Brachial Plexus and Shoulder Girdle Muscles

Brachial Plexus Overview

• The brachial plexus is formed by anterior rami of spinal nerves C5-T1.
• It consists of roots, trunks, divisions, cords, and terminal branches.

Nerves from Brachial Plexus

• The long thoracic nerve arises from the roots and trunks of the brachial plexus.
• The median nerve is formed by the joining of the medial and lateral cords.
• The thoracodorsal nerve is a branch of the posterior cord.
• The radial nerve is not a branch of the lateral cord.
• The ulnar nerve is not a branch of the medial cord.

Cords of the Brachial Plexus

• The lateral cord is formed from the anterior divisions of the superior and middle trunks.
• The posterior cord is formed from the posterior divisions of all three trunks.
• The medial cord is formed from the anterior division of the inferior trunk.

Terminal Branches

• The brachial plexus typically has five terminal branches: median, ulnar, musculocutaneous, axillary, and radial.

Anatomical Relations

• The roots of the brachial plexus pass through the scalene muscles.
• The upper and back part of the neck and shoulders is covered by the upper part of the trapezius muscle.

Muscle Innervations

• The upper fibers of the trapezius are innervated by the accessory nerve (CN XI).
• The rhomboids minor and major are innervated by the dorsal scapular nerve.
• The levator scapulae muscle is also innervated by the dorsal scapular nerve.
• The pectoralis minor is innervated by the medial pectoral nerve.
• The serratus anterior muscle is innervated by the long thoracic nerve.
• The pectoralis major muscle is innervated by the lateral and medial pectoral nerves.
• The latissimus dorsi muscle is innervated by the thoracodorsal nerve.
• The subclavius muscle is innervated by the nerve to subclavius.

Muscle Functions

• The primary actions of the upper fibers of the trapezius include elevation and upward rotation of the scapula.
• The rhomboids minor muscle primarily retracts the scapula.
• The primary function of the trapezius muscle includes scapular elevation, retraction, and rotation.
• The primary actions of the pectoralis major include adduction and medial rotation of the humerus.
• The serratus anterior muscle is crucial for scapular protraction and stabilization.
• The middle fibers of the trapezius are primarily involved in retracting the scapula.

Pec Minor Actions

• Pectoralis minor has similar actions to pectoralis major, including stabilization of the scapula.
• Actions that pectoralis minor can perform at the scapula include depression, protraction, and downward rotation.

General Notes

• Almost all branches of the brachial plexus arise from the cords.
• The supraclavicular part gives rise to nerves like the long thoracic nerve.
• The infraclavicular part gives rise to nerves such as the subscapular nerve.
• The dorsal scapular nerve arises from the supraclavicular part of the plexus.

Test your knowledge of the brachial plexus and shoulder girdle muscles in this anatomy quiz. Covering topics from Moore's Clinically Oriented Anatomy, this quiz will assess your understanding of upper limb anatomy. Prepare for your in-person class with Dr. K. Lumsden and Dr. M. Doroudi at Boucher Campus or Toronto Campus.