Transmission across a chemical synapse is one way because
Correct answer: B. the neurotransmitter is released only from the presynaptic knob and receptors are only on the postsynaptic membrane
- A. the postsynaptic membrane is thicker
- B. the neurotransmitter is released only from the presynaptic knob and receptors are only on the postsynaptic membrane
- C. the synaptic cleft is too wide for diffusion in the reverse direction
- D. the impulse loses all its energy at the synapse
Explanation
Vesicles of transmitter are stored on one side only and the matching receptors are on the other, so the signal cannot cross backwards even though diffusion itself has no preferred direction. This one way valve is what gives the nervous system its organised pathways. The cleft is only about 20 nanometres wide, so diffusion across it takes well under a millisecond.
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About Neurons and Nerve Impulse
Neurons receive and transmit information through dendrites, the cell body and axons. The topic explains resting potential, depolarization, repolarization, refractory periods and saltatory conduction, followed by synaptic transmission through neurotransmitters. An action potential is distinct from the graded potential produced at a receptor.
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