brachial plexus

brachial plexus - THE BRACHIAL PLEXUS Required...

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THE BRACHIAL PLEXUS Required Reading—336-341 I. INTRODUCTION 1. The brachial plexus is a somatic nerve plexus formed by intercommunications among the ventral rami of the lower four cervical nerves ( C 5 - C 8) and the first thoracic nerve (T 1). The plexus is responsible for the motor innervation to all of the muscles of the upper limbwith the exception of the trapezius and levator scapula. It supplies all of the cutaneous innervation of the upper limb with the exception of the area of the axilla( armpit) (supplied by the intercostobrachial nerve), an area just above the point of the shoulder (supplied by supraclavicular nerves) and the dorsal scapular area which is supplied by cutaneous branches of dorsal rami. The brachial plexus communicates with the sympathetic trunk by gray rami communicates that join all the roots of the plexus and are derived from the middle and inferior cervical sympathetic ganglia and the first thoracic sympathetic ganglion. 2. Prefixed Brachial Plexus —Occurs when the C 4 ventral ramus contributes to the brachial plexus. Contributions to the plexus usually come from C 4 - C 8. 3. Postfixed Brachial Plexus —Occurs when the T 2 ventral ramus contributes to the brachial plexus. Contributions to the plexus usually come from C 6 - T 2. II. FORMATION OF THE BRACHIAL PLEXUS (Fig. 1) 1. Roots 1. The ventral rami of spinal nerves C5 to T1 are referred to as the roots of the plexus. 2. Trunks 1. Shortly after emerging from the intervertebral foramina , these 5 roots unite to form three trunks. 2. The ventral rami of C5 & C6 unite to form the Upper Trunk. 3. The ventral ramus of C 7 continues as the Middle Trunk. 4. The ventral rami of C 8 & T 1 unite to form the Lower Trunk. 3. Divisions 1. Each trunk splits into an anterior division and a posterior division. 2. The anterior divisions usually supply flexor muscles 3. The posterior divisions usually supply extensor muscles. 4. Cords 1. The anterior divisions of the upper and middle trunks unite to form the lateral cord . 2. The anterior division of the lower trunk forms the medial cord. 3. All 3 posterior divisions from each of the 3 cords all unite to form the posterior cord. 4. The cords are named according to their position relative to the axillary artery.
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5. Terminal Branches are mixed nerves containing both sensory and motor axons. 1. Musculocutaneous nerve is derived from the lateral cord. 1. This nerve innervates the muscles in the flexor compartment of the arm 2. Carries sensation from the lateral ( radial) side of the forearm. (Figs. 2,3) 2. Ulnar nerve is derived from the medial cord 1. Motor innervation is mainly to intrinsic muscles of the hand 2. Sensory innervation is from the medial ( ulnar) 1 & 1/2 digits ( the 5th. and 1/2 of the 4th. digits). (Figs. 2,3) 3. Median nerve is derived from both the lateral and medial cords
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brachial plexus - THE BRACHIAL PLEXUS Required...

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