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All 13 Flashcards — Synaptic transmission
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Question
What is a synapse?
Answer
The **junction (gap)** between two neurons, where a signal passes from one to the next using a **chemical** (neurotransmitter).
Question
What is the synaptic cleft?
Answer
The **narrow gap** between the two neurons that the neurotransmitter **diffuses across**.
Question
What is a neurotransmitter?
Answer
The **chemical messenger** released into the synaptic cleft that carries the signal across the gap.
Question
What is stored in synaptic vesicles?
Answer
**Neurotransmitter** — ready to be released from the presynaptic neuron.
Question
Why is the signal carried by a chemical at a synapse, not electricity?
Answer
The two neurons are separated by the cleft; electricity cannot cross the gap, so a **neurotransmitter** bridges it.
Question
What triggers vesicles to fuse with the presynaptic membrane?
Answer
**Calcium ions (Ca²⁺) entering** the presynaptic neuron when the impulse arrives.
Question
How is neurotransmitter released into the cleft?
Answer
By **exocytosis** — vesicles fuse with the presynaptic membrane and empty their contents into the cleft.
Question
Describe the release of neurotransmitter (3 steps).
Answer
**Ca²⁺ enters** → **vesicles fuse** with the presynaptic membrane → neurotransmitter **released by exocytosis** into the cleft.
Question
What happens when neurotransmitter binds the postsynaptic receptors?
Answer
**Ion channels open**, **Na⁺ enters**, and the postsynaptic membrane **depolarises** (an EPSP).
Question
What is an excitatory postsynaptic potential (EPSP)?
Answer
A **depolarisation** of the postsynaptic membrane caused by neurotransmitter binding — it makes a new impulse **more likely**.
Question
Distinguish the presynaptic from the postsynaptic membrane.
Answer
**Presynaptic** = holds vesicles and **releases** neurotransmitter; **postsynaptic** = carries receptors and **receives** it.
Question
Why is it an advantage that the synaptic cleft is narrow?
Answer
It gives a **short diffusion distance**, so the neurotransmitter crosses **quickly** and transmission is **fast**.
Question
Which ion enters the POSTsynaptic neuron to depolarise it?
Answer
**Sodium (Na⁺)** — it enters through channels opened by the neurotransmitter.
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Topic 3.5 hub
Neural signalling
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