When Mr. Valdez thought his 1-year-old daughter had fallen down the stairs, his heartbeat accelerated, his blood pressure rose, and he began to perspire heavily. Mr. Valdez's state of arousal was activated by his nervous system

Sympathetic Nervous System.

Explanation:

Sympathetic nervous system is one of the parts of Autonomic nervous system and the other part is Parasympathetic nervous system.

As a whole the autonomic nervous system controls the unconscious responses of our body.

The main function of the Sympathetic nervous system is to stimulate the 3F response of the body. Here 3F refers to Fight, Flight and Freeze. Adrenal gland is stimulated by this system which secretes adrenaline. Due to the effect of adrenaline heart neat increases, blood pressure increases, pupils dilate, sweat glands are activated, peristalsis in the gut is inhibited, and kidney secretion increases.