10-Minute Neuroscience: Neurons
Summary
TLDRThis neuroscience video explores the structure and function of neurons, the basic units of the nervous system. It explains how neurons communicate via electrical and chemical signals, including action potentials and neurotransmitters, and highlights the complexity of their interconnections in the brain. The script also categorizes neurons based on their structure and function, distinguishing between multipolar, bipolar, unipolar, and pseudo-unipolar neurons, as well as motor, sensory, and interneurons.
Takeaways
- 🧠 Neurons are the fundamental units of the nervous system, specialized for transmitting and receiving information.
- 🔌 Neurons communicate with one another and with other types of tissues, such as muscles or glands, through electrical and chemical signals.
- 🌟 There are approximately 86 billion neurons in a typical human brain, forming an incredibly complex network of connections.
- 🔬 Neurons come in various shapes and sizes, with over 1000 different types, each with unique functions and structures.
- 🚀 Action potentials are the main type of electrical signals in neurons, created by the flow of ions that generate an impulse to travel along the neuron.
- 💊 Neurotransmitters are chemical signals that can be released to influence the response of the next neuron in the communication chain.
- 🌱 Dendrites are the input areas of neurons, featuring receptors that interact with neurotransmitters and receive messages from other neurons.
- 🏠 The cell body, or soma, is the metabolic center of the neuron, containing the nucleus and organelles for protein synthesis and other functions.
- 🔋 The axon hillock integrates incoming signals to determine if they are strong enough to initiate an action potential.
- 🚄 The axon conducts action potentials at high speeds, varying in size and length, and is often myelinated to increase signal propagation speed.
- 🔗 Synapses are specialized regions where neurons communicate without direct contact, separated by a synaptic cleft.
- 📊 Neurons can be categorized based on the number of processes extending from the cell body, such as multipolar, bipolar, and unipolar neurons.
- 🔄 Interneurons are the most common type of neuron, acting as intermediaries for information transmission within the nervous system.
Q & A
What are the fundamental units of the nervous system?
-The fundamental units of the nervous system are neurons, which are specialized for transmitting and receiving information.
How many neurons are estimated to be in a typical human brain?
-Current estimates suggest there are about 86 billion neurons in a typical human brain.
What are the two main types of signals neurons use to communicate?
-Neurons primarily use electrical signals called action potentials and chemical signals called neurotransmitters to communicate.
What is the role of dendrites in a neuron?
-Dendrites are the part of the neuron that typically receives messages from other neurons and can be thought of as an input area for the neuron.
What is the function of the cell body or soma in a neuron?
-The cell body, or soma, is the metabolic center of the neuron, containing the nucleus and organelles involved in various cellular processes.
What is the axon hillock and its role in a neuron?
-The axon hillock is a region where changes in the electrical properties of the cell are integrated to determine if incoming signals are strong enough to initiate an action potential.
How does the axon contribute to the neuron's function?
-Axons conduct action potentials at very rapid speeds and vary in size, acting as the pathway for signals to travel from one end of a neuron to another.
What is myelin and how does it affect the neuron's signal propagation?
-Myelin is a lipid-rich insulatory material that covers axons, speeding up the propagation of electrical signals by preventing current leakage and allowing it to regenerate at nodes of Ranvier.
What are the axon terminals and their significance?
-Axon terminals, or synaptic boutons, are the branching endings of an axon where they communicate with other neurons at specialized regions called synapses.
What is a synapse and its importance in neuronal communication?
-A synapse is a specialized region where neurons communicate without direct contact, separated by a very small space called the synaptic cleft, allowing neurotransmitters to influence the postsynaptic neuron.
How are neurons categorized based on the number of processes extending from the cell body?
-Neurons are categorized into three main groups based on the number of processes: multipolar (one axon and many dendrites), bipolar (one axon and one dendritic structure), and unipolar (a single extension with branches that act as axons and dendrites).
What are the different functional classifications of neurons?
-Neurons can be classified based on function into motor neurons, which control movement, sensory neurons, which carry sensory signals, and interneurons, which act as intermediaries for information processing within the nervous system.
Outlines
🧠 Introduction to Neurons and Their Communication
This paragraph introduces the concept of neurons as the fundamental units of the nervous system, emphasizing their role in transmitting and receiving information through electrical and chemical signals. The video script delves into the structure and function of neurons, highlighting the complexity of their connections, with an estimated 86 billion neurons in the human brain forming a vast network of communication. It also touches on the variety of neuron shapes and types, mentioning over 1000 different kinds, and explains the basic mechanism of neuron communication through action potentials and neurotransmitters. The paragraph sets the stage for a deeper exploration of neuron anatomy and function in subsequent discussions.
