During week 4, the developing diaphragm is located at

A. Although it may seem unusual, the adult diaphragm has its embryological beginning at the cervical level (C3, C4, C5). Nerve roots from C3, C4, and C5 enter the developing diaphragm, bringing both motor and sensory innervation. With the subsequent rapid growth of the neural tube, there is an apparent descent of the diaphragm to its adult levels (thoracic and lumbar). However, the diaphragm retains its innervation from C3, C4, and C5, which explains the unusually long phrenic nerves.