* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Download 突觸與神經訊號傳遞 - 國立交通大學開放式課程
Activity-dependent plasticity wikipedia , lookup
Clinical neurochemistry wikipedia , lookup
Premovement neuronal activity wikipedia , lookup
Axon guidance wikipedia , lookup
Multielectrode array wikipedia , lookup
Signal transduction wikipedia , lookup
Neuroregeneration wikipedia , lookup
Optogenetics wikipedia , lookup
Feature detection (nervous system) wikipedia , lookup
Circumventricular organs wikipedia , lookup
Development of the nervous system wikipedia , lookup
Patch clamp wikipedia , lookup
Neuromuscular junction wikipedia , lookup
Neurotransmitter wikipedia , lookup
Neuroanatomy wikipedia , lookup
Membrane potential wikipedia , lookup
Nonsynaptic plasticity wikipedia , lookup
Action potential wikipedia , lookup
Biological neuron model wikipedia , lookup
Node of Ranvier wikipedia , lookup
Synaptic gating wikipedia , lookup
Channelrhodopsin wikipedia , lookup
Single-unit recording wikipedia , lookup
Neuropsychopharmacology wikipedia , lookup
Resting potential wikipedia , lookup
Synaptogenesis wikipedia , lookup
Electrophysiology wikipedia , lookup
Nervous system network models wikipedia , lookup
End-plate potential wikipedia , lookup
Molecular neuroscience wikipedia , lookup
Chapter 48 神經元、突觸與神經訊號傳遞 Neurons, Synapses, and Signaling Outline 神經系統簡介 神經系統主要構成元素 The Structure of Neurons Neurons Glial Cells Neuronal Signaling Resting Potential (Ion Channels and Pumps) Action Potential Neural Communication at Synapses 國立交通大學生物科技學系 柯立偉老師 1 ※ 神經系統簡介 ※ • • Nervous systems process information in three stages: sensory input, integration, and motor output Many animals have a complex nervous system that consists of A 中樞神經系統 (central nervous system, CNS) where integration takes place; this includes the brain and a nerve cord A 周邊神經系統 (peripheral nervous system, PNS), which carries information into and out of the CNS The 神經元 (neurons) of the PNS, when bundled together, form 神經 (nerves) Sensory input 輸入 Sensor Integration 整合 感官受器 Motor output 輸出 Effector Peripheral nervous system (PNS) 周邊神經系統 Central nervous system (CNS) 中樞神經系統 Figure 48.3 Summary of information processing ※ 神經系統主要構成元素 ※ • Sensory neuron 感覺神經元 Sensors detect external stimuli and internal conditions and transmit information along sensory neurons • Interneuron 連絡神經元 Sensory information is sent to the brain or ganglia, where interneurons integrate the information • Motor neuron 運動神經元 Motor output leaves the brain or ganglia via motor neurons, which trigger muscle or gland activity 國立交通大學生物科技學系 柯立偉老師 2 ※ The Structure of Neurons ※ (CH48-1) The Structure of Neurons: Neurons: • The basic signaling units, are distinguished by their form, function, location, and interconnectivity within the nervous system. • Neurons take in information, make a “decision” about it following some relatively simple rules, and then, by changes in their activity levels, pass it along to other neurons. • Close relations to the morphological or structural, specializations of neurons Glial cells (also called Neuroglial Cell; 膠質細胞): • The other type of cell in the nervous system • More numerous than neurons, more than half of the brain’s volume • Non-neuronal cell, supportive function to brain Structure of Neurons (input) postsynaptic 粒腺體 synapse 細胞核 Soma 哺乳動物 胞器 組織器官 核糖體 蛋白質 presynaptic (output) 國立交通大學生物科技學系 柯立偉老師 細胞質 Synapse dendrites 3 Structure of Neurons Dendrites樹突 Presynaptic cell (output) Stimulus 粒線體 內質網 細胞核 Synapse突觸 Signal direction 高基式體 Axon 軸突 核醣體 Cell body (Soma) Synaptic terminals Synaptic terminals Neurotransmitter Postsynaptic cell (input) Figure 48.4 Neuron structure and organization Information across the synapse in the form of chemical messengers called neurotransmitters. Structure of Neurons As with most cells, the cell body contains metabolic (新陳代謝) machinery that maintains the neuron. Machinery includes a