Central Nervous System: Crash Course Anatomy & Physiology #11

Summary

This script explores the intricacies of the human brain, focusing on its specialized regions and their functions. It narrates the story of James, who developed Broca's aphasia after a stroke, highlighting the brain's ability to adapt and communicate through singing. The video delves into the brain's development from a neural tube to its adult structures, emphasizing the importance of location in brain function and the impact of injuries on our understanding of its complexity.

Takeaways

• 🧠 The brain is a complex organ with specific regions responsible for particular functions, as illustrated by James's experience with Broca's aphasia.
• 🗣️ Broca's area, located in the left hemisphere of the brain, is crucial for language production, and damage to it can result in an inability to speak intelligibly.
• 🎶 Broca's aphasia can sometimes be mitigated through singing, which engages a different part of the brain responsible for language processing.
• 🧬 Our understanding of brain function has been significantly advanced by studying the effects of injuries to different brain regions.
• 🌐 The nervous system is divided into the central nervous system (CNS), which includes the brain and spinal cord, and the peripheral nervous system (PNS).
• 🔄 The CNS integrates sensory information from the PNS and coordinates responses, while the spinal cord facilitates communication between the brain and the body.
• 🦴 The brain and spinal cord are protected by the skull and vertebrae, as well as by meninges and cerebrospinal fluid.
• 👶 The development of the brain begins with a neural tube that differentiates into various vesicles, eventually forming the adult brain structures.
• 🧠 The brainstem, cerebellum, and diencephalon are part of the lower brain structures that regulate basic life functions and emotional responses.
• 🤔 The cerebrum, or the cerebral cortex, is the largest part of the brain and is responsible for higher cognitive functions such as thinking, learning, and consciousness.
• 🔗 The corpus callosum connects the left and right hemispheres of the cerebrum, allowing for communication between them and coordination of complex functions.

Q & A

What happened to James at the age of 45 that affected his ability to speak?

James suffered a stroke at the age of 45, which damaged Broca's area in the left hemisphere of his brain, resulting in Broca's aphasia and an inability to produce intelligible words.

What is Broca's aphasia and how does it affect language abilities?

Broca's aphasia is a language disorder caused by damage to Broca's area in the brain. It often leaves sufferers with the ability to understand speech but an inability to produce intelligible words, although they may still intonate as if speaking a whole sentence.

How did therapy help James regain some communication abilities after his stroke?

Therapy helped James by teaching him to communicate through singing, which uses a different region of the brain, analogous to Broca's area but located on the right side.

What is the significance of the brain's specialization in understanding James's case?

The specialization of the brain into specific regions with specific functions is significant because it explains how damage to a particular area, like Broca's area, can result in specific deficits, such as Broca's aphasia.

What are the two main networks of the nervous system and their roles?

The two main networks of the nervous system are the central nervous system, consisting of the brain and spinal cord, which integrates sensory information and coordinates responses, and the peripheral nervous system, which collects sensory information from the body.

What is the role of the spinal cord in the nervous system?

The spinal cord conducts two-way signals between the brain and the rest of the body, governs basic muscle reflexes, and patterns that operate without the brain's conscious control.

How is the brain protected within the skull?

The brain is protected by the bones of the vertebrae and cranium, membrane layers known as meninges, and is bathed in cerebrospinal fluid, which allows it to float somewhat in the skull, reducing its weight and impact during movement.

What are the three primary brain vesicles that develop from the neural tube in an embryo?

The three primary brain vesicles that develop from the neural tube are the prosencephalon (forebrain), mesencephalon (midbrain), and rhombencephalon (hindbrain).

What are the five secondary vesicles that form from the primary brain vesicles during embryonic development?

The five secondary vesicles are the telencephalon, diencephalon (from the prosencephalon), mesencephalon (midbrain remains undivided), metencephalon, and myelencephalon (from the rhombencephalon).

What are the main components of the brainstem and their functions?

The brainstem's main components are the midbrain, pons, and medulla oblongata. They regulate vital involuntary functions such as heartbeat, lung function, sleep, appetite, pain sensitivity, and awareness.

What is the cerebrum and what are its primary functions?

The cerebrum is the largest part of the brain, consisting of the cerebral cortex and the underlying white matter. It is responsible for voluntary movements, advanced cognitive functions, emotion regulation, consciousness, and sensory processing.

How does the cerebrum adapt to its growth within the confines of the skull?

The cerebrum adapts to its growth by forming gyri (small ridges) and sulci (grooves), which increase its surface area and allow it to fit within the skull.

What is the role of the corpus callosum in the brain?

The corpus callosum is a bundle of myelinated axon fibers that connects the left and right hemispheres of the cerebrum, allowing them to communicate with each other.

What are the four main lobes of the cerebral hemispheres and their associated functions?

The four main lobes are the frontal lobe (muscle control, cognitive functions, and language comprehension), the occipital lobe (visual processing), the parietal lobe (touch, pain, and pressure sensation), and the temporal lobe (auditory processing and language).

