RT Book, Section A1 Jochum, Denis A2 Atchabahian, Arthur A2 Gupta, Ruchir SR Print(0) ID 57262519 T1 Chapter 131. Brachial Plexus T2 The Anesthesia Guide YR 2013 FD 2013 PB The McGraw-Hill Companies PP New York, NY SN 978-0-07-176049-2 LK accessanesthesiology.mhmedical.com/content.aspx?aid=57262519 RD 2024/10/08 AB Two independent layers from the roots to terminal branches: A simple and constant dorsal layer: extensor and supinator musclesA complex and variable ventral layer: flexor and pronator muscles: This explains the variations and the relationships between the median, musculocutaneous, and ulnar nervesThe brachial plexus can be: “Prefixed” with a contribution from C4 (two thirds of cases), orNormal, or“Postfixed,” with the participation of T2Or even spread in both directions: Clinical significance of these variations because motor and sensory distributions are modifiedOrigin of the trunks: Upper trunk: confluence of the ventral branches of C5 and C6 (C4 participation, prefixed plexus)Middle trunk: ventral division of C7Lower trunk: confluence of the ventral branches of C8 and T1Constitution of the cords (most common configuration): Lateral cord: confluence of ventral divisions of upper and middle trunks (80% of cases)Medial cord: ventral division of lower trunk (95% of cases)Posterior cord: confluence of dorsal divisions of the three trunks (70% of cases)Constitution of terminal nerves = branches (at distal edge of the pectoralis minor muscle): Posterior cord: posterior plane of the brachial plexus, with mainly radial and axillary nervesLateral and medial cords: anterior plane of the brachial plexus with mainly the median nerve, as well as musculocutaneous and ulnar nerves