nucleus(細胞核), endoplasmic reticulum (內質 網), ribosomes(核醣體), mitochondria(粒線體), Golgi apparatus(高爾 基體), and other intracellular organelles(胞器). Surrounded by the neuronal membrane (細胞膜) composed of a lipid bilayer (雙層脂質), and suspended in cytoplasm (細胞質) Lipids (fatty material) are not water soluble (不溶於水), and thus form a barrier (屏障) to watery soluble materials (水溶性物質, ex. sodium, potassium ions, proteins, and other molecules) 國立交通大學生物科技學系 柯立偉老師 4 Structure of Neurons Neuron’s organelles, including its nucleus, are in the cell body. Dendrites Stimulus The dendrites, highly branched extensions that receive signals from other neurons. Nucleus The axon is typically a much longer extension that transmits signals to other cells at synapses. The cone-shaped base of an axon is called the axon hillock. Axon hillock Presynaptic cell Cell body Axon Signal A synapse is a junction between an axon direction and another cell. Synapse The synaptic terminal of one axon passes information across the synapse in the form of chemical messengers called neurotransmitters. Synaptic terminals Information is transmitted from a Postsynaptic Neurotransmitter presynaptic cell (a neuron) to a cell postsynaptic cell (a neuron, muscle, or Figure 48.4 Neuron structure & organization gland cell). Structure of Neurons Dendrites: after the synapse with respect to info. flow (postsynaptic) Axon: before the synapse with respect to info. flow (presynaptic) Most of neurons are both presynaptic and postsynaptic. Activity within a neuron involves changes in the electrical state, but at synapses the signal between neurons is usually mediated by chemical transmission. (但仍有存在少數的 electrical synapse) Dendrites with varied and complex forms: 1. 位於小腦的cerebella Purkinje cells正面像大樹一樣茂密,側面較薄 2. spinal motor neurons或thalamus neurons:其dendrites較簡約 3. Hippocampal neuron: dendrites上有 “spines”結構 →spines是little knobs attached by small necks to the surface of dendrites, 而synapse則座落在spines上 4. 有些neurons 其cell body上即直接有synapse (而無spines) 國立交通大學生物科技學系 柯立偉老師 5 A diagrammatic representation of the soma and dendritic tree of a Purkinje cell from the cerebellum Figure 2.3 Soma and dendritic tree of a Purkinje cell from the cerebellum. The Purkinje cells are arrayed in rows in the cerebellum. Each one has a large dendritic tree that is wider in one direction than the other. Diagrammatic ventral horn motor neuron Figure 2.4 Ventral-horn motor neuron. Multipolar neurons located in the spinal cord send their axons out the ventral root to make synapses on muscle fibers. 國立交通大學生物科技學系 柯立偉老師 6 Structure of Neurons Axon: 將neuron的電信號傳出(output)到axon terminal synapse處 axon terminal有特殊造型及intracellular結構, that enable communication via the release of neurotransmitters, (the chemical substances that transmit the signal between neurons at chemical synapses) The dendrites and the axon of a neuron are extensions of the cell body. Their internal volume is filled with the same cytoplasm (細胞質) that fills the cell body. Cell body, dendrites and axon 是組成神經元的主要部分,彼此之間 主要溝通是靠electrical signaling 國立交通大學生物科技學系 柯立偉老師 7 Four General Morphological Classes of Neurons Unipolar: Figure 2.6 Only one process,分岔形成樹突和 Axon Terminals.(出現於無脊神經系統) Bipolar: Dendrite Axon Two processes (one axon and one dendrite),負責sensory processes, 出現於聽覺、視覺、嗅覺系統中。 Ex. Bipolar retinal cell (Fig. 1.13) Multipolar: One axon and many dendrites. 存在於很多神經系統中,主要是Motor and sensory processing Neurons in the Brain,大部分都是這類神經 元 Figure 2.5 亦是Multipolar Neuron. Pseudounipolar: 出現unipoloar神經元,但獨特的是樹突和 軸突融合在一起, 出現於Dorsal-root ganglia of the spinal cord,為somatosensory cells… 神經系統主要構成元素(Review) Dendrites Axon Cell body Portion of axon Sensory neuron Interneurons Motor neuron Figure 48.5 Structural diversity of neurons Cell bodies and dendrites are black in these diagrams; axons are red. In the sensory neuron, unlike the other neurons here, the cell body is located partway along the axon that conveys signals from the dendrites to the axon’s terminal branches. 