Brachial Plexus PDF, Western University

©  The Brachial Plexus Dr. Sean McWatt, PhD [email protected] © Danny Quirk Artwork Learning Outcomes By the end of this lesson, you will be able to… Describe the structure and function of the brachial ple...

©  The Brachial Plexus Dr. Sean McWatt, PhD [email protected] © Danny Quirk Artwork Learning Outcomes By the end of this lesson, you will be able to… Describe the structure and function of the brachial plexus in upper limb innervation Label a diagram of the brachial plexus and its branches Hypothesize clinical implications of lesions at various sites along the cervical spinal cord and sections of the brachial plexus Recall: Contents of the Axilla The axilla is a very action-packed and important region for major veins, arteries, and nerves that travel from the neck and thorax into the upper limb. Anterior view Gilroy, Anatomy: An Essential Textbook, Copyright © 2013 by Thieme Brachial Plexus Embryology of Dermatomes ~ Week 5 ~ Week 6 A dermatome is an area of skin supplied by one spinal nerve and its ganglion. Though, there is some overlap. Ventral axial line A basic understanding of limb development can help demystify the organization of dermatomes in adult anatomy! But it won’t be tested… Adult C8 Anterior views Moore et al., The Developing Human. All rights reserved. © Elsevier 2012, evolve.elsevier.com/ Brachial Plexus Really Thirsty? Drink Cold Beer! C5 Middle The brachial plexus C5 C6 scalene m. gives branches that C7 C6 innervate the entire C8 Anterior scalene m. C7 upper limb. T1 C8 Subclavian a. T1 The ‘ROOTS’ of the brachial plexus Formed from anterior rami of spinal nerves Since it is comprised of the anterior rami of spinal nerves C5 to T1, the brachial plexus and its Axillary a. nerves contain both motor and sensory fibers. Anterior view Gilroy, Anatomy: An Essential Textbook, Copyright © 2013 by Thieme Agur and Dalley, Grant’s Atlas of Anatomy, 13th Ed. Copyright © 2013 by Lippincott Williams and Wilkins Brachial Plexus Anterior rami C5-T1 form the ROOTS The roots combine to form TRUNKS Really Thirsty? Drink Cold Beer! The trunks separate into DIVISIONS Divisions collect to form CORDS The cords give major BRANCHES YIY A P A P C5 P A C6 C7 C8 T1 The “M” of the brachial plexus is a key landmark you can use to orient yourself to the major branches. By identifying the musculocutaneous, median, and ulnar nerves, you can more easily identify related structures as you work proximally or distally. Anterior view Agur and Dalley, Grant’s Atlas of Anatomy, 13th Ed. Copyright © 2013 by Lippincott Williams and Wilkins Brachial Plexus A P A P P A Each trunk gives an anterior and a posterior division. The posterior divisions collect to form the posterior cord and the anterior divisions contribute to the lateral or medial cords. Anterior view Agur and Dalley, Grant’s Atlas of Anatomy, 13th Ed. Copyright © 2013 by Lippincott Williams and Wilkins Brachial Plexus The axilla is where most of the action is, as the cords have many small branches that emerge to innervate the walls of the axilla and Y the remainder of the upper limb. A P A IY P P A DIVISIONS found deep to the clavicle Anterior view Agur and Dalley, Grant’s Atlas of Anatomy, 13th Ed. Copyright © 2013 by Lippincott Williams and Wilkins Brachial Plexus C5 Really Thirsty? Drink Cold Beer! C6 There are five main branches that travel throughout the upper limb to innervate muscles in the different C7 compartments of each segment. C8 Axillary n. There are also several smaller T1 branches that innervate more proximal muscles of the shoulder, chest, and back. Anterior view Agur and Dalley, Grant’s Atlas of Anatomy, 13th Ed. Copyright © 2013 by Lippincott Williams and Wilkins Upper vs. Lower Trunk Injury Anterior view Upper brachial plexus trunk injury Proximal muscles affected Weakness/atrophy of the shoulder external rotators and upper arm flexors C5 Depending on the dermatome severity of the injury, symptoms T1 can include muscle dermatome weakness, paralysis, C7 and C8 or atrophy, and/or dermatomes Lower brachial plexus C6 pain, numbness, or dermatome trunk injury tingling in the skin Distal muscles affected Paralysis/atrophy of long digital flexors and of the affected intrinsic hand muscles → ‘clawing’ of hand dermatome. Anterior view Posterior view Gilroy, Anatomy: An Essential Textbook, Copyright © 2013 by Thieme Brachial Plexus Injuries Waiter’s tip position Weak arm muscles and forearm extensors Upper brachial These images plexus lesion Lateral Erb-Duchenne Palsy depict some of the hyperextension common scenarios of the neck causing brachial plexus injuries. Signs of such Clawed hand injuries can present Weakness of intrinsic hand muscles and at rest or when the finger flexors patient is instructed to attempt a Lower brachial movement. plexus lesion Hyperabduction Dejerine-Klumpke Palsy of the arm Drake, Gray’s Anatomy for Students, 2nd Ed., Copyright © 2009 by Churchill Livingstone