The Neuron

Summary

In this educational video, Paul Andersen explains the neuron as the fundamental unit of the nervous system. He details the neuron's anatomy, including the cell body, dendrites, and axon, and how they facilitate the transmission of information via neurotransmitters and action potentials. He also discusses the myelin sheath's role in speeding up signal transmission and the structural and functional classifications of neurons, such as multipolar, bipolar, unipolar, and axonic neurons, as well as sensory, motor, and interneurons. The explanation aims to clarify the neuron's complexity and its crucial role in our body's response to environmental stimuli.

Takeaways

• 🧠 The neuron is the fundamental unit of the nervous system, responsible for receiving and transmitting information.
• 🐛 In simple animals like a nematode worm, the nervous system is composed of only 302 neurons, yet they are intricately connected.
• 🧬 Humans have approximately 100 billion neurons, most of which are located in the brain and spinal cord.
• 🏠 The cell body of a neuron is the central part, containing typical cellular structures like the nucleus and Golgi apparatus.
• 🌐 Dendrites are extensions from the cell body that receive information in the form of neurotransmitters from other neurons.
• 🚀 The axon is the part of the neuron responsible for transmitting information, starting at the axon hillock and extending to the terminals.
• 🔌 Synapses are the gaps between neurons where information is passed from one neuron to another.
• 🛡️ Myelin sheaths are insulating layers that wrap around some axons to facilitate faster transmission of signals.
• 🔍 Neurons can be classified structurally based on the number of poles or extensions coming from the cell body, such as multipolar, bipolar, unipolar, and axonic neurons.
• 🔬 Neurons are also classified functionally into sensory (afferent) neurons that bring information into the central nervous system, and motor (efferent) neurons that send information out to effectors like muscles and glands.
• 🔄 Interneurons are neurons that connect between sensory and motor neurons within the central nervous system, facilitating complex interactions.

Q & A

What is the basic unit of the nervous system?

The basic unit of the nervous system is the neuron.

How many neurons does a simple animal like a nematode worm have?

A nematode worm has approximately 302 neurons.

How many neurons are present in the human body?

The human body contains about a hundred billion neurons.

What is the primary function of the cell body of a neuron?

The cell body, or soma, is the metabolic center of the neuron, containing the nucleus and organelles like the Golgi apparatus and mitochondria.

What are dendrites and what is their role in a neuron?

Dendrites are extensions of the neuron cell body that receive information in the form of neurotransmitters from other neurons.

What is the axon and what does it transmit?

The axon is responsible for transmitting information away from the neuron. It begins at the axon hillock and moves toward the axon terminals.

What is an action potential and how does it relate to the neuron's function?

An action potential is an electrical signal that travels along the neuron's axon, allowing the neuron to send information to the next neuron.

What is a Myelin sheath and how does it aid in the transmission of information in the axon?

A Myelin sheath is a protective covering around some axons, made by Schwann cells, that insulates the nerve and allows information to travel more quickly.

What is the structural classification of neurons based on, and what are the common types?

Neurons are structurally classified based on the number of poles or extensions coming off the cell body. Common types include multipolar, bipolar, unipolar, and axonic neurons.

What is the difference between sensory neurons and motor neurons in terms of their function?

Sensory neurons, also known as afferent neurons, bring information into the central nervous system from the environment. Motor neurons, on the other hand, send information out to effectors such as muscles and glands.

What are inter neurons and what is their role in the nervous system?

Inter neurons are neurons that make connections between sensory and motor neurons within the central nervous system, facilitating communication between different parts of the nervous system.

Outlines

00:00

🧠 Neuron Basics and Structure

Paul Andersen introduces the neuron as the fundamental unit of the nervous system, explaining its role in processing information from the environment. He contrasts the simplicity of a nematode worm's 302 neurons with the complexity of human's 100 billion neurons, mostly in the brain and spinal cord. The neuron's anatomy is detailed, including the cell body with its typical cellular components like the nucleus and mitochondria, and the extensions known as dendrites that receive neurotransmitters from other neurons. The axon's function in transmitting information is also discussed, highlighting the axon hillock and terminals, and the role of synapses in neuron-to-neuron communication. The importance of action potential in signal transmission is mentioned, with a reference to a related video for further details. Additionally, the role of myelin sheaths in insulating and speeding up signal transmission along axons is explained.