國立交通大學生物科技學系 柯立偉老師 8 ※ Glial Cells (膠質細胞) ※ Glial cell (neuroglial cell or glia), amount 10 times of neurons, more than half of the brain’s volume. Main role is structural support to neurons. Glial cells existed in CNS – central nervous system (含 brain 及 spinal cord), and PNS – peripheral nervous system (含sensory / motors inputs / outputs to the brain及 spinal cord) Central Nervous has three main types of glial cells: Astrocytes, Oligodendrocytes and Microglial Cells. (Fig. 2.7) Glial Cells (Nerve Glue) Peripheral nervous system Schwann cell Central nervous system Myelin (髓鞘) glial 80 m Astrocyte (星形膠質細胞) Microglia (小膠質細胞) Oligodendrocyte (少突膠質細胞) Glia Figure 48.6 Glia in the mammalian brain The glia are labeled red, the DNA in nuclei is labeled blur, and the dendrites of neurons are labeled green. Cell bodies of neurons 國立交通大學生物科技學系 柯立偉老師 9 Myelin Glial (髓鞘膠質細胞) These glia provide layers of membrane that insulate axons Oilgodendrocyte: provide myelin for multiple neurons Schawnn cell: provide myelin for individual neuron Main Differences between Oligodendrocyte and Schwann Cell Two Types of Myelin-Producing Cells Number of Axons Cell Type Location Schwann Cell Peripheral Nervous System One Oligodendrocyte Central Nervous System Many 國立交通大學生物科技學系 柯立偉老師 Myelinated by One Cell 10 Astrocytes Cultured astrocyte: Star-shaped, their many arms span all around neurons. Large glial cells having round or radially (放射狀) symmetric forms End feet: Astrocytes make contact with blood vessels at specialization. Permit the astrocyte to transport ions across the vascular wall and to create a barrier (障礙) between the tissues of the central nervous system Activated astrocytes Astrocyte Functions: Structural support Metabolic support (新陳代謝) Transmitter reuptake and release (重複攝取和釋放) Regulation of ion concentration in the extracellular space Modulation of synaptic transmission Vasomodulation (血管舒縮) Promotion of the myelinating activity of oligodendrocytes Guiding neurons as they migrate to their ultimate destination Secreting growth factors to stimulate neuronal growth (分泌生長因素刺激神經成長) Blood-brain barrier (BBB): astrocytic barrier between neuronal tissue and blood (扮演保護CNS重要角色,許多藥物無法通過此屏障) 國立交通大學生物科技學系 柯立偉老師 11 What is Blood brain barrier (BBB) The blood brain barrier is both a physical barrier and a system of cellular transport mechanisms. It maintains homeostasis (體內平衡) by restricting the entrances of potentially harmful (有害的) chemicals from the blood, and by allowing the entrance of essential nutrients (必須營養). It plays a vital role in protecting the central nervous system from blood-borne (血 液輸送) agents or chemical compounds (化合物) that might unduly (不正常性) affect neuronal activity. Many drugs can not across the BBB, and certain neuroactive agents, such as dopamine (多巴胺) and norepinephrine (正腎上腺素), when placed in the blood, do not across the BBB. Microglia Small and irregularly shaped and come Activated into play when tissue is damaged. Act as phagocytes (噬菌細胞, 如白血球 等), cleaning up CNS debris (碎屑), Resting responsible for producing an inflammatory (發炎反應) reaction to insults (損傷) (Streit et al., 2004) May play a role in neurodegenerative disorders (神經退化性疾病) such as Alzheimer‘s disease, dementia (癡呆), multiple sclerosis (硬化) and Amyotrophic lateral sclerosis (肌萎縮性脊髓側索硬化 國立交通大學生物科技學系 柯立偉老師 12 Activation of microglia cells in a tissue section from human brain Activated (in diseased cerebral cortex) Resting Activated (Phagocytosis) Overview of Neurons Presynaptic cell (output) Dendrites 樹突 粒線體 細胞核 Stimulus 內質網 Axon hillock 高基式體 Nucleus Cell body (Soma) 軸突 突觸 Signal direction Axon 髓鞘 核醣體 Layers of myelin Axon Myelin sheath Schwann cell Nodes of Ranvier Synapse Schwann cell Nucleus of Schwann cell Synaptic terminals Synaptic terminals Neurotransmitter 國立交通大學生物科技學系 柯立偉老師 Postsynaptic cell (input) 13 ※ Neuronal Signaling ※ (CH48-2) The goal of neuronal processing is to take in information, evaluate it, pass a signal to other neurons, forming local and long-distance circuits and networks Current flow is mediated by ionic currents carried by electrically charged atoms (ions), such as Sodium (Na+) 鈉 Potassium (K+) 鉀 Chloride (Cl-) 氯 Neural Membrane Potential Neuronal membrane: a bilayer of lipid molecules (Membrane 不 溶於水,因此可控制水溶性 (Water-soluble)物質進出) A barrier to ions, proteins及其他可溶於(內外) cellular fluid的 molecules. Neuronal membrane含有ion channels及active transporters (pumps)及receptor molecules. Resting membrane potential: neuronal membrane內外的電 位差,約-70mv,可由glass pipette electrode with fine tip,刺入 neuron細胞內量測到 此乃因Ion channels對進出Ions 之控制達成 國立交通大學生物科技學系 柯立偉老師 14 Ion Channels and Pump Ion channels: 由"transmembrane proteins”所型成的pore (氣孔), actual passageways (通道), 可使Ions (Na+, K+, Cl-)藉此進出 neurons. 有2類channels 1.passive (nongated): 允許特定的Ion因密度gradients而隨時進出 neurons. →open to certain ions 2.gated: can be opened or closed by electrical, chemical or physical stimuli. Permeability (滲透性): the extend to which a channel permits ions to cross membrane The membrane is more permeable to K+ than Na+, Cl-, (稱為selectively permeable) (因neuronal membrane has many more nongated (無柵式) K+ — selective channels than nongated Na+ channels及 other nongated channels) Ion Channels and Pump Resting membrane potential Properties of the membrane combined with the active pumping of ions across the neuronal membrane lead to ionic concentration gradients (離子濃度變 化) for Na+, K+ and Cl-, and charged proteins (A-) across the membrane. 國立交通大學生物科技學系 柯立偉老師 15 Ion Channels and Pump Active transporters: Na+/ K+ ATPase pump可主動move Na+ (K+) 出(進) membrane. ATP (adenosine triphosphate) 為一種energy-storing molecules,可提 供transmembrane pumps所需的fuel. Pumps是enzymes酵素(proteins) 構成,可以切斷chemical bond (連結) in a ATP molecule而釋放能量以 move 3個Na+ out of the cell及 move 2個K+ into the cell. 改變neuron內外濃度差,造成concentration gradients In resting state, neuron內有較高濃度的K+,而neuron外有較高濃度的Na+. 1.Selective membrane permeability及 2.Transmembrane ionic concentration gradients act together to create differences in charge across the membrane. Ion Channels and Pump Resting potential process as follows: (a) Pumps建立ionic concentration gradients 使得more Na+ outside the neuron and more K+ inside the neuron. (b) a的 gradients 產生一個force要將 Na+由outside neuron推入inside neuron K+由inside neuron推出outside neuron 由High concentration => From inside to outside →推進Low concentration 但因membrane is more permeable (leaky) (易滲透) to K+ than Na+, the force of the concentration gradient pushes more K+ out of the cell. (c) b中因較多K+被移至neuron外,使得neuron外較 外 相斥 neuron內的電壓高(正),而產生electrical K 相吸 gradient,而造成K+越來越難流出. 內 + 國立交通大學生物科技學系 柯立偉老師 16 Ion Channels and Pump (d) b與c的2股gradients (electrical電場及ionic concentration離子場) are in opposition to (意見相反) one another w.r.t. K+,而最後會達成 electrochemical equilibrium,即離子場將K+經nongated K+ channel 推出neuron外的force = 電場將K+留在neuron內的力 (e) d的電化平衡情況下, the small difference in charge across the membrane 型成了resting membrane potential,內外電壓差約 - 40~ - 90mv (neuron內較外電場低) (f) e在resting狀況下的neuron像是一個電池,含有potential energy,而可 經由active pumps改變membrane potential而產生電流(信號) → active Process Overview of Neural Communication 一個neuron與其他cells在synapses進行溝通: 接收輸入信號之 synapses位於dendrites或cell body,而送出輸出信號之synapse位 於axon terminals. The process of Neuronal signaling has several stages: 1.Neurons receive signals in either chemical form (如neurotransmitter 或嗅覺分子) or physical form (如skin之somatosensory之觸覺、eye之 photoreceptors之光線) 2.Stage1之信號改變postsynaptic neurons之membrane,而產生在neuron 內及週遭之電流(current flow) 3.The current flow is mediated by ionic current carried by ions (如Na+, K+, Cl-) that are dissolved in the fluid inside and outside of neurons. 4.當一個neuron整合夠多currents from many synaptic inputs或sensory inputs,則會產生Spikes狀的long-distance signals (action potentials), 而neuron中產生spikes的區域叫spike triggering zone. 