At the synapse between two neurons, communication occurs through a complex process involving electrical and chemical signals:
- Arrival of Action Potential: An electrical nerve impulse, called an action potential, travels down the axon of the presynaptic neuron to its terminal (axon terminal)
- Neurotransmitter Release: The action potential triggers the opening of voltage-gated calcium channels, allowing calcium ions to enter the presynaptic terminal. This calcium influx causes synaptic vesicles filled with neurotransmitters to move toward and fuse with the presynaptic membrane through a process involving SNARE proteins and synaptotagmin as a calcium sensor
- Diffusion Across Synaptic Cleft: Neurotransmitters are released into the synaptic cleft, a tiny gap (~20-40 nm) between the presynaptic neuron and the postsynaptic neuron
- Binding to Postsynaptic Receptors: The neurotransmitters diffuse across the cleft and bind to specific receptors on the postsynaptic neuron's membrane. This binding causes ion channels to open or close, altering the postsynaptic membrane's permeability to ions such as Na⁺, K⁺, Ca²⁺, or Cl⁻
- Postsynaptic Potential Generation: Depending on the ions involved, the postsynaptic neuron may become depolarized (excited) or hyperpolarized (inhibited). If sufficiently excited, it generates its own action potential, continuing the signal transmission
- Neurotransmitter Clearance: After receptor activation, neurotransmitters are rapidly removed from the synaptic cleft by enzymatic degradation, reuptake into the presynaptic neuron, or diffusion away, preventing continuous stimulation
This synaptic transmission allows neurons to communicate efficiently and regulate neural circuits in the brain and nervous system
. In summary, the synapse converts an electrical signal in one neuron into a chemical signal that crosses the synaptic gap and then back into an electrical signal in the next neuron, enabling neural communication
