Final answer:
Damage to the cervical nerves would primarily affect b) diaphragm movement, as these nerves are responsible for sending signals that control diaphragm contractions necessary for breathing.
Step-by-step explanation:
The respiratory action most affected by damage to the cervical nerves would be b) diaphragm movement.
These nerves, specifically the phrenic nerve which arises from nerves C3, C4, and C5, are crucial for transmitting signals that cause the diaphragm to contract and relax during breathing.
If the cervical nerves are damaged, the signaling to the diaphragm can be disrupted, leading to difficulties with breathing due to the inability of the diaphragm to function properly.