📚 3.43 The Nervous System: Impulses, Synapses and Reflexes | 3.43 神经系统：冲动、突触与反射
The nervous system is the master coordinator of the body, allowing rapid detection of and response to changes in the external and internal environment. For Edexcel IGCSE Biology, a solid grasp of neurone structure, impulse generation, synaptic transmission and reflex arcs is essential. This article covers those core topics, from resting potentials to the knee-jerk reflex, and compares nervous and hormonal control.
神经系统是人体的主协调器，能够快速检测并应对内外环境的变化。对于 Edexcel IGCSE 生物学来说，牢固掌握神经元结构、冲动产生、突触传递与反射弧至关重要。本文涵盖了从静息电位到膝跳反射的核心主题，并比较了神经控制与激素控制。
1. The Nervous System: An Overview | 神经系统概述
The human nervous system is split into the central nervous system (CNS), comprising the brain and spinal cord, and the peripheral nervous system (PNS), made up of nerves that connect the CNS to sense organs, muscles and glands. The CNS acts as the processing centre, integrating information and making decisions, while the PNS carries sensory signals towards the CNS and motor commands away from the CNS.
人类神经系统分为中枢神经系统（CNS）和周围神经系统（PNS），前者由脑和脊髓组成，后者由连接 CNS 与感觉器官、肌肉及腺体的神经构成。CNS 作为处理中心，整合信息并做出决策，而 PNS 将感觉信号传向 CNS，将运动指令传出 CNS。
processed. If a response is required, impulses are sent along motor neurones to effectors – way is: stimulus → receptor → sensory neurone → CNS → motor neurone → effector → response.
刺激是指环境中被感受器检测到的任何变化。感受器将刺激的能量转导（转换）为电冲动，称为神经冲动或动作电位。冲动沿着感觉神经元传至 CNS，在那里进行处理。如果需要做出反应，冲动便沿着运动神经元传至效应器——肌肉收缩或腺体分泌。因此基本通路为：刺激 → 感受器 → 感觉神经元 → CNS → 运动神经元 → 效应器 → 反应。
2. Neurones: The Functional Units | 神经元：功能单位
Neurones (nerve cells) are highly specialised for the transmission of electrical impulses. A typical neurone has a cell body containing the nucleus and most of the cytoplasm, numerous short dendrites that receive impulses from other neurones or receptors, and a long axon that carries impulses away from the cell body. The axon often branches at its end into synaptic terminals that make contacts with other neurones or effectors.
神经元（神经细胞）高度特化，专门用于传递电冲动。一个典型的神经元拥有含细胞核和大部分细胞质的细胞体、许多从其他神经元或感受器接收冲动的短树
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