📚 Nervous System Key Points | 神经系统 考点精讲
The nervous system allows organisms to detect changes in their environment and respond accordingly. Understanding its structure and function is essential for the IGCSE WJEC Biology exam. This article covers key points, from neurone types and reflex arcs to the detailed workings of the human eye.
神经系统使生物体能探测环境变化并作出相应反应。理解其结构和功能对 IGCSE WJEC 生物考试至关重要。本文涵盖从神经元类型、反射弧到人眼详细工作机制的关键考点。
1. The Structure of the Nervous System | 神经系统的结构
The nervous system is divided into two main parts: the central nervous system (CNS), consisting of the brain and spinal cord, and the peripheral nervous system (PNS), consisting of nerves that connect the CNS to the rest of the body.
神经系统分为两个主要部分：由脑和脊髓组成的中枢神经系统 (CNS)，以及由连接 CNS 与身体其余部分的神经组成的周围神经系统 (PNS)。
The brain processes information and coordinates responses, while the spinal cord relays information and controls reflex actions. Sensory neurones carry impulses from receptors to the CNS, and motor neurones carry impulses from the CNS to effectors.
脑处理信息并协调反应，脊髓传递信息并控制反射动作。感觉神经元将冲动从感受器传至 CNS，运动神经元将冲动从 CNS 传至效应器。
2. Neurones: The Building Blocks | 神经元：基本单位
Neurones are specialised cells that transmit electrical impulses. They share common features: a cell body containing the nucleus, dendrites that receive impulses, and an axon that carries impulses away. The axon is often covered by a myelin sheath, which insulates and speeds up impulse transmission.
神经元是传递电冲动的特化细胞。它们具有共同特征：含细胞核的胞体、接受冲动的树突，以及将冲动传出的轴突。轴突常被髓鞘包裹，髓鞘起到绝缘和加速冲动传递的作用。
In the WJEC specification, three types of neurone are particularly important: sensory, relay, and motor. Their structure varies according to their function in the nervous pathway.
在 WJEC 大纲中，三种神经元尤为重要：感觉神经元、中间神经元和运动神经元。它们的结构因其在神经通路中的功能而异。
3. Sensory Neurones | 感觉神经元
A sensory neurone carries impulses from a receptor, such as the skin or a sense organ, towards the central nervous system. It has a long dendrite that connects directly to the receptor, and a relatively short axon that enters the spinal cord or brain.
感觉神经元将冲动从感受器（如皮肤或感觉器官）传向中枢神经系统。它有一个直接与感受器相连的长树突，以及一个进入脊髓或脑的较短轴突。
The cell body of a sensory neurone is typically located just outside the spinal cord, in a swelling called the dorsal root ganglion. This location helps to protect the cell body while maintaining a direct sensory pathway.
感觉神经元的胞体通常位于脊髓外的一个膨大处，称为背根神经节。这种位置有助于保护胞体，同时维持直接的感觉通路。
4. Relay Neurones | 中间神经元
Relay neurones, also called interneurones, are found entirely within the central nervous system. They connect sensory neurones to motor neurones and allow complex integration of information. They have short axons and many dendrites for forming multiple connections.
中间神经元，也称联络神经元，完全位于中枢神经系统内。它们连接感觉神经元和运动神经元，并允许信息的复杂整合。它们轴突短，树突多，可形成多种连接。
In a reflex arc, the relay neurone is the link in the spinal cord that can produce a rapid automatic response without the brain being immediately involved. This makes reflex actions extremely fast.
在反射弧中，中间神经元是脊髓中的连接点，可在不立即涉及大脑的情况下产生快速自动反应。这使得反射动作极其迅速。
5. Motor Neurones | 运动神经元
A motor neurone carries impulses from the central nervous system to an effector, which is usually a muscle or a gland. It has a short dendrite and a very long axon that reaches all the way to the effector organ. The cell body is located inside the CNS.
运动神经元将冲动从中枢神经系统传递到效应器，效应器通常是肌肉或腺体。它树突短，轴突很长，一直延伸到效应器器官。胞体位于 CNS 内。
The axon terminal branches into several endings that form neuromuscular junctions with muscle fibres. When an impulse arrives, neurotransmitter is released that causes the muscle to contract.
