Gray and white matter | Organ Systems | MCAT | Khan Academy

Summary

This video explains the gray and white matter of the central nervous system, focusing on their differences in the brain and spinal cord. Gray matter, containing neuron somas, is found inside the spinal cord but on the outer cortex of the brain. White matter, made of myelinated axons, is on the outside of the spinal cord and deeper within the brain. The video also touches on the brain's 'nuclei,' clusters of gray matter, and the tracts, which are pathways of axons, highlighting the CNS's role in motor, sensory, and higher cognitive functions.

Takeaways

• 🧠 The central nervous system includes the brain and spinal cord, with gray matter containing most neuron somas and white matter containing myelinated axons.
• 🎨 Despite being called gray and white matter, these areas aren't literally gray or white but appear so due to how tissue is prepared after removal from the body.
• 🦋 In the spinal cord, gray matter is mostly on the inside, forming an 'H' or butterfly shape, while white matter is mostly on the outside.
• 🍞 Sections of the spinal cord are like slices of bread, showing how the gray and white matter are distributed at different levels.
• 🧩 In the brain, gray matter is mostly on the outside, forming the cortex, with the cerebral cortex covering the cerebrum and the cerebellar cortex covering the cerebellum.
• 🧱 White matter in the brain is mostly on the inside, beneath the cerebral cortex and in deeper areas like the brain stem.
• 🏛️ Deep gray matter in the brain is referred to as nuclei, which contain neuron somas and are found in regions beyond the cortex.
• 🚄 Collections of axons in the white matter, called 'tracts,' travel together to different areas of the central nervous system, often carrying similar information.
• 💡 The central nervous system is responsible for motor, sensory, and automatic functions, as well as higher functions like cognition, emotion, and consciousness.
• 🌍 Higher functions, such as consciousness and cognition, are heavily associated with the cerebral cortex and other specialized parts of the brain.

Q & A

What is the primary difference between gray matter and white matter in the central nervous system?

Gray matter contains most of the neuron somas, while white matter consists of myelinated axons.

Why are gray matter and white matter given those names?

These names are based on the appearance of the tissues when prepared in certain ways. Gray matter appears gray, and white matter appears whitish, although in life they are actually different tan colors.

How is the distribution of gray and white matter different in the spinal cord versus the brain?

In the spinal cord, gray matter is mostly on the inside in an 'H' or butterfly shape, while white matter is on the outside. In the brain, gray matter forms a layer on the outside (called cortex), and white matter is mostly found inside.

What is the 'cortex' in the brain, and what are its different types?

The cortex is the outer layer of gray matter in the brain. There are two main types: the cerebral cortex, which covers the cerebrum, and the cerebellar cortex, which covers the cerebellum.

What are 'nuclei' in the brain, and how are they different from the cortex?

Nuclei are clusters of gray matter deep inside the brain. Unlike the cortex, which forms the outer layer of gray matter, nuclei are found within the white matter of the brain.

What are 'tracts' in the white matter of the central nervous system?

Tracts are collections of myelinated axons that travel together to carry information between different parts of the central nervous system.

How does the central nervous system support higher functions like cognition and emotion?

The cerebral cortex, which contains gray matter on the surface of the cerebrum, is particularly involved in higher functions such as cognition, emotion, and consciousness. Other brain regions also play a role in these processes.

Why does the gray matter in the brain have a different location compared to the spinal cord?

In the brain, gray matter forms the cortex on the outside to facilitate complex functions like cognition, while in the spinal cord, gray matter is located inside, where it helps manage more direct motor and sensory processing.

What role do myelinated axons in the white matter play in the central nervous system?

Myelinated axons in the white matter are responsible for fast transmission of signals across different areas of the central nervous system, enabling communication between various regions.

How is the spinal cord organized in terms of gray and white matter distribution?

In the spinal cord, gray matter forms an 'H' or butterfly shape at the center, containing neuron somas, while white matter surrounds it on the outside, consisting of myelinated axons.

Outlines

00:00

🧠 Gray and White Matter in the Central Nervous System

This paragraph discusses the distinction between gray and white matter in the central nervous system, which includes the brain and spinal cord. Gray matter contains most of the neuron cell bodies and is found in distinct areas, such as the 'H' or butterfly shape in the spinal cord and the outer layer of the brain known as the cortex. White matter, on the other hand, consists mainly of myelinated axons and is located primarily on the outside of the spinal cord and within the brain beneath the cortex. The names 'gray' and 'white' matter come from the appearance of these areas after specific tissue preparation, despite their natural coloration being more of a tan. The distribution of these matters varies between the brain and spinal cord, with gray matter predominantly on the inside of the spinal cord and on the outside of the brain.

05:02

🚦 Neuron Axons and Tracts in the Central Nervous System

The second paragraph delves into the structure and function of neuron axons and their collective organization in the central nervous system. Axons that travel together, often carrying similar information, are grouped into what are known as tracts. These tracts facilitate communication between different parts of the nervous system. The central nervous system is composed of a vast number of neurons that serve various functions, including motor, sensory, and automatic functions, as well as higher functions such as cognition, emotion, and consciousness. The cerebral cortex, the outer layer of gray matter in the cerebrum, plays a significant role in these higher functions, along with other areas of the brain.

