📚 IB & AQA Biology: Nervous System Essentials | IB AQA 生物：神经系统考点精讲
The nervous system is a rapid communication network that detects and responds to stimuli using electrical and chemical signals. For both IB and AQA specifications, you must be confident with neuron structure, the generation and propagation of action potentials, synaptic transmission, and simple reflex arcs. This guide breaks down the most exam-relevant material into clear, bilingual explanations.
神经系统是一个利用电信号和化学信号快速检测并响应刺激的通信网络。在 IB 和 AQA 大纲中，你必须熟练掌握神经元结构、动作电位的产生与传导、突触传递和简单反射弧。本文以清晰的双语讲解拆解最常考的知识点。
1. Organisation of the Nervous System | 神经系统的组成
The nervous system is divided into the central nervous system (CNS), comprising the brain and spinal cord, and the peripheral nervous system (PNS), made up of all nerves outside the CNS. The PNS is further subdivided into sensory (afferent) and motor (efferent) pathways.
神经系统分为中枢神经系统（CNS），包括脑和脊髓，以及周围神经系统（PNS），由 CNS 以外的所有神经组成。PNS 进一步分为感觉（传入）通路和运动（传出）通路。
Motor pathways can be somatic (voluntary control of skeletal muscle) or autonomic (involuntary control of internal organs). The autonomic system is itself split into sympathetic and parasympathetic divisions, which often have opposing effects.
运动通路可分为躯体运动（骨骼肌的随意控制）和自主运动（内脏器官的非随意控制）。自主神经系统又分为交感神经和副交感神经，它们通常具有相反的作用。
2. Structure of a Motor Neurone | 运动神经元结构
A typical motor neurone has a cell body containing the nucleus, numerous short dendrites that receive impulses, and a long axon that carries impulses away. The axon is insulated by a myelin sheath formed by Schwann cells, with gaps called nodes of Ranvier.
典型的运动神经元有一个含有细胞核的胞体、许多接受冲动的短树突，以及一根将冲动传出的长轴突。轴突由施万细胞形成的髓鞘包裹绝缘，中间有郎飞结。
The end of the axon branches into synaptic knobs (terminal boutons) that contain vesicles of neurotransmitter. In AQA, you must label and describe the roles of each part; in IB, you may also need to compare myelinated and non-myelinated neurones.
轴突末端分支形成突触终扣（末梢），内含装载神经递质的囊泡。AQA 要求标注并描述各部分功能；IB 可能还需要比较有髓神经元和无髓神经元。
3. Resting Potential | 静息电位
When a neurone is not transmitting an impulse, the inside of the axon is negatively charged relative to the outside. This resting potential is typically around -70 mV. It is established by the sodium-potassium pump (Na⁺/K⁺ ATPase), which actively transports 3 Na⁺ out and 2 K⁺ in, and by differential permeability of the membrane.
当神经元不传递冲动时，轴突内部相对于外部带负电荷。这一静息电位通常在 -70 mV 左右。它由钠钾泵（Na⁺/K⁺-ATP酶）主动运出 3 个 Na⁺、运入 2 个 K⁺，以及膜对不同离子的通透性差异共同建立。
The membrane is more permeable to K⁺ than to Na⁺ at rest, so K⁺ diffuses out down its concentration gradient, leaving behind negative organic anions inside. This creates the negative membrane potential.
静息时膜对 K⁺ 的通透性大于对 Na⁺ 的通透性，因此 K⁺ 顺浓度梯度外流，在膜内留下带负电的有机阴离子，从而形成负的膜电位。
4. Action Potential | 动作电位
An action potential is a rapid, temporary reversal of membrane potential caused by sequential opening and closing of voltage-gated ion channels. If a threshold (around -55 mV) is reached, an all-or-nothing response is triggered.
动作电位是由电压门控离子通道依次开放和关闭引起的膜电位快速、短暂反转。一旦达到阈值（约 -55 mV），就会触发“全或无”反应。
Depolarisation: Na⁺ channels open → Na⁺ rushes in → inside becomes +30 mV.
去极化：Na⁺ 通道开放 → Na⁺ 大量内流 → 内部变为 +30 mV。
Repolarisation: Na⁺ channels inactivate, K⁺ channels open → K⁺ efflux → potential falls.
复极化：Na⁺ 通道失活，K⁺ 通道开放 → K⁺ 外流 → 电位下降。
Hyperpolarisation: K⁺ channels slow to close → potential undershoots resting level → then Na⁺/K⁺ pump restores resting state.