轴突末端分支成若干末梢，与肌纤维形成神经肌肉接头。当冲动到达时，释放神经递质，引起肌肉收缩。
6. The Reflex Arc | 反射弧
A reflex action is an automatic, rapid response to a stimulus that does not involve conscious thought. The pathway of a simple reflex arc is: stimulus → receptor → sensory neurone → relay neurone (in spinal cord) → motor neurone → effector → response.
反射动作是对刺激的自动、快速反应，不涉及意识思维。简单反射弧的途径是：刺激 → 感受器 → 感觉神经元 → 中间神经元（在脊髓）→ 运动神经元 → 效应器 → 反应。
A common example is the withdrawal reflex when touching a hot object. The heat stimulates temperature receptors in the skin, impulses travel to the spinal cord, and a relay neurone instantly activates motor neurones to the biceps muscle, pulling the hand away. At the same time, other motor neurones carrying impulses to the triceps are inhibited to allow the movement.
一个常见例子是接触灼热物体时的缩手反射。热量刺激皮肤中的温度感受器，冲动传至脊髓，中间神经元立即激活通向肱二头肌的运动神经元，将手拉回。同时，通向肱三头肌的其他运动神经元被抑制，以允许该动作发生。
Stimulus → Receptor → Sensory Neurone → Relay Neurone → Motor Neurone → Effector → Response
刺激 → 感受器 → 感觉神经元 → 中间神经元 → 运动神经元 → 效应器 → 反应
7. Synapses and Neurotransmitters | 突触与神经递质
A synapse is a tiny gap between two neurones. When an electrical impulse arrives at the presynaptic terminal, vesicles release a chemical neurotransmitter (such as acetylcholine) into the synaptic cleft.
突触是两个神经元之间的微小间隙。当电冲动到达突触前末梢时，囊泡释放化学神经递质（如乙酰胆碱）到突触间隙。
The neurotransmitter diffuses across the cleft and binds to specific receptors on the postsynaptic membrane. This binding may trigger a new electrical impulse in the next neurone. The neurotransmitter is then rapidly broken down or reabsorbed to prevent continuous stimulation.
神经递质扩散通过间隙，与突触后膜上的特异性受体结合。这种结合可触发下一个神经元产生新的电冲动。随后神经递质被迅速分解或重吸收，以防止持续刺激。
Synapses ensure that impulses travel in only one direction and allow integration of signals from multiple neurones. Many drugs and toxins act by interfering with synaptic transmission.
突触确保冲动仅沿一个方向传递，并允许整合来自多个神经元的信号。许多药物和毒素通过干扰突触传递起作用。
8. The Human Eye: Structure | 人眼的结构
The eye is a sense organ containing photoreceptors that detect light. Key structures include the cornea, iris, lens, retina, optic nerve, and suspensory ligaments. The cornea refracts light; the iris controls the pupil size; the lens fine-tunes focus; the retina contains rod and cone cells.
眼睛是含有探测光线的光感受器的感觉器官。关键结构包括角膜、虹膜、晶状体、视网膜、视神经和悬韧带。角膜折射光线；虹膜控制瞳孔大小；晶状体精细调节焦距；视网膜含有视杆细胞和视锥细胞。
The pupil is the hole in the centre of the iris that allows light to enter. The retina converts light energy into electrical impulses, which travel through the optic nerve to the brain for interpretation.
瞳孔是虹膜中央让光线进入的孔。视网膜将光能转换为电冲动，通过视神经传至大脑进行解释。
| Structure | Function |
|---|---|
| Cornea | Refracts light entering the eye |
| Iris | Adjusts pupil size to control light entry |
| Lens | Changes shape to focus light on retina |
| Retina | Contains photoreceptors; forms image |
| Optic nerve | Transmits impulses to brain |
| 结构 | 功能 |
|---|---|
| 角膜 | 折射进入眼睛的光线 |
| 虹膜 | 调节瞳孔大小控制进光量 |
| 晶状体 | 改变形状将光线聚焦于视网膜 |
| 视网膜 | 含光感受器；形成图像 |
| 视神经 | 传递冲动至大脑 |
9. Accommodation | 晶状体调节
Accommodation is the process by which the lens changes shape to focus light from objects at different distances onto the retina. For near objects, the ciliary muscles contract, suspensory ligaments slacken, and the lens becomes fatter and more convex, increasing its refractive power.