Keywords

💡Gray Matter

Gray matter refers to the areas in the central nervous system that contain most of the neuron cell bodies or somas. It is called 'gray' due to its appearance when the tissue is prepared in certain ways after being removed from the body. In the video, gray matter is depicted as having a butterfly or 'H' shape in the spinal cord, located internally, and in the brain, it is primarily on the outside, forming the cerebral cortex. The gray matter is crucial for the video's theme as it is the central hub for neuronal processing and communication.

💡White Matter

White matter consists mainly of myelinated axons, which are axons wrapped in a fatty substance called myelin. This myelin sheath gives the white matter its pale appearance, contrasting with the gray matter. In the video, white matter in the spinal cord is described as being mostly on the outside, whereas in the brain, it is primarily found on the inside, beneath the cerebral cortex. The white matter is essential for the video's narrative as it facilitates the transmission of signals across different regions of the nervous system.

💡Neuron Somas

Neuron somas, also known as the cell bodies of neurons, are the central part of a neuron that contains the nucleus. The video explains that most neuron somas are located in the gray matter of the central nervous system, which is why gray matter appears darker. The neuron somas are vital for understanding the video's content as they are the main sites of metabolic activity and synthesis within neurons.

💡Myelinated Axons

Myelinated axons are nerve fibers that are encased in a myelin sheath, which allows for faster transmission of electrical impulses. The video mentions that these axons are primarily found in the white matter. Understanding myelinated axons is key to grasping the video's message about how the nervous system efficiently transmits signals.

💡Central Nervous System (CNS)

The central nervous system, or CNS, includes the brain and spinal cord and serves as the primary control center for the body. The video script discusses the distribution of gray and white matter within the CNS, emphasizing the different roles these areas play in processing information. The CNS is the main subject of the video, making it a central keyword.

💡Spinal Cord

The spinal cord is a part of the central nervous system that extends from the brain down to the vertebral column. In the video, the spinal cord's gray matter is depicted as having an 'H' or butterfly shape, located internally, with white matter surrounding it externally. The spinal cord's structure is crucial for understanding the video's discussion on the layout of gray and white matter.

💡Brain

The brain is the command center of the nervous system and is composed of various regions, including the cerebrum, cerebellum, and brainstem. The video script contrasts the distribution of gray and white matter in the brain with that of the spinal cord, noting that gray matter in the brain is mostly on the outside, forming the cortex. The brain's structure is integral to the video's exploration of the nervous system.

💡Cerebral Cortex

The cerebral cortex is the outer layer of the cerebrum and is composed of gray matter. As discussed in the video, it contains most of the neuron somas and is involved in higher brain functions such as cognition, emotion, and consciousness. The cerebral cortex is highlighted in the video as a key area where the gray matter's role in higher functions is emphasized.

💡Cerebellar Cortex

The cerebellar cortex is the outer layer of the cerebellum and, like the cerebral cortex, is made up of gray matter. The video mentions that it also contains neuron somas. The cerebellar cortex plays a role in coordinating movement and is an example of how gray matter is distributed in different parts of the brain.

💡Nuclei

Nuclei are clusters of gray matter found deep within the brain. The video script explains that these areas, unlike the cortex, are not on the surface but are essential for various brain functions. The concept of nuclei is important for understanding the video's message about the diverse distribution and roles of gray matter within the brain.

💡Tracts

Tracts are collections of axons that travel together in the white matter of the central nervous system. The video script describes how these tracts facilitate communication between different parts of the nervous system. Tracts are a key concept in the video as they illustrate how the white matter contributes to the nervous system's connectivity.

Highlights

Introduction to gray and white matter in the central nervous system.

Gray matter contains most of the neuron somas in the central nervous system.

White matter primarily consists of myelinated axons in the central nervous system.

The terms 'gray' and 'white' matter come from the appearance of the tissues after preparation, not their real-life colors.

In the spinal cord, gray matter is organized in an 'H' or butterfly shape and is located on the inside.

White matter is located on the outside of the spinal cord, surrounding the gray matter.

The brain’s gray matter is mostly on the outside, forming a layer called the 'cortex.'

The cerebral cortex refers to the gray matter covering the cerebrum, while the cerebellar cortex refers to the cortex covering the cerebellum.

The brain’s white matter is mostly on the inside, beneath the cerebral cortex.

Deep areas of gray matter in the brain are called 'nuclei,' which are different from the outer cortex.

Collections of axons traveling together in the central nervous system are called 'tracts,' which carry similar types of information.

Tracts in the central nervous system transport information between different regions.

The central nervous system handles motor, sensory, and autonomic functions, among others.

Higher brain functions, such as cognition, emotion, and consciousness, are primarily managed in the cerebral cortex.

Certain parts of the brain play significant roles in higher nervous system functions, beyond basic sensory and motor tasks.

Transcripts

Voiceover: In this video,

I'm gonna talk about gray and white matter.

In the central nervous system,

which is mostly the brain and the spinal cord,

there are areas called "gray matter"

gray matter,

that contain most of the "neuron somas".

