Introduction to Psychology 10th Edition by Rod Plotnik,Haig Kouyoumdjian

Exercise 2

Once started, the action potential will reach the end bulbs at the end of the axon. The action potential excites the end bulbs and causes them to secrete (a) _____ that were stored in the end bulbs. Neurotransmitters function like chemical keys that unlock chemical locks or (b) _____ , which are located on neighboring neurons, muscles, or other organs. If neurotransmitters open the receptors' locks on neighboring cells, they are said to be (c) _____. If neurotransmitters block the receptors' locks, they are said to be (d) _____. Because of these different actions, neurotransmitters can cause different and even opposite responses in neurons, muscles, or organs. Chemicals that are smaller than neurotransmitters yet are also used by neurons to communicate with each other are called (e) _____.