🔬 Anatomy of a Neuron and Its Functional Classification
This paragraph provides a detailed examination of the neuron's anatomy, describing its components such as dendrites, the cell body or soma, the axon hillock, the axon, and axon terminals or synaptic boutons. It explains the role of dendrites in receiving messages, the soma as the metabolic center, and the axon's function in conducting action potentials. The paragraph also discusses the myelin sheath and nodes of Ranvier, which facilitate rapid signal transmission. Furthermore, it explores the concept of synapses, where neurotransmitters are released to communicate with other neurons. The summary also categorizes neurons based on the number of processes extending from the cell body into multipolar, bipolar, and unipolar neurons, as well as functionally into motor, sensory, and interneurons, with further subdivisions into projection, relay, and local interneurons. This comprehensive overview offers insights into the diversity and specialized roles of neurons within the nervous system.
Mindmap
Keywords
💡Neurons
💡Action Potentials
💡Neurotransmitters
💡Dendrites
💡Cell Body (Soma)
💡Axon
💡Myelin
💡Nodes of Ranvier
💡Synapses
💡Presynaptic Neuron
💡Postsynaptic Neuron
💡Classification of Neurons
Highlights
Neurons are the fundamental units of the nervous system, specialized for transmitting and receiving information.
Neurons communicate with one another and with cells in other tissues, such as muscles or glands.
There are approximately 86 billion neurons in a typical human brain, forming complex circuitry.
Neurons can vary greatly in shape and size, with over 1000 different types.
Most neurons use electrical and chemical signals, such as action potentials and neurotransmitters, for communication.
Dendrites are the input area of a neuron, typically receiving messages from other neurons.
The cell body, or soma, is the metabolic center of the neuron, containing the nucleus and organelles.
The axon hillock integrates signals to determine if the neuron should initiate an action potential.
Axons conduct action potentials at speeds from 1 to 100 m/s.
Myelin is an insulatory material that speeds up electrical signal propagation in axons.
Nodes of Ranvier are gaps in myelin that allow for the regeneration of action potentials.
Axon terminals, or synaptic boutons, are where neurons communicate at synapses.
Synapses are specialized regions where neurons communicate without direct contact.
Neurons can be categorized based on the number of processes extending from the cell body: multipolar, bipolar, and unipolar.
Multipolar neurons are the most common type, with a single axon and many dendrites.
Bipolar neurons have one axon and one dendritic structure, important in sensory systems.
Unipolar neurons have a single extension that branches into an axon and dendrites, common in invertebrates.
Pseudo-unipolar neurons are a variant of bipolar neurons, carrying sensory signals to the spinal cord.
Neurons can also be classified by function, such as motor neurons for movement control and sensory neurons for signal transmission.
Internurons are neurons that pass information between other neurons, serving as intermediaries.
Projection interneurons have long axons for long-distance signal transmission, while local interneurons form short connections for local circuits.
Transcripts
Hi everyone, welcome to 10 minute neuroscience. In this installment,
I’ll be talking about neurons, the fundamental units of the nervous system. I’ll cover their
basic structure and function and then I’ll talk about some ways we can categorize neurons.
Neurons have some unique functions that form the basis for the powerful information processing
capabilities of the nervous system. They’re specialized for transmitting and receiving
information, and they can communicate with one another as well as with cells in other types of
tissues (like muscles or glands). They can also carry information (such as sensory information)
from the rest of the body to the brain. Something else worth noting about neurons is that there are
a lot of them. Current estimates suggest there's about 86 billion neurons in a typical human brain,
and those neurons create a very complex circuitry as each neuron forms many connections—usually
thousands of connections—with other neurons. This creates anywhere from hundreds of trillions
to maybe more than a quadrillion areas in a human brain where neurons communicate with one another.
So if you look at a neuroscience textbook, you’ll see an image of a neuron that looks
something like this, and this is what we’ll use for our discussion of the neuron today.
But it’s important to note that neurons come in all shapes and sizes—there are
over 1000 different types—and most of them don’t look just like this one–so you can
see here some examples of different types of neurons found throughout the nervous system.
They look quite different, but they're all variations on a theme, and most of them have
the same general components—those general components are what we’ll focus on today.
Before we get into those components let me just say something about how neurons communicate,
because it will make the anatomy we’ll talk about next easier to understand. I’ll have other videos
that cover these topics more in-depth but I’ll just provide a quick summary here.
Most neurons use electrical and chemical signals to send messages throughout the
brain. The main type of electrical signals are called action potentials; they’re created when
charged particles called ions flow into neurons and generate an electrical impulse that can travel
from one end of a neuron to another. These action potentials can cause the release of
chemical signals called neurotransmitters, and neurotransmitters can travel from one
neuron to the next neuron and either generate a response or inhibit a response in the next neuron.
By relying on these mechanisms, neurons can spread signals throughout the brain
in a fraction of a second. (I should point out that there are neurons that don’t use
neurotransmitters and rely solely on electrical signals to communicate with one another,
but we won’t focus on them here because they’re relatively rare in the adult nervous system.)
OK, so let’s talk a bit about these different parts of a neuron. So first, on the right side
of this cell you can see a number of branch-like extensions jutting out from a circular structure
that otherwise resembles a typical cell. These extensions are called dendrites. The word dendrite
comes from a Greek word that means tree-like, and the name fits because dendrites bear a resemblance
to tree branches. Dendrites are the part of the neuron that typically receives messages from
other neurons. To accomplish this, on the surface of dendrites are proteins called receptors that
neurotransmitters can interact with. Because dendrites are typically where information
in a neuron is received, they can generally be thought of as an input area for the neuron.
