📚 IGCSE AQA Biology: Nervous System Revision | 神经系统考点精讲
The nervous system enables organisms to detect changes in their environment and to coordinate rapid responses. In IGCSE AQA Biology, you need to understand the structure and function of neurones, reflex arcs, synapses, the brain, and the eye. This guide breaks down every key topic into clear, paired English–Chinese explanations to support your revision.
神经系统使生物体能够探测环境变化并协调快速反应。在 IGCSE AQA 生物学中，你需要理解神经元的结构与功能、反射弧、突触、大脑和眼睛。这篇指南将所有关键主题分解为清晰的中英对照讲解，帮助你复习。
1. The Nervous System Overview | 神经系统概述
The nervous system is divided into the central nervous system (CNS), consisting of the brain and spinal cord, and the peripheral nervous system (PNS), made up of nerves connecting the CNS to the rest of the body. It allows rapid communication through electrical impulses.
神经系统分为中枢神经系统（由脑和脊髓组成）和周围神经系统（由连接中枢神经系统与身体其余部分的神经构成）。它通过电冲动实现快速通讯。
Receptors detect stimuli (changes in the environment), and effectors (muscles or glands) bring about responses. The sequence is: stimulus → receptor → sensory neurone → coordinator (CNS) → motor neurone → effector → response.
感受器探测刺激（环境变化），效应器（肌肉或腺体）产生反应。顺序是：刺激 → 感受器 → 感觉神经元 → 协调中枢（中枢神经系统） → 运动神经元 → 效应器 → 反应。
The nervous system uses electrical signals, which travel along neurones at high speed, enabling immediate reactions such as pulling your hand away from a hot object.
神经系统利用电信号沿神经元高速传播，从而产生即时反应，例如将手从烫物上缩回。
2. Neurones: Building Blocks | 神经元：基本单位
A neurone (nerve cell) is specialised to carry electrical impulses. It has a cell body containing the nucleus, dendrites that receive signals, and a long axon that transmits impulses away from the cell body. Many axons are covered by a myelin sheath, which insulates and speeds up conduction.
神经元（神经细胞）是专门传递电冲动的细胞。它具有含细胞核的细胞体、接收信号的树突，以及将冲动传离细胞体的长轴突。许多轴突被髓鞘包裹，髓鞘起到绝缘并加速传导的作用。
The myelin sheath is formed by Schwann cells and has gaps called nodes of Ranvier, where the impulse jumps, allowing saltatory conduction. This makes transmission much faster in myelinated neurones.
髓鞘由施万细胞形成，并有称为郎飞结的间隙，冲动在这些结处跳跃传导，实现跳跃式传导，使得有髓神经元的传输速度大大加快。
At the end of the axon are synaptic knobs, which pass signals to the next neurone or effector across a synapse. Dendrites are highly branched to collect impulses from many other neurones.
轴突末端有突触小体，通过突触将信号传递给下一个神经元或效应器。树突高度分支，以便从许多其他神经元收集冲动。
3. Types of Neurones | 神经元类型
There are three main types of neurone: sensory neurones, relay (connector) neurones, and motor neurones. Sensory neurones carry impulses from receptors to the CNS. Their cell bodies are located outside the CNS, in structures called dorsal root ganglia.
神经元主要有三种类型：感觉神经元、中间（联络）神经元和运动神经元。感觉神经元将冲动从感受器传到中枢神经系统。其细胞体位于中枢神经系统之外，称作背根神经节的结构中。
Relay neurones are found entirely within the CNS. They connect sensory neurones to motor neurones and process information. They have many short dendrites and a short axon.
中间神经元完全位于中枢神经系统内部。它们将感觉神经元与运动神经元连接起来，并处理信息。它们有许多短小的树突和一条短轴突。
Motor neurones transmit impulses from the CNS to effectors (muscles or glands). Their cell bodies are in the CNS, and they have long axons extending out to the effector. The effector then produces a response, such as muscle contraction.
运动神经元将冲动从中枢神经系统传到效应器（肌肉或腺体）。它们的细胞体位于中枢神经系统内，具有伸向效应器的长轴突。效应器随后产生反应，如肌肉收缩。
4. The Reflex Arc | 反射弧
A reflex action is an automatic, involuntary response to a stimulus that protects the body from harm. It follows a specific pathway called the reflex arc, which bypasses the brain to produce a very fast response.
反射是身体为避免伤害而对刺激做出的自动、不随意的反应。它遵循一条特定通路，称为反射弧，该通路绕开大脑以产生极快的反应。
A typical reflex arc involves: receptor → sensory neurone → relay neurone in the spinal cord → motor neurone → effector. For example, touching a sharp object triggers pain receptors, the impulse travels to the spinal cord, a relay neurone directly connects to a motor neurone, and the effector muscle contracts to withdraw the hand.
