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Synapses & Neurotransmitters Cheat Sheet
A printable reference covering synapse structure, neurotransmitter release, receptors, reuptake, summation, and excitatory and inhibitory signaling for grades 11-12.
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Synapses are the junctions where neurons communicate with other neurons, muscle cells, or gland cells. This cheat sheet helps students connect action potentials to chemical signaling and understand how information moves through the nervous system. It is useful for reviewing nervous system physiology, cell communication, and the biological basis of behavior. Grade 11-12 students need these ideas for topics such as reflexes, drugs, learning, and neurological disorders. The core process begins when an action potential reaches the axon terminal and opens voltage-gated calcium channels. Calcium ions trigger vesicles to release neurotransmitters into the synaptic cleft, where they bind to receptors on the postsynaptic membrane. Excitatory signals make a postsynaptic neuron more likely to fire, while inhibitory signals make it less likely to fire. Signal strength depends on receptor type, neurotransmitter removal, and the combined effects of many synapses.
Key Facts
- A chemical synapse includes the presynaptic terminal, synaptic cleft, and postsynaptic membrane.
- An action potential reaching the axon terminal opens voltage-gated Ca2+ channels, causing Ca2+ to enter the presynaptic neuron.
- Ca2+ influx triggers synaptic vesicles to fuse with the presynaptic membrane and release neurotransmitter by exocytosis.
- Neurotransmitters bind to specific receptors, so the effect depends on both the chemical messenger and the receptor type.
- An excitatory postsynaptic potential, or EPSP, depolarizes the postsynaptic membrane and moves membrane potential closer to threshold.
- An inhibitory postsynaptic potential, or IPSP, hyperpolarizes the postsynaptic membrane or stabilizes it below threshold.
- Neurotransmitter action is ended by reuptake, enzymatic breakdown, or diffusion away from the synaptic cleft.
- Temporal summation adds signals that arrive close together in time, while spatial summation adds signals from different synapses.
Vocabulary
- Synapse
- A specialized junction where a neuron communicates with another neuron, muscle cell, or gland cell.
- Neurotransmitter
- A chemical messenger released by a presynaptic neuron that affects a postsynaptic cell.
- Synaptic cleft
- The tiny gap between the presynaptic terminal and the postsynaptic membrane.
- Receptor
- A protein on the postsynaptic membrane that binds a specific neurotransmitter and starts a cellular response.
- Reuptake
- The process in which neurotransmitter molecules are transported back into the presynaptic neuron.
- Summation
- The adding together of postsynaptic potentials to determine whether the neuron reaches threshold.
Common Mistakes to Avoid
- Saying neurotransmitters cross directly through the postsynaptic membrane is wrong because they usually bind to receptors on the membrane instead.
- Forgetting the role of Ca2+ is wrong because calcium entry is the trigger that causes vesicles to release neurotransmitter.
- Assuming every neurotransmitter is always excitatory is wrong because the effect depends on the receptor and can be excitatory or inhibitory.
- Confusing reuptake with receptor binding is wrong because reuptake removes neurotransmitter from the cleft, while receptor binding starts the postsynaptic response.
- Treating one small EPSP as enough to fire an action potential is wrong because the axon hillock usually requires summed input to reach threshold.
Practice Questions
- 1 A neuron has a resting membrane potential of -70 mV and a threshold of -55 mV. If EPSPs of +5 mV, +4 mV, and +6 mV arrive together, does the neuron reach threshold?
- 2 A postsynaptic neuron is at -68 mV. An IPSP changes the membrane potential by -7 mV. What is the new membrane potential?
- 3 List the correct order of events from an action potential arriving at the axon terminal to neurotransmitter removal from the synaptic cleft.
- 4 Explain why the same neurotransmitter can produce different effects in different target cells.