3. Which of the following about neuron is incorrect? (A) It is a polarized cell. (B) Peripheral nervous system includes autonomic and somatic nervous systems. (C) The generation of action potential is related to the electrochemical gradient across the plasma membrane. (D) Myelin sheath is a protein-rich substance that surrounds the axon of some neurons, forming an electrically insulating layer. (E) Neurofilaments are intermediate filaments found in neurons.