| Feature | Electrical Synapse | Chemical Synapse |
|---|---|---|
| Mechanism | Direct ionic flow via gap junctions | Neurotransmitter release and binding |
| Speed | Virtually instantaneous (no delay) | Synaptic delay (0.3 to 5 ms) |
| Direction | Often bidirectional | Strictly unidirectional |
| Plasticity | Low; mainly for synchronization | High; basis for learning and memory |
| Distance | Membranes are very close (~3.5 nm) | Larger gap (~20-50 nm) |
EPSP vs. IPSP: Excitatory Postsynaptic Potentials (EPSPs) depolarize the membrane (e.g., by opening channels), moving it closer to the threshold. Inhibitory Postsynaptic Potentials (IPSPs) hyperpolarize the membrane (e.g., by opening or channels), moving it further from the threshold.
Temporal Summation: This occurs when a single presynaptic neuron fires multiple action potentials in rapid succession. The resulting PSPs overlap in time to reach the threshold at the axon hillock.
Spatial Summation: This occurs when multiple different presynaptic neurons fire simultaneously at different locations on the postsynaptic cell. The individual PSPs add together to determine the final membrane potential change.
Identify the Ion: Always check which ion is moving and in which direction. For example, moving into a cell or moving out of a cell both cause inhibition (IPSP).
The Calcium Trigger: In exam questions regarding the 'link' between electrical and chemical signals, the answer is almost always the influx of .
Termination is Key: Don't forget that stopping the signal is as important as starting it. Questions often focus on what happens when reuptake or enzymatic degradation (like Acetylcholinesterase) is blocked.
Directionality: Remember that chemical synapses are unidirectional. Information flows from the axon terminal to the dendrite or cell body, never the reverse.
Neurotransmitter Entry: A common mistake is thinking that neurotransmitters enter the postsynaptic cell. They do NOT; they only bind to receptors on the outside of the membrane to trigger a response.
Excitatory vs. Inhibitory: Students often think a specific neurotransmitter is always excitatory or always inhibitory. In reality, the effect is determined by the receptor type on the postsynaptic cell, not the chemical itself.
Calcium vs. Sodium: Do not confuse the influx of the action potential with the influx of the synapse. Sodium propagates the signal down the axon, while calcium triggers the release of the message at the end.
