origin:
    • Short head: arises with coracobrachialis from the tip of the coracoid process.
    • Long head: arises from the supraglenoid tubercle.
  • Insertion:
    • Tendon into the radial tuberosity.
    • Bicipital aponeurosis into deep fascia of the medial forearm.
  • Nerve Supply: Musculocutaneous nerve, with a separate branch for both heads.
  • Action:
    • Powerful supinator of the forearm.
    • Flexion of the supinated forearm at the elbow.
    • The long head supports the shoulder joint.
    • The short head flexes the arm at the shoulder.
• Coracobrachialis:
  • Origin: Arises with the short head of biceps from the tip of the coracoid process.
  • Insertion: Middle of the medial border of the humerus
  • Nerve Supply: Musculocutaneous nerve.
  • Action: Helps in flexion of the arm at the shoulder joint.
• Brachialis:
  • Origin: Lower half of the anterior surface of the humerus.
  • Insertion: Tuberosity of the ulna on the anterior surface of the coracoid process.
  • Nerve Supply:
    • Musculocutaneous nerve.
    • Radial nerve
  • Action: Flexion of the forearm at the elbow joint.
• Triceps:
  • The only muscle on the back of the humerus, corresponding to the brachialis and biceps.

Brachial Artery

• Begins at the lower border of the teres major muscle as a continuation of the axillary artery.
• Terminates in front of the neck of the radius by dividing into the radial and ulnar arteries..
• Accompanied by two venae comitantes.
• Course: Descends downwards and laterally, initially medial to the humerus.

Relations of the Brachial Artery

• Upper 1/2 of the Arm:
  • Anteriorly: skin and fasciae.
  • Posteriorly: radial nerve separates it from the long head of triceps.
  • Laterally: median nerve, coracobrachialis, and short head of biceps.
  • Medially: ulnar nerve, basilic vein, and medial cutaneous nerve.
• Middle of the Arm (at Insertion of Coracobrachialis):
  • Median nerve crosses the artery from lateral to medial (front or back of the artery).
• Lower 1/2 of the Arm:
  • Anteriorly: skin and fasciae.
  • Posteriorly: brachialis muscle separates it from the humerus.
  • Laterally: biceps muscle.
  • Medially: median nerve.
• Cubital Fossa:
  • Anteriorly: skin, fasciae, bicipital aponeurosis, and median cubital vein.
  • Posteriorly: tendon of brachialis muscle.
  • Laterally: tendon of biceps muscle
  • Medially: median nerve

Branches of the Brachial Artery

• Profunda brachii artery (largest branch):
  • Arises just below the lower border of the teres major muscle.
  • Accompanies the radial nerve in the spiral groove to the lateral side of the arm.
  • Branches:
    • Ascending branch (deltoid branch): anastomoses with the descending branch of the posterior circumflex humeral artery.
    • Anterior descending branch (radial collateral): pierces the lateral intermuscular septum, accompanies the radial nerve, and ends in front of the lateral epicondyle by anastomosing with the radial recurrent artery.
    • Posterior descending branch (middle collateral): anastomoses with the interosseous recurrent artery.
    • Muscular branches: to triceps.
    • Nutrient: to the humerus in the spiral groove.
• Superior ulnar collateral artery:
  • Arises at the middle of the arm, opposite the insertion of the coracobrachialis.
  • Pierces the medial intermuscular septum to reach the back of the medial epicondyle.
  • Anastomoses with the posterior ulnar recurrent artery.
• Inferior ulnar collateral artery:
  • Arises two inches above the elbow.
  • Divides into two branches:
    • Anterior branch: descends in front of the medial epicondyle and anastomoses with the anterior ulnar recurrent artery.
    • Posterior branch: pierces the medial intermuscular septum to reach the back of the medial epicondyle, anastomosing with the posterior ulnar recurrent artery.
• Nutrient artery: to the humerus.

Surface Anatomy

• Draw a line between two points:
  • Point (1) on the posterior fold of the axilla where the pulsations of the axillary artery can be felt.
  • Point (2) in the cubital fossa medial to the tendon of biceps (midway between the two epicondyles).

Axillary Nerve

• Arises from the posterior cord of the brachial plexus (C5, 6) behind the third part of the axillary artery.
• Passes over the subscapularis and curves backward below it to enter the quadrangular space.
• In the quadrangular space, it's accompanied by the posterior circumflex humeral vessels, both structures come into contact with the surgical neck of the humerus.
• It winds laterally around the surgical neck immediately below the shoulder joint and comes under cover of the deltoid muscle where it divdes into anterior and posterior divisions.
• Branches:
  • Articular branch: supplies the shoulder joint.
  • Posterior division: passes along the posterior border of the deltoid and ends as the upper lateral cutaneous nerve of the arm.
    • Branches to the deltoid.
    • Branch to the teres minor.
    • Upper lateral cutaneous nerve of the arm: supplies skin on the upper part of the lateral side of the arm.
  • Anterior division: runs anteriorly in front of the surgical neck and ends in the deltoid.

Effect of Injury to the Axillary Nerve

• Sources of Injury:
  • Fractures of the surgical neck of the humerus.
  • Downward dislocation of the head of the humerus.
  • Compression by an axillary crutch.
• Consequences:
  • Paralysis of the deltoid and teres minor, causing:
    • Failure of abduction of the arm (15° to 90°).
    • Flattening of the shoulder contour.
  • Affection of external rotation.
  • Loss of cutaneous sensation over the lower half of the deltoid. (The skin over the upper half of the deltoid is supplied by the lateral supraclavicular nerve from the cervical plexus).

Suprascapular Nerve

• Arises from the upper trunk of the brachial plexus in the neck (C5, 6).
• Runs downwards and laterally to reach the upper border of the scapula with the suprascapular artery.
• Passes deep to the suprascapular ligament while suprascapular vessels pass superficial to the ligament.
• Enters the supraspinous fossa and passes through the spinoglenoid notch to reach the infraspinous fossa.
• Distribution:
  • Supraspinatus muscle.
  • Infraspinatus muscle.
  • Shoulder and acromioclavicular joints.

Suprascapular Nerve Injury

• Presents as vague shoulder pain with associated weakness in shoulder abduction and external rotation.
• The suprascapular nerve supplies both the supraspinatus and infraspinatus muscles.

Test your knowledge on the anatomy of the upper arm, including its layers, compartments, and key muscles. This quiz covers both the anterior (flexor) and posterior (extensor) compartments, along with the associated nerves and blood vessels. Perfect for students of anatomy and physiology!