The phrenic nerve goes from the spinal cord to the diaphragm, a large muscle at the bottom of your chest that mediates breathing activity.
Axons of the phrenic nerve come from the phrenic nucleus situated at spinal cervical segments C3, C4, and C5.
Most of the axons About 75% of people have an accessory phrenic branch that comes from C5 and even C6. The sternocleidomastoid muscle is the long muscle that goes from the angle of your jaw to the head of clavicle, the long horizontal bone that goes from your shoulder to the front base of your neck.
Various branches of the phrenic nerve head down behind the sternocleidomastoid, joining together at the subclavian vein (a vein that is under the clavicle) and descending downward into the chest.