Name: how neurons signal at synapses
Uploaded: 2019-08-01T08:26:57.000Z
Duration: 2 min 47 s
Channel: JoVE

K12 Standards

Alabama Course of Study Science

9-12

Human Anatomy and Physiology

from-molecules-to-organisms-structures-and-processes

From Molecules to Organisms: Structures and Processes

9-12.HA.1.5.c

The Synapse

神経系の細胞は、基本的な身体機能から感覚刺激まで、常に情報を送受信しています。ニューロンは、活動電位と呼ばれる 電気信号と通信します。これらの活動電位は細胞体で発生し、軸索に沿って軸索末端に移動し、そこで次の細胞に渡されます。2つのニューロンが出会うポイントはシナプスと呼ばれます。電気シナプスは、ギャップ結合を使用して 細胞間の直接通信を可能にし、多くの場合、急速な活動の調整に関与しています。ただし、ほとんどのシナプスは、シナプス間隙、シナプス前細胞として知られる 信号を送信するニューロンと シナプス後細胞と呼ばれるシナプス後細胞と呼ばれる 物理的空間を含む化学シナプスです。活動電位はシナプス間隙を通過できないため、ニューロンはシナプスで 電気信号を化学信号に変換します。これは、神経伝達物質として知られる 分子の放出によって達成されます。多くの神経伝達物質があり、それぞれが興奮性グルタミン酸 および抑制性GABAを含むシナプス後ニューロンに 効果をもたらします。活動電位がシナプス前終末に達すると、シナプス前膜の 電位依存性カルシウムチャネルが開きます。カルシウムは細胞に突入し、小胞と膜の融合と 神経伝達物質のシナプス間隙への放出を 引き起こします。これらは、シナプス後細胞の受容体に 結合することができます。神経伝達物質の受容体への結合により、シナプス後膜電位が 増加または減少し、シナプス後細胞で活動電位が開始されるポテンシャルが 変化する場合があります。ニューロンは何千ものシナプスを持ち、多くの細胞から情報を受け取ることができます。これらの信号は、細胞がメッセージを 転送するかどうかを決定する シナプス後ニューロンの 細胞体で結合されます。シナプス後受容体に短時間結合した後、神経伝達物質は拡散、分解，再利用されます。シナプス前細胞の再取り込みタンパク質は、多くの場合、神経伝達物質のリサイクルに関与しています。シナプスを横切る神経伝達物質の 放出と結合により、活動電位の電気信号が 隣接するニューロンに伝達されます。この多段階プロセスは、ニューロン機能にとって重要です。

Xu-Friedman, Matthew A. "Measuring the Basic Physiological Properties of Synapses." Cold Spring Harbor Protocols 2017, no. 1 (2017年1月1日): pdb.top089680.<a href="https://doi.org/10.1101/pdb.top089680">[ソース]</a>

Sheng, Morgan, and Eunjoon Kim. "The Postsynaptic Organization of Synapses." Cold Spring Harbor Perspectives in Biology 3, no. 12 (2011年12月1日): a005678.<a href="https://doi.org/10.1101/cshperspect.a005678">[ソース]</a>

シナプス

神経細胞は、自分の電気信号を他の神経細胞に伝えることで、お互いにコミュニケーションをとっています。シナプスとは、2つのニューロンが出会って信号を交換する場所のことです。シナプスでは、信号を送る側の神経細胞をシナプス前細胞、メッセージを受け取る側の神経細胞をシナプス後細胞と呼びます。なお、ほとんどの神経細胞は、情報の送信と受信の両方を行うため、シナプス前細胞とシナプス後細胞の両方を持つことができます。 
 
 電気的シナプスは、シナプス前細胞とシナプス後細胞がギャップ結合と呼ばれるタンパク質によって物理的に結合しているシナプスの一種で、電気信号がシナプス後細胞に直接伝達されます。このシナプスの特徴は、電気信号の伝達が非常に速く、時には数ミリ秒という速さで伝達され、エネルギーを必要としないことです。これは、ザリガニが捕食者の存在を感じて運動反応を起こすような、逃避行動に関わる回路によく用いられます。
 
