Transmission across a chemical synapse is one way because
- 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.
Related questions
In a neurone, impulses are carried away from the cell body by the
A myelinated neurone conducts impulses faster than an unmyelinated one because
The resting potential of about minus 70 millivolts across the membrane of a neurone is maintained mainly by
The rapid depolarisation phase of an action potential is caused by
The all or none law of nerve impulse conduction states that