Which of the following statements about the nervous system is correct? a. the nervous system is regulated by the endocrine system. b. the nervous system emits only chemical signals. c. the nervous system communicates through the bloodstream. d. the nervous system sends neurotransmitters to communicate internally.

The answer is D. The nervous system sends neurotransmitters to communicate internally.

The nervous system coordinates the activity of muscles, organs by sending neurotransmitters. Neurotransmitters are chemicals which move across the synapses to the next neuron. The messages  which travel in the nerves are sent through a number of nerve cells called neurons. Synapses are the spaces between these cells.