- Neurons communicate with one another at junctions called synapses. At a synapse, one neuron sends a message to a target neuron—another cell.
- Most synapses are chemical; these synapses communicate using chemical messengers. Other synapses are electrical; in these synapses, ions flow directly between cells.
- At a chemical synapse, an action potential triggers the presynaptic neuron to release neurotransmitters. These molecules bind to receptors on the postsynaptic cell and make it more or less likely to fire an action potential.
Electrical or chemical transmission?
- Some people thought that signaling across a synapse involved the flow of ions directly from one neuron into another—electrical transmission.
- Other people thought it depended on the release of a chemical from one neuron, causing a response in the receiving neuron—chemical transmission.
Overview of transmission at chemical synapses
Excitatory and inhibitory postsynaptic potentials
- In some cases, the change makes the target cell more likely to fire its own action potential. In this case, the shift in membrane potential is called an excitatory postsynaptic potential, or EPSP.
- In other cases, the change makes the target cell less likely to fire an action potential and is called an inhibitory post-synaptic potential, or IPSP.
Spatial and temporal summation
- The integration of postsynaptic potentials that occur in different locations—but at about the same time—is known as spatial summation.
- The integration of postsynaptic potentials that occur in the same place—but at slightly different times—is called temporal summation.