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Lecture 13 – The brachial plexus Learning goals The brachial plexus Describe the spinal cord segments that give rise to the brachial plexus Briefly describe the structure & function of the brachial plexus Describe the effects of muscle innervations of an upper of lower brachial plexus injury Readings: CH4 – the shoulder girdle Brachial Plexus Supplies the pectoral girdle & entire upper limb Consists of a branching network of nerves Derived from the anterior rami C5-T1 spinal nerves most branches arise within the axilla Organisation of the brachial plexus Roots in the inferior part of the neck, the roots unite to form 3 trunks Trunks superior, middle & inferior Divisions anterior & posterior cords lateral, posterior & medial Trunks, divisions, cords in relation to axillary artery 5 roots give rise to 3 trunks superior union of C5 & C6 middle trunk continuation of C7 root Interior trunk union of C8 & T1 roots Lie in the posterior triangle of the neck (can palpate) Each trunk divides into anterior & posterior divisions Within the Axilla the divisions combine to produce 3 cords Lateral cord superior & middle trunks of the anterior division unite to form the lateral cord Medial cord anterior division of the inferior trunk continues as the medial cord posterior cord all 3 trunks of the posterior division unit to form the posterior cord Named according to their relationship with the axillary artery Each cord ends at the lower border of the pectoralis minor Each cord divides into terminal branches Lateral cord Musculocutaneous nerve & lateral root of the median nerve Medial cod Ulnar nerve & medial root of the median nerve Posterior cord Axillary & radial nerves Cords of the Brachial Plexus Lateral cord Musculocutaneous nerve (C5 – C7) o Innervates flexor muscles of the arm (specifically those on the ulnar/medial side e.g. flexor digitorum superficialis & profundus) Median nerve, lateral root Medial cord Ulnar nerve (C8-T1) o Innervates flexor muscles of forearm (FCU, medial FDP), hypothenar eminence, intrinsic hand muscles. Sensation medial hand Median nerve (C6-T1),, medial root o Innervates forearm flexors, thenar eminence, 1st 2nd lumbricals. Sensation lateral palm Ulnar nerve damage Indicated by: An inability to adduct or abduct the 4 fingers, but not the thumb o Lumbricals & interossei Weakness in flexing & adducting the wrist Loss of sensation over the little finger Also: pressure on elbow when in flexion Median Nerve injuries Indicated by: Numbness, tingling & pain in the palm & fingers Weak thumb movement s Inability to pronate the forearm Difficulty in proper wrist flexion