典型的反射弧包括：感受器 → 感觉神经元 → 脊髓中的中间神经元 → 运动神经元 → 效应器。例如，触碰尖锐物体会触发痛觉感受器，冲动传到脊髓，中间神经元直接与运动神经元连接，效应器肌肉随即收缩将手缩回。
Synapses within the reflex arc ensure the impulse flows in one direction only. The brain is later informed of the event, but the reflex occurs without conscious thought, minimising reaction time.
反射弧中的突触确保冲动仅沿一个方向传递。大脑随后会得知该事件，但反射是在无意识思考下发生的，从而最小化反应时间。
5. Synapses | 突触
A synapse is a junction between two neurones, or between a neurone and an effector. The small gap is called the synaptic cleft. When an electrical impulse arrives at the presynaptic neurone, it triggers the release of neurotransmitter molecules from vesicles.
突触是两个神经元之间，或神经元与效应器之间的连接点。这个微小的间隙称为突触间隙。当电冲动到达突触前神经元时，它会触发囊泡释放神经递质分子。
The neurotransmitter diffuses across the synaptic cleft and binds to specific receptor proteins on the postsynaptic membrane. This binding opens ion channels, generating a new electrical impulse in the postsynaptic neurone.
神经递质扩散穿过突触间隙，并与突触后膜上的特定受体蛋白结合。这种结合会打开离子通道，在突触后神经元中产生新的电冲动。
Synapses ensure unidirectional transmission because only the presynaptic neurone releases neurotransmitter and only the postsynaptic membrane has the receptors. After transmission, enzymes break down the neurotransmitter or it is reabsorbed to prevent continuous stimulation.
突触确保单向传递，因为只有突触前神经元释放神经递质，而只有突触后膜具有受体。传递后，酶会分解神经递质或将其重新吸收，以防止持续刺激。
6. Structure and Function of the Brain | 大脑的结构与功能
Although the spinal cord can coordinate reflexes, the brain controls complex behaviours. In IGCSE AQA, you need to know three main regions: the cerebral cortex (cerebrum), cerebellum, and medulla oblongata.
虽然脊髓可以协调反射，但大脑控制复杂行为。在 IGCSE AQA 中，你需要了解三个主要区域：大脑皮层（大脑）、小脑和延髓。
The cerebral cortex is the largest part, responsible for consciousness, intelligence, memory, language, and processing sensory information. It is highly folded in humans, increasing surface area for more neurones.
大脑皮层是最大部分，负责意识、智力、记忆、语言和处理感觉信息。人类的大脑皮层高度折叠，增加了表面积以容纳更多神经元。
The cerebellum coordinates muscle movements and controls balance and posture. It ensures movements are smooth and precise. The medulla oblongata controls automatic activities like heartbeat, breathing, and blood pressure, working without conscious effort.
小脑协调肌肉运动，控制平衡和姿势，确保运动平滑精确。延髓控制心跳、呼吸和血压等自主活动，无需意识参与即可工作。
Scientists have mapped brain functions using MRI scans, studying patients with brain damage, and electrically stimulating different areas during surgery. This evidence shows the localisation of specific functions.
科学家通过 MRI 扫描、研究脑损伤患者以及手术中电刺激不同区域来绘制脑功能图谱。这些证据显示了特定功能的局部定位。
7. The Eye: Anatomy | 眼睛的结构
The eye is a sense organ containing light receptor cells. Key structures you must know: cornea, iris, pupil, lens, retina, optic nerve, ciliary muscles, and suspensory ligaments. Light enters through the cornea, which refracts it, then passes through the pupil, whose size is controlled by the iris.
眼睛是包含光感受器细胞的感觉器官。你必须掌握的关键结构有：角膜、虹膜、瞳孔、晶状体、视网膜、视神经、睫状肌和悬韧带。光线通过角膜进入，角膜使其折射，然后穿过瞳孔，瞳孔大小由虹膜控制。
The lens further focuses light onto the retina, which contains rod and cone cells. Rods detect light intensity, while cones detect colour. The fovea, a region of the retina packed with cones, gives the sharpest colour vision.
晶状体进一步将光线聚焦到视网膜上，视网膜含有视杆细胞和视锥细胞。视杆细胞探测光强度，视锥细胞探测颜色。中央凹是视网膜上一个密集分布视锥细胞的区域，提供最清晰的色觉。
The optic nerve carries impulses from the retina to the brain. Where the optic nerve leaves the eye, there are no light-sensitive cells, creating a blind spot. The sclera is the tough outer protective layer, and the choroid layer prevents internal reflection of light.
