📚 Nervous Communication | 神经通讯
Nervous communication is the process by which animals detect stimuli and coordinate rapid responses through electrical impulses and chemical signals. This topic explains how neurones generate and transmit action potentials, and how information crosses synapses to produce coordinated behaviour.
神经通讯是指动物通过电冲动和化学信号检测刺激并协调快速反应的过程。本主题解释神经元如何产生和传导动作电位，以及信息如何跨越突触传递，从而产生协调的行为。
1. Neurones and Their Functions | 神经元及其功能
Neurones are specialised cells that transmit electrical impulses. A typical motor neurone has a cell body, dendrites, an axon and synaptic terminal knobs. Sensory neurones carry impulses from receptors to the central nervous system (CNS), relay neurones connect sensory and motor neurones, and motor neurones carry impulses from the CNS to effectors such as muscles and glands.
神经元是传递电冲动的特化细胞。一个典型的运动神经元具有细胞体、树突、轴突和突触末梢。感觉神经元将冲动从感受器传至中枢神经系统（CNS），中间神经元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，如肌肉和腺体。
The cell body contains the nucleus and most organelles. Dendrites receive signals from other neurones. The axon is a long fibre that conducts impulses away from the cell body. In many neurones, Schwann cells wrap around the axon to form a myelin sheath, which speeds up transmission.
细胞体含有细胞核和大多数细胞器。树突接收来自其他神经元的信号。轴突是一根长纤维，将冲动传离细胞体。在许多神经元中，施万细胞包裹轴突形成髓鞘，从而加快传导速度。
2. Resting Potential | 静息电位
When a neurone is not transmitting an impulse, the inside of the axon is negatively charged relative to the outside. The potential difference across the membrane is about -70 mV and is called the resting potential.
当神经元不传递冲动时，轴突内部相对于外部带负电。跨膜的电位差约为 -70 mV，称为静息电位。
The resting potential is established by the sodium-potassium pump, which actively transports 3 Na⁺ out of the cell for every 2 K⁺ moved in. The membrane is more permeable to K⁺ than to Na⁺ at rest, so K⁺ diffuses out down its concentration gradient. This leaves the inside more negative.
静息电位由钠钾泵建立，该泵每主动转运 3 个 Na⁺ 出细胞，同时将 2 个 K⁺ 转运入细胞。静息时膜对 K⁺ 的通透性大于对 Na⁺ 的通透性，因此 K⁺ 沿浓度梯度向外扩散。这使得膜内更负。
Large negatively charged proteins and organic ions also remain inside the axon and contribute to the negative charge. The combined effect of ion pumping and selective permeability maintains the resting potential.
带负电的大分子蛋白质和有机离子也留在轴突内部，有助于形成负电荷。离子泵和选择性通透性的共同作用维持了静息电位。
3. Action Potential | 动作电位
An action potential is a rapid, temporary reversal of the membrane potential. When a stimulus is strong enough to reach the threshold potential of about -55 mV, voltage-gated Na⁺ channels open and Na⁺ floods into the axon. The membrane depolarises and may reach about +40 mV.
动作电位是膜电位的快速、短暂逆转。当刺激足够强，达到约 -55 mV 的阈电位时，电压门控 Na⁺ 通道打开，Na⁺ 大量涌入轴突。膜发生去极化，可达到约 +40 mV。
At the peak, Na⁺ channels close and voltage-gated K⁺ channels open. K⁺ diffuses out, causing repolarisation. There is often a temporary overshoot called hyperpolarisation, before the resting potential is restored by the sodium-potassium pump.
在峰值时，Na⁺ 通道关闭，电压门控 K⁺ 通道打开。K⁺ 向外扩散，引起复极化。在钠钾泵恢复静息电位之前，通常会出现暂时的超射，称为超极化。
The action potential follows the all-or-nothing law: if the threshold is reached, a full action potential is produced; if not, no impulse is generated. The size of the action potential remains constant regardless of stimulus strength.
动作电位遵循“全或无”定律：如果达到阈值，就会产生完整的动作电位；如果未达到，则不会产生冲动。无论刺激强度如何，动作电位的大小保持恒定。
4. Propagation of Action Potentials | 动作电位的传导
An action potential in one region of the axon acts as a stimulus for the adjacent region. Local electric currents cause the next section of membrane to depolarise, opening voltage-gated Na⁺ channels there. In this way, a wave of depolarisation travels along the axon.