超极化：K⁺ 通道关闭较慢 → 电位低于静息水平 → 随后钠钾泵恢复静息状态。
The refractory period ensures impulses travel in one direction and limits their frequency.
不应期确保冲动单向传导并限制其频率。
5. Saltatory Conduction | 跳跃传导
In myelinated axons, action potentials only occur at the nodes of Ranvier because the myelin sheath acts as an insulator. The impulse appears to jump from node to node – this is saltatory conduction.
在有髓轴突中，由于髓鞘起绝缘作用，动作电位只发生在郎飞结处。冲动仿佛从结到结跳跃传播——这就是跳跃传导。
Saltatory conduction greatly increases the speed of impulse propagation compared to continuous conduction in non-myelinated neurones. Greater axon diameter also increases speed.
与无髓神经元的连续传导相比，跳跃传导大大提高了冲动传播速度。轴突直径较大也可提高速度。
6. Synaptic Transmission | 突触传递
When an action potential arrives at the synaptic knob, it opens voltage-gated Ca²⁺ channels. Ca²⁺ influx triggers vesicles containing neurotransmitter to fuse with the presynaptic membrane and release their contents into the synaptic cleft by exocytosis.
当动作电位到达突触终扣时，会打开电压门控 Ca²⁺ 通道。Ca²⁺ 内流促使含有神经递质的囊泡与突触前膜融合，通过胞吐作用将递质释放到突触间隙。
The neurotransmitter diffuses across the cleft and binds to specific receptor proteins on the postsynaptic membrane. This binding opens ligand-gated ion channels, generating a postsynaptic potential. The effect can be excitatory (e.g., Na⁺ entry → depolarisation) or inhibitory (e.g., Cl⁻ entry or K⁺ exit → hyperpolarisation).
神经递质扩散穿过间隙，与突触后膜上特异性受体蛋白结合。这一结合打开配体门控离子通道，产生突触后电位。效应可以是兴奋性的（如 Na⁺ 内流 → 去极化）或抑制性的（如 Cl⁻ 内流或 K⁺ 外流 → 超极化）。
The neurotransmitter is then rapidly removed from the cleft by reuptake, enzymatic breakdown, or diffusion to prevent continuous stimulation.
然后神经递质会通过重摄取、酶促降解或扩散等方式被迅速从间隙清除，以防持续刺激。
7. Excitatory and Inhibitory Synapses | 兴奋性与抑制性突触
Summation is the process by which multiple presynaptic inputs are combined to determine whether the postsynaptic neurone fires an action potential. Spatial summation involves inputs from several synapses at the same time, and temporal summation involves repeated impulses from one synapse in quick succession.
总和是指多个突触前输入整合在一起，决定突触后神经元是否发放动作电位的过程。空间总和涉及同一时间来自多个突触的输入，时间总和涉及同一突触快速连续发放的冲动。
Excitatory postsynaptic potentials (EPSPs) depolarise the membrane, while inhibitory postsynaptic potentials (IPSPs) hyperpolarise it. If the net depolarisation at the axon hillock reaches threshold, an action potential is generated.
兴奋性突触后电位（EPSP）使膜去极化，而抑制性突触后电位（IPSP）使膜超极化。如果轴丘处的净去极化达到阈值，就产生动作电位。
Common neurotransmitters: acetylcholine (excitatory at neuromuscular junctions), GABA (inhibitory in the brain), dopamine, serotonin, and noradrenaline. IB requires knowledge of the effects of psychoactive drugs on synaptic transmission.
常见神经递质：乙酰胆碱（在神经-肌肉接头处起兴奋作用）、GABA（在大脑中起抑制作用）、多巴胺、血清素和去甲肾上腺素。IB 要求了解精神活性药物对突触传递的影响。
8. The Reflex Arc | 反射弧
A reflex arc is the simplest neural pathway that produces a rapid, involuntary response to a stimulus, bypassing conscious brain processing. The basic components are: receptor → sensory neurone → relay neurone (in spinal cord) → motor neurone → effector.
反射弧是产生快速、非自主刺激反应的最简单神经通路，绕过了大脑意识加工。基本组成为：感受器 → 感觉神经元 → 中间神经元（位于脊髓） → 运动神经元 → 效应器。
The knee-jerk reflex is a classic example: tapping the patellar tendon stretches the quadriceps muscle spindles (receptor), impulses travel along sensory neurone to the spinal cord, synapse directly with motor neurone, which stimulates the muscle to contract. In AQA, you may also need to describe the withdrawal reflex (e.g., touching a hot object).
