What happens at the synapse between two neurons?

At the synapse, which is the junction between two neurons (nerve cells) or between a neuron and a target cell (such as a muscle or gland cell), communication occurs through a process called synaptic transmission. The synapse is a crucial site for the transmission of signals in the nervous system. Here's a general overview of what happens at the synapse:

1. Presynaptic Neuron:
   • The neuron that sends the signal is called the presynaptic neuron. It has an axon, a long, slender extension that ends in small structures called axon terminals or synaptic knobs.
2. Synaptic Cleft:
   • The synaptic cleft is a small gap or space between the axon terminals of the presynaptic neuron and the dendrites or cell body of the postsynaptic neuron.
3. Neurotransmitter Release:
   • When an action potential (electrical signal) reaches the axon terminals of the presynaptic neuron, it triggers the release of neurotransmitters. Neurotransmitters are chemical messengers stored in vesicles within the axon terminals.
4. Diffusion of Neurotransmitters:
   • Neurotransmitters, released into the synaptic cleft, diffuse across the gap toward the postsynaptic neuron.
5. Receptor Binding:
   • Neurotransmitters bind to receptor molecules on the postsynaptic neuron. These receptors are typically proteins located on the surface of the postsynaptic membrane.
6. Postsynaptic Potential:
   • The binding of neurotransmitters to receptors on the postsynaptic neuron generates a postsynaptic potential, which is a change in the electrical potential of the postsynaptic cell membrane.
7. Signal Integration:
   • If the postsynaptic potential is strong enough (reaches a threshold), it may trigger an action potential in the postsynaptic neuron. If the potential is subthreshold, it may not lead to an action potential.
8. Neurotransmitter Inactivation or Reuptake:
   • To end the signal, neurotransmitters in the synaptic cleft are either broken down by enzymes or taken back up into the presynaptic neuron in a process called reuptake.
9. Termination of Signal:
   • The termination of the signal prevents continuous stimulation, allowing the synapse to reset for subsequent signals.

The process described above is part of excitatory synaptic transmission, where the neurotransmitters depolarize the postsynaptic membrane, making it more likely for an action potential to occur. There is also inhibitory synaptic transmission, where neurotransmitters hyperpolarize the postsynaptic membrane, making it less likely for an action potential to occur.

The specificity of synaptic transmission, the ability to transmit signals selectively, and the modulation of signal strength contribute to the complexity and precision of nervous system function. The study of synaptic transmission is crucial for understanding various aspects of neural communication and how disruptions in this process may contribute to neurological disorders.