Neurological tone refers to the resistance of muscles to passive movement, indicating the integrity of the central nervous system. Clonus is a series of involuntary, rhythmic muscle contractions, often a sign of upper motor neuron lesions. Reactive pupils respond appropriately to light, reflecting brainstem function. Assessing these features is crucial for diagnosing neurological conditions, such as stroke or spinal cord injury, where abnormal findings can indicate significant underlying pathology.