What happened at the synapse ? between two neurones?

At a synapse between two neurons, several important events occur to facilitate the transmission of information, which is typically in the form of electrical signals or action potentials, from one neuron to another. The synapse is the junction or connection point between two neurons, and the process at the synapse involves chemical signaling. Here is a general overview of what happens at a synapse:

1. Presynaptic Neuron: The neuron that sends the signal is called the presynaptic neuron. When an action potential reaches the axon terminal (the end of the presynaptic neuron), it triggers the release of neurotransmitters.
2. Neurotransmitter Release: Action potentials cause voltage-dependent calcium channels in the presynaptic neuron to open. Calcium ions flow into the axon terminal, leading to the fusion of synaptic vesicles (small sacs) with the cell membrane. These vesicles contain neurotransmitters, which are chemical messengers.
3. Neurotransmitter Diffusion: The neurotransmitters are released into the synaptic cleft, which is the small gap between the presynaptic neuron's axon terminal and the postsynaptic neuron's dendrites. The neurotransmitters diffuse across this gap.
4. Postsynaptic Neuron: The neuron that receives the signal is called the postsynaptic neuron. The dendrites of the postsynaptic neuron have receptors that can bind to the neurotransmitters released by the presynaptic neuron.
5. Neurotransmitter Binding: When neurotransmitters bind to the receptors on the postsynaptic neuron, it can result in a change in the postsynaptic neuron's membrane potential. This can lead to either an excitatory or inhibitory response in the postsynaptic neuron, depending on the type of neurotransmitter and receptor interaction.
6. Generation of Postsynaptic Potential: If the neurotransmitter-receptor interaction is excitatory, it can lead to a depolarization of the postsynaptic neuron's membrane, making it more likely to generate its own action potential. Conversely, if the interaction is inhibitory, it can lead to hyperpolarization, making it less likely for the postsynaptic neuron to generate an action potential.
7. Integration: The postsynaptic neuron integrates the signals it receives from multiple synapses to determine whether to generate an action potential. If the summation of signals is sufficient to reach the neuron's threshold, an action potential may be initiated in the postsynaptic neuron.
8. Termination of Signal: The neurotransmitter signal must be terminated to allow for precise signaling. This can occur through various mechanisms, such as enzymatic degradation of neurotransmitters, reuptake by the presynaptic neuron, or diffusion away from the synapse.

This process of synaptic transmission is essential for communication between neurons and forms the basis of information processing in the nervous system. The ability to transmit signals from one neuron to another and modulate the strength of these connections plays a crucial role in neural networks and the functioning of the entire nervous system.