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Chapter 48

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Chapter 48

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  1. Chapter 48 Neurons, synapses, and signaling

  2. 주요 내용 • Neuron organization and structure reflect function in information center • Ion pumps and ion channels maintain the resting potential of a neuron (신경세포의 휴지막전위 유지에는 이온펌프와 채널이 필수) • 3. Action potentials are the signals conducted by axons (활동전위는 축색에 의해 전도되는 신호) • 4. Neurons communicate with other cells at synapses (신경세포간 정보교환 장소는 시냅스?)

  3. Sensory input Integration Sensor Motor output Effector Central nervoussystem (CNS) Peripheral nervoussystem (PNS) Figure 48.3 Information Processing • Nervous systems process information in three stages • 정보처리 3단계: 감각정보 입력 통합 운동정보 출력 • Sensory input, integration, and motor output

  4. Synapticterminals Neuron Structure (신경세포의 구조) • Most of a neuron’s organelles • Are located in the cell body Synaptic terminal (시냅스 말단 ) Dendrites (수상돌기) Cell body Synapse (시냅스) Nucleus Signal direction Axon hillock (축색둔덕) Presynaptic cell (시냅스전 신경세포) Postsynaptic cell (시냅스후 신경세포) Axon (축색) Myelin sheath 척추동물의 신경세포 구조 Figure 48.4

  5. Dendrites Axon Cell body (c) Motor neuron (b) Interneurons Figure 48.5a–c (a) Sensory neuron 신경세포의 다양한 얼굴 • Neurons have a wide variety of shapes • That reflect their input and output interactions 자극/신호전달

  6. Supporting Cells (Glia) : 49장에서 추가설명 • Glia (meaning “glue”)are supporting cells • That are essential for the structural integrity of the nervous system and for the normal functioning of neurons • Astrocytes in the CNS • Oligodendrocytes (in the CNS) • Schwann cells (in the PNS) • 세포구조는 Fig. 40.5에서 이미 설명

  7. 신경세포의 휴지막전위 유지에는 이온펌프와 채널이 필수 • Concept 48.2: Ion pumps and ion channels maintain the resting potential of a neuron • 막안팎의반대양상의 charge는막전위를 생성 • Across its plasma membrane, every cell has a voltage • Called a membrane potential • The membrane potential of a resting neuron is its resting potential (-60  -80 mV) • The inside of a cell is negative relative to the outside

  8. TECHNIQUE APPLICATION Electrophysiologists use intracellular recording to measure the membrane potential of neurons and other cells. A microelectrode is made from a glass capillary tube filled with an electrically conductive salt solution. One end of the tube tapers to an extremely fine tip (diameter < 1 µm). While looking through a microscope, the experimenter uses a micropositioner to insert the tip of the microelectrode into a cell. A voltage recorder (usually an oscilloscope or a computer-based system) measures the voltage between the microelectrode tip inside the cell and a reference electrode placed in the solution outside the cell. Microelectrode –70 mV Voltage recorder Referenceelectrode (세포바깥의 용액 속에 위치함) Figure 48.9 막전위의 측정:전기생리학 • The membrane potential of a cell can be measured

  9. Formation of the Resting Potential (휴지막전위) • The resting potential is the membrane potential of a neuron that is not transmitting signals • Potassium ions and sodium ions play an essential role in the formation of the resting potential • The two ions gradients are maintained by sodium-potassium pumps  the resulting voltage difference is only a few mVs (see Table 48.1) • Why is there a voltage difference of 60-80 mV in a resting neuron? -Ion movement via ion channels having selective permeability (K+ and Na+)

  10. Inner chamber Outer chamber Inner chamber Outer chamber –90mV +62 mV + – + – 150 mMNaCl 150 mMKCL 5 mMKCL 15 mMNaCl Cl– + – + – K+ Na+ Cl– + – Potassiumchannel Sodium channel + – Artificialmembrane (b) Membrane selectively permeable to Na+ Figure 48.8a, b (a) Membrane selectively permeable to K+ Modeling the resting potential (휴지막 전위) • By modeling a mammalian neuron with an artificial membrane • We can gain a better understanding of the resting potential of a neuron

  11. The magnitude of the membrane voltage at equilibrium for a particular ion is called that ion’s equilibrium potential Eion=62mV(log[ion]outside/[ion]in) : Nernst equation EK = 62mV (log 5/150) = -90 mV ENa = 62mV (log 150/5) = +62 mV

