Phrenic

The phrenic nerve is a mixed motor/sensory nerve which originates from the C3-C5 spinal nerves in the neck. The nerve is important for breathing because it provides exclusive motor control of the diaphragm, the primary muscle of respiration. In humans, the right and left phrenic nerves are primarily supplied by the C4 spinal nerve, but there is also contribution from the C3 and C5 spinal nerves. From its origin in the neck, the nerve travels downward into the chest to pass between the heart and lungs towards the diaphragm. In addition to motor fibers, the phrenic nerve contains sensory fibers, which receive input from the central tendon of the diaphragm and the mediastinal pleura, as well as some sympathetic nerve fibers. Although the nerve receives contributions from nerves roots of the cervical plexus and the brachial plexus, it is usually considered separate from either plexus.

The cervical plexus is formed by the ventral rami of the upper four cervical nerves and the upper part of fifth cervical ventral ramus. the network of rami is located deep to the sternocleidomastoid within the neck. the cervical plexus innervates muscles of the neck and areas of skin on the head, neck and chest. the deep branches innervate muscles, while the superficial branches supply areas of skin. a long branch (primarily of fibers of c4 and with contributions of fibers from c3 and c5; nervus phrenicus) innervates muscles of the diaphragm. the cervical plexus also communicates with the cranial nerves vagus nerve and hypoglossal nerve.