cutaneous nerves and dermatomes

C5, C6, C7, C8 and T1 all supply the skin of the arm and forearm

in the brachial plexus, C5 and C6 join to become the upper trunk, C7 is the middle trunk and C8 and T1 join to become the lower trunk.

each of the three trunks have two divisions, a posterior and an anterior division. all three posterior divsions join to become the posterior cord, the anterior division of the upper and middle trunks become the lateral cord and the anterior division of the lower trunk becomes the medial cord.

the lateral cord has three branches, the lateral pectoral nerve, the lateral cord of the median nerve and the musculocutaneous nerve. the important one fo these nerves for this case is the musculocutaneous nerve, which innervates muscles of the anterior compartment of the arm (coracobrachialis, biceps brachii and brachialis) and goes on to become the lateral cutaneous nerve of the forearm. tracing this nerve back through the brachial plexus, its roots are C5 and C6.

the posterior cord has five branches, axillary nerve, radial nerve, upper and lower subscapular nerves and the thoracodorsal nerve. of importance in this case is the axillary and radial nerves. the axillary nerve innervates deltoid in the arm and a patch of skin across the arm known as the ‘regiments badge’, while the radial nerve innervates the triceps and the skin of the posterior and inferolateral arm as well as the posterior forearm and the dorsum of the hand. tracing it back through the brachial plexus, the radial and axillary nerves stem from all five roots that make the brachial plexus.

the medial cord has five branches, the medial pectoral nerve, the medial cutaneous nerve of the arm and forearm, the ulnar nerve and the medial root of the median nerve. of importance in this case is all the nerves except the medial pectoral, as they all supply different areas of the arm. the medial cutaneous nerve of the arm supplies the skin of the medial side of the arm and the medial nerve of the forearm supplies the skin of the medial side of the forearm. the ulnar nerve supplies some muscles but most importantly in the PCL case, it supplies the skin of the hand medial to axial line of digit four. and finally the median nerve supplies the muscles of the anterior forearm as well as palmar skin. tracing these nerves bac through the plexus, they originate from C8 and T1 trunks.

i hope thats all i had to cover, but ill bring in a picture of the dermatomes and the brachial plexus on friday to help explain…

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~ by pcl4 on August 18, 2008.

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