调节是晶状体改变形状，将来自不同距离物体的光线聚焦于视网膜的过程。看近物时，睫状肌收缩，悬韧带松弛，晶状体变得更凸更厚，增加屈光力。
For distant objects, the ciliary muscles relax, suspensory ligaments tighten, and the lens is pulled thin and flat, reducing refractive power. This reflex adjustment allows clear vision across a range of distances.
看远物时，睫状肌舒张，悬韧带拉紧，晶状体被拉得薄而扁平，降低屈光力。这种反射性调节使我们能看清远近不同物体。
Problems with accommodation include short-sightedness (myopia), where the eyeball is too long or the lens too strong, causing distant objects to appear blurry. Long-sightedness (hyperopia) occurs when the eyeball is too short or the lens too weak, making near objects blurry.
调节问题包括近视（myopia），即眼球过长或晶状体屈光力过强，导致远物模糊。远视（hyperopia）则是眼球过短或晶状体屈光力过弱，导致近物模糊。
10. Pupil Reflex | 瞳孔反射
The pupil reflex controls the amount of light entering the eye, protecting the retina and optimising vision. In bright light, the circular muscles of the iris contract, making the pupil smaller (constriction). In dim light, the radial muscles contract, making the pupil larger (dilation).
瞳孔反射控制进入眼睛的光量，保护视网膜并优化视力。在强光下，虹膜环状肌收缩，瞳孔变小（收缩）。在弱光下，辐射状肌收缩，瞳孔变大（扩张）。
This is an involuntary reflex coordinated by the autonomic nervous system. The change in pupil size occurs rapidly via a reflex arc involving the retina, optic nerve, brain stem, and motor neurones to the iris muscles.
这是一种由自主神经系统协调的不随意反射。瞳孔大小的变化通过一个涉及视网膜、视神经、脑干和通向虹膜肌的运动神经元的反射弧快速发生。
11. Comparing Neurone Types | 神经元类型比较
| Feature | Sensory | Relay | Motor |
|---|---|---|---|
| Direction | From receptor to CNS | Within CNS | From CNS to effector |
| Cell body position | In dorsal root ganglion | Inside CNS | Inside CNS |
| Axon length | Short | Short | Long |
| Dendrite | Long | Many, short | Short |
| 特征 | 感觉神经元 | 中间神经元 | 运动神经元 |
|---|---|---|---|
| 传递方向 | 从感受器到CNS | 在CNS内 | 从CNS到效应器 |
| 胞体位置 | 背根神经节 | CNS内 | CNS内 |
| 轴突长度 | 短 | 短 | 长 |
| 树突 | 长 | 多个，短 | 短 |
12. Summary and Exam Tips | 总结与考试技巧
Mastering the nervous system topic requires understanding the sequence of events in a reflex arc, the structure and function of different neurones, synaptic transmission, and the eye’s accommodation and pupil reflex. Use labelled diagrams to support your answers in the exam.
掌握神经系统主题需要理解反射弧事件序列、不同神经元的结构和功能、突触传递，以及眼睛的调节和瞳孔反射。考试中善用带标签的图示来支持你的答案。
Key terms to use accurately: receptor, effector, impulse, myelin sheath, neurotransmitter, synapse, ciliary muscle, suspensory ligament. Be prepared to explain how a reflex arc works step by step and to interpret tables or diagrams of the eye.
需准确使用的关键词：感受器、效应器、冲动、髓鞘、神经递质、突触、睫状肌、悬韧带。准备好逐步解释反射弧的工作原理，并分析眼睛的图表。
Published by TutorHao | Biology Revision Series | aleveler.com
更多咨询请联系16621398022（同微信）
屏轩国际教育cambridge primary/secondary checkpoint, cat4, ukiset,ukcat,igcse,alevel,PAT,STEP,MAT, ibdp,ap,ssat,sat,sat2课程辅导，国外大学本科硕士研究生博士课程论文辅导Cancel reply