Anatomy of Brachial Plexus Quiz

Brachial Plexus and Axilla

• The brachial plexus is a network of nerves that innervate the upper limb.
• It is formed by the anterior rami of spinal nerves C5-T1.
• The plexus has roots, trunks, divisions, cords, and branches.
• The axillary region contains the axillary artery, brachial plexus, and lymphatics.
• The axillary artery is a continuation of the subclavian artery and its branches include branches that supply the shoulder, scapula and arm.

Axilla Borders

• Apex: Cervico-axillary canal, passageway between neck and axilla.
• Base: Thoracic wall and medial aspect of humerus.
• Posterior wall: Scapula and subscapularis, teres major, and latissimus dorsi.
• Anterior wall: Pectoralis major and minor.
• Lateral wall: Intertubercular sulcus on the humerus.
• Medial wall: Thoracic wall (1st–4th ribs).

Axilla Contents

• Axillary vessels: Axillary artery and vein, lymphatic vessels.
• Brachial plexus: Network of nerves supplying the upper limb.
• Lymphatics: Lymphatic vessels that drain various regions of the body.

Axillary Lymph Nodes

• There are five principal groups: pectoral, subscapular, humeral, central, and apical.
• These groups are arranged in a pattern that mirrors the shape of the axilla.
• The apical nodes receive lymph from other axillary nodes and cephalic vein lymphatics.
• The central nodes receive lymph from the humeral, subscapular, and pectoral nodes.
• The humeral nodes receive lymph from most of the upper limb.
• The subscapular nodes receive lymph from the posterior thoracic wall and scapular region.
• The pectoral nodes receive lymph mainly from the anterior thoracic wall, including most of the breast.

Nerves of Brachial Plexus

• Musculocutaneous nerve: Innervates anterior compartment arm muscles, lateral forearm.
• Median nerve: Innervates forearm & hand muscles, and some hand cutaneous area.
• Ulnar nerve: Innervates forearm & hand muscles, and some hand cutaneous area.
• Axillary nerve: Innervates shoulder muscles, part of shoulder skin.
• Radial nerve: Innervates posterior compartment arm and forearm muscles and part of the dorsum of the hand.

Brachial Plexus Roots, Trunks, Divisions and Cords

• The roots comprise the anterior rami of c5, c6, c7, c8, and t1.
• These roots merge to form superior, middle, and inferior trunks.
• These three trunks branch to form anterior and posterior divisions
• From the divisions the cords are formed, which are the lateral, medial, and posterior cords.
• The cords give rise to named peripheral nerves.

Humeral Fractures

• Proximal: Surgical neck damage may affect nerves and muscles of the shoulder.
• Midshaft: Radial nerve damage affects wrist extension and cutaneous sensitivity to part of the hand.
• Distal: Supracondylar injuries may impact median nerve function (handgrip, and sensation changes) or ulnar nerve (loss of wrist flexion, handgrip).

Elbow Joint

• It's a hinge joint (flexion/extension only).
• The joint capsule has an outer fibrous layer and an inner synovial membrane.
• The olecranon bursae cushion the elbow.

Arm overview

• The arm moves at the elbow and glenohumeral joint.
• The anterior compartment muscles control flexion, supination.
• The posterior compartment muscles control extension.

Arterial Supply

• The axillary artery delivers blood to the shoulder, arm.
• Branches (e.g., brachial artery) supply the upper limb.
• There are collateral and recurrent arteries for blood flow to all tissues.

Venous & Lymph Drainage

• Blood from the upper limb drains into the veins, and then to axillary and eventually the superior vena cava.
• Lymph fluid from the upper limb is drained to the axillary lymph nodes and ultimately returns to the venous blood stream.

Cubital Fossa

• A triangular region in the forearm; contains important structures for blood draws/assessments.
• Contains: Biceps tendon, median nerve, brachial artery, and median cubital vein.

Clinical Correlates

• Describes how various injury/disorders affect anatomy of the arm.
• Example of Erb's Palsy (upper trunk injury) or Klumpke's Palsy (lower trunk injury).
• Demonstrates some clinical applications of the brachial plexus (e.g blood draws, injury, blood pressure).

Dermatomes

• Shows cutaneous distribution for each spinal nerve.
• Clinically important for diagnosis of nerve damage.

Muscles in the Anterior and Posterior Compartments of the Arm

• Anterior: Contains muscles for flexion, supination (muscles like biceps brachii, coracobrachialis, brachialis).
• Posterior: Contains muscles for extension of the arm, elbow, and forearm (muscles like triceps brachii, anconeus). Their origins, insertions and actions are important to know.

Nerve root contributions

• The various nerves of the brachial plexus are supplied by multiple spinal cord segments. These segments are represented in the table of muscle innervated and their main actions to be performed.

Quiz Time

• It's time for a quiz about the topic!
• Use the above notes to prepare for the quiz.