📚 IGCSE CIE Biology: Nervous System – Key Points Revision | IGCSE CIE 生物：神经系统 考点精讲
The nervous system is one of the most important coordination systems in living organisms. It allows animals to detect stimuli, process information, and trigger rapid responses that are essential for survival. In IGCSE CIE Biology, you need to understand the structure and function of neurones, reflex arcs, synapses, the central nervous system, and the eye as a sense organ.
神经系统是生物体内最重要的协调系统之一。它使动物能够探测刺激、处理信息并引发快速反应，这对生存至关重要。在 IGCSE CIE 生物学中，你需要理解神经元的结构与功能、反射弧、突触、中枢神经系统以及作为感觉器官的眼睛。
1. Overview of the Nervous System | 神经系统概述
The nervous system is divided into the central nervous system (CNS) and the peripheral nervous system (PNS). The CNS consists of the brain and spinal cord, while the PNS comprises all the nerves that connect the CNS to receptors and effectors throughout the body.
神经系统分为中枢神经系统 (CNS) 和外周神经系统 (PNS)。中枢神经系统由脑和脊髓组成，而外周神经系统包括将中枢神经系统与全身感受器和效应器连接起来的所有神经。
Receptors detect changes in the environment (stimuli) and generate nerve impulses. These impulses are transmitted via sensory neurones to the CNS, where they are processed. The CNS then sends impulses along motor neurones to effectors, which are usually muscles or glands, bringing about a response.
感受器探测环境的变化（刺激）并产生神经冲动。这些冲动通过感觉神经元传至中枢神经系统进行处理。中枢神经系统再沿着运动神经元将冲动发送到效应器（通常是肌肉或腺体），从而产生反应。
2. Neurones: Structure and Types | 神经元的结构与类型
Neurones are specialised cells that carry electrical impulses. All neurones have a cell body containing the nucleus, dendrites that receive impulses, and an axon that transmits impulses away from the cell body. Many axons are covered by a myelin sheath, which insulates the axon and speeds up impulse conduction.
神经元是传导电冲动的特化细胞。所有神经元都有一个含有细胞核的细胞体、接收冲动的树突以及将冲动传导离开细胞体的轴突。许多轴突被髓鞘覆盖，髓鞘使轴突绝缘并加快冲动传导。
Sensory neurones carry impulses from receptors to the CNS. They have a long dendron that brings impulses toward the cell body and a relatively short axon. Motor neurones transmit impulses from the CNS to effectors; they possess many short dendrites and a long axon. Relay neurones (interneurones) are found entirely within the CNS, connecting sensory and motor neurones. They have short dendrites and a short axon.
感觉神经元将冲动从感受器传至中枢神经系统。它们有一根长树突将冲动带向细胞体以及一根较短的轴突。运动神经元将冲动从中枢神经系统传至效应器；它们有许多短树突和一根长轴突。中间神经元（联络神经元）完全位于中枢神经系统内，连接感觉与运动神经元。它们具有短树突和短轴突。
3. The Reflex Arc | 反射弧
A reflex action is an automatic, involuntary response to a stimulus that does not require conscious thought. The pathway of a reflex, known as the reflex arc, involves a receptor, a sensory neurone, a relay neurone (in the spinal cord or brain), a motor neurone, and an effector.
反射动作是对刺激的一种自动、不随意的反应，不需要意识思维。反射的通路称为反射弧，包括感受器、感觉神经元、中间神经元（在脊髓或大脑中）、运动神经元和效应器。
In a typical withdrawal reflex, such as touching a hot object, heat stimulates pain receptors in the skin. The sensory neurone sends an impulse to the spinal cord, where it synapses with a relay neurone. The relay neurone immediately passes the impulse to a motor neurone, causing the biceps muscle to contract and pull the hand away. This entire sequence occurs before the brain is even aware of the pain.
在一个典型的缩手反射中，例如触摸灼热物体，热量刺激皮肤中的痛觉感受器。感觉神经元向脊髓发送冲动，并与一个中间神经元形成突触。中间神经元立即将冲动传递给运动神经元，使二头肌收缩并将手抽回。整个序列在大脑感知到疼痛之前就已发生。
Reflex arcs are essential because they produce rapid protective responses, minimising damage without the delay of processing in the brain.
反射弧至关重要，因为它们能产生快速保护性反应，在没有大脑处理延迟的情况下将损伤降到最低。
4. Synapses and Neurotransmitters | 突触和神经递质
A synapse is the junction between two neurones. When a nerve impulse reaches the end of the presynaptic neurone, it triggers the release of neurotransmitter molecules from vesicles into the synaptic cleft. These chemicals diffuse across the cleft and bind to specific receptors on the postsynaptic neurone, generating a new impulse.