 これに対して、化学的なシナプスでの伝達は段階的に行われます。活動電位が軸索末端に到達すると、電位依存性のカルシウムチャネルが開き、カルシウムイオンが入り込みます。これらのイオンは、神経伝達物質を含む小胞が細胞膜と融合するきっかけとなり、神経伝達物質をシナプス間隙と呼ばれる2つのニューロンの間の小さな空間に放出します。これらの神経伝達物質（グルタミン酸、GABA、ドーパミン、セロトニンなど）は、シナプス後の細胞膜にある特定の受容体に結合できます。神経伝達物質は受容体に結合した後、シナプス間隙からリサイクルされたり、分解されたり、拡散したりします。 
 
 人間の脳では化学的なシナプスが主流であり、神経伝達物質の放出に伴う遅延があるため、電気的なシナプスに比べて有利です。まず、少数または多数の小胞が放出され、シナプス後の反応が多様になります。次に、異なる受容体との結合により、シナプス後細胞の膜電位が上昇または低下する可能性があります。さらに、シナプス間隙での神経伝達物質の利用可能性は、リサイクルと拡散によって調節されます。このようにして、化学的シナプスは、高度に制御され、微調整されたニューロンシグナル伝達を実現しています。

ニューロンは、電気信号を他のニューロンに渡すことにより、互いに通信します。シナプスは、2つのニューロンが交換するために出会う場所です...

Education

JoVE Core

Biology

生物学

Human Biology

ヒト生物学

Nervous System

神経系

KEY TERMS AND CONCEPTS

主要用語と概念

how neurons signal at synapses

Neurons communicate through synapses, the points where two neurons meet to pass on signals. At a synapse, the sending neuron is the presynaptic cell, and the receiving neuron is the postsynaptic cell. Most neurons can serve in both roles because they send and receive information.

Electrical synapses move signals directly between cells. The presynaptic and postsynaptic cells are linked by gap junctions, which are proteins that physically connect them. This type of synapse can pass electrical signals extremely quickly, sometimes in a fraction of a millisecond, and it does not require energy input. It is useful in escape circuits, such as the crayfish pathway that connects the detection of a predator to the motor response.

Chemical synapses work in a step-by-step way. When an action potential reaches the end of the axon terminal, voltage-gated calcium channels open and calcium ions enter the cell. These ions trigger vesicles filled with neurotransmitters to fuse with the cell membrane and release their contents into the synaptic cleft, the small space between neurons.

The released neurotransmitters, including glutamate, GABA, dopamine, and serotonin, bind to specific receptors on the postsynaptic membrane. After binding, they may be recycled, broken down, or diffuse away from the synaptic cleft. Chemical synapses are the main type in the human brain. Their delay allows more control, since different numbers of vesicles can be released and different receptors can produce either an increase or decrease in membrane potential. This regulation helps make neuronal signaling highly fine-tuned.

How Neurons Signal at Synapses

what is a nervous system?

Nervous System Parts and Control

The nervous system is a network of specialized cells that keeps the body working and helps it respond to the world around it. It controls essential functions such as heart rate and breathing. It also supports movement that helps an organism escape danger. In vertebrates, the nervous system has two major parts: the central nervous system, or CNS, and the peripheral nervous system, or PNS. The CNS includes the brain, spinal cord, and retina, which is the sensory tissue of the visual system. The...

the parasympathetic nervous system

Rest and Digest: Parasympathetic Control

The parasympathetic nervous system helps the body stay calm and return to a rested state. It is one of the two major divisions of the autonomic nervous system, which controls many unconscious functions such as heart rate and digestion. Its neurons are found in the brain and the peripheral nervous system, and they send axons to muscles, organs, and glands. This system is often called the “rest and digest” system because it supports body processes that restore homeostasis. It is most active...