视神经将冲动从视网膜传至大脑。视神经离开眼睛的部位没有感光细胞，从而形成盲点。巩膜是坚韧的外保护层，脉络膜层防止光线在眼内内部反射。
8. Accommodation and Pupil Reflex | 调节与瞳孔反射
Accommodation is the eye’s ability to focus on objects at different distances by changing the shape of the lens. To focus on a near object, the ciliary muscles contract, suspensory ligaments slacken, and the lens becomes thicker and more curved, increasing its refractive power.
调节是眼睛通过改变晶状体的形状来聚焦不同距离物体的能力。要聚焦近处物体，睫状肌收缩，悬韧带松弛，晶状体变得更厚、更弯曲，从而增强其折射能力。
For distant objects, the ciliary muscles relax, suspensory ligaments tighten, pulling the lens into a thinner, flatter shape. This reduces refraction so that light from far objects is focused precisely on the retina.
对于远处物体，睫状肌放松，悬韧带拉紧，将晶状体拉成更薄、更扁平的形状。这降低了折射，使来自远处物体的光线精确聚焦在视网膜上。
The pupil reflex controls the amount of light entering the eye. In bright light, circular muscles in the iris contract, radial muscles relax, and the pupil constricts. In dim light, radial muscles contract, circular muscles relax, and the pupil dilates. This reflex protects the retina from excessive light and improves vision in low light.
瞳孔反射控制进入眼睛的光线量。在强光下，虹膜环状肌收缩，辐射状肌放松，瞳孔缩小。在弱光下，辐射状肌收缩，环状肌放松，瞳孔扩大。此反射保护视网膜免受过度光线伤害，并改善弱光下的视力。
9. Eye Defects and Correction | 视力缺陷与矫正
Two common eye defects are myopia (short‑sightedness) and hyperopia (long‑sightedness). In myopia, the eyeball is too long or the lens is too curved, so light focuses in front of the retina. Distant objects appear blurry. It is corrected with a concave (diverging) lens.
两种常见的视力缺陷是近视和远视。近视时，眼球过长或晶状体曲率过大，光线聚焦在视网膜前方，远处物体看起来模糊。矫正用凹（发散）透镜。
In hyperopia, the eyeball is too short or the lens is too flat, causing light to focus behind the retina. Near objects are blurry. A convex (converging) lens is used to correct this by adding additional focusing power.
远视时，眼球过短或晶状体过扁平，导致光线聚焦在视网膜后方，近处物体模糊。使用凸（会聚）透镜增加额外的聚焦能力来矫正。
Other technologies include laser eye surgery to reshape the cornea, and replacement lens surgery for severe cases. Spectacles and contact lenses remain the simplest solutions, but you only need to know the lens types for IGCSE AQA.
其他技术包括重塑角膜的激光眼科手术，以及针对严重病例的晶状体置换手术。眼镜和隐形眼镜仍是最简单的解决方案，但 IGCSE AQA 只需了解透镜类型。
10. Nervous vs Hormonal Control | 神经控制与激素控制比较
The body uses both the nervous and endocrine (hormonal) systems for coordination and control. The nervous system uses electrical impulses along neurones, producing rapid, short‑lived responses, whereas the endocrine system uses chemical hormones transported in the blood, leading to slower but longer‑lasting effects.
身体同时使用神经系统和内分泌（激素）系统进行协调与控制。神经系统利用电冲动沿神经元传递，产生快速但短暂的反应；而内分泌系统利用通过血液运输的化学激素，导致较慢但效果更持久。
A key difference is the pathway: nervous signals travel by dedicated neurones to specific effectors, while hormones are carried in the bloodstream and can affect multiple target organs. For example, the nervous system stimulates muscle contraction for a reflex, while insulin regulates blood glucose over a longer period.
一个关键区别在于通路：神经信号通过专用的神经元传向特定效应器，而激素由血流携带，可影响多个靶器官。例如，神经系统刺激肌肉收缩以完成反射，而胰岛素在较长时间内调节血糖。
Both systems often interact. The hypothalamus in the brain links nervous signals to hormonal responses, such as controlling the pituitary gland. The nervous system’s speed is crucial for survival, but hormonal control is essential for processes like growth and reproduction.
两个系统经常相互作用。下丘脑将神经信号与激素反应联系起来，例如控制脑垂体。神经系统的速度对生存至关重要，但激素控制对生长和生殖等过程必不可少。
| Feature | Nervous System | Hormonal System |
|---|---|---|
| Signal type | Electrical impulses | Chemical hormones |
| Speed | Very fast | Slower |
| Duration | Short‑lived | Long‑lasting |
| Pathway | Specific neurones to specific effectors | Bloodstream to multiple targets |
特征对比表如下：
| 特征 | 神经系统 | 激素系统 |
|---|---|---|
| 信号类型 | 电冲动 | 化学激素 |
| 速度 | 非常快 | 较慢 |
| 持续时间 | 短暂 | 持久 |
| 通路 | 特定神经元到特定效应器 | 经血流到多个靶标 |
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