Usually, the uppermost cervical spinal cord segment (C1) lacks a posterior root. Thus, there are 7 pairs of cervical hind roots but 8 cervical spinal cord segments.
The nerve fibres of the roots C(1)2 to C4 are part of the cervical braid (cervicalis plexus) which gives rise to the skin and skeletal muscle nerves of the neck and the diaphragma;
The nerve fibers of the roots C5 to C8 are part of the brachial plexus (plexus) which gives rise to the skin and skeletal muscle nerves of the shoulder, arm and hand,