Which of the following statements is true of the parasympathetic nervous system (PNS)?

• A. It increases heart rate and dilates pupils.
• B. It is responsible for the fight or flight response.
• C. It uses norepinephrine as its primary neurotransmitter at target organs.
• D. It promotes rest and digest activities in the body.

Answer: (D)

Verified step by step guidance

1. Step 1: Begin by understanding the parasympathetic nervous system (PNS). The PNS is a division of the autonomic nervous system responsible for regulating 'rest and digest' activities, such as reducing heart rate, promoting digestion, and conserving energy.
2. Step 2: Compare the functions of the PNS with the sympathetic nervous system (SNS). The SNS is responsible for 'fight or flight' responses, such as increasing heart rate, dilating pupils, and preparing the body for action. This distinction helps eliminate incorrect options.
3. Step 3: Analyze the neurotransmitters used by the PNS. The primary neurotransmitter at target organs for the PNS is acetylcholine, not norepinephrine. Norepinephrine is primarily used by the SNS, which further eliminates another incorrect option.
4. Step 4: Evaluate the statement 'It promotes rest and digest activities in the body.' This aligns with the known functions of the PNS, such as stimulating digestion, reducing heart rate, and promoting relaxation.
5. Step 5: Conclude that the correct answer is the statement that describes the PNS as promoting rest and digest activities, based on its physiological role and neurotransmitter usage.