4. Place these steps in temporal order, first to last. 1. Diffusion of neurotransmitter
across the synaptic cleft. 2. Binding of neurotransmitter to its receptor. 3. Influx of
calcium into the presynaptic terminal. 4. Release of neurotransmitter. 5. Generation of
an action potential at the postsynaptic membrane. 6. Influx of sodium ions.
a. 3, 4, 1, 6, 5, 2
b. 4, 3, 1, 6, 2 ,5
c. 1, 2, 3, 4, 5, 6
d. 3, 4, 1, 2, 6, 5
Synaptic Transmission Steps Order: CSIR NET MCQ Solved
The correct sequence of synaptic transmission steps is 3, 4, 1, 2, 6, 5, making option d the right answer.
Correct Sequence Explained
Synaptic transmission begins with calcium influx (3) into the presynaptic terminal triggered by depolarization from an arriving action potential, opening voltage-gated calcium channels. This calcium triggers synaptic vesicles to fuse with the presynaptic membrane, releasing neurotransmitter (4) into the synaptic cleft. The neurotransmitter then diffuses across the cleft (1) and binds to postsynaptic receptors (2), often opening ligand-gated ion channels. For excitatory transmission, this allows sodium influx (6), depolarizing the postsynaptic membrane to generate an action potential (5).
Option Analysis
a. 3, 4, 1, 6, 5, 2: Incorrect because sodium influx (6) cannot precede receptor binding (2); binding must occur first to open sodium channels.
b. 4, 3, 1, 6, 2, 5: Wrong as neurotransmitter release (4) cannot happen before calcium influx (3), which is required for vesicle fusion.
c. 1, 2, 3, 4, 5, 6: Invalid since diffusion (1) and binding (2) are postsynaptic events that follow presynaptic calcium (3) and release (4).
d. 3, 4, 1, 2, 6, 5: Correct, as it follows the precise presynaptic-to-postsynaptic temporal order established in neuroscience.
Synaptic transmission steps order forms a critical sequence in neuronal communication, essential for CSIR NET Life Sciences aspirants tackling neural control questions. This process ensures precise signal relay across the synapse, from presynaptic calcium signaling to postsynaptic action potential generation.
Presynaptic Events
Calcium ions enter the terminal (step 3), prompting neurotransmitter release (4) via vesicle exocytosis. Diffusion follows (1) as molecules cross the 20-40 nm cleft.
Postsynaptic Cascade
Receptor binding (2) activates ionotropic channels, enabling sodium influx (6) for depolarization. Threshold reach triggers the postsynaptic action potential (5).