膝跳反射是经典例子：叩击髌腱牵拉股四头肌肌梭（感受器），冲动沿感觉神经元传至脊髓，直接与运动神经元形成突触，后者使肌肉收缩。AQA 还可能要求描述缩回反射（如触碰烫物）。
A reflex arc ensures a faster response than voluntary movement as it involves fewer synapses and a shorter neuronal pathway.
反射弧比随意运动响应更快，因为它涉及的突触较少、神经通路更短。
9. Comparing Nervous and Hormonal Communication | 神经与激素通讯的比较
| Feature / 特征 | Nervous / 神经 | Hormonal / 激素 |
|---|---|---|
| Signal type / 信号形式 | Electrical & chemical (neurotransmitters) | Chemical (hormones in blood) |
| Speed / 速度 | Very fast (ms) | Slower (seconds to days) |
| Duration / 持续时间 | Short-lived, stops when impulse ends | Long-lasting until hormone broken down |
| Pathway / 途径 | Specific, via neurones to target cells | Widespread, via blood; only target cells respond |
| Response type / 响应类型 | Localised, precise (e.g., muscle contraction) | Widespread, often systemic (e.g., growth) |
This comparison table is a common 6-mark question style in AQA and a topic for data analysis in IB.
该对比表是 AQA 常见的 6 分题型，也是 IB 数据分析的常见话题。
10. Common Exam Misconceptions | 常见考试误区
· Stating that sodium ions diffuse out during depolarisation – they actually diffuse in. · Confusing ‘re-polarisation’ with ‘resting potential restoration’ – the latter involves the Na⁺/K⁺ pump, not just K⁺ efflux. · Forgetting that synaptic transmission is unidirectional due to vesicle and receptor location. · Using ‘speed’ instead of ‘frequency’ when describing how the nervous system encodes stimulus strength (all action potentials are the same size).
· 误认为去极化时钠离子外流——实则是内流。· 混淆“复极化”与“静息电位恢复”——后者需钠钾泵参与，而不仅仅是 K⁺ 外流。· 忘记突触传递因囊泡和受体位置而具有单向性。· 在描述神经系统如何编码刺激强度时错用“速度”一词（所有动作电位幅度相同，强度由频率编码）。
In IB, ensure you can explain the effect of neonicotinoid pesticides on insects by their action as acetylcholine receptor agonists. For AQA, practice interpreting graphs of membrane potential changes and synapse function.
在 IB 中，确保你能解释新烟碱类杀虫剂通过作为乙酰胆碱受体激动剂对昆虫产生的影响。对于 AQA，要练习解读膜电位变化图和突触功能图。
11. Key Diagrams to Master | 必须掌握的示意图
You should be able to sketch and annotate a graph of a generic action potential, labelling resting potential, threshold, depolarisation, repolarisation, hyperpolarisation, and the refractory period. Also label the opening and closing of Na⁺ and K⁺ channels.
你应该能够绘制并标注动作电位通用曲线图，标出静息电位、阈值、去极化、复极化、超极化和不应期。同时标注 Na⁺ 和 K⁺ 通道的开闭情况。
Diagrams of a cholinergic synapse showing vesicles, cleft, receptors, and neurotransmitter removal are essential for both syllabi.
胆碱能突触示意图中需展示囊泡、间隙、受体和神经递质清除方式，这对两个大纲都至关重要。
12. Linking to Homeostasis and Behaviour | 与稳态及行为的联系
The nervous system works alongside the endocrine system to maintain homeostasis. Thermoregulation and blood glucose control involve sensory detection, nervous coordination, and effector responses. In IB, linking to behaviour such as fight-or-flight responses is valuable.
神经系统与内分泌系统协同维持稳态。体温调节和血糖控制都涉及感觉检测、神经协调和效应器应答。在 IB 中，可与斗争或逃跑反应等行为建立联系。
Understanding synaptic transmission also helps explain how drugs, toxins, and medical conditions affect the body. Remember that summation and inhibition allow fine control of neural pathways.
理解突触传递还有助于解释药物、毒素和疾病如何影响身体。记住总和与抑制使得神经通路能够精细控制。
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