Which neurological sign might be present if there is increased pressure against CN3?

When there is increased pressure against cranial nerve three (CN3), one of the primary neurological signs that can manifest is dilated pupils. This phenomenon occurs because CN3 is responsible for controlling most of the eye's movements as well as the constriction of the pupil. Increased intracranial pressure or mass effect can compress and impair the function of CN3, leading to a disturbance in its ability to constrict the pupils. As a result, the pupils may become dilated and unreactive to light, indicating potential neurological compromise.

The other choices relate to different neurological signs or pathways. Facial droop is typically associated with lower motor neuron lesions affecting facial muscles and is often seen in conditions affecting cranial nerve seven (CN7). Decreased reflexes in the limbs can indicate lower motor neuron damage or widespread neurological impairment but are not directly linked to CN3 involvement. Constricted pupils would typically suggest increased parasympathetic activity or damage to sympathetic pathways rather than pressure on CN3. Therefore, recognizing dilated pupils as a sign of CN3 involvement is crucial in assessing potential neurological emergencies.