📚 Neuronal Communication Exam Practice | 5.3 神经元通讯真题精练
This article provides a focused revision on neuronal communication with exam-style questions and detailed explanations. Mastering the generation and transmission of nerve impulses is essential for A-Level Biology success. By working through model answers, you will learn how to structure your knowledge to meet the demands of different exam boards.
本文围绕神经元通讯专题进行真题精练，提供详尽解析。掌握神经冲动的产生与传递是A-Level生物取得高分的关键。通过对标准答案的演练，你将学会如何组织知识，应对不同考试局的题目要求。
1. Understanding Neuronal Communication | 理解神经元通讯
Neuronal communication involves the transmission of information along neurones and across synapses. This process relies on changes in membrane potential and the release of neurotransmitters. Key exam topics include the ionic basis of the resting potential, the all-or-nothing action potential, saltatory conduction, and synaptic integration. Marks are awarded for using precise terminology such as ‘depolarisation’, ‘repolarisation’ and ‘refractory period’.
神经元通讯涉及信息沿神经元和跨突触的传递。这一过程依赖于膜电位的变化和神经递质的释放。常考主题包括静息电位的离子基础、全或无的动作电位、跳跃传导以及突触整合。答题时使用 ‘depolarisation’、’repolarisation’ 和 ‘refractory period’ 等精确术语能够获得分数。
A typical A-Level question might ask: ‘Explain why the nerve impulse is described as an all-or-nothing response.’ (2 marks). The expected answer highlights that an action potential is only triggered if the threshold potential is reached, and that its size remains constant regardless of stimulus strength.
一道常见的A-Level题目会问：“解释为何神经冲动被描述为全或无反应。”（2分）。标准答案强调动作电位只有在达到阈电位时才会被触发，且无论刺激强度如何，其幅度保持不变。
2. Resting Potential and Action Potential | 静息电位与动作电位
The resting potential (about –70 mV) is maintained by the unequal distribution of ions across the axon membrane, largely due to the sodium-potassium pump and differential permeability. The Na⁺/K⁺ pump actively transports 3 Na⁺ out and 2 K⁺ in, using ATP. Potassium ions diffuse out more readily than sodium ions diffuse in, creating a negative interior. Organic anions remain inside, contributing to the negative charge.
静息电位（约 –70 mV）是由轴突膜两侧离子分布不均维持的，主要靠钠钾泵和差异通透性。钠钾泵利用ATP主动转运3个Na⁺出膜、2个K⁺进膜。钾离子比钠离子更容易外流，使膜内带负电。有机阴离子留在膜内，进一步维持负电荷。
Exam Question (4 marks): Explain how the resting potential is maintained. Model answer: The membrane is more permeable to K⁺ than Na⁺ at rest; K⁺ diffuses out through leak channels, leaving behind organic anions. The Na⁺/K⁺ pump actively transports Na⁺ out and K⁺ in, maintaining the concentration gradients.
真题（4分）：解释静息电位如何维持。标准答案：静息时膜对K⁺的通透性大于Na⁺；K⁺通过漏通道外流，留下有机阴离子。钠钾泵主动转运Na⁺出、K⁺入，维持浓度梯度。
During an action potential, a stimulus depolarises the membrane to threshold (around –55 mV). Voltage-gated Na⁺ channels open, Na⁺ rushes in, causing further depolarisation. At about +40 mV, Na⁺ channels inactivate and voltage-gated K⁺ channels open; K⁺ leaves, repolarising the membrane. A brief hyperpolarisation may occur before the resting potential is restored.
