Nerve Plexusus - Peripheral Nerves

Nerve Plexusus

At the level of the limbs, the anterior branches of the spinal nerves form networks (plexusus) in which fibers are exchanged. The resulting nerve trunks, which then ex- tend to the periphery, possess a newly or-ganized supply of fibers derived from differ- ent spinal nerves.Cervical plexus. The plexus of the neck is formed by the anterior branch of the first  four  spinal  nerves.  The  followingnerves originate here: the lesser occipital nerve(B18), the greater auricular nerve (B19),the transverse nerve of theneck (B20), the supraclavicular nerves (B21), thephrenic nerve (B22), and also the roots oft he deep cervical ansa (B23).Brachial plexus. The plexus of the arm is formed by the anterior branches of spinal nerves C5 to C8 and by a part of the T1 nerve. We distinguish between a section lying above the clavicle, the supraclavicular part, and a section lying below the clavicle, the infraclavicular part. The anterior branches pass through the scalene gap into the poste- rior cervical triangle, where they form three primary trunks above the clavicle:     

! The superior trunk (B24) (C5, C6)

! The medial trunk (B25) (C7)

! The inferior trunk (B26) (C8, T1)  

The nerves that originate here form the su- praclavicular part. Below the clavicle, three secondary cords form; they are named according to their position relative to the axillary artery (B27):        

! The lateral cord (B28) (from the anterior branches of the superior and medial trunks)       

! The medial cord (B29) (from the anterior branch of the inferior trunk)

! The posterior cord (B30) (from the dorsal branches of the three trunks)

The lateral cord gives rise to the musculocu- taneous nerve(B31). The remaining fibers the median loop (B32) and unite to form the median nerve (B33). The medial cord gives rise to the ulnar nerve (B34), the medial cutaneous nerve of the forearm (B35),and the medial cutaneous nerve of the arm (B36 ). The posterior cord gives off the axil-lary nerve (B37) and continues as the radial nerve (B38).