Outlines

00:00

🧠 Brain Function and Recovery: James' Story

The script introduces James, a 45-year-old professional and father, who suffered a stroke that led to Broca's aphasia, an impairment in language production. Despite regaining some abilities, James was unable to speak intelligibly. Through therapy, he discovered a unique way to communicate by singing, which leverages a different part of the brain. This case illustrates the brain's specialization and adaptability, highlighting the importance of Broca's area and the potential for alternative communication pathways.

05:01

🔬 Understanding the Brain's Structure and Development

This paragraph delves into the anatomy and development of the human brain. It explains the brain's evolution from a simple neural tube into more complex structures, including the brainstem, cerebellum, diencephalon, and cerebral hemispheres. The narrative describes the function of the brainstem in regulating vital functions and the role of the cerebellum in muscle coordination. It also touches on the diencephalon's involvement in homeostasis and the limbic system's connection to emotions. The paragraph culminates in the discussion of the telencephalon, which develops into the cerebrum, responsible for higher cognitive functions. The script also mentions the importance of the corpus callosum in inter-hemispheric communication and the division of the cerebral cortex into lobes with distinct roles.

Keywords

💡Broca’s area

Broca’s area is a region in the left hemisphere of the brain that is critical for speech production and language processing. In the video's narrative, it is mentioned that damage to this area due to a stroke resulted in Broca’s aphasia, a condition where individuals can understand language but struggle to produce intelligible speech. The script uses James' story to illustrate this concept, showing how the brain's specific regions are responsible for particular functions.

💡Broca’s aphasia

Broca’s aphasia is a language disorder characterized by the ability to understand language but difficulty in speech production. The video script describes how this condition can affect an individual's ability to communicate, as seen with James who could only repeat the word 'too' after his stroke. The script also explains that therapy can sometimes help by teaching patients to sing, as it engages a different part of the brain.

💡Cerebellum

The cerebellum is a region of the brain that plays a key role in motor control and coordination. In the script, it is mentioned as one of the structures that develop from the neural tube, emphasizing its importance in muscle activity coordination. It is part of the lower sections of the brain that undergo less dramatic changes during development compared to other regions.

💡Brainstem

The brainstem is a crucial part of the central nervous system that connects the brain to the spinal cord and is responsible for regulating many vital functions. The script describes its components—the midbrain, pons, and medulla oblongata—and how they are involved in basic life functions such as heart rate, breathing, and sleep. The brainstem is also highlighted for its role in relaying sensory information to higher brain regions.

💡Diencephalon

The diencephalon, also known as the interbrain, is a region that includes structures like the thalamus and hypothalamus, which are involved in homeostasis, alertness, and reproductive activity. The script explains its role in regulating strong emotions and instinctual pursuits, referring to it as part of the 'reptilian brain' shared with less complex animals.

💡Cerebrum

The cerebrum is the largest part of the human brain, responsible for higher cognitive functions such as thinking, learning, and consciousness. The script describes its development from the telencephalon and its composition of the cerebral cortex and white matter. It also explains how the cerebrum's growth led to the formation of gyri and sulci to fit within the skull and its division into lobes with distinct functions.

💡Cerebral cortex

The cerebral cortex is the outer layer of the cerebrum, composed of gray matter, and is involved in higher brain functions. The script mentions it as the site of complex processing, requiring a large number of synapses, which is why the cerebrum has many folds to accommodate the increased nervous tissue.

💡Corpus callosum

The corpus callosum is a bundle of nerve fibers that connects the two hemispheres of the cerebrum, allowing them to communicate. The script describes it as a crucial structure for interhemispheric communication, facilitating the integration of information processed by the separate lobes.

💡Lobes

Lobes are the distinct regions of the cerebral hemispheres, each with specific functions. The script details the four main lobes: the frontal lobe (muscle control and cognitive functions), the occipital lobe (visual processing), the parietal lobe (touch, pain, and pressure sensations), and the temporal lobe (auditory processing and language).

💡Peripheral nervous system

The peripheral nervous system is the part of the nervous system that connects the central nervous system to the rest of the body. The script briefly mentions it as essential for the brain to interact with the external environment, setting up the topic for the next lessons in the series.

💡Nervous tissue

Nervous tissue is the fundamental component of the nervous system, including the brain and spinal cord. The script describes it as fragile and jelly-like, requiring protection by the skull and vertebrae, as well as cerebrospinal fluid, to prevent injury.

Highlights

James, a healthy professional and father, suffered a stroke at 45, resulting in Broca’s aphasia which impaired his speech but left comprehension intact.

Broca’s area in the left hemisphere is crucial for language production, and its damage can cause Broca’s aphasia.

Individuals with Broca’s aphasia can understand speech but struggle to produce intelligible words.

James could respond to questions by repeating the word 'too', indicating some speech capability despite Broca’s aphasia.

Singing therapy can help treat Broca’s aphasia by engaging a different brain region analogous to Broca’s area.

James regained communication ability through singing and relearning to speak by training the right side of his brain.

Studying brain injuries has significantly contributed to our understanding of the brain's specific functions.

The brain is composed of specialized regions, each with specific functions, illustrating the concept of 'Everything is local' in brain function.

The central nervous system integrates sensory information and coordinates responses, including conscious and unconscious activities.