动作电位期间，刺激使膜去极化到达阈电位（约 –55 mV）。电压门控Na⁺通道开放，Na⁺涌入，进一步去极化。在约+40 mV时，Na⁺通道失活，电压门控K⁺通道开放；K⁺外流，使膜复极化。在恢复静息电位前可能出现短暂超极化。
| Phase 阶段 | Membrane Permeability Changes 膜通透性变化 |
|---|---|
| Depolarisation 去极化 | Na⁺ permeability increases dramatically; Na⁺ channels open 对Na⁺通透性急剧增加；Na⁺通道开放 |
| Repolarisation 复极化 | Na⁺ permeability falls (inactivation); K⁺ permeability increases (K⁺ channels open) Na⁺通透性下降（失活）；K⁺通透性增加（K⁺通道开放） |
| Hyperpolarisation 超极化 | K⁺ permeability remains high briefly before closing K⁺通透性短暂维持高水平，随后关闭 |
3. Propagation of Action Potentials | 动作电位的传导
Action potentials propagate along an axon by local currents. In unmyelinated neurones, depolarisation spreads to adjacent regions, causing sequential opening of voltage-gated channels. In myelinated neurones, the myelin sheath acts as an insulator, preventing ion leakage. Action potentials only occur at nodes of Ranvier, where there is a high density of ion channels. This saltatory conduction allows the impulse to jump from node to node, greatly increasing speed and conserving ATP, as fewer action potentials are needed per unit length.
动作电位通过局部电流沿轴突传导。在无髓神经元中，去极化传播到相邻区域，引起电压门控通道依次开放。在有髓神经元中，髓鞘起绝缘作用，阻止离子泄漏。动作电位只在郎飞结处发生，那里离子通道密度高。这种跳跃传导使冲动从一个结跳至下一结，极大提高速度并节省ATP，因为单位长度所需动作电位更少。
Exam Question (3 marks): Explain how a myelinated axon conducts impulses faster than a non-myelinated axon. Answer: Myelin prevents ion movement across the membrane, so depolarisation only occurs at nodes; local currents jump from node to node (saltatory conduction); this reduces the number of action potentials, speeding up transmission.
真题（3分）：解释有髓轴突为何比无髓轴突传导更快。答案：髓鞘阻止离子跨膜移动，因此去极化仅发生在结处；局部电流从一结跳至下一结（跳跃传导）；这减少了动作电位发生次数，加速传导。
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Myelinated: high speed, energy-efficient, nodes of Ranvier 有髓：高速，节能，有郎飞结
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Unmyelinated: slower, continuous propagation, entire membrane involved 无髓：较慢，连续传播，整段膜参与
4. Structure of a Synapse | 突触的结构
A typical cholinergic synapse consists of a presynaptic terminal containing many mitochondria and synaptic vesicles filled with acetylcholine (ACh), a narrow synaptic cleft, and a postsynaptic membrane with specific receptor proteins. The membrane of the postsynaptic cell also contains acetylcholinesterase, an enzyme that hydrolyses ACh. Exam diagrams often require you to label: synaptic vesicle, neurotransmitter, receptor, synaptic cleft, and mitochondrion.
典型的胆碱能突触由含大量线粒体和充满乙酰胆碱（ACh）的突触小泡的突触前末梢、狭窄的突触间隙以及具有特异性受体蛋白的突触后膜组成。突触后细胞膜还含有乙酰胆碱酯酶，该酶可水解ACh。考试中的示意图常要求标注：突触小泡、神经递质、受体、突触间隙和线粒体。
Question (4 marks): Describe the structure of a synapse. Answer: Presynaptic knob with vesicles containing neurotransmitter; synaptic cleft (gap between neurones); postsynaptic membrane with receptor proteins; mitochondria in presynaptic knob to provide ATP for neurotransmitter synthesis and vesicle movement.
问题（4分）：描述突触的结构。答案：突触前膨大含含有神经递质的小泡；突触间隙（神经元之间的间隙）；突触后膜上具有受体蛋白；突触前膨大中的线粒体提供ATP用于递质合成和小泡移动。
5. Process of Synaptic Transmission | 突触传递的过程
When an action potential arrives at the presynaptic terminal, it depolarises the membrane, opening voltage-gated Ca²⁺ channels. Ca²⁺ ions diffuse into the terminal. This influx causes synaptic vesicles to move to and fuse with the presynaptic membrane, releasing ACh into the cleft by exocytosis. ACh diffuses across the cleft and binds to receptor proteins on the postsynaptic membrane. This causes Na⁺ channels to open, Na⁺ ions enter, and if the postsynaptic potential exceeds threshold, an action potential is initiated. To stop the signal, acetylcholinesterase breaks ACh down into choline and acetate, which are reabsorbed.