  12. 휴지막전위 (-60 to -80mV)의 의미: • The resting potential is much closer to EK than to ENa : there are many open potassium channels but only a small number of open sodium channels • 막의 이온투과성이 변하면 막전위는 휴지막전위 상태에서 값이 변할 수 있음 (즉, 휴지막전위 상태에서는 세포막의 K+에 대한 이온투과성이 높지만 만약 Na+에 대한 투과성이 높아지면 막전위는 ENa (+62mV)쪽으로 이동하게 됨)

  13. 활동전위는 축색에 의해 전도되는 신호 • Concept 48.3: Action potentials are the signals conducted by axons • If a cell has gated ion channels • Its membrane potential may change in response to stimuli that open or close those channels • 세포가 gated ion channel을 가지면 이온채널의 개폐를 조절하는 자극에 반응하여 특정이온에 대한 막의 투과성에 영향을 미쳐 막전위도 변하게 됨

  14. Hyperpolarization and depolarization • Hyperpolarization: Opening the potassium channels increases the membrane’s permeability to K+ making the inside of the membrane more negative  Shifting the membrane potential toward EK (-90mV) • Depolarization: Opening some other types of ion channels causes opposite effects, making the inside of the membrane less negative (Na+ ion channels)  Shifting the membrane potential toward ENa (+62mV)

  15. Stimuli +50 0 Membrane potential (mV) Threshold (-55) –50 Restingpotential Hyperpolarizations –100 0 1 2 3 4 5 Time (msec) (a) Graded hyperpolarizations produced by two stimuli that increase membrane permeability to K+. The larger stimulus producesa larger hyperpolarization. Figure 48.10a 자극에 의한 과분극현상 • Some stimuli trigger a graded hyperpolarization (과분극) • An increase in the magnitude of the membrane potential • K+이온에 대한 막투과성을 증가시키는 자극에 의해 원래의 막전위 값이 증가하는 현상

  16. Stimuli +50 0 Membrane potential (mV) –50 Threshold Restingpotential Depolarizations –100 0 1 2 3 4 5 Time (msec) (b) Graded depolarizations produced by two stimuli that increase membrane permeability to Na+.The larger stimulus produces alarger depolarization. Figure 48.10b 탈분극현상: Na+이온에 대한 막투과성을 증가시키는 자극에 의해 막전위가 역전되는 현상 • Other stimuli trigger a graded depolarization • A reduction in the magnitude of the membrane potential

  17. 탈분극과 과분극 모두 자극의 크기에 영향을 받는다 • Hyperpolarization and depolarization • Are both called graded potentials because the magnitude of the change in membrane potential varies with the strength of the stimulus

  18. Production of Action Potentials (활동전위의 생성) • In most neurons, depolarizations • Are graded only up to a certain membrane voltage, called the threshold (역치) • A stimulus strong enough to produce a depolarization that reaches the threshold • Triggers a different type of response, called an action potential • 역위에 도달할 수 있는 탈분극을 만들 수 있는 충분히 강한 자극이 유도하는 새로운 반응을 활동전위라 함 • 활동전위는 축색을 따라 정보를 전달하는 새로운 종류의 신호라 할 수 있음 Figure 48.10c Stronger depolarizing stimulus +50 Actionpotential 0 Membrane potential (mV) Threshold –50 Restingpotential –100 0123456 Time (msec) (c) Action potential triggered by a depolarization that reaches the threshold.

  19. 활동전위 생성의 주요 조절인자 (see fig. 48.11)  Resting state: Both voltage-gated Na+ channels and voltage-gated K+ channels: Are involved in the production of an action potential  Depolarization: When a stimulus depolarizes the membrane • Na+ channels open, allowing Na+ to diffuse into the cell  Rising phase of action potential: Na+ influx makes the inside of the membrane positive •  Falling phase of the action potential: As the action potential subsides (falls) • Mostsodium channels become inactivated. Most K+ channels open, and K+ flows out of the cell • Undershoot: Some potassium channels are still open. Returns to its resting state

  20. Conduction of Action Potentials • An action potential can travel long distances • By regenerating itself along the axon (활동전위는 축색을 따라 재생성되며 긴 거리를 이동함) • At the site where the action potential is generated, usually the axon hillock(축색둔덕) • An electrical current depolarizes the neighboring region of the axon membrane (축생생성부위는 보통 축색둔덕이라하며 전류에 의해 축색막 주변의 탈분극을 유도함)

