How do the neurotransmitters generate an impulse in adjacent neuron?
Neurotransmitters generate an impulse in an adjacent neuron through a process called synaptic transmission. Here's an overview of the steps involved:
1. Action Potential Arrival:
- An action potential traveling down the presynaptic neuron (the neuron sending the signal) reaches the synaptic terminal (the knob-like structure at the end of the neuron).
2. Calcium Influx:
- The depolarization of the presynaptic terminal causes voltage-gated calcium channels to open. Calcium ions (Ca2+) rush into the neuron from the extracellular space.
3. Neurotransmitter Release:
- The influx of calcium ions triggers the fusion of neurotransmitter-containing vesicles with the presynaptic membrane.
- This fusion process releases neurotransmitters into the synaptic cleft, the narrow gap between the presynaptic and postsynaptic neurons.
4. Neurotransmitter Binding:
- The neurotransmitters released into the synaptic cleft diffuse across and bind to specific receptors on the postsynaptic membrane (the membrane of the neuron receiving the signal).
5. Ion Channel Openings:
- Binding of neurotransmitters to their receptors opens ion channels in the postsynaptic membrane. These channels can be either excitatory (allowing positively charged ions like sodium to flow in) or inhibitory (allowing negatively charged ions like chloride to flow in or positively charged ions like potassium to flow out).
6. Generation of Postsynaptic Potential:
- The flow of ions into or out of the postsynaptic neuron creates a change in the membrane potential called a postsynaptic potential (PSP). An excitatory PSP (EPSP) makes the membrane more positive (depolarized), while an inhibitory PSP (IPSP) makes it more negative (hyperpolarized).
7. Action Potential Generation:
- If the EPSP reaches a certain threshold, it causes the postsynaptic membrane to reach the threshold potential. This leads to the opening of voltage-gated sodium channels and the generation of an action potential in the postsynaptic neuron. This action potential then propagates down the postsynaptic neuron.
It's important to note that multiple EPSPs and IPSPs can be integrated in the postsynaptic neuron to determine whether the membrane potential reaches the threshold, resulting in an action potential. Additionally, neurotransmitters can affect a wide range of cellular processes and modulate neuronal activity beyond their immediate effects on ionotropic and metabotropic receptors.