Neurotransmitters and Neurohormones

Abstract

Abstract We have seen in the previous two chapters that a neuron is in large part an elaborate and intricately regulated machine for the secretion of a variety of chemicals. Why do cells go to all this trouble? Although direct electrical connections between nerve cells also play an essential role (see Chapter 8), it is chemical signaling that mediates much of the intercellular communication among nerve cells within the central nervous system. In addition, the transfer of information into the nervous system from sensory organs and the output from the nervous sys tem in the form of muscular contraction are mediated by extracellular chemical messengers. In this chapter we will discuss in a systematic way the different classes of neurotransmitters and neurohormones, some of which we have already met in other contexts. Subsequent chapters will deal with receptors on the target cell that recognize and bind these substances and with the transduction mechanisms that are involved in converting the extracellular chemical signal into an appropriate response (usually electrical) in the target cell.