Final answer:
The main building blocks of the nervous system are neurons, which consist of a cell body, dendrites, and an axon. Neurons are the structural and functional units necessary for nervous system communication.
Step-by-step explanation:
The main building blocks of the nervous system are neurons. A neuron consists of three main parts: the cell body (soma), dendrites, and an axon. The cell body contains the nucleus and other essential organelles. Dendrites are branching extensions that receive signals from other neurons, while the axon is a long projection that transmits signals to other neurons or target cells. The axon often has a myelin sheath, which is an insulating layer produced by glial cells, enhancing signal transmission along the axon. Neurons communicate through synapses where the axon terminal of one neuron meets the dendrite or soma of another. The correct answer to the student's question is 'B .neurons', as they are the fundamental structural and functional units of the nervous system.