Which muscle group is affected first by nondepolarizing neuromuscular blockers during paralysis?

The first muscle group affected by nondepolarizing neuromuscular blockers during paralysis is the facial and ocular muscles. This occurs because nondepolarizing neuromuscular blockers act at the neuromuscular junction by competitively inhibiting the action of acetylcholine on nicotinic receptors at the motor end plate.

The small, rapidly contracting muscles of the face and eyes are more sensitive to the effects of these agents compared to larger muscle groups. These smaller muscles have a higher density of nicotinic receptors, which makes them the most susceptible to the blockade, resulting in weakness or paralysis in these areas first. Furthermore, because facial and ocular muscles are used for precise and fine motor control, they are typically overshadowed in pharmacological action compared to larger muscle groups, such as those in the limbs and diaphragm, which are targeted subsequently.

This characteristic pattern of paralysis is significant in clinical settings, particularly during surgeries where neuromuscular blocking agents are used for muscle relaxation, as it helps healthcare professionals predict and monitor the onset of paralysis during procedures.