Nervous System and Spinal Cord

Synapses and Neurotransmitters

Neurons communicate with one another using electrical and chemical signals via junctions called synapses.

The synapse is the location of signal transmission from one neuron (the presynaptic neuron) to another receiving neuron (the postsynaptic neuron), muscle, or gland. Neurons communicate with one another chemically if the axon terminal is in direct contact with the postsynaptic cell. In these cases, ions flow directly between cells. However, most synapses are chemical, and electrical signals from the presynaptic neuron are converted to the release of a neurotransmitter, which is a chemical that binds to receptors in the plasma membrane of the postsynaptic cell. During a chemical synapse, an action potential reaches the axon terminal of a presynaptic neuron, and neurotransmitters are released from synaptic vesicles, which are structures that hold neurotransmitters, into the gap between cells, or synaptic cleft. Neurotransmitters bind to receptors on the membrane of the next cell and make this cell either more or less likely to fire an action potential, depending on the nature of the neurotransmitter.

Neurotransmitters have an excitatory or inhibitory effect on postsynaptic neurons or glands. Common neurotransmitters include the following:

  • glutamate—an amino acid used to activate synapses in the CNS
  • serotonin—considered to play a critical role in depression; regulates many functions, including sleep, appetite, and mood
  • acetylcholine—activates skeletal muscle and can inhibit or excite organs of the autonomic nervous system
  • dopamine—regulates motor behavior and the brain's pleasure and reward centers
  • epinephrine—plays a key role in the fight-or-flight response by allowing the body to respond to emergency situations

Neuronal Synapse

Communication between the axon terminal of a presynaptic neuron and postsynaptic neuron occurs across a synapse. With the help of neurotransmitters, chemical messaging can be sent from the synaptic vesicles of a neuron to the postsynaptic end of a receiving neuron.