Transcript 시냅스후 활동전위의 생성

Chapter 48
Neurons, synapses, and
signaling
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
주요 내용
1. Neuron organization and structure reflect function in
information center
2. 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?)
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Information Processing
• Nervous systems process information in three
stages
• 정보처리 3단계: 감각정보 입력 통합 운동정보 출력
– Sensory input, integration, and motor output
Sensory input
Integration
Sensor
Motor output
Figure 48.3
Effector
Peripheral nervous
system (PNS)
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Central nervous
system (CNS)
Neuron Structure (신경세포의 구조)
• Most of a neuron’s organelles
– Are located in the cell body
Dendrites (수상돌기)
Synaptic terminal
(시냅스 말단 )
Cell body
Synapse
(시냅스)
Nucleus
Axon hillock
(축색둔덕)
Signal
direction
Presynaptic cell
(시냅스전 신경세포)
Postsynaptic cell
(시냅스후 신경세포)
Axon
(축색) Myelin sheath
Figure 48.4
척추동물의 신경세포 구조
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Synaptic
terminals
신경세포의 다양한 얼굴
• Neurons have a wide variety of shapes
– That reflect their input and output interactions
Dendrites
Axon
자극/신호전달
Cell
body
Figure 48.5a–c (a) Sensory neuron
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(b) Interneurons
(c) Motor neuron
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
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
신경세포의 휴지막전위 유지에는 이온펌프와 채널이 필수
• Concept 48.2: Ion pumps and ion channels
maintain the resting potential of a neuron
• 막안팎의 반대양상의 charge는 막전위를 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
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막전위의 측정:전기생리학
• The membrane potential of a cell can be
measured
APPLICATION Electrophysiologists use intracellular recording to measure the membrane potential of
neurons and other cells.
TECHNIQUE
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
Figure 48.9
Reference
electrode (세포바깥의 용액 속에 위치함)
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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 sodiumpotassium 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+)
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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
Outer
chamber
–90mV
+62 mV
+
–
150 mM
KCL
5 mM
KCL
+
Cl–
Artificial
membrane
–
+
–
Figure 48.8a, b (a) Membrane selectively permeable to K+
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Outer
chamber
–
150 mM
NaCl
15 mM
NaCl
Cl–
K+
Potassium
channel
Inner
chamber
+
Inner
chamber
+
–
Sodium +
channel
–
Na+
(b) Membrane selectively permeable to Na+
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
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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)
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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
특정 이온에 대한 막의 투과성에 영향을 미쳐
막전위도 변하게 됨
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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)
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자극에 의한 과분극현상
• Some stimuli trigger a
graded hyperpolarization
(과분극)
Stimuli
– An increase in the
magnitude of the
membrane potential
– K+이온에 대한 막투과성을
증가시키는 자극에 의해
원래의 막전위 값이
증가하는 현상
Membrane potential (mV)
+50
0
–50 Threshold (-55)
Resting
potential 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 produces
Figure 48.10a a larger hyperpolarization.
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탈분극현상: Na+이온에 대한 막투과성을 증가시키는
자극에 의해 막전위가 역전되는 현상
– A reduction in the
magnitude of the
membrane potential
Stimuli
+50
Membrane potential (mV)
• Other stimuli trigger a
graded depolarization
0
–50
Threshold
Resting Depolarizations
potential
–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 a
Figure 48.10b larger depolarization.
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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
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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
Figure 48.10c
depolarization that reaches the threshold
Stronger depolarizing stimulus
–
–
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
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Membrane potential (mV)
– Triggers a different type of response,
called an action potential
+50
Action
potential
0
–50
Threshold
Resting
potential
–100
0 1 2 3 4 5 6
Time (msec)
(c) Action potential triggered by a
depolarization that reaches the
threshold.
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)
– Most sodium 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
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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)
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활동전위의 전도 과정
Figure 48.12
Axon
 나트륨이온의
유입으로 활동전위
생성
Action
potential
–
–
+
+
+
+
+
+
+
–
–
–
–
–
–
+
+
–
–
–
–
–
–
–
–
+
+
+
+
+
+
+
Na+
활동전위의 탈분극은
이웃으로 퍼져나가며,
그곳에서 활동전위는
재생성됨.
이 부위의 왼쪽에서는
포타슘이온의 방출로
재분극이 유도됨.
