How nerve signals are transmitted at a synapse?
The transmission of nerve signals, or action potentials, across a synapse follows a specific process known as synaptic transmission. This process relies on the interaction between neurons (nerve cells) and the release and detection of neurotransmitters. Here is an overview of the steps involved in synaptic transmission:
Preparation:
1. An action potential reaches the pre-synaptic neuron, which is the neuron sending the signal.
2. This triggers the opening of voltage-gated calcium channels in the pre-synaptic membrane.
3. Calcium ions (Ca2+) enter the pre-synaptic terminal (end of the neuron).
Neurotransmitter Release:
4. Influx of calcium ions causes the release of neurotransmitters from storage vesicles within the pre-synaptic neuron through a process called exocytosis.
5. The neurotransmitters are released into the synaptic cleft, which is the space between the pre-synaptic and post-synaptic neurons.
Neurotransmitter Binding:
6. Neurotransmitter molecules diffuse across the synaptic cleft.
7. They bind to specific receptors on the post-synaptic neuron's membrane.
Post-synaptic Potential:
8. Binding of neurotransmitters to receptors on the post-synaptic membrane causes the opening of ion channels, allowing ions such as sodium (Na+), potassium (K+), or chloride (Cl-) to flow into or out of the post-synaptic neuron.
9. This change in ion concentrations changes the electrical potential across the post-synaptic membrane, creating a post-synaptic potential (PSP).
10. The PSP can be either excitatory (EPSP), which makes it more likely for the post-synaptic neuron to reach the threshold for firing an action potential, or inhibitory (IPSP), which makes it less likely.
Action Potential Generation:
11. If the combined effect of all PSPs on the post-synaptic neuron reaches the threshold of excitation (a certain level of membrane depolarization), an action potential is generated in the post-synaptic neuron.
12. This action potential propagates away from the synapse, continuing the transmission of the nerve signal.
Termination:
13. After their release, neurotransmitters are quickly removed from the synaptic cleft through three main mechanisms:
a. Enzymatic degradation: Enzymes break down the neurotransmitters.
b. Reuptake: Neurotransmitters are reabsorbed into the pre-synaptic neuron.
c. Diffusion: Neurotransmitters diffuse away from the synapse.
14. The removal of neurotransmitters helps reset the synapse for the next round of synaptic transmission.
It's important to note that synaptic transmission can be influenced by various factors, including the type of neurotransmitter involved, the concentration of neurotransmitters, and the sensitivity of post-synaptic receptors. Additionally, the activity of synapses can change over time through processes such as long-term potentiation and long-term depression, which are important for learning and memory.