当动作电位到达突触前末梢，膜去极化，电压门控Ca²⁺通道开放。Ca²⁺扩散进入末梢。这一内流促使突触小泡移动并与突触前膜融合，通过胞吐将ACh释放入间隙。ACh扩散穿过间隙，与突触后膜上的受体蛋白结合。这导致Na⁺通道开放，Na⁺进入，若突触后电位超过阈电位，便产生动作电位。为终止信号，乙酰胆碱酯酶将ACh分解为胆碱和乙酸盐，两者被重吸收。
Exam Question (6 marks): Describe the sequence of events at a cholinergic synapse from when an action potential arrives. Model answer: 1. Action potential depolarises presynaptic membrane. 2. Voltage-gated Ca²⁺ channels open and Ca²⁺ enters. 3. Vesicles fuse with membrane and release ACh by exocytosis. 4. ACh diffuses across cleft and binds to receptors. 5. Na⁺ channels open, postsynaptic membrane depolarises (EPSP). 6. Acetylcholinesterase breaks down ACh to stop continuous stimulation.
真题（6分）：描述动作电位到达后胆碱能突触发生的事件顺序。标准答案：1.动作电位使突触前膜去极化。2.电压门控Ca²⁺通道开放，Ca²⁺进入。3.小泡与膜融合，以胞吐方式释放ACh。4.ACh扩散过间隙并与受体结合。5.Na⁺通道开放，突触后膜去极化（EPSP）。6.乙酰胆碱酯酶分解ACh以终止持续刺激。
6. Neurotransmitters and Receptors | 神经递质与受体
ACh is an excitatory neurotransmitter at neuromuscular junctions but can be inhibitory in other contexts. Other common neurotransmitters include GABA (inhibitory), noradrenaline, dopamine, and serotonin. Receptors may be ionotropic (e.g., ligand-gated Na⁺ channels) or metabotropic (G-protein-coupled receptors). An understanding of the difference is often tested: ionotropic receptors directly open ion channels, whereas metabotropic receptors activate a second messenger cascade.
ACh在神经肌肉接头是兴奋性递质，但在其他部位可能是抑制性的。其他常见神经递质包括GABA（抑制性）、去甲肾上腺素、多巴胺和血清素。受体可分为离子型（如配体门控Na⁺通道）或代谢型（G蛋白偶联受体）。两者区别常考：离子型受体直接开放离子通道，而代谢型受体激活第二信使级联反应。
Question (1 mark): State one example of an inhibitory neurotransmitter. Answer: GABA (gamma-aminobutyric acid).
问题（1分）：举出一种抑制性神经递质。答案：GABA（γ-氨基丁酸）。
Excitatory synapses typically open Na⁺ channels, causing depolarisation (EPSP). Inhibitory synapses open Cl⁻ or K⁺ channels, making the inside more negative (IPSP), thus moving the membrane potential further from threshold.
兴奋性突触通常开放Na⁺通道，导致去极化（EPSP）。抑制性突触开放Cl⁻或K⁺通道，使膜内更负（IPSP），从而让膜电位远离阈电位。
7. Excitatory and Inhibitory Postsynaptic Potentials | 兴奋性与抑制性突触后电位
An excitatory postsynaptic potential (EPSP) is a small, local depolarisation caused by the influx of Na⁺. If a single EPSP is insufficient to reach threshold, it decays passively. Inhibitory postsynaptic potentials (IPSPs) result from Cl⁻ influx or K⁺ efflux, hyperpolarising the membrane. The interplay between EPSPs and IPSPs determines whether the postsynaptic neurone fires an action potential. Many exam questions ask you to explain how inhibition is achieved.
兴奋性突触后电位（EPSP）是由Na⁺内流引起的小幅度局部去极化。若单个EPSP不足以达到阈电位，它会被动衰减。抑制性突触后电位（IPSP）由Cl⁻内流或K⁺外流引起，使膜超极化。EPSP与IPSP的相互作用决定突触后神经元是否会发放动作电位。许多考题要求你解释抑制是如何实现的。
Question (3 marks): Explain how an inhibitory synapse reduces the likelihood of an action potential. Answer: Inhibitory neurotransmitter opens Cl⁻ channels; Cl⁻ enters/down the electrochemical gradient, making the inside more
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