  21. – + + + + + + – – + + + + + + – – + + + + + + 활동전위의 전도 과정 Figure 48.12 Axon Actionpotential  나트륨이온의 유입으로 활동전위 생성 An action potential is generated as Na+ flows inward across the membrane at one location. 1 + + – – – – – – Na+ – – – – – – + + • 활동전위의 탈분극은 이웃으로 퍼져나가며, 그곳에서 활동전위는 재생성됨. 이 부위의 왼쪽에서는 포타슘이온의 방출로 재분극이 유도됨. Actionpotential 2 The depolarization of the action potential spreads to the neighboring region of the membrane, re-initiating the action potential there. To the left of this region, the membrane is repolarizing as K+ flows outward. K+ – – + – – – + – Na+ – – – – – – + + – – + + + + + + K+ Actionpotential The depolarization-repolarization process isrepeated 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. 3  탈분극과 재분극 과정이 반복되며 세포막 안팎의 국부적인 전류형성으로 활동전위는 축색을 따라 이동하게 됨 K+ – – – – + + + + – + + + + – – – Na+ – – – + + – + + – + + – – – + + K+

  22. Conduction Speed (전도속도) • The speed of an action potential • Increases with the diameter of an axon • 전기저항은 전도체(전선)의 직경에 반비례하므로 전선에 해당하는 축색의 직경이 클수록 활동전위의 전도속도는 증가함 • 절연체의 존재는 전도속도를 증가시킴. 신경세포에서 절연체에 해당하는 myelin sheath가 그 역할을 함 • In vertebrates, axons are myelinated • Also causing the speed of an action potential to increase

  23. Node of Ranvier Layers of myelin Axon Schwann cell Schwann cell Nodes of Ranvier Nucleus of Schwann cell Axon Myelin sheath 0.1 µm Figure 48.13 Supporting Cells (Glia) • Oligodendrocytes (in the CNS) and Schwann cells (in the PNS): 미엘린 시스를 형성 • Are glia that form the myelin sheaths around the axons of many vertebrate neurons

  24. Schwann cell Depolarized region(node of Ranvier) Myelin sheath – –– – – – ++ + Cell body ++ ++ + Axon – – – ++ + – – – Figure 48.14 미엘린으로 둘러싸인 축색의 활동전위는 랑비에르 결절 사이를 건너뛰는 도약전도가 가능함 (축지법) • Action potentials in myelinated axons • Jump between the nodes of Ranvier in a process called saltatory conduction (도약전도)

  25. 신경세포간 정보교환 장소는 시냅스 • Concept 48.4: Neurons communicate with other cells at synapses • In an electrical synapse • Electrical current flows directly from one cell to another via a gap junction • The vast majority of synapses • Are chemical synapses which involve the release of a chemical neurotransmitter by the presynaptic neuron

  26. When an action potential reaches a terminal • The final result is the release of neurotransmitters into the synaptic cleft Postsynaptic cell Presynapticcell Na+ 5 Neuro-transmitter Synaptic vesiclescontainingneurotransmitter K+ Action potential arrives Presynapticmembrane Postsynaptic membrane Ligand-gatedion channel Voltage-gatedCa2+ channel Ca2+ 1 4 Postsynaptic membrane 6 2 3 Synaptic cleft Ligand-gatedion channels Figure 48.15

  27. 화학적 시냅스에서의 활동전위 전도 활동전위가 시냅스말단의 세포막을 탈분극시킴 Voltage-gated Ca++ channel가 열리고 칼슘이온이 유입됨 칼슘이온농도의 증가로 시냅스의 소낭이 시냅스전 세포막과 융합됨 소낭에서 신경전달물질이 시냅스 틈새로 방출됨 신경전달물질은 시냅스후 세포막의 ligand-gated ion channel의 수용체 부위와 결합함으로써 이온의 유입 신경전달물질이 수용체에서 방출되고 채널은 폐쇄됨. 신경전달물질은 다른 세포에 흡수되거나 효소에 의해 분해됨으로서 시냅스 틈에서 제거됨

  28. Postsynapticneuron Synapticterminalof presynapticneurons 5 µm Figure 48.16 화학적 시냅스의 시냅스전 뉴런: 신경전달물질 분비 • In a chemical synapse, a presynaptic neuron • Releases chemical neurotransmitters, which are stored in the synaptic terminal

