Final answer:
Neurotransmitters are the chemicals that stimulate action potentials in postsynaptic cells by binding to receptor proteins, which opens ligand-gated ion channels, leading to either excitatory or inhibitory postsynaptic potentials.
Step-by-step explanation:
Chemicals Stimulating Action Potentials
The chemicals that stimulate action potentials in postsynaptic cells are neurotransmitters. When an action potential reaches the axon terminal, it triggers the opening of voltage-gated calcium channels. Calcium ions (Ca2+) enter the presynaptic neuron, leading to the release of neurotransmitters into the synaptic cleft. These neurotransmitters then bind to receptors on the postsynaptic membrane.
Types of Gates Opened by Neurotransmitters
When a neurotransmitter binds to its receptor protein in the postsynaptic membrane, it specifically opens ligand-gated ion channels (also called chemically-gated channels). For instance, the binding of acetylcholine at the neuromuscular junction opens ligand-gated sodium channels, causing an influx of Na+ ions and a subsequent excitatory postsynaptic potential (EPSP), which makes the postsynaptic neuron more likely to fire an action potential. Conversely, other neurotransmitters like GABA can open ligand-gated chloride channels, leading to an influx of Cl− ions and an inhibitory postsynaptic potential (IPSP), which makes the postsynaptic neuron less likely to fire an action potential.