Final answer:
The effect of a neurotransmitter on a postsynaptic cell is dependent on the receptor protein. Different neurotransmitters can have excitatory or inhibitory effects on the cell, based on the type of receptor they bind to. Some neurotransmitters can have varied effects on different target cells.
Step-by-step explanation:
The effect of a neurotransmitter on the postsynaptic element is entirely dependent on the receptor protein. When a neurotransmitter binds to a receptor on the postsynaptic cell, it can either depolarize or hyperpolarize the cell, depending on the type of receptor. For example, acetylcholine can depolarize postsynaptic cells when it binds to the nicotinic receptor, but it can cause either depolarization or hyperpolarization when it binds to the muscarinic receptor.
Neurotransmitters can have different effects on various target cells because they activate different types of receptors. Some neurotransmitters can excite one set of cells, inhibit others, and have modulatory effects on still others. However, some neurotransmitters consistently have the same effects on other cells.