📚 GCSE CIE Biology: The Nervous System Revision Guide | GCSE CIE 生物：神经系统考点精讲
The nervous system allows organisms to detect changes in their environment (stimuli) and coordinate appropriate responses. It uses electrical impulses to transmit signals rapidly along specialised cells called neurones. This revision guide covers all the key points required for the CIE GCSE Biology syllabus, including neurone structure, types of neurones, reflex arcs and synaptic transmission.
神经系统让生物体能够探测环境中的变化（刺激）并协调适当的反应。它以电冲动的形式沿着称为神经元的特化细胞快速传递信号。这份复习指南涵盖了 CIE GCSE 生物教学大纲要求的所有关键知识点，包括神经元的结构、神经元的类型、反射弧以及突触传递。
1. Overview of the Nervous System | 神经系统总览
The mammalian nervous system is divided into the central nervous system (CNS) and the peripheral nervous system (PNS). The CNS consists of the brain and the spinal cord, which process and integrate information. The PNS is made up of nerves that connect the CNS to receptors and effectors all over the body.
哺乳动物的神经系统分为中枢神经系统（CNS）和周围神经系统（PNS）。中枢神经系统由脑和脊髓组成，负责处理并整合信息。周围神经系统则由连接中枢神经系统与全身感受器和效应器的神经构成。
Receptors are specialised cells that detect stimuli such as light, sound, pressure, temperature and chemicals. Effectors are muscles or glands that carry out responses. The nervous system is the fastest method of control in the body, working alongside the slower hormonal system.
感受器是能够探测光、声、压力、温度和化学物质等刺激的特化细胞。效应器是执行反应的肌肉或腺体。神经系统是体内最快的控制方式，它与较慢的激素系统协同工作。
2. Structure of a Neurone | 神经元的结构
Neurones are highly differentiated cells adapted to transmit electrical impulses. A typical motor neurone has a cell body containing the nucleus, many short dendrites that receive impulses, and a long axon that carries impulses away from the cell body. The axon is insulated by a fatty myelin sheath made from Schwann cells, which speeds up impulse transmission.
神经元是高度分化的细胞，适于传递电冲动。一个典型的运动神经元具有含有细胞核的细胞体、许多接收冲动的短树突，以及将冲动从细胞体传走的长轴突。轴突由施万细胞形成的脂肪性髓鞘绝缘，这可以加快冲动的传递。
The myelin sheath has gaps called nodes of Ranvier, where the axon membrane is exposed. In sensory neurones the cell body is located along the axon outside the CNS. Relay neurones have very short axons and are found entirely within the CNS.
髓鞘上有一些称为郎飞结的间隙，轴突膜在这些地方裸露。在感觉神经元中，细胞体位于中枢神经系统外的轴突上。中间神经元拥有很短的轴突，整个细胞完全位于中枢神经系统内。
3. Sensory Neurones | 感觉神经元
Sensory neurones carry impulses from receptors in sense organs and the skin toward the CNS. They have a distinct structure: the cell body is positioned off the main fibre, with a long dendron bringing the impulse from the receptor. The axon then carries the signal into the spinal cord.
感觉神经元将冲动从感觉器官和皮肤中的感受器传到中枢神经系统。它们的结构独特：细胞体位于主纤维的旁边，由一条长树突将冲动从感受器引入，然后轴突把信号带进脊髓。
The direction of impulse travel is always from receptor to CNS. Sensory neurones are also called afferent neurones. They form the first part of a reflex arc, ensuring the body can react immediately to a potentially harmful stimulus.
冲动的传递方向总是从感受器到中枢神经系统。感觉神经元也称为传入神经元。它们构成反射弧的第一个环节，确保身体能对潜在的有害刺激做出即时反应。
4. Relay (Intermediate) Neurones | 中间神经元
Relay neurones are found inside the CNS and connect sensory neurones to motor neurones. They have short dendrites and a short axon, allowing them to pass signals over very short distances within the grey matter of the spinal cord or brain. Cell bodies are grouped together to form nuclei in the CNS.
中间神经元位于中枢神经系统内，负责连接感觉神经元和运动神经元。它们拥有短树突和短轴突，能够在脊髓或大脑的灰质内以极短距离传递信号。细胞体聚集成群，形成中枢神经系统中的神经核。
These neurones integrate information and are responsible for the processing stage of a reflex. In a simple three-neurone reflex arc, the relay neurone receives a signal from a sensory neurone and sends it on to a motor neurone. Some reflexes are monosynaptic, bypassing the relay neurone entirely.
