Axilla & Brachial Plexus Anatomy Quiz

Axilla & Brachial Plexus

• The axilla is the gateway to the upper limb, acting as a transition zone between the neck and arm.
• It's shaped like a pyramid with four walls, an inlet (apex), and a base.
• The axillary inlet connects to the neck superiorly.
• Its borders include the clavicle anteriorly, the scapula posteriorly, and the first rib medially.
• The floor of the axilla is formed by the skin of the armpit.

Contents of the Axilla

• Brachial plexus: a network of nerves controlling upper limb function.
• Axillary artery: the main blood vessel supplying the upper limb.
• Axillary vein: a major vein draining blood from the upper limb.
• Axillary lymph nodes: crucial for immune function in the region.
• Tail of the breast in females: a portion of breast tissue extending into the axilla.

Brachial Plexus Formation

• The brachial plexus is composed of the anterior rami of spinal nerves C5, C6, C7, C8, and most of T1.
• It has five stages, beginning with roots in the neck, then passing trunks behind the clavicle
• Following the trunks, divisions form, then cords in the axilla.
• Finally, terminal branches emerge, creating nerves that innervate various muscles and functions of the upper limb.

Brachial Plexus Cords

• Three cords, the lateral, medial, and posterior cords, emerge from the divisions of the brachial plexus.
• Each cord is associated with specific branches.
  • The lateral cord contains the lateral pectoral nerve, musculocutaneous nerve, and lateral root of the median nerve.
  • The medial cord contains the medial pectoral nerve, medial cutaneous nerve of the forearm, medial root of median nerve, and ulnar nerve.
  • The posterior cord contains the upper and lower subscapular nerves, nerve to latissimus dorsi, radial nerve and the axillary nerve.

Axillary Nerve

• Originating from the posterior cord of the brachial plexus:
• It passes through the quadrangular space, entering the posterior scapular region
• Provides sensation from the skin over the deltoid muscle and also innervates the deltoid and teres minor muscles.

Axillary Artery

• The main artery supplying the upper limb.
• Begins at the lateral border of the first rib.
• Becomes the brachial artery at the lower border of the teres major muscle.
• Branches: anterior and posterior circumflex humeral arteries.

Scapular Region Muscles

• Supraspinatus: Initiates abduction (0-15°) of the shoulder, supplies nerves by suprascapular nerve.
• Infraspinatus: Lateral rotation at the shoulder, supplies nerves by suprascapular nerve.
• Teres minor: Lateral rotation at the shoulder, supplied by the axillary nerve.
• Teres major: Medial rotation, extension, and adduction of the shoulder, supplied by the lower subscapular nerve.
• Subscapularis: Medial rotation at the shoulder, supplied by the upper and lower subscapular nerves.
• Deltoid: Flexion, extension, and abduction of the shoulder; supplied by the axillary nerve.

Other muscles of the back and their nerve supply and actions

• Trapezius: Elevation and depression of the shoulder. Spinal accessory nerve.
• Levator scapulae: Elevation of the shoulder. Dorsal scapular nerve.
• Rhomboid major and minor: Retraction of the scapula. Dorsal scapular nerve.
• Latissimus dorsi: Extends and medially rotates the humerus. Thoracodorsal nerve.

Spaces of the Scapular Region

• Posterior Quadrangular Space: Contains the axillary nerve.
• Upper Triangular Space: Contains the suprascapular nerve.
• Lower Triangular Space: Contains the radial nerve.