How does an impulse cross a synapse?
Reveal answer
Impulse arrives → neurotransmitter released → diffuses across gap → binds receptors → new impulse.
Key words: neurotransmitter · diffuses
3(j) CO-ORDINATION AND RESPONSE · RECALL
3.39 Neurotransmitters at synapses
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Why one-way at synapses?
Reveal answer
Released only on one side, receptors only on the other.
Key words: receptors
What is the gap between neurones called?
Reveal answer
A synapse.
Key words: synapse
What is meant by the term synapse?
Reveal answer
Junction through which one neurone communicates with another cell.
Key words: synapse
What is meant by the term neurotransmitter?
Reveal answer
Chemical messenger released from a neurone at a synapse.
Key words: neurotransmitter
What is meant by the term synaptic cleft?
Reveal answer
Narrow gap between pre- and postsynaptic cells.
Key words: synaptic cleft
What is meant by the term reuptake?
Reveal answer
Transport of released neurotransmitter back into the presynaptic cell.
Key words: reuptake
Across a synapse: for Presynaptic axon, give the main event and the signal form.
Reveal answer
Main event: Impulse arrives. Signal form: Electrical.
Key words: Presynaptic axon
Across a synapse: for Presynaptic ending, give the main event and the signal form.
Reveal answer
Main event: Vesicles release neurotransmitter. Signal form: Electrical → chemical.
Key words: Presynaptic ending
Across a synapse: for Synaptic cleft, give the main event and the signal form.
Reveal answer
Main event: Neurotransmitter diffuses. Signal form: Chemical.
Key words: Synaptic cleft
Across a synapse: for Postsynaptic membrane, give the main event and the signal form.
Reveal answer
Main event: Receptors bind transmitter and alter ion flow. Signal form: Chemical → electrical.
Key words: Postsynaptic membrane
Across a synapse: for After transmission, give the main event and the signal form.
Reveal answer
Main event: Breakdown or reuptake removes transmitter. Signal form: Signal terminates.
Key words: After transmission
True or false, and why? “The electrical impulse jumps directly through empty space.”
Reveal answer
False. A neurotransmitter normally diffuses across the cleft.
True or false, and why? “Neurotransmitter remains in the cleft permanently.”
Reveal answer
False. It is removed by breakdown, diffusion or reuptake.
True or false, and why? “Every synapse always triggers a new impulse.”
Reveal answer
False. Inputs may excite or inhibit, and threshold may not be reached.