Neurons are the basic unit of the nervous system. They are connected to each other through connections called synapses. Presynaptic neurons are neurons that send signals to other neurons, while postsynaptic neurons are neurons that receive signals from other neurons. The presynaptic neuron releases neurotransmitters which can be received by the postsynaptic neuron, thus allowing information to flow between neurons. The postsynaptic neuron then sends its own signals to other neurons, or to muscles or glands.
Presynaptic neurons are responsible for the release of neurotransmitters, which can be either excitatory or inhibitory. Excitatory neurotransmitters increase the chances of the postsynaptic neuron firing an action potential, while inhibitory neurotransmitters decrease the chances of the postsynaptic neuron firing an action potential. Postsynaptic neurons receive the neurotransmitters and use them to determine whether to fire an action potential or not. Postsynaptic neurons can also receive signals from other neurons, muscles, or glands, and use this information to decide whether or not to fire an action potential.