Answer : 3. "neurons"
Explanation :

1. Neurons are the building blocks of the nervous system. They receive and transmit signals to different parts of the body. This is done in both physical and electrical forms. Many different types of neurons facilitate the transmission of information.

2. Neurons are the structural and functional unit of the nervous system. All neurons have three distinct parts – dendrites, the cell body, and the axon. Neuron structure is specially adapted to quickly carry messages in the form of electrical signals over large distances in the body.