突触是两个神经元之间的接合点。当神经冲动到达突触前神经元的末梢时，它会触发囊泡释放神经递质分子到突触间隙中。这些化学物质扩散穿过间隙，并与突触后神经元上的特定受体结合，产生新的冲动。
Synapses ensure that impulses travel in only one direction, from the presynaptic to the postsynaptic neurone. They also allow integration of signals, as a postsynaptic neurone may receive inputs from many presynaptic neurones. Some drugs and toxins affect synaptic transmission, for example by blocking receptors or inhibiting the breakdown of neurotransmitters.
突触确保冲动仅沿一个方向传播，即从突触前神经元到突触后神经元。它们还能整合信号，因为一个突触后神经元可能接收来自许多突触前神经元的输入。某些药物和毒素会影响突触传递，例如通过阻断受体或抑制神经递质的分解。
5. Central Nervous System: Brain and Spinal Cord | 中枢神经系统：大脑和脊髓
The brain is the body’s main control centre. The cerebrum is the largest part, responsible for conscious thought, memory, language, and voluntary actions. The cerebellum coordinates muscle movement and maintains balance. The medulla oblongata controls involuntary processes such as heart rate and breathing. The hypothalamus regulates body temperature and water balance.
大脑是身体的主要控制中心。大脑（端脑）是最大的部分，负责意识思维、记忆、语言和随意动作。小脑协调肌肉运动并维持平衡。延髓控制心率、呼吸等不随意过程。下丘脑调节体温和水分平衡。
The spinal cord is a column of nerve tissue that runs from the brain down the vertebral column. It serves as a relay for impulses between the brain and the rest of the body and is also the centre for many reflex actions. Damage to the spinal cord can result in loss of sensation and paralysis below the injured area.
脊髓是一束神经组织，从大脑向下贯穿脊柱。它充当大脑与身体其他部分之间的冲动中继站，也是许多反射动作的中枢。脊髓受损可导致受伤部位以下的感丧失和瘫痪。
6. The Eye as a Sense Organ | 作为感觉器官的眼睛
The eye detects light and converts it into nerve impulses, allowing us to see. Light enters through the transparent cornea, passes through the aqueous humour, and then through the pupil, which is the hole in the centre of the coloured iris. The lens focuses light onto the retina at the back of the eye.
眼睛探测光线并将其转换为神经冲动，使我们能够看见。光线通过透明角膜进入，穿过房水，然后穿过瞳孔（有色虹膜中央的孔）。晶状体将光线聚焦到眼球后部的视网膜上。
The retina contains photoreceptors: rods, which are sensitive to dim light and detect shapes, and cones, which detect colour and detail in bright light. The fovea is a region of the retina with a high density of cones, giving the sharpest vision. Nerve impulses from the retina travel along the optic nerve to the brain, where they are interpreted as images. The blind spot is where the optic nerve leaves the eye; it has no photoreceptors.
视网膜含有感光细胞：视杆细胞对弱光敏感并检测形状，视锥细胞在强光下检测颜色和细节。中央凹是视网膜上锥细胞密度最高的区域，提供最清晰的视觉。来自视网膜的神经冲动沿视神经传递到大脑，被解读为图像。盲点是视神经离开眼睛的位置，该处没有感光细胞。
The sclera is the tough white outer coat of the eye. The choroid is a dark layer rich in blood vessels that nourishes the retina. The ciliary muscles and suspensory ligaments hold the lens in place and change its shape.
巩膜是眼球坚韧的白色外壳。脉络膜是富含血管的暗色层，为视网膜提供营养。睫状肌和悬韧带固定晶状体并改变其形状。
7. Accommodation: Focusing on Near and Distant Objects | 调节：对近处和远处物体聚焦
Accommodation is the process by which the eye adjusts the shape of the lens to focus light from objects at different distances onto the retina. For near objects, the ciliary muscles contract, which releases tension on the suspensory ligaments. The lens becomes more convex (thicker), increasing its refractive power and bending light rays more to achieve a sharp image on the retina.
调节是眼睛调整晶状体形状以将不同距离物体的光线聚焦在视网膜上的过程。观察近处物体时，睫状肌收缩，悬韧带的张力减小。晶状体变得更凸（更厚），增加了屈光力，使光线更多地弯折以在视网膜上形成清晰图像。
For distant objects, the ciliary muscles relax, pulling the suspensory ligaments taut. This flattens the lens, reducing its refractive power so that parallel light rays from distant objects are brought to a focus exactly on the retina.
