Name: how neurons send signals
Uploaded: 2025-10-23T11:49:29.000Z
Duration: 1 min 31 s
Channel: JoVE

ニューロンとは神経系の細胞で 電気信号を送ります。ニューロンにはさまざまな形と大きさがありますが 共通の機能を持っています。すべてのニューロンには細胞体(Soma)があり 核があります。また、ほとんどのニューロンには樹状突起があり アクソンが細胞体から出ています。樹状突起は通常、多くの枝を持ち シナプスと呼ばれる接合部位で 他のニューロンからの信号を受け取ります。これに対して、アクソンは ニューロンと他の細胞に信号を送ります。細胞体とアクソンをつなぐ軸索小丘は 神経系の基本形態である電気信号の 活動電位を引き起こします。アクソンは脂肪質のミエリン鞘を覆っており ミエリン鞘は、電気信号が送られる際に 信号を保つ断熱の役割を持つ グリアと呼ばれる細胞に守られています。ランビエ絞輪とはミエリン鞘の隙間であり アクソンを通る活動電位が繰り返し起こる部位です。アクソンの端はターミナルで シナプス小胞があり 神経伝達物質分子で満たされています。活動電位がターミナルに到達すると 神経伝達物質が細胞とシナプスの間のスペースである シナプス間隙に放出されます。チャネルの種類に応じて 神経伝達物質は次の細胞への 信号送信を助けます。

「ヒトの星状細胞:健康な脳の構造と機能」 脳の構造と機能 222, no. 5 (2017): 2017–29.[<a href="https://doi.org/10.1007/s00429-017-1383-5" target="__blank">ソース</a>]

ニューロンの構造

<h4>概要</h4>
 
 ニューロンは、電気化学的な信号を生成・伝達する神経系の主要な細胞です。ニューロンは、主にシナプスと呼ばれる特定の結合部で神経伝達物質を用いて相互にコミュニケーションをとります。ニューロンは、その機能に応じてさまざまな形をしていますが、多くの場合、細胞体から伸びる軸索と樹状突起という3つの主要な構造を共有しています。 
 
 <h4>ニューロンの構造と機能</h4>
 
 神経細胞の細胞体（ソーマ）には、核や細胞機能に必要な小器官が存在します。細胞体からは、信号の送受信に特化した細い構造物が伸びています。通常、樹状突起は信号を受け取り、軸索は他の神経細胞や筋肉細胞などの他の細胞に信号を伝えます。ニューロンが他の細胞と接続する点をシナプスと呼びます。
 
 神経細胞が入力を受けるのは、主にシナプス後末端です。シナプス後末端は、樹状突起から突き出たスパインと呼ばれる小さな突起に多く存在します。神経伝達物質やその他の化学的シグナルの受容体があります。樹状突起は大きく分岐していることが多く、何万もの入力を受ける神経細胞もあります。神経細胞は樹状突起で信号を受け取ることが多いですが、細胞体など他の場所にもシナプスを持つことがあります。
 
 シナプスで受信した信号は、樹状突起を伝って体細胞に到達し、体細胞は信号を処理して、メッセージを送信すべきかどうかを判断します。活動電位は、ニューロンが生成する主要な電気信号です。活動電位は、情報を次の細胞に伝え、体細胞と軸索の接合部である軸索丘で最初に発生します。
 
 軸索の長さは様々だが、非常に長いものもあり、例えば、脊髄から足まで伸びているものもあります。長い軸索は通常、軸索を絶縁する脂肪質のミエリン鞘に包まれており、電気信号の維持に役立っています。ミエリン鞘は、神経系の細胞の一種であるグリアによって作られます。ミエリン化された軸索では、活動電位はランヴィエの節（ミエリンの隙間）ごとに再生され、軸索の末端であるシナプス前末端に到達するまで再生されます。
 
 シナプス前末端には、神経伝達物質を溜めておく小胞があります。活動電位をきっかけに、小胞は細胞膜に融合してエキソサイトーシスを起こし、神経伝達物質をシナプス間隙に放出します。神経伝達物質の種類によって、シナプス後の細胞に与える影響は異なります。興奮性シナプスではシナプス後細胞に活動電位が発生する可能性が高くなり、抑制性シナプスでは活動電位が発生する可能性が低くなります。 
 