the sympathetic nervous system

Sympathetic Stress Response and Body Changes

The sympathetic nervous system helps the body respond to stress and danger. It is one of the two main divisions of the autonomic nervous system. When it turns on, it prepares the body for action and puts lower-priority functions, such as digestion, on hold. This response is often called the fight-or-flight system. A surprise exam can trigger it, and students may notice a tight stomach, a dry mouth, and a fast heartbeat. In a real threat, the system shifts blood away from the digestive system...

the blood-brain barrier

How the Blood-Brain Barrier Works

The blood-brain barrier is a specialized system of blood vessels that helps control what enters the brain. It delivers nutrients from the blood while tightly regulating ions, molecules, pathogens, and other substances. This semipermeable barrier protects the brain and also makes it harder to deliver some therapies. The blood-brain barrier includes several cellular parts, especially endothelial cells and astrocytes. These cells share a common basement membrane and regulate movement between the...

neuron structure

How Neurons Send Signals

Neurons send signals through a clear set of structures that let them receive, process, and pass on information. They are the main cells of the nervous system and use electrochemical signals to communicate. Neurons also talk to other cells through neurotransmitters at junctions called synapses. Most neurons share three main parts: a cell body, also called the soma, dendrites, and an axon. The soma holds the nucleus and other organelles needed for cell function. Dendrites usually receive...

glial cells

Glial Cells and Nervous System Support

Glial cells support the nervous system and work alongside neurons. They are one of the two main cell types in the nervous system. Unlike neurons, glia do not send electrical signals, but they help with nearly every other part of nervous system function. In humans, glial cells are about as numerous as neurons in the brain. In the central nervous system, glia include astrocytes, oligodendrocytes, microglia, and ependymal cells. Astrocytes are the most common glial cells. They form organized,...

action potentials

How Nerve Signals Travel in Axons

Neurons send signals through action potentials, the rapid electrical changes that move along the axon. These signals lead to neurotransmitter release at axon terminals, which passes information through the nervous system. An action potential is an all-or-none change in membrane potential, the voltage across a cell membrane. A neuron usually has a resting membrane potential of about -70 millivolts. When it receives signals from neurotransmitters or sensory input, the membrane can become more...

the resting membrane potential

How Neurons Keep a Negative Resting Charge

Neurons keep a negative resting charge across their membrane. This electrical difference, called the membrane potential, comes from how ions move and how the membrane lets them pass. In a resting neuron, the inside is typically around -70 millivolts and is more negative than the outside, so the cell is polarized. Two main factors create this resting state. First, the membrane is selectively permeable, which means most ions and molecules cannot cross the lipid bilayer without help from ion...

long-term potentiation

Synaptic Strengthening in Learning and Memory

Long-term potentiation, or LTP, is a form of synaptic strengthening in the brain. It changes the strength of chemical synapses over time between pre- and postsynaptic neurons. LTP works against long-term depression, or LTD, which weakens synapses. Together, LTP and LTD are major mechanisms behind learning and memory. LTP can happen when a presynaptic neuron fires again and again and keeps stimulating a postsynaptic neuron. This is called Hebbian LTP, based on Donald Hebb’s idea that neurons...

long-term depression

Synaptic Pruning in Long-term Depression

Long-term depression, or LTD, is a form of synaptic plasticity that weakens chemical synapses over time. It acts between presynaptic and postsynaptic neurons. LTD works in opposition to long-term potentiation, or LTP, which strengthens synapses. Together, LTD and LTP are two of the main mechanisms behind learning and memory. LTD helps the brain avoid staying locked in a fully strengthened state. If synapses were always maximally strengthened, the brain would become less efficient and it would...

the synapse

Neurons communicate through synapses, the points where two neurons meet to pass on signals. At a synapse, the sending neuron is the presynaptic cell, and the receiving neuron is the postsynaptic cell. Most neurons can serve in both roles because they send and receive information. Electrical synapses move signals directly between cells. The presynaptic and postsynaptic cells are linked by gap junctions, which are proteins that physically connect them. This type of synapse can pass electrical...

key terms and concepts

Learn how neurons signal through electrical and chemical synapses, from gap junctions and calcium entry to neurotransmitters and receptors.

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How Neurons Signal at Synapses

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