听力原文： There are many kinds of nerve cells, and this chapter deals mainly with three kinds. The sensory nerve cells carry messages of heat, light, sound and pressure from the skin, muscles and organs inside the body. Motor nerve cells carry messages to the muscles, and this causes the muscles to move. Connecting nerve cells go between the sensory nerve cells and motor nerve cells. After the messages go from the spinal cord to the brain, the brain sends messages through the motor nerve cells to the muscles. All these different nerve cells help us to see, hear, taste, smell and feel. Now if you have no further questions about Chapter Seven, we'll go on to talk about the chemical processes involving the transfer of messages. (33)