Keywords

💡Neuron

A neuron is the fundamental unit of the nervous system, responsible for receiving, processing, and transmitting information through electrical and chemical signals. In the video, neurons are highlighted as the basic building blocks of the nervous system, with different types and functions, and are essential to the video's theme of explaining the basics of the nervous system.

💡Nervous System

The nervous system is the body's network of nerves and neurons that coordinate body functions and respond to stimuli. It is central to the video's narrative, as it sets the stage for discussing the role and structure of neurons, from simple organisms with few neurons to complex systems like the human brain and spinal cord.

💡Cell Body

The cell body, also known as the soma, is the central part of a neuron that contains the nucleus and other organelles. It is the metabolic center of the neuron. In the script, the cell body is described as the starting point for understanding neuron anatomy, emphasizing its typical cellular functions within the nervous system.

💡Dendrites

Dendrites are the branching extensions of a neuron that receive signals from other neurons in the form of neurotransmitters. They are crucial for the neuron's ability to integrate information. The video script mentions dendrites as the receiving end of the neuron, highlighting their role in information intake.

💡Axon

The axon is the long, singular extension of a neuron that transmits electrical impulses to other neurons, muscles, or glands. It is key to the neuron's function of sending information. The script explains the axon's role in transmitting information, starting from the axon hillock and moving to the terminals.

💡Action Potential

An action potential is the electrical signal that travels along the axon, allowing for rapid communication between neurons. The video script refers to action potentials as the mechanism by which neurons transmit information, although it directs viewers to another video for a more detailed explanation.

💡Myelin Sheath

The myelin sheath is a protective layer that wraps around some axons, increasing the speed at which electrical signals travel. It is formed by glial cells called Schwann cells. The script describes myelin sheaths as insulators that facilitate faster nerve impulse transmission, particularly in long axons.

💡Synapse

A synapse is the junction between two neurons where information is passed from one to another through neurotransmitters. It is the point of connection between neurons. The video script explains synapses as the gaps between neurons that allow for the transfer of information, emphasizing their importance in neural communication.

💡Structural Classification

Structural classification refers to the categorization of neurons based on their shape and the number of extensions from the cell body. The video script uses this classification to differentiate between multipolar, bipolar, unipolar, and axonic neurons, providing a framework for understanding the diversity of neuron types.

💡Functional Classification

Functional classification categorizes neurons based on their role in the nervous system, such as sensory neurons that detect stimuli and motor neurons that activate muscles or glands. The script discusses this classification to explain how neurons are involved in both receiving information and generating responses.

💡Interneurons

Interneuron is a type of neuron that connects other neurons within the central nervous system, facilitating communication between sensory and motor neurons. The video script mentions interneurons as the middlemen in the neural network, playing a crucial role in processing and relaying information within the nervous system.

Highlights

Neurons are the basic unit of the nervous system, essential for receiving and responding to information from the environment.

A simple animal like a nematode worm has only 302 neurons, which allows for complex information processing.

Humans possess approximately 100 billion neurons, most of which are in the brain and spinal cord.

The cell body of a neuron, containing the nucleus and other organelles, is the center of metabolic activity.

Dendrites are extensions that receive information in the form of neurotransmitters from other neurons.

The axon is responsible for transmitting information, starting at the axon hillock and moving to the terminals.

Synapses are the gaps between neurons where information is passed on to the next neuron.

Action potentials are the mechanism by which neurons send information, detailed in a separate video.

Myelin sheaths insulate axons, allowing for faster transmission of information, and are produced by Schwann cells.

Nerve fibers are axons wrapped in myelin sheaths, facilitating rapid signal transmission.

Neurons can be classified structurally based on the number of poles or extensions coming off the cell body.

Multipolar neurons are the most common type, with multiple dendrites and a single axon.

Bipolar neurons are rare and transmit information from sensory receptors in the eyes and nose.

Unipolar neurons, also known as pseudo-unipolar in vertebrates, are sensory neurons that transmit information to the CNS.

Axonic neurons, found in the brain, are less understood and have no distinct axon.

Neurons can also be functionally classified as sensory, motor, or interneurons based on their role in information processing.

Sensory or afferent neurons bring information from the environment to the central nervous system.

Motor neurons transmit information from the CNS to effectors like muscles and glands.