这些神经元负责信息的整合与反射的处理环节。在一个简单的三神经元反射弧中，中间神经元从感觉神经元接收信号并将其传递给运动神经元。有些反射是单突触的，完全绕过中间神经元。
5. Motor Neurones | 运动神经元
Motor neurones transmit impulses from the CNS to effectors such as muscles and glands. Their cell bodies are located inside the spinal cord or brain, and they send long axons out through spinal nerves to reach the target organ. At the muscle fibre, the motor neurone forms a neuromuscular junction.
运动神经元将冲动从中枢神经系统传递到肌肉和腺体等效应器。它们的细胞体位于脊髓或大脑内，并通过脊神经发出长轴突到达目标器官。在肌纤维处，运动神经元形成神经肌肉接头。
Motor neurones are also known as efferent neurones. Their myelin sheaths are well developed to speed up transmission, which is vital when an immediate response is needed, such as pulling a hand away from a hot surface.
运动神经元也称为传出神经元。它们的髓鞘十分发达，能够加快传递速度，这对于需要立即反应的情形（比如把手从滚烫表面抽离）至关重要。
6. The Synapse – Structure and Function | 突触的结构与功能
A synapse is the junction between two neurones where the electrical impulse is converted into a chemical signal to cross the gap. The presynaptic neurone ends in a synaptic knob containing vesicles filled with neurotransmitter. The postsynaptic neurone has receptor proteins on its membrane.
突触是两个神经元之间的连接点，在这里电冲动被转换为化学信号以越过间隙。突触前神经元末端是含有神经递质囊泡的突触小体。突触后神经元的膜上带有受体蛋白。
The synaptic cleft is the narrow (about 20 nm) space between them. Synaptic transmission ensures impulses travel in one direction only, as receptors are only found on the postsynaptic membrane. This unidirectionality is a key feature of the reflex arc.
突触间隙是它们之间狭窄（约 20 nm）的空间。突触传递确保冲动只沿一个方向传播，因为受体只存在于突触后膜上。这种单向性是反射弧的一个关键特征。
7. Neurotransmitters and Synaptic Transmission | 神经递质与突触传递
When an impulse arrives at the synaptic knob, it causes vesicles to fuse with the presynaptic membrane and release neurotransmitter molecules into the cleft by exocytosis. The neurotransmitter diffuses across and binds to specific receptors on the postsynaptic membrane, causing ion channels to open.
当冲动到达突触小体时，会促使囊泡与突触前膜融合并以胞吐方式将神经递质分子释放到间隙中。神经递质扩散穿过间隙，与突触后膜上的特异性受体结合，使离子通道打开。
This generates a new electrical impulse in the postsynaptic neurone if the threshold is reached. Once the signal has been passed, the neurotransmitter is rapidly broken down by enzymes (e.g., acetylcholinesterase breaks down acetylcholine) or reabsorbed into the presynaptic knob to stop continuous stimulation.
如果达到阈值，这就在突触后神经元中产生一个新的电冲动。信号传递之后，神经递质迅速被酶分解（例如乙酰胆碱酯酶分解乙酰胆碱）或被重新摄取进入突触小体，以避免持续刺激。
8. The Reflex Arc – A Rapid Involuntary Response | 反射弧——快速的无意识反应
A reflex is a rapid, automatic response to a stimulus that does not involve conscious thought. The pathway is called a reflex arc. It involves a receptor detecting the stimulus, a sensory neurone transmitting the impulse to the spinal cord, a relay neurone processing the impulse, and a motor neurone sending the impulse to an effector.
反射是对刺激产生的快速、自动反应，不需要意识参与。该通路称为反射弧。它包括：感受器探测刺激，感觉神经元将冲动传至脊髓，中间神经元处理冲动，运动神经元将冲动传至效应器。
The effector then produces the response, such as muscle contraction or gland secretion. Because the impulse only travels as far as the spinal cord and back, the response time is minimised. The brain is informed later, but the reflex action occurs without delay.
