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.