轴突某一区域的动作电位可刺激相邻区域。局部电流使下一段膜去极化，打开那里的电压门控 Na⁺ 通道。这样，去极化波沿轴突传播。
During the refractory period, the membrane cannot generate another action potential. This ensures that impulses travel in one direction and limits the frequency of impulses. It also prevents overlap between successive action potentials.
在不应期内，膜无法产生另一个动作电位。这确保了冲动单向传导，并限制了冲动的频率。它还能防止连续动作电位之间发生重叠。
Stronger stimuli do not produce larger action potentials; instead, they increase the frequency of action potentials. The brain interprets stimulus intensity by the number and frequency of impulses arriving per second.
更强的刺激不会产生更大的动作电位，而是增加动作电位的频率。大脑根据每秒到达的冲动数量和频率来解释刺激强度。
5. Saltatory Conduction and Myelination | 跳跃传导与髓鞘化
In myelinated neurones, the myelin sheath acts as an electrical insulator. Action potentials occur only at the nodes of Ranvier, the small gaps between Schwann cells. The impulse appears to jump from node to node, a process called saltatory conduction.
在有髓神经元中，髓鞘起到电绝缘体的作用。动作电位只发生在郎飞结，即施万细胞之间的小间隙。冲动似乎从一个结跳跃到下一个结，这一过程称为跳跃传导。
Saltatory conduction is much faster than continuous conduction in unmyelinated neurones. It also conserves energy because less active transport is needed to restore ion gradients after each impulse.
跳跃传导比无髓神经元的连续传导快得多。它还能节省能量，因为每次冲动后恢复离子梯度所需的主动转运较少。
In unmyelinated neurones, the action potential travels continuously along the whole membrane. This is slower because every section of the membrane must undergo depolarisation and repolarisation in sequence.
在无髓神经元中，动作电位沿整个膜连续传导。这种传导较慢，因为膜的每一段都必须依次进行去极化和复极化。
6. Synaptic Transmission | 突触传递
A synapse is the junction between two neurones. The presynaptic neurone ends in a synaptic knob containing vesicles filled with a neurotransmitter. The postsynaptic membrane contains specific receptor proteins.
突触是两个神经元之间的连接处。突触前神经元末端是突触小体，其中含有充满神经递质的囊泡。突触后膜含有特定的受体蛋白。
When an action potential arrives at the presynaptic knob, voltage-gated Ca²⁺ channels open. Calcium ions enter the knob and cause vesicles to move to and fuse with the presynaptic membrane. The neurotransmitter is released by exocytosis into the synaptic cleft.
当动作电位到达突触小体时，电压门控 Ca²⁺ 通道打开。钙离子进入小体，促使囊泡向突触前膜移动并与其融合。神经递质通过胞吐作用释放到突触间隙。
The neurotransmitter diffuses across the cleft and binds to receptors on the postsynaptic membrane. This opens ligand-gated ion channels, allowing Na⁺ to enter and generating a new action potential in the postsynaptic neurone if the threshold is reached.
神经递质扩散穿过突触间隙，并与突触后膜上的受体结合。这会打开配体门控离子通道，使 Na⁺ 进入，如果达到阈值，就会在突触后神经元中产生新的动作电位。
7. Neurotransmitters and Receptors | 神经递质与受体
Acetylcholine is a common neurotransmitter in the peripheral nervous system and at neuromuscular junctions. It is broken down by acetylcholinesterase in the synaptic cleft, which prevents continuous stimulation of the postsynaptic membrane.
乙酰胆碱是周围神经系统和神经肌肉接头中常见的神经递质。它在突触间隙中被乙酰胆碱酯酶分解，从而防止突触后膜受到持续刺激。
Other neurotransmitters include noradrenaline, dopamine and GABA. Excitatory neurotransmitters cause depolarisation of the postsynaptic membrane, while inhibitory neurotransmitters cause hyperpolarisation, making an action potential less likely.