Innervation ‘Gradient’ (Anterior) Musculocutaneous n. Median n. Ulnar n. (C5–C7) (C5–T1) (C8–T1) From lateral cord From medial and From medial cord lateral cords ANTERIOR ARM For the most part, anterior rami from the higher (more superior) spinal levels of the brachial plexus innervate ANTERIOR FOREARM more proximal structures, …and some hand while those from the HAND …and some lower (more inferior) anterior forearm spinal levels innervate more distal structures. Anterior views Gilroy, Anatomy: An Essential Textbook, Copyright © 2013 by Thieme Innervation ‘Gradient’ (Posterior) Radial n. Axillary n. (C5–T1) (C5–C6) From posterior cord From posterior cord A similar gradient pattern of innervation is seen with the branches of the posterior cord, the axillary and radial nerves. POSTERIOR ARM AND Since the radial nerve carries FOREARM ALL of the spinal levels included in the brachial plexus, it innervates A LOT! DELTIOID AND TERES MINOR Anterior views Gilroy, Anatomy: An Essential Textbook, Copyright © 2013 by Thieme Other Branches… Rhomboid minor m. Suprascapular n. Dorsal scapular n. (C5 –C6) (C5) Levator Supraspinatus m. scapulae m. Infraspinatus m. Posterior view Rhomboid Posterior view Long thoracic n. (C5–C7) major m. Damage to specific branches Winged of the brachial plexus can “C5, C6, C7, scapula cause specific defects, fly to Lesion of long thoracic n. especially among entire Serratus heaven!” anterior m. groups of muscles that are http://tiny.cc/2r5gdz only innervated by one nerve. Sagittal view (right) Posterior view Gilroy, Anatomy: An Essential Textbook, Copyright © 2013 by Thieme Other Branches… Lateral pectoral n. (C5 –C7) Upper and lower subscapular nn. Medial pectoral n. (C5–C6) (C8 –T1) Branches from the posterior cord (thoracodorsal, upper subscapular, and lower subscapular nerves) innervate muscles of the posterior wall of the axilla. Branches from the anterior (i.e., lateral and medial) cords (medial and lateral pectoral nerves) innervate the muscles of the Thoracodorsal n. anterior wall of the axilla. (C6–C8) Anterior view Gilroy, Anatomy: An Essential Textbook, Copyright © 2013 by Thieme Brachial Plexus Lesions Dorsal scapular n. C5 One-by-one, Remember, CV consider everything distal lesions at the C6 to the lesion is sites indicated impacted! CVI by a red X… N. to subclavius C7 Which CVII components Lateral pectoral n. C8 and/or nerves of the brachial Axillary n. TI plexus are T1 impacted? Long thoracic n. Upper subscapular n. Thoracodorsal n. What Lower subscapular n. functional Medial pectoral n. deficits might Medial cutaneous n. of the arm Medial cutaneous n. of the forearm you see? Anterior view Agur and Dalley, Grant’s Atlas of Anatomy, 13th Ed. Copyright © 2013 by Lippincott Williams and Wilkins Myotome Assessment C5 Arm C6 abduction Forearm Myotomes are flexion groups of muscles Anterior view innervated by the same spinal level. C7 Forearm extension T1 C8 Finger adduction Finger and abduction Sagittal view (left) flexion Clinicians tend to test myotomes by assessing actions at the most distal limit of each spinal level. Lateral view (left) Anterior view Drake, Gray’s Anatomy for Students, 2nd Ed., Copyright © 2009 by Churchill Livingstone Brachial Plexus Injuries A patient presents with ‘Saturday Night Palsy’ – a compression injury to the brachial plexus Pain/loss of caused by passing out sensation with their arm over the Throughout posterior Wrist drop aspect of upper limb Inactive wrist back of a chair. extensors What nerve has been injured? Radial n. injury From the posterior cord Wrist extension Netter, Atlas of Human Anatomy 6th Ed., Copyright © 2014 by Elsevier Gilroy, Anatomy: An Essential Textbook, Copyright © 2013 by Thieme Simplified Nerve Chart Branches Nerves Muscle(s) innervated Spinal levels from Long thoracic n. Serratus anterior m. C5–C7 Roots Dorsal scapular n. Levator scapulae, rhomboid major, rhomboid minor mm. C5 Trunks Suprascapular n. Supraspinatus, infraspinatus mm. C5–C6 Medial pectoral n. Pectoralis major, pectoralis minor mm. C8–T1 Lateral pectoral n. Pectoralis major, (pectoralis minor) mm. C5–C7 Cords Thoracodorsal n. Latissimus dorsi m. C6–C8 Upper subscapular n. Subscapularis m. C5–C6 Lower subscapular n. Subscapularis, teres major mm. C5–C6 Axillary n. Deltoid, teres minor mm. C5–C6 Radial n. Posterior compartment of arm, posterior compartment of forearm C5–T1 Major terminal Musculocutaneous n. Anterior compartment of arm C5–C7 branches Median n. Anterior compartment of forearm, some intrinsic hand C5–T1 Ulnar n. Some anterior compartment of forearm, intrinsic hand C8–T1 Label and colour-code me! Summary By now, you should better understand how to… Describe the structure and function of the brachial plexus in upper limb innervation Label a diagram of the brachial plexus and its branches Hypothesize clinical implications of lesions at various sites along the cervical spinal cord and sections of the brachial plexus  © [email protected]