國立交通大學生物科技學系 柯立偉老師 17 Overview of Neural Communication 5. Long-distance signals, action potentials, travel down the axon to its terminals, where causes the release of neurotransmitters at synapses. 國立交通大學生物科技學系 柯立偉老師 18 Resting Potential • Sodium-potassium pumps (鈉鉀幫浦) use the energy of ATP to maintain these K+ and Na+ gradients across the plasma membrane. • In a mammalian neuron at resting potential, the concentration of K+ is highest inside the cell, while the concentration of Na+ is highest outside the cell. These concentration gradients represent chemical potential energy. Figure 48.7 The basis of the membrane potential Key OUTSIDE OF CELL Na K Sodium-potassium pump Potassium (K) channel Sodium (Na) channel INSIDE OF CELL Resting Potential • The opening of ion channels in the plasma membrane converts chemical potential to electrical potential. • A neuron at resting potential contains many open K+ channels and fewer open Na+ channels; K+ significantly diffuses out of the cell. • The resulting buildup of negative charge within the neuron is the major source of membrane potential. Figure 48.7 The basis of the membrane potential OUTSIDE OF CELL Key Na K Sodium-potassium pump Potassium channel Sodium channel INSIDE OF CELL 國立交通大學生物科技學系 柯立偉老師 19 ※ Action Potential ※ (CH48-3) Changes in membrane potential occur because neurons contain gated ion channels that open or close in response to stimuli. Hyperpolarization 超極化 •When gated K+ channels open, K+ diffuses out, making the inside of the cell more negative and having an increase in magnitude of the membrane potential. Stimulus 50 Membrane potential (mV) (a) Graded hyperpolarizations produced by two stimuli that increase membrane permeability to K 0 50 Threshold Resting potential Hyperpolarizations 100 0 1 2 3 4 5 Figure 48.10a Time (msec) Action Potential Depolarization 去極化 (b) Graded depolarizations produced by two stimuli that increase membrane permeability to Na Membrane potential (mV) • A reduction in the magnitude of the membrane potential when other types of ion channels open. For example, depolarization occurs if gated Na+ channels open and Na+ diffuses into the cell. 0 50 100 Figure 48.10b 國立交通大學生物科技學系 柯立偉老師 Stimulus 50 Threshold Resting potential Depolarizations 0 1 2 3 4 5 Time (msec) 20 Action Potential If a depolarization shifts the membrane potential sufficiently, it results in a massive change in membrane voltage called an action potential. • Action potentials have a constant magnitude, are all-or-none, and transmit signals over long distances. • They arise because some ion channels are voltage-gated, opening or closing when the membrane potential passes a certain level. Strong depolarizing stimulus Membrane potential (mV) (c) Action potential triggered by a depolarization that reaches the threshold Figure 48.10c 50 Action potential 0 50 Threshold Resting potential 100 0 1 2 3 4 5 6 Time (msec) Generation of Action Potentials An action potential can be considered as a series of stages Membrane potential (mV) 50 Figure 48.11 Action potential 3 0 2 4 50 1 5 Threshold 1 Resting potential 100 At resting potential Time 1. Most voltage-gated sodium (Na+) channels are closed; most of the voltage-gated potassium (K+) channels are also closed. When an action potential is generated 2. Voltage-gated Na+ channels open first and Na+ flows into the cell which is called the depolariztion. 3. During the rising phase, the threshold is crossed, and the membrane potential increases. 4. During the falling phase, voltage-gated Na+ channels become inactivated; voltage-gated K+ channels open, and K+ flows out of the cell. 5. During the undershoot, membrane permeability to K+ is at first higher than at rest, then voltage-gated K+ channels close and resting potential is restored. 