然后效应器产生反应，例如肌肉收缩或腺体分泌。由于冲动只传到脊髓并折返，反应时间得以最小化。大脑随后才会收到信息，但反射动作在毫无延迟的情况下发生。
9. The Knee-jerk Reflex – A Worked Example | 膝跳反射实例分析
The knee-jerk (patellar) reflex is a classic example of a spinal reflex. Striking the patellar tendon just below the kneecap activates stretch receptors in the quadriceps muscle. An impulse travels along a sensory neurone directly to the spinal cord. In this monosynaptic reflex, the sensory neurone synapses directly with a motor neurone.
膝跳反射是一个典型的脊髓反射例子。轻叩膝盖骨下方的髌腱，会激活股四头肌中的牵张感受器。冲动沿感觉神经元直接传到脊髓。在这个单突触反射中，感觉神经元与运动神经元直接形成突触。
The motor neurone carries the impulse back to the quadriceps muscle, causing it to contract and extend the leg. At the same time, an inhibitory interneurone sends a signal to relax the antagonistic hamstring muscle. This demonstrates how reflexes can be coordinated and protective.
运动神经元将冲动带回股四头肌，使其收缩并伸展腿部。同时，一个抑制性中间神经元发送信号使拮抗的腘绳肌放松。这表明反射可以是协调且具有保护作用的。
10. Central Nervous System and Spinal Cord Structure | 中枢神经系统与脊髓结构
The spinal cord is protected by the vertebral column and is composed of white matter and grey matter. Grey matter, at the centre, contains neurone cell bodies and synapses. White matter surrounds the grey matter and contains myelinated axons that form ascending and descending tracts carrying signals to and from the brain.
脊髓受脊柱保护，由白质和灰质构成。中央的灰质包含神经元细胞体和突触。白质环绕灰质，含有形成上下行传导束的有髓轴突，这些传导束负责向大脑和从大脑传递信号。
The dorsal root of a spinal nerve brings sensory neurones into the spinal cord, while the ventral root takes the axons of motor neurones out. The cell bodies of sensory neurones are located in the dorsal root ganglion. This organisation is a common exam question.
脊神经的背根将感觉神经元引入脊髓，而腹根则把运动神经元的轴突传出。感觉神经元的细胞体位于背根神经节内。这种布局是常见的考试题目。
11. Electrical Impulses and Speed of Conduction | 电冲动与传导速度
Neurones transmit signals as action potentials, which are brief reversals of electrical potential across the cell membrane. This is caused by the rapid movement of sodium ions (Na⁺) into the axon and potassium ions (K⁺) out. The process is known as depolarisation and repolarisation.
神经元以动作电位的形式传递信号，这是细胞膜两侧电位的短暂反转。这是由钠离子（Na⁺）迅速流入轴突和钾离子（K⁺）流出引起的。该过程称为去极化和复极化。
Myelination increases conduction speed through saltatory conduction, where the impulse jumps from one node of Ranvier to the next. Factors that increase speed include a larger axon diameter and a higher temperature (up to an optimum). These principles often appear in data analysis questions.
髓鞘化通过跳跃传导增加传导速度，冲动从上一个郎飞结跳到下一个。增加传导速度的因素包括较大的轴突直径和较高的温度（到最适温度为止）。这些原理经常出现在数据分析题中。
12. Comparison of Nervous and Hormonal Control | 神经控制与激素控制的比较
The nervous system and the endocrine system are the body’s two main coordination systems. Nervous control uses electrical impulses along neurones and is very rapid, acting on specific muscles or glands. Hormonal control uses chemical messengers transported in the blood and is often slower but longer-lasting and more widespread.
神经系统和内分泌系统是人体两个主要的协调系统。神经控制利用沿神经元传递的电冲动，速度很快，作用于特定的肌肉或腺体。激素控制使用由血液运输的化学信使，通常较慢但更持久且作用更广泛。
A comparison table helps to remember key differences: transmission speed (milliseconds vs seconds to hours); duration of response (short-lived vs long-lasting); target area (localised vs widespread). Both systems work together, as seen in the fight-or-flight response where the nervous system triggers rapid release of adrenaline.
通过对比表格有助于记住关键区别：传递速度（毫秒级对秒到小时级）；反应持续时间（短暂对持久）；作用范围（局部对广泛）。两个系统协同工作，例如在争斗或逃跑反应中，神经系统触发肾上腺素的快速释放。
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