  29. (1) Generation of postsynaptic potentials : directway • The process of direct synaptic transmission • Involves the binding of neurotransmitters to ligand-gated ion channels (신경전달물질과 ligand-gated ion channel의 결합) • Neurotransmitter binding • Causes the ion channels to open, generating a postsynaptic potential (시냅스후 활동전위의 생성) • Postsynaptic potentials fall into two categories • Excitatory postsynaptic potentials (EPSPs): Na+과 K+의 출입으로 막전위를 역치에 도달하게 하는 탈분극 유도 • Inhibitory postsynaptic potentials (IPSPs): K+이온의 방출로 유도되는 신경전달물질의 작용으로 과분극 초래하여 막전위가 역치로부터 더 멀어지게 함

  30. Terminal branch of presynaptic neuron Postsynaptic neuron E1 Threshold of axon of postsynaptic neuron 0 Restingpotential Membrane potential (mV) –70 E1 E1 (a) Subthreshold, nosummation Figure 48.17a Summation of Postsynaptic Potentials • Since most neurons have many synapses on their dendrites and cell body • A single EPSP is usually too small to trigger an action potential in a postsynaptic neuron

  31. E1 Axonhillock Actionpotential E1 E1 (b) Temporal summation Figure 48.17b 서로 다른 두 개의 EPSP의 시간합 효과 • If two EPSPs are produced in rapid succession • An effect called temporal summation (시간합) occurs 하나의 시냅스에서 두 개의 EPSP가 빠르게 연속적으로 일어나면 동일한 시앱스후 뉴런에 시간합 효과를 통해 활동전위 생성 가능함

  32. E1 E2 Actionpotential E1 + E2 (c) Spatial summation Figure 48.17c 서로 다른 두 개의 EPSP의 공간합 효과 • In spatial summation • EPSPs produced nearly simultaneously by different synapses on the same postsynaptic neuron add together 서로 다른 시냅스에서 거의 동시에 생성된 두 개의 EPSP가 동일한 시냅스후 뉴런에 도달하면 공간합 효과를 유도하여 활동전위 생성 가능함

  33. E1 I E1 I E1 + I (d) Spatial summationof EPSP and IPSP Figure 48.17d IPSP에 의한 EPSP 효과의 억제 • Through summation • An IPSP can counter the effect of an EPSP

  34. (2) Modulated signaling at synapses: Indirect way • In indirect synaptic transmission • A neurotransmitter binds to a metatropic receptor that is not part of an ion channel • This binding activates a signal transduction pathway • Involving a second messenger in the postsynaptic cell, producing a slowly developing but long-lasting effect 간접 시냅스 전도는 이온채널이 아닌 수용체에 신경전달물질이 결합하여 시냅스후 뉴런에 cAMP와 같은 2nd messenger을 유도하여 느리지만 효과가 오래 지속되는 효과를 나타냄

  35. Table 48.2 주요 신경전달물질:각 신경세포마다 동일한 물질에 대한 반응은 다르다 48.2 From Tyrosine From Trp

  36. Acetylcholine • Acetylcholine • Is one of the most common neurotransmitters in both vertebrates and invertebrates • Can be inhibitory or excitatory • Ac Receptor at neuromuscular junction in PNS or CNS : this ionotropic Rc binds nicotine  act as psychological stimulant • Metabotropic Ac receptor at CNS and heart  reduction of heart pumps • ex: sarin gas inhibits acetylcholiesterase • Botulinum toxin inhibits release of acetylcholine

  37. Biogenic Amines • Biogenic amines : derived from amino acids • Include epinephrine, norepinephrine (adrenaline), dopamine, and serotonin • Are active in the CNS and PNS • 잠, 무드, 주의력, 학습 등에 영향을 줌 파킨슨병: 뇌의 도파민 부족 각성제 (LSD)는 도파민과 세레토닌의 수용체에 결합 우울증 치료제(Prozac): 뇌 속의 노르에피네피린 또는 세레토닌의 농도를 증가시킴

  38. Gases • Gases such as nitric oxide and carbon monoxide • Are local regulators in the PNS • CO: Heme oxygenase에 의해 합성, 뇌에서는 시상하부 호르몬을 조절하며 말초신경계에서는 억제성 신경전달물질로 작용하여 장의 평활근을 과분극시킴 • NO: 남성의 성기발기 유도 (NO는 성기의 모세혈관 근육을 이완시켜 혈액공급 증대), 비아그라는 이와같은 NO의 근육이완작용을 느리게하는 효소를 저해하는 효과를 나타냄