Synapses and Chemical Communication
From electrical to chemical signaling
What is a synapse?
A synapse is a specialized junction where one cell communicates with another. At chemical synapses, the sending neuron releases neurotransmitters into a small gap called the synaptic cleft, and the receiving cell detects them with receptors.
How transmission works
When an action potential reaches the axon terminal, it can trigger entry, which causes vesicles to fuse with the membrane and release neurotransmitter. The neurotransmitter then binds to receptors on the postsynaptic cell.
Chemical synaptic transmission
-
1
Step 1: Action potential arrives at the terminal
-
2
Step 2: Calcium channels open
-
3
Step 3: Vesicles release neurotransmitter
-
4
Step 4: Receptors detect the neurotransmitter
-
5
Step 5: The postsynaptic cell responds
Important distinction
Electrical signaling in the axon is fast and all-or-none; chemical signaling at synapses is flexible and can amplify or reduce the message.
What triggers neurotransmitter release at many synapses?
Calcium entry helps vesicles fuse and release neurotransmitter.
Correct answer: Calcium entry into the axon terminal
What is the synaptic cleft?
It is the space neurotransmitters cross.
Correct answer: the small gap between communicating cells at a synapse
Common synapse terms
| Term | Meaning |
|---|---|
| Presynaptic | The sending side of the synapse |
| Postsynaptic | The receiving side of the synapse |
| Neurotransmitter | A chemical messenger |
| Receptor | A protein that detects the messenger |