Choose the correct answer from the options given below:

Choose the correct sequence of neuronal structures involved in synaptic transmission.
A. Post synaptic membrane
B. Synaptic vesicles
C. Terminal button
D. Axon
E. Synaptic cleft

Correct option is D

Synaptic transmission is the process by which neurons communicate with each other via neurotransmitters across the synapse. The correct sequence is:
Correct Answer: (4) D → C → B → E → A

D - Axon (First Step)
-Electrical impulses, known as action potentials, travel down the axon toward the synapse, transmitting signals to the next neuron or target cell.
-The axon is covered by the myelin sheath, which speeds up signal transmission through saltatory conduction.
-Example: The axon of a motor neuron carries signals to muscle fibers, enabling movement and coordination.

C - Terminal Button (Second Step)
-The axon terminal, or terminal button, is the endpoint of the neuron where synaptic vesicles are stored.
-When an action potential reaches the terminal button, calcium channels open, allowing calcium ions to enter and trigger neurotransmitter release.
-Example: At the neuromuscular junction, acetylcholine is released from the terminal button, stimulating muscle contraction.

B - Synaptic Vesicles (Third Step)
-Synaptic vesicles are small membrane-bound sacs that contain neurotransmitters such as dopamine, serotonin, and acetylcholine.
-When the action potential reaches the terminal button, synaptic vesicles fuse with the presynaptic membrane in a process called exocytosis, releasing neurotransmitters into the synaptic cleft.
-The number of neurotransmitters released depends on the frequency and strength of the action potential.

E - Synaptic Cleft (Fourth Step)
-The synaptic cleft is the small gap (about 20-40 nanometers wide) between the presynaptic neuron and the postsynaptic neuron or muscle cell.
-Neurotransmitters diffuse across this gap to bind to receptors on the postsynaptic membrane.
-The synaptic cleft ensures that signals travel in one direction and prevents direct electrical connection between neurons.

A - Postsynaptic Membrane (Final Step)
-Neurotransmitters bind to specific receptors on the postsynaptic membrane, triggering a response in the receiving neuron or target cell.
-Depending on the type of neurotransmitter and receptor, the response can be excitatory (promoting a new action potential) or inhibitory (preventing further signaling).
-Once the neurotransmitter has completed its function, it is either broken down by enzymes, reabsorbed into the presynaptic neuron (reuptake), or diffuses away to prevent excessive signaling.