 <h4>神経細胞の形態</h4>
 
 神経細胞の全体的な形、つまり形態は、その機能に大きく関係しています。少ない樹状突起と1本の軸索を持つ神経細胞もあれば、非常に複雑な樹状突起を持つ神経細胞もあり、また、生物の体長を超える軸索を持つ神経細胞もあります。このような多様な形態は、しばしばニューロンの種類を定義するのに用いられます。シナプス結合の数は、細胞が信号に反応する方法に影響を与えます。そのため、樹状突起の形態と、そこに含まれるシナプスの数は、ニューロンの種類を決定する重要な特徴となります。また、末梢神経系では、樹状突起が細胞の受容野を決定し、細胞が感受性を示す身体上の物理的な空間を決定することもあります。
 
 <h4>神経細胞の構造を視覚化する技術</h4>
 
 19世紀末から20世紀初頭にかけて、スペインの解剖学者であるサンティアゴ・ラモン・イ・カハール（Santiago Ramon y Cajal）は、個々の神経細胞を追跡し、その本質についての基本的な洞察を与えた先駆者でした。カハールは、細胞を細部まで描き出すことに成功しました。イタリアの生物学者カミロ・ゴルジ（Camillo Golgi）の名を冠して開発された染色法を用いて、脳内のさまざまな種類の細胞の構造を追跡することができました。また、特定の情報を処理するために一緒に活性化される神経細胞のネットワークである神経回路の基本的な接続もスケッチしました。

概要

ニューロンは、電気化学信号を生成および伝達する神経系の主要なタイプの細胞です。彼らは主にそれぞれと通信します...

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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

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 signals, while the axon carries signals onward to other neurons or to muscle cells.

Neurons receive input mainly at postsynaptic terminals, which are often found on small bumps called spines on dendrites. These spines contain receptors for neurotransmitters and other chemical signals. Because dendrites can branch a great deal, some neurons can collect tens of thousands of inputs. Neurons can also have synapses on other parts of the cell, such as the cell body.

Signals that arrive at synapses move down the dendrite to the soma. The cell then processes the message and decides whether to pass it on. If it does, the main electrical signal, called an action potential, starts at the axon hillock, the junction between the soma and the axon.

Axons can vary in length and may be very long. Some extend from the spinal cord all the way to the foot. Longer axons are often wrapped in a fatty myelin sheath, which insulates the axon and helps keep the electrical signal going. Glia, another type of nervous system cell, make the myelin sheath.

In myelinated axons, the action potential is regenerated at each node of Ranvier, which is one of the repeated gaps in the myelin. The signal continues this way until it reaches the presynaptic terminal at the end of the axon. That terminal contains vesicles filled with neurotransmitters.

When an action potential arrives, the vesicles fuse with the cell membrane and release neurotransmitters into the synaptic cleft, the gap between cells at a synapse. Different neurotransmitters can affect the postsynaptic cell in different ways. An excitatory synapse makes an action potential more likely, while an inhibitory synapse makes it less likely.

Neuron shape, or morphology, can vary a lot and often matches function. Some neurons have few dendritic processes and one axon, while others have highly branched dendritic trees or axons that span the length of the organism. Scientists often use these shapes to help define neuron types.

The number of synaptic connections also affects how a cell responds to signals. For neurons in the peripheral nervous system, dendrites can help define the receptive field, which is the physical area of the body that the cell senses. The form of the dendrites and the number of synapses they contain are important clues about neuron function.

The study of neuron shape was advanced by Santiago Ramon y Cajal in the late 19th and early 20th century. He traced individual neurons and made detailed drawings that still show a great deal of information. Using the staining method developed by Camillo Golgi, he was able to map many cell types in the brain and sketch basic neuronal circuits, which are networks of neurons that work together to process specific information.

How Neurons Send Signals

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

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

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...

key terms and concepts

Learn how neurons receive, process, and transmit signals through dendrites, axons, myelin, synapses, and neurotransmitters in this high school science page.

How Neurons Send Signals | JoVE K12

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How Neurons Send Signals

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