After being startled awake, Merilee realizes that the noise she heard was the closet rod breaking from the weight of her winter coats. Knowing that, she begins to calm down and her heart stops racing. Clearly, Merrilee's _____ nervous system has now been activated.

The Central nervous system (CNS) is formed by the brain and spinal cord while the Peripheral nervous system (PNS) connects the CNS to all the other parts of the body. The PNS is the one who carry messages from the organs and senses to the CNS.

The PNS has two subdivisions:

somatic nervous system

autonomic nervous system.

The first one is in charge on sensory and motor information to and from the CNS. The second one is in charge of our internal glands and organs.

Now, the autonomic nervous system has 2 subdivisions

sympathetic nervous system: They contain sensory nerves.
parasympathetic nervous system: Have control over the heart, lungs, liver and stomach

Merilee wakes up scared but she realizes that the sound she heard was coming from the closet rod. Her heart stops racing. First, since we are talking about an specific part of the body we are talking about the Peripheral nervous system.

The autonomic nervous system is the one in charge of our glands and organs (this question talks about the heart so we are talking about the ANS). Finally, it is the parasympathetic nervous system in particular the one that controls the heart and therefore the one who has now been activated.