What characterizes the tonic-clonic phase of a seizure?

The tonic-clonic phase of a seizure, often referred to as a grand mal seizure, is characterized primarily by the muscular contraction phase, which can be quite violent. During this phase, the individual may experience intense muscle stiffness (tonic phase) followed by rhythmic jerking of the limbs (clonic phase). This violent muscular activity results from the brain's abnormal electrical discharges, leading to contractions in multiple muscle groups.

The intense, involuntary muscle contractions are a defining feature of this phase and are often what witnesses observe most dramatically. After the clonic phase, the person may be left in a postictal state, which can involve confusion, fatigue, and disorientation, but the hallmark of the tonic-clonic seizure is indeed the violent muscular contractions that occur during the event.

In contrast, the other options, like involuntary eye movement, gradual loss of consciousness, or increased heart rate, may be seen in different types of seizures or as accompanying symptoms but do not specifically characterize the tonic-clonic phase itself.