Question

explain the process of synaptic transmission, beginning with the neurotransmitters at the axon terminal of the presynaptic cell and ending with the impulse being sent down the postsynaptic cell.

Explanation:

The process of synaptic transmission involves the release of neurotransmitters from the presynaptic neuron's axon terminal, their diffusion and binding to postsynaptic receptors, generation of postsynaptic potentials, summation to reach the action potential threshold (leading to an action potential in the postsynaptic neuron), and termination of the neurotransmitter's action. This process is fundamental in neural communication and is studied in the subfield of Biology (specifically Neuroscience, a sub - field of Biology) as it pertains to the functioning of neurons and the nervous system.

Answer:

1. Neurotransmitter Release: When an action potential reaches the axon terminal of the presynaptic neuron, voltage - gated calcium channels open. Calcium ions ($Ca^{2 +}$) enter the axon terminal, triggering the fusion of synaptic vesicles (containing neurotransmitters) with the presynaptic membrane. The neurotransmitters are then released into the synaptic cleft (the space between the presynaptic and postsynaptic neurons) via exocytosis.
2. Neurotransmitter Binding: The released neurotransmitters diffuse across the synaptic cleft and bind to specific receptor proteins on the postsynaptic membrane. These receptors are often ligand - gated ion channels. For example, in the case of excitatory neurotransmitters like glutamate, binding to receptors can cause the ion channels to open, allowing positively charged ions (such as $Na^{+}$) to enter the postsynaptic neuron.
3. Postsynaptic Potential Generation: The binding of neurotransmitters to receptors leads to a change in the postsynaptic membrane potential. If the neurotransmitter is excitatory, it can cause a depolarization of the postsynaptic membrane, known as an excitatory postsynaptic potential (EPSP). If the neurotransmitter is inhibitory, it can cause a hyperpolarization, known as an inhibitory postsynaptic potential (IPSP).
4. Summation and Action Potential Initiation: The postsynaptic potentials (EPSPs and IPSPs) can summate (add up) either spatially (from multiple synapses) or temporally (from multiple potentials at the same synapse). If the sum of these potentials reaches the threshold for firing an action potential (usually around - 55 mV for many neurons) at the axon hillock of the postsynaptic neuron, an action potential is generated and then propagated down the axon of the postsynaptic cell.
5. Neurotransmitter Termination: To end the synaptic transmission, the neurotransmitters in the synaptic cleft are removed. This can occur through reuptake (the neurotransmitter is taken back into the presynaptic neuron by specific transporters), enzymatic degradation (e.g., acetylcholinesterase degrades acetylcholine), or diffusion away from the synapse.