Internurons facilitate connections between sensory and motor neurons within the CNS.

Transcripts

Hi, it's Paul, Andersen and in this video

I'm going to go over the basics of the neuron. The neuron is the basic unit in the nervous system. in a simple animal like

A nematode worm, they only have 302 neurons,

But what they allow them to do is to take information in from their surroundings and respond to that

Information. if you look at how those 302 neurons are connected it's very complex. Now humans are quite a bit bigger

And we have a hundred billion neurons in our body.

Most of those are centered in the central nervous system in the brain and the spinal Cord,

But the basic unit of our nervous system is the same: it's the neuron. If we look at the neuron

Anatomy and remove all the other neurons that the center is going to be what's called the cell body.

This is a typical cell. It's metabolizing. Cell. It's taking an energy

It's using that energy and so it's going to have a nucleus. It's going to have Golgi apparatus

Mitochondria, it's a typical cell but there are extensions of those cell bodies called the dendrites. Those dendrites are connected to other neurons

and they're taking information in in the form of neurotransmitters. In fact this whole side of the neuron is receiving information

We then have the axon the axon is where we're transmitting

Information it begins at the Axon hillock and is going to move to the terminals now remember the terminals

There's a synapse that connects us to other neurons, but the signal is going to move in this direction

We're taking in information from the dendrites the cell body, and then we can send information to the next neuron now

How do we do that is through an action potential and I have a video that

I'll put a link to where I go into the specifics of how that occurs

But certain axons in our body are really really long and for that information to travel quickly. We will wrap them in Myelin sheaths

It's a schwann Cell that's wrapped around it the way

It works is we put the voltage-gated channels in between that and it acts to insulate that nerve

It allows the information to travel more readily down that axon.

And, we generally say if you have an axon that's wrapped in Myelin sheath. We call that a nerve fiber inside our body now

We're taking in information as well

So there's going to be another neuron that's connected to both the cell body and the dendrites of that cell

But there's going to be a gap between these two and we call that a synapse

It's a connection between neurons. Again

I Have another video on the synapse if you want to dig into the specifics especially of how chemical synapses work neurons are classified in two

Ways first way is due to their structural classification, so if we take the cell body of a typical neuron

like this multipolar neuron

The way you can figure out what what type of a neuron is is?

Find the cell body and figure out how many poles are coming off of that cell body?

So if we count them, we have a number of different dendrites that are coming off of this neuron

And then we have at one axon that's coming off, and so we call that a multipolar neuron

This is the most common neuron that we have in our body if we look at the next one

We find the cell body again. How many poles do we have coming off of it?

We've got the axon coming out and the dendrite coming in and so we call this a bipolar neuron Bipolar Neurons are very rare

They transmit information from the receptors in our eye

receptors in our nose

If we look at the next one, here's the cell body you can see there's only one pole coming off of that

It's actually a fused axon and dendrite and we call that a unipolar neuron. Now in vertebrates

It's sometimes referred to as the pseudo uni-polar neuron these are going to be most of the sensory neurons in our body

They're taking information in and transmitting that back into the central nervous system

And then if we look on the next one if we look at that

You can see there's no axon on it as at all so we call that an Axonic neuron

These are found in the brain, and they're not super understood now there are a lot of other structural classifications

But these are the general ones that you're going to find in a typical anatomy class?

Now neurons can also be classified according to their functional classification those that take in information

stimulus coming in from our environment

And then the response that we have so if we kind of move that to the central nervous system

We're looking at a cross-section of the spine so we're taking information in from receptors

So these could be in the skin for example touch receptors heat receptors pain receptors

And so we have to transmit that information to the central nervous system. So those neurons that bring information in are

Sometimes refer to as sensory neurons or afferent neurons you can see this is a unipolar neuron

And it's transmitting that information into the central nervous system, and then we have information going back out

We're sending information out to effectors in our body: could be muscles, could be glands. And, we're going to call those motor neurons

They're moving away from the center

sometimes we refer to those as

afferent neurons as well now there should be connections between those neurons those aren't all the neurons we have in our body and so we

Also have these connections in the middle and those are going to be called inter neurons

And so that's the neuron

How did you do can you remember the different parts of the neuron do you remember that these are the dendrites the cell body?

Do you remember what type of a neuron this is if not go back and rewind it?

But those are neurons those are the basics, and I hope that was helpful