Atlas of Human Anatomy by Netter

Motor fibers from C1 and C2 directly innervate thyrohyoid (an infrahyoid strap muscle)
Motor fibers from C2, 3 form the descending cervical nerve
Ansa cervicalis
Loop formed by descending branch from hypoglossal nerve (superior root) (C1) and descending cervical nerve (inferior root)
(C2,C3)
Branches from ansa innervate remaining infrahyoid strap muscles
a. Omohyoid
b. Sternohyoid
c. Sternothyroid
Motor fibers from C3, C4, and C5 contribute to roots of phrenic nerve
Phrenic nerve
Formed by branches of anterior rami of C3, C4, and C5 spinal nerves
Contains a mix of fibers
Sole motor supply to the diaphragm
Sensory fibers from the central part of the diaphragm (sensory fibers from periphery provided by intercostal nerves)
Sympathetic nerve fibers from the cervical sympathetic ganglia to smooth muscle of blood vessel walls