 탈분극과 재분극
과정이 반복되며 세포막
안팎의 국부적인
전류형성으로 활동전위는
축색을 따라 이동하게 됨
Action
potential
K+
+
+
–
–
–
+
–
–
+
+
–
+
+
+
An action potential is generated
as Na+ flows inward across the
membrane at one location.
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.
3
The depolarization-repolarization 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.
+
+
–
–
–
–
+
+
–
–
–
–
–
–
+
+
+
+
Na+
1
K+
Action
potential
K+
+
+
+
–
–
–
–
–
–
+
–
+
+
Na+
+ +
+
–
–
–
–
–
+
+
+
+
+
+
–
–
–
–
+
K+
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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
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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
Node of Ranvier
Layers of myelin
Axon
Schwann
cell
Axon
Myelin sheath
Nodes of
Ranvier
Schwann
cell
Nucleus of
Schwann cell
Figure 48.13
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0.1 µm
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)
Schwann cell
Depolarized region
(node of Ranvier)
Myelin
sheath
––
–
Cell body
Figure 48.14
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+
++
+
++
–––
––
–
+
+
+
++
Axon
––
–
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
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• When an action potential reaches a terminal
–
The final result is the release of neurotransmitters into the
synaptic cleft
Postsynaptic cell
Presynaptic
cell
Synaptic vesicles
containing
neurotransmitter
Action
potential
arrives
5
Presynaptic
membrane
Neurotransmitter
Postsynaptic
membrane
Ligandgated
ion channel
Voltage-gated
Ca2+ channel
1
Na+
K+
Ca2+
4
2
Synaptic cleft
Postsynaptic
membrane
6
3
Ligand-gated
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Cummings
channels
Figure 48.15
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
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화학적 시냅스의 시냅스전 뉴런: 신경전달물질 분비
• In a chemical synapse, a presynaptic neuron
– Releases chemical neurotransmitters, which
are stored in the synaptic terminal
Postsynaptic
neuron
5 µm
Synaptic
terminal
of presynaptic
neurons
Figure 48.16
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(1) Generation of postsynaptic potentials : direct way
• The process of direct synaptic transmission
– Involves the binding of neurotransmitters to ligandgated 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
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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
Terminal branch of
presynaptic neuron
Membrane potential (mV)
Postsynaptic
neuron
E1
Threshold of axon of
postsynaptic neuron
0
Resting
potential
–70
E1
Figure 48.17a
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E1
(a) Subthreshold, no
summation
서로 다른 두 개의 EPSP의 시간합 효과
• If two EPSPs are produced in rapid succession
– An effect called temporal summation (시간합)
occurs
E
1
하나의 시냅스에서 두 개의
EPSP가 빠르게 연속적으로
일어나면 동일한 시앱스후
뉴런에 시간합 효과를 통해
활동전위 생성 가능함
Axon
hillock
Action
potential
E1
E1
(b) Temporal summation
Figure 48.17b
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서로 다른 두 개의 EPSP의 공간합 효과
• In spatial summation
– EPSPs produced nearly simultaneously by different
synapses on the same postsynaptic neuron add
together
E
1
E2
서로 다른 시냅스에서 거의
동시에 생성된 두 개의 EPSP가
동일한 시냅스후 뉴런에
도달하면 공간합 효과를
유도하여 활동전위 생성 가능함
Action
potential
E1 + E2
(c) Spatial summation
Figure 48.17c
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IPSP에 의한 EPSP 효과의 억제
• Through summation
– An IPSP can counter the effect of an EPSP
E1
I
E1
Figure 48.17d
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I
(d) Spatial summation
of EPSP and IPSP
E1 + I
(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
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주요 신경전달물질: 각 신경세포마다 동일한 물질에 대한 반응은 다르다
48.2
From Tyrosine
From Trp
Table 48.2
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Acetylcholine
• Acetylcholine
– Is one of the most common neurotransmitters
in both vertebrates and invertebrates
– Can be inhibitory or excitatory
(1) Ac Receptor at neuromuscular junction in PNS or
CNS : this ionotropic Rc binds nicotine  act as
psychological stimulant
(2) Metabotropic Ac receptor at CNS and heart 
reduction of heart pumps
ex: sarin gas inhibits acetylcholiesterase
Botulinum toxin inhibits release of acetylcholine
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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
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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
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings