Which of the following is true of the neurotransmitter serotonin?

• A. Serotonin is primarily an excitatory neurotransmitter in the motor cortex.
• B. Serotonin is the main neurotransmitter responsible for muscle contraction.
• C. Serotonin levels are unrelated to depression or anxiety disorders.
• D. Serotonin is involved in regulating mood, appetite, and sleep.

Answer: (D)

Verified step by step guidance

1. Understand that serotonin is a neurotransmitter, which means it is a chemical messenger that transmits signals across synapses between neurons in the brain and other parts of the nervous system.
2. Recognize that serotonin is not primarily excitatory in the motor cortex; instead, it has diverse roles depending on the brain region and receptor type.
3. Note that serotonin is not the main neurotransmitter responsible for muscle contraction; that role is primarily played by acetylcholine.
4. Acknowledge that serotonin levels are indeed related to mood disorders such as depression and anxiety, meaning the statement that they are unrelated is false.
5. Conclude that serotonin's key functions include regulating mood, appetite, and sleep, which aligns with the correct answer provided.