其他神经递质包括去甲肾上腺素、多巴胺和 GABA。兴奋性神经递质使突触后膜去极化，而抑制性神经递质引起超极化，使动作电位更不容易产生。
| Type | Effect on postsynaptic membrane | Example |
| Excitatory | Depolarisation, opens Na⁺ channels | Acetylcholine |
| Inhibitory | Hyperpolarisation, opens Cl⁻ or K⁺ channels | GABA |
类型 | 对突触后膜的影响 | 示例
兴奋性 | 去极化，打开 Na⁺ 通道 | 乙酰胆碱
抑制性 | 超极化，打开 Cl⁻ 或 K⁺ 通道 | GABA
8. Summation and Inhibition | 总和与抑制
A single presynaptic action potential may release only a small amount of neurotransmitter. Temporal summation occurs when several impulses arrive in quick succession from the same presynaptic neurone. Spatial summation occurs when impulses arrive simultaneously from several presynaptic neurones. In both cases, the excitatory postsynaptic potentials add together to reach the threshold.
单个突触前动作电位可能只释放少量神经递质。时间总和是指来自同一突触前神经元的多个冲动快速连续到达。空间总和是指来自多个突触前神经元的冲动同时到达。在这两种情况下，兴奋性突触后电位相加，达到阈值。
Inhibitory synapses release neurotransmitters that open Cl⁻ or K⁺ channels, making the inside of the postsynaptic membrane more negative. This inhibitory postsynaptic potential can cancel out excitatory inputs, preventing an action potential from being generated.
抑制性突触释放神经递质，打开 Cl⁻ 或 K⁺ 通道，使突触后膜内部更负。这种抑制性突触后电位可以抵消兴奋性输入，阻止动作电位的产生。
The balance between excitatory and inhibitory inputs at any moment determines whether a postsynaptic neurone fires. This integration allows the nervous system to process complex information and make decisions.
任何时刻兴奋性和抑制性输入之间的平衡决定了突触后神经元是否发放冲动。这种整合使神经系统能够处理复杂信息并作出决策。
9. Drugs and Synapses | 药物与突触
Many drugs and toxins affect synaptic transmission. They may mimic neurotransmitters, block receptors, inhibit breakdown enzymes, or prevent release. For example, organophosphates inhibit acetylcholinesterase, so acetylcholine accumulates and causes overstimulation of muscles.
许多药物和毒素会影响突触传递。它们可能模拟神经递质、阻断受体、抑制分解酶或阻止释放。例如，有机磷酸酯抑制乙酰胆碱酯酶，使乙酰胆碱积累并引起肌肉过度兴奋。
Nicotine mimics acetylcholine at certain receptors, while curare blocks acetylcholine receptors and can cause paralysis. Understanding synapses helps explain how medicines and toxins change nervous coordination.
尼古丁在某些受体上模拟乙酰胆碱，而箭毒阻断乙酰胆碱受体，可导致瘫痪。理解突触有助于解释药物和毒素如何改变神经协调。
Some drugs increase the release of a neurotransmitter, while others prevent its reuptake from the synaptic cleft. These actions can enhance or reduce signalling in specific pathways of the brain.
有些药物增加神经递质的释放，而另一些则阻止神经递质从突触间隙被再摄取。这些作用可以增强或减弱大脑特定通路的信号传递。
10. Reflex Arcs | 反射弧
A reflex arc is the simplest nerve pathway that produces a rapid, involuntary response to a stimulus. It involves a receptor, a sensory neurone, a relay neurone in the CNS, a motor neurone and an effector. The pathway bypasses conscious areas of the brain, allowing a faster response.
反射弧是产生快速、不随意反应的最简单神经通路。它涉及感受器、感觉神经元、中枢神经系统中的中间神经元、运动神经元和效应器。该通路绕过大脑的意识区域，从而产生更快的反应。
In the knee-jerk reflex, stretching the patellar tendon sends impulses along a sensory neurone to the spinal cord. The sensory neurone synapses directly with a motor neurone, which stimulates the quadriceps muscle to contract. This is an example of a spinal reflex with only one synapse in the CNS.
在膝跳反射中，牵拉髌腱会沿感觉神经元向脊髓发送冲动。感觉神经元直接与运动神经元形成突触，运动神经元刺激股四头肌收缩。这是中枢神经系统中只有一个突触的脊髓反射的例子。
Reflex arcs have survival value because they allow the body to respond to danger before the brain has processed the information consciously. They also control automatic processes such as blinking and withdrawing from painful stimuli.
反射弧具有生存价值，因为它们使身体能在脑有意识地处理信息之前对危险作出反应。它们还控制自动过程，如眨眼和缩回疼痛刺激。
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