國立交通大學生物科技學系 柯立偉老師 21 Key Na K Action potential OUTSIDE OF CELL Sodium channel 3 0 50 2 Depolarization 4 Falling phase of the action potential 50 Membrane potential (mV) 3 Rising phase of the action potential Threshold 2 1 4 5 1 Resting potential 100 Time Potassium channel Figure 48.11 INSIDE OF CELL Inactivation loop 1 Resting state 5 Undershoot Conduction of Action Potentials • At the site where the action potential is generated, usually the axon hillock, an electrical current depolarizes the neighboring region of the axon membrane. • Action potentials travel in only one direction: toward the synaptic terminals. • Inactivated Na+ channels behind the zone of depolarization prevent the action potential from traveling backwards. • The axons are insulated by a myelin sheath, which causes an action potential’s speed to increase. • Myelin sheaths are made by glia— oligodendrocytes in the CNS and Schwann cells in the PNS. 國立交通大學生物科技學系 柯立偉老師 22 Conduction of Action Potentials Figure 48.12 An action potential is generated as Na+ flows inward across the membrane at one location. Axon Plasma membrane The depolarization of the action Action Action potential potential 11 Na Na K K 22 Cytosol Action potential Na Na potential spreads to the neighboring region of the membrane, reinitiating the action potential there. To the left of this region, the membrane is repolarizing as K+ flows outward. The depolarization-repolarization K K K 3 process is repeated in the next region of the membrane. In this way, local currents of ions across the plasma membrane cause the action potential to be propagated along the length of the axon. Action potential Na K Conduction of Action Potentials Schwann cell Depolarized region (node of Ranvier) Cell body Axon Myelin sheath Figure 48.14 Saltatory conduction Action potentials are formed only at nodes of Ranvier, gaps in the myelin sheath where voltage-gated Na+ channels are found. Action potentials in myelinated axons jump between the nodes of Ranvier in a process called saltatory conduction 國立交通大學生物科技學系 柯立偉老師 23 ※ Neural Communication at Synapses ※ (CH48-4) Most synapses are chemical synapses. The presynaptic neuron synthesizes and packages the neurotransmitter in synaptic vesicles located in the synaptic terminal. The action potential causes the release of the neurotransmitter. The neurotransmitter diffuses across the synaptic cleft and is received by the postsynaptic cell. Presynaptic cell Postsynaptic cell Figure 48.15 A chemical synapse. 1 Axon Synaptic vesicle Postsynaptic containing neurotransmitter membrane Synaptic cleft Presynaptic membrane 3 K Ca2 2 Voltage-gated Ca2 channel Ligand-gated ion channels 4 Na Neural Communication at Synapses Direct synaptic transmission involves binding of neurotransmitters to ligand-gated ion channels in the postsynaptic cell. Neurotransmitter binding causes ion channels to open, allows specific ions to diffuse across the postsynaptic membrane and generating a postsynaptic potential. Presynaptic cell Postsynaptic cell Figure 48.15 A chemical synapse. 1 Axon Synaptic vesicle Postsynaptic containing neurotransmitter membrane Synaptic cleft Presynaptic membrane 3 K Ca2 2 Voltage-gated Ca2 channel 國立交通大學生物科技學系 柯立偉老師 Ligand-gated ion channels 4 Na 24 Generation of Postsynaptic Potentials Postsynaptic potentials fall into two categories • Excitatory postsynaptic potentials (興奮性突觸後電位EPSPs) are depolarizations that bring the membrane potential toward threshold. • Inhibitory postsynaptic potentials (抑制性突觸後電位IPSPs) are hyperpolarizations that move the membrane potential farther from threshold E1 E2 E1 E1 E2 Postsynaptic neuron Membrane potential (mV) Figure 48.17 Terminal branch of presynaptic neuron E1 E2 E2 Axon hillock I I I I 0 Action potential Threshold of axon of postsynaptic neuron Resting potential Action potential 70 E1 E1 (a) Subthreshold, no summation E1 E1 (b) Temporal summation 國立交通大學生物科技學系 柯立偉老師 E1 E2 (c) Spatial summation E1 I E1 I (d) Spatial summation of EPSP and IPSP 25