So most of the neuron somas in the central nervous system

are found in the gray matter.

And then there are other areas called "white matter".

And the white matter of the central nervous system,

is most of the "myelinated axons".

Myelinated, so axons that are wrapped in myelin.

Myelinated axons.

And these are actually kinda funny names for

these parts of the central nervous system

because they're really not gray or white.

They're all kind of different tan colors, in life.

But when the tissue is prepared certain ways

after being removed from the body,

it can have a grayish appearance

or a more whitish appearance.

And so these are the names that have stuck

for these general areas,

the gray matter and the white matter.

Now, the distribution of gray matter and white matter

is a little different between the spinal cord and the brain.

If we look first at the spinal cord here,

and here we have a really nice illustration

of some different sections of the spinal cord.

So right over here.

What these drawings represent

are different levels of the spinal cord.

Like if we made little sections of it.

Like if we were cutting a loaf of bread

and kind of cut from the top down to the bottom.

And then we're looking down at these sections from the top,

so that we're kind of looking down this way

at the different sections over here in these drawings.

And what we see in the spinal cord

is that most of the gray matter of the spinal cord

is on the inside, this kind of "H" shape

or this butterfly shape of gray matter.

And the white matter of the spinal cord

is mostly on the outside,

all this stuff outside of this "H" shape of gray matter.

And it's a little hard to see on these drawings,

so let me just take, like this one, for example

and let me just draw it here, just a little bigger.

So I'll just draw kind of an oval

like we're looking down at the top

of a section of the spinal cord.

And on the inside is gonna be the gray matter,

that's gonna be in this kind of "H" shape

or this butterfly shape.

Let me just draw the back part, here.

And all of this stuff would be gray matter.

So, it would be lots of neuron somas

that would give it a different color

from the white matter on the outside.

Let me just draw in a little bit of white

right here on the outside,

because that's how the spinal cord is set up,

with most of it's myelinated axons

forming white matter on the outside.

Except for this little bit here where the

gray matter goes to the very back of the spinal cord.

Now, for the brain, it's a little different

than it is for the spinal cord.

So let's take a look at the brain

and make it a little bigger with this drawing over here.

And on this drawing, we're gonna be looking

at the brain from the left side.

Let me just write that up here.

So this is the brain from the left side,

like we're looking over this way at the brain,

with the cerebrum on top

and the cerebellum back here,

and then the brain stem,

we just see a little bit right here.

And then this drawing is gonna be

of kinda the inside of the brain,

like if we cut along the brain kinda like this,

through a bunch of the cerebrum and the brain stem.

And we're kind of looking at it from the front.

So we're looking at it this way,

after cutting it through here,

so that we can look at the inside of the brain tissue.

Now, where the spinal cord had gray matter

mostly on the inside, the brain actually

has gray matter mostly on the outside.

So here you can see this layer of gray matter

that's going all the way around the outside

of the cerebrum here.

And this layer of gray matter on the outside of

most of the brain, is called "cortex".

Cortex.

And this cortex covering the surface of the cerebrum

is called the cerebral cortex.

And the cortex covering the cerebellum down here,

is called the cerebellar cortex.

And that's all gray matter

on the outside of those parts of the brain

that contain most of the neuron somas.

I'll just draw some little circles here

to represent neuron somas.

Although, they're actually much smaller than this,

if we did it to scale.

And also, kind of the reverse of the spinal cord,

where most of the white matter

was on the outside of the spinal cord,

most of the white matter of the brain is on the inside.

So this lighter colored stuff here,

under the cerebral cortex, this is all white matter

deep inside the cerebrum

and white matter down here in the brain stem.

Now, there are some other areas

deep in the brain that are gray matter,

that contain lot's of neuron somas, like this right here.

And instead of calling these areas "cortex",

like the gray matter on the outside,

the gray matter that's kinda deep in the brain,

we call "nuclei".

One would be a "nucleus" and multiple is "nuclei".

And there are multiple nuclei deep in the brain,

these areas of gray matter.

Like here are several right here,

and here's another one right here.

Now, in the white matter of the central nervous system,

are collections of axons

that are traveling together to different areas.

I'll just draw a dash line to show

that these axons are gonna keep going.

But there are multiple neuron-axons

that are kind of traveling together.

They're starting in a similar area

and they're heading to a similar area

somewhere else in the central nervous system.

And collections of axons traveling together

in the central nervous system, we call "tracts".

Tracts.

So this would be one tract, right here.

And a tract could have many, many axons in it

carrying, often a very similar kind of information

from one part of the central nervous system

to another part of the central nervous system.

The central nervous system has a huge

number of neurons in it, doing lots of different functions.

In addition to neurons involved in

motor, sensory, and automatic functions,

like we talked about with the peripheral nervous system,

the central nervous system also has lots of neurons

participating in the higher functions of the nervous system.

That is, participating in cognition,

emotion and consciousnesses.

And that's particularly in the cerebral cortex,

all this gray matter on the outside of the cerebrum.

And certain other parts of the brain are very involved

in those higher functions of the nervous system, as well.