📚 Coordination and Response in Humans | 人体的协调与反应
All living organisms must detect changes in their internal and external environments and produce appropriate responses. In humans, this is achieved by two major communication systems: the nervous system and the endocrine system. This article reviews the key structures, pathways and exam points for Cambridge IGCSE Science.
所有生物体都必须检测内外部环境的变化并作出适当反应。在人体中，这由两大通讯系统完成：神经系统和内分泌系统。本文回顾剑桥 IGCSE 科学中这一主题的关键结构、通路和考点。
1. The Need for Coordination | 协调的必要性
Organisms face constantly changing conditions, such as temperature, light, sound, touch and chemical signals. A stimulus is any change in the environment that can be detected by receptors. Coordination links detection of a stimulus to a response, which is carried out by an effector, usually a muscle or a gland.
生物体面临着不断变化的条件，例如温度、光、声、触摸和化学信号。刺激是环境中能够被感受器检测到的任何变化。协调作用将刺激的检测与反应联系起来，反应由效应器（通常是肌肉或腺体）完成。
Without coordination, the body cannot maintain a stable internal environment or avoid danger. Examples include pulling the hand away from a hot object and adjusting the pupil size in bright light.
如果没有协调作用，身体无法维持稳定的内环境或躲避危险。例子包括手遇热物体迅速缩回，以及在强光下调节瞳孔大小。
2. The Nervous System: An Overview | 神经系统概述
The human 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.
人体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，周围神经系统由连接中枢神经系统与身体其他部分的神经组成。
The CNS acts as the processing centre: it receives sensory information, decides on a response and sends motor commands. The PNS carries signals in both directions, allowing rapid communication between receptors, the CNS and effectors.
中枢神经系统起到处理中心的作用：它接收感觉信息、决定反应并发送运动指令。周围神经系统双向传递信号，使感受器、中枢神经系统和效应器之间能够快速通讯。
3. Neurones and Their Types | 神经元及其类型
Neurones are specialised cells that transmit electrical impulses. A typical motor neurone has a cell body, dendrites, an axon and axon terminals. The axon is often covered by a myelin sheath, which insulates the fibre and speeds up impulse transmission.
神经元是传递电冲动的特化细胞。典型的运动神经元具有细胞体、树突、轴突和轴突末梢。轴突通常由髓鞘包裹，髓鞘起绝缘作用并加快冲动传递速度。
There are three main types: sensory neurones carry impulses from receptors to the CNS; relay neurones connect sensory and motor neurones within the CNS; motor neurones carry impulses from the CNS to effectors.
神经元有三种主要类型：感觉神经元将冲动从感受器传至中枢神经系统；中继神经元在中枢神经系统内连接感觉神经元和运动神经元；运动神经元将冲动从中枢神经系统传至效应器。
4. Reflex Arcs | 反射弧
imulus → receptor → sensory neurone → relay neurone → motor neurone → effector → response.
反射是对刺激的快速、自动且不随意的反应，可保护身体免受伤害。反射的通路称为反射弧，其顺序为：刺激 → 感受器 → 感觉神经元 → 中继神经元 → 运动神经元 → 效应器 → 反应。
In a withdrawal reflex, such as touching a hot surface, the heat stimulates pain receptors in the skin. Impulses travel along a sensory neurone to the spinal cord, cross a synapse to a relay neurone, then to a motor neurone. The motor neurone triggers contraction of the biceps muscle, pulling the hand away.
在缩手反射中，例如碰到高温表面，热会刺激皮肤中的痛觉感受器。冲动沿感觉神经元传到脊髓，经突触传到中继神经元，再传到运动神经元。运动神经元引发肱二头肌收缩，将手拉回。
Because the reflex arc passes through the spinal cord rather than conscious areas of the brain, the response is very fast and occurs before the brain becomes aware of the pain.
由于反射弧经过脊髓而非脑的有意识区域，因此反应非常迅速，且发生在脑感知疼痛之前。
5. Synapses | 突触
A synapse is a junction between two neurones. When an impulse reaches the end of a neurone, a chemical neurotransmitter is released into the synaptic gap. The chemical diffuses across the gap and binds to receptors on the next neurone, generating a new impulse.
突触是两个神经元之间的连接点。当冲动到达神经元末梢时，会向突触间隙释放一种化学神经递质。该化学物质扩散穿过间隙，与下一个神经元上的受体结合，产生新的冲动。
Synapses ensure that impulses travel in one direction only because neurotransmitter is released from the presynaptic side and receptors are located on the postsynaptic membrane. This is a common exam point.
突触确保冲动只能沿一个方向传递，因为神经递质由突触前侧释放，而受体位于突触后膜上。这是常见的考点。
6. The Endocrine System | 内分泌系统
The endocrine system uses hormones: chemical messengers produced by endocrine glands and transported in the blood to target organs. Hormones are usually slower to act than nerve impulses but their effects often last longer.
内分泌系统使用激素：由内分泌腺产生并通过血液运送到靶器官的化学信使。激素的作用通常比神经冲动的速度慢，但作用持续时间往往更长。
Important endocrine glands include the pituitary gland, thyroid gland, adrenal glands, pancreas and ovaries or testes. Each hormone has specific target cells with complementary receptors.
重要的内分泌腺包括垂体、甲状腺、肾上腺、胰腺以及卵巢或睾丸。每种激素都有带有互补受体的特定靶细胞。
7. Comparing Nervous and Hormonal Control | 神经控制与激素控制对比
The table below summarises the main differences between nervous and hormonal communication.
下表总结了神经通讯与激素通讯的主要区别。
| Feature 特征 | Nervous system 神经系统 | Endocrine system 内分泌系统 |
|---|---|---|
| Signal 信号 | Electrical impulse 电冲动 | Chemical hormone 化学激素 |
| Pathway 途径 | Neurones 神经元 | Blood 血液 |
| Speed 速度 | Very fast 非常快 | Slower 较慢 |
| Duration 持续时间 | Short-lived 短暂 | Long-lasting 持久 |
You should be able to state that both systems use chemical signalling at some stage: a synapse uses neurotransmitter, while the endocrine system uses hormones in the blood.
你应当能够指出，两个系统在某个阶段都使用化学信号：突触使用神经递质，而内分泌系统使用血液中的激素。
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