The part of the neuron that most resembles a typical cell is called the cell body or soma
(and soma is another Greek word that means body). The cell body is the metabolic center of the cell.
It contains the nucleus (which contains the DNA), it contains organelles that are involved in doing
things like making proteins, and it’s the site of the synthesis of various other neural components.
Sticking out from one side of the cell body you can see this little
hill-like area, that’s called the axon hillock.
When information is received at the dendrites, it causes changes in the electrical properties
of the cell, and the axon hillock is a region where those changes are integrated
to determine if the incoming signals are strong enough for the neuron to initiate
its own action potential. This process of integrating signals is called summation.
If a neuron fires an action potential, the impulse will travel down this structure called the axon
at very rapid speeds ranging from 1 to 100 m/s. So axons act to conduct action potentials. They
vary in size and can range from the order of micrometers, or millionths of a meter,
to up to about a meter in humans for the axons that run from the spinal cord to the foot.
Because there are so many neurons in the brain, by some estimates if you took all the neurons out
of the brain and laid them end to end, the axons would stretch over 100,000 miles—that’s enough
to wrap around the globe about 4 times. Axons are usually (although not always) covered in
a lipid-rich insulatory material called myelin (and that's what this purple striped structure
is representing here). Myelin helps to speed up the propagation of electrical signals down the
axon. It prevents the current from leaking out of the axon, but also it has these gaps in the
myelin called nodes of Ranvier---that's what this little area is here, a node of Ranvier.
And Ranvier is just the name of the scientist who discovered these).
At these gaps are channels that allow positively charged sodium ions to flow into the neuron. This
influx of positively-charged ions helps to regenerate the action potential and
move it down the axon (this is something else that I’ll talk about more in another video).
At the end of the axon, you see that the structure branches out into endings we call axon terminals
or synaptic boutons.
The word bouton is French for button.
The axon terminals are often situated very close to the dendrites of another neuron (although they
can be situated next to any component of other neurons), and they communicate with
other neurons at specialized regions called synapses. So this right here is a synapse.
The neurons that communicate at a synapse don't typically come into contact with one another,
but the space separating them is very small: often only about 20-40 nanometers wide. I
know a nanometer is not something we can easily conceptualize, but for comparison,
a human hair is about 80,000-100,000 nanometers wide. So the space between neurons is very, very,
very tiny. That space is called a synaptic cleft. The neuron whose axon terminals end
at the synaptic cleft is called the presynaptic neuron (and that would be this black neuron here),
while the neuron on the other side of the synaptic cleft is called the postsynaptic neuron (that
would be this blue neuron here). When an action potential reaches the axon terminal it can cause
chemicals called neurotransmitters to be released into that synaptic cleft. The neurotransmitters
can then bind or attach to receptors on the postsynaptic neuron, and either increase or
decrease the likelihood that the postsynaptic neuron will fire an action potential of its own.
So those are the basic components of a neuron. Again most neurons have those defined regions but
they still often differ from one another in other substantial ways. We can use those differences to
group neurons into some broad categories. One way of categorizing neurons is based on the number of
processes that extend from the cell body. Using this method of classification, there are three
main groups of neurons: multipolar, bipolar, and unipolar. Multipolar neurons are the most common
type of neuron in the human nervous system and the nervous systems of other vertebrates. Multipolar
neurons usually have a single axon and many dendrites. They come in various shapes and sizes.
The length of their axons varies as does the extent of their dendritic branching, so they can
still look very different from one another, but all of them are modifications on a similar plan.
Bipolar neurons have a cell body that gives rise to two extensions: one axon and one
dendritic structure. Sensory systems, like the visual system, rely heavily on bipolar neurons.
Unipolar neurons have a single extension that has multiple branches, one of which
acts as the axon and others that form dendrites. Unipolar neurons are the simplest type of neuron,
and are common in invertebrate nervous systems but not very common in humans and other vertebrates.
There are also variants of bipolar neurons called pseudo-unipolar neurons. These cells
initially form as bipolar neurons, but the dendrite and the axon fuse together
to form a single process that extends from part of the cell body. Pseudo-unipolar
neurons carry sensory signals, such as information about touch to the spinal cord.
Neurons can also be classified based on function. Motor neurons, for example,
are responsible for controlling movement. So they have axons that form synapses with muscles to
cause those muscles to contract. Sensory neurons carry sensory signals back to the spinal cord
and brain. This would include information, for example, about touch, smell, vision,
etc. But the vast majority of neurons in the nervous system are considered interneurons,
which are neurons that receive information from neurons and then pass it on to other neurons. So
they act as the intermediaries for neurons. These interneurons are also often subdivided
into two types: projection or relay interneurons and local interneurons. Projection interneurons
typically have long axons that carry signals over long distances, such as from one part of
the brain to another. Local interneurons, on the other hand, form connections with other
neurons nearby. So, they have short axons and are involved in creating local circuits.
So that is your basic summary of neurons. Thanks for watching!
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