Anatomy and Physiology II Practice Test

The phrenic nerve is the primary nerve responsible for innervating the diaphragm, which is crucial for respiration. It originates from the cervical spinal roots C3, C4, and C5 and descends into the thorax to reach the diaphragm. When it stimulates the diaphragm, it causes the muscle to contract, leading to inhalation as the diaphragm moves downward and enlarges the thoracic cavity.

The significance of the diaphragm in breathing cannot be overstated, as it is the main muscle involved in the process, enabling deeper and more efficient inhalation. Proper phrenic nerve function is essential; injury or impairment of this nerve can lead to diaphragmatic paralysis, significantly affecting breathing.

Other nerves mentioned, such as the vagus, radial, and pulmonary nerves, serve different functions. The vagus nerve is involved in parasympathetic control of the heart and digestive tract, while the radial nerve innervates muscles of the arm and hand. Pulmonary nerves are involved in the autonomic regulation of the lungs but do not directly control the diaphragm's movement. Hence, the phrenic nerve stands out as the correct answer for its specific role in diaphragm innervation.