观察远处物体时，睫状肌松弛，悬韧带被拉紧。这使得晶状体变扁，减小了屈光力，从而使来自远处物体的平行光线正好聚焦在视网膜上。
8. The Pupil Reflex | 瞳孔反射
The pupil reflex controls the amount of light entering the eye to protect the retina from damage and to optimise vision in different light intensities. In bright light, circular muscles in the iris contract and radial muscles relax. This makes the pupil constrict (become smaller), limiting light entry.
瞳孔反射控制进入眼睛的光量，以保护视网膜免受损伤并在不同光强下优化视觉。在强光下，虹膜中的环状肌收缩，辐射肌松弛。这使得瞳孔缩小（变小），限制光线进入。
In dim light, the radial muscles contract and the circular muscles relax, causing the pupil to dilate (become larger). More light enters, improving vision under low-light conditions. This reflex is coordinated by the brain, but it occurs involuntarily.
在弱光下，辐射肌收缩，环状肌松弛，导致瞳孔扩大（变大）。更多光线进入，改善低光条件下的视力。这种反射由大脑协调，但属于不随意过程。
9. Common Eye Defects: Myopia and Hyperopia | 常见眼睛缺陷：近视和远视
Myopia (short-sightedness) occurs when the eyeball is too long or the lens is too powerful, causing light to be focused in front of the retina. Distant objects appear blurred, while near objects remain clear. Myopia is corrected using a concave (diverging) lens, which spreads out light rays before they enter the eye, shifting the focus back onto the retina.
近视（短视）发生在眼球过长或晶状体屈光力过强时，导致光线聚焦在视网膜前方。远处物体显得模糊，而近处物体保持清晰。近视使用凹透镜（发散透镜）矫正，它使光线在进入眼睛前发散，将焦点后移至视网膜上。
Hyperopia (long-sightedness) is caused by the eyeball being too short or the lens being too weak, resulting in light being focused behind the retina. Near objects appear blurred. A convex (converging) lens is used to correct hyperopia, converging light rays slightly before they reach the eye so the focus falls on the retina.
远视（长视）由眼球过短或晶状体屈光力过弱引起，导致光线聚焦在视网膜后方。近处物体变得模糊。使用凸透镜（会聚透镜）矫正远视，在光线到达眼睛前使其稍微会聚，使焦点落在视网膜上。
10. Comparing Nervous and Hormonal Control | 神经系统与激素控制的比较
The nervous system and the endocrine system are the body’s two main coordination systems. The nervous system uses electrical impulses transmitted along neurones. These impulses travel very quickly, producing rapid, short-lived, and highly localised responses such as muscle contraction.
神经系统和内分泌系统是人体两个主要的协调系统。神经系统利用沿神经元传导的电信号。这些冲动传播速度极快，产生快速、短暂且高度局部的反应，例如肌肉收缩。
The endocrine system releases hormones, which are chemical messengers, directly into the blood. Hormones travel more slowly to all parts of the body but affect only specific target cells that have complementary receptors. The effects of hormones are generally slower to develop, but they are often more widespread and longer lasting than nervous responses.
内分泌系统将激素（化学信使）直接释放到血液中。激素较慢地输送到全身，但仅影响具有互补受体的特定靶细胞。激素的作用通常发展较慢，但往往比神经反应更广泛、更持久。
For example, the nervous system controls a reflex like blinking, which takes a fraction of a second. In contrast, the hormone adrenaline prepares the body for ‘fight or flight’ over several seconds to minutes.
例如，神经系统控制像眨眼这样的反射，仅需几分之一秒。相比之下，激素肾上腺素在数秒至数分钟内使身体为“战或逃”做好准备。
11. Key Terms Summary | 关键术语总结
Stimulus: A change in the internal or external environment detectable by an organism.
刺激：生物体能够检测到的内部或外部环境变化。
Receptor: A specialised cell or organ that detects a stimulus and generates a nerve impulse.
感受器：探测刺激并产生神经冲动的特化细胞或器官。
Effector: A muscle or gland that brings about a response to a stimulus.
效应器：对刺激产生反应的肌肉或腺体。
Synapse: A gap between two neurones where neurotransmitters transmit the impulse.
突触：两个神经元之间的间隙，神经递质在此传递冲动。
Neurotransmitter: A chemical released at the end of a neurone to pass an impulse across a synapse.
神经递质：神经元末梢释放的化学物质，用于将冲动传递过突触。
Reflex action: A fast, automatic response to a stimulus that does not involve conscious thought.
反射动作：对刺激的一种快速、自动的反应，不涉及意识思维。
Accommodation: The ability of the eye to change the shape of the lens to focus on near or distant objects.
调节：眼睛改变晶状体形状以对近处或远处物体聚焦的能力。
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