The spinal cord conducts signals between the brain and the body and governs basic muscle reflexes.

The brain and spinal cord are protected by the vertebrae, meninges, and cerebrospinal fluid within the skull.

The brain's development from a neural tube into specialized regions illustrates a division of labor for different functions.

The prosencephalon, mesencephalon, and rhombencephalon are primary brain vesicles that further develop into adult brain structures.

The brainstem, consisting of the midbrain, pons, and medulla oblongata, regulates basic vital functions.

The diencephalon includes the thalamus and hypothalamus, playing roles in homeostasis, alertness, and reproductive activity.

The telencephalon develops into the cerebrum, the largest part of the brain responsible for higher cognitive functions.

The cerebral cortex and white matter of the cerebrum are responsible for voluntary movements and advanced cognitive functions.

The corpus callosum connects the left and right hemispheres of the cerebrum, facilitating communication between them.

Different lobes of the cerebral hemispheres have distinct functions, such as the frontal lobe in muscle control and cognitive functions.

The occipital lobe is responsible for processing visual information, while the parietal lobe processes touch, pain, and pressure.

The temporal lobe sorts auditory information and contains Wernicke’s area, important for language production.

The limbic system, including the hippocampus and amygdala, is central to emotions and memory.

Transcripts

James was healthy professional, a father of two. He had lots of friends, loved telling

jokes, and played softball on Sundays.

Then one day, at the age of 45, he suffered a stroke. He bounced back fairly quickly,

with one major exception: He was no longer able to speak. The stroke damaged a specific

area in the left hemisphere of his brain called Broca’s area, and left him with what’s

known as Broca’s aphasia.

Broca’s area is partly responsible for the ability to produce and process language, and

Broca’s aphasia often leaves its sufferers with some ability to understand speech, but

an inability to produce intelligible words.

James could understand his wife when she asked if he wanted cereal for breakfast, but he

could only respond by repeating the word “too” -- although he could still intonate as though

he were speaking a whole sentence.

Then, after some time and therapy, something rather unexpected happened -- James regained

some ability to communicate through singing.

Broca’s aphasia can sometimes be treated by teaching patients to sing, because singing

uses a different region of the brain -- one that’s on the right side and that’s analogous

to Broca’s area on the left.

So after some practice, James could sing words, and he eventually relearned how to talk by

teaching the right side of his brain to speak rather than sing.

Whether it’s a stroke affecting your speech, a tumor destroying your memory, a concussion

affecting your aggression, or that fateful iron rod that shot straight through Phineas Gage’s

skull -- a lot of what we know about how the brain works has come through studying injuries to it.

And what we’ve learned so far is that, even though it looks like a 1.4-kilogram lump of

gray, congealed oatmeal, the brain is made up of super-specific areas that have super-specific functions.

You might actually say the same thing about your brain that’s sometimes said about politics:

Everything is local.

You’ll remember that our nervous system is divided into two main networks that work

in harmony -- the central nervous system, consisting of your amazing brain and spinal

cord, and the peripheral nervous system, made up of the nerves coming out of that central nervous system.

The central nervous system’s main game is integrating the sensory information that the

peripheral system collects from all over the body, and responding to it by coordinating

both conscious and unconscious activity.

The sun is bright, so I’ll shade my eyes; I’m hungry, so I’m calling the pizza man;

the phone is ringing, maybe I’ll answer it.

All these sensations, thoughts, and directions process through this two-part system.

It’s the brain, of course, that sorts out all that sensory information and gives orders.

It also carries out your most complex functions, like thinking, and feeling, and remembering.

Meanwhile, your spinal cord conducts two-way signals between your brain and the rest of

your body, while also governing basic muscle reflexes and patterns that don’t need your

brain’s blessing to work -- this is how a chicken can still run around even if the

poor thing has been decapitated.

Both your spinal cord and brain are made of fragile, jelly-like nervous tissue that is

extremely susceptible to injury.

So all that goo is well-protected by the bones of your vertebrae and cranium, as well as

membrane layers, or meninges, before being bathed in a cushy waterbed of clear cerebrospinal fluid.

This fluid actually allows your brain to float somewhat in your skull, reducing its weight

and letting it slosh around while you and your head are free to move.

But even with all that extra protection, your brain is still vulnerable. And one thing James’s

story taught us is that its vulnerabilities can be incredibly specific, because your brain

is divided into specialized regions that may, or may not, interact with each other to produce a given action.

We can better understand this division of labor by looking at how the brain first develops

into its main component parts.

Inside a developing embryo, the central nervous system starts off as a humble little neural tube.

Soon the caudal, or lower, end of the tube stretches out, forming the spinal cord, while

the cranial end begins to expand, divide, and enlarge into three primary brain vesicles,

or interconnected chambers.

This is kind of your proto-brain.

We call these chambers the prosencephalon, the mesencephalon, and the rhombencephalon

-- or forebrain, midbrain, and hindbrain.

By an embryo’s fifth week of development, these main three chambers start morphing into

five secondary vesicles that essentially form the roots of what will become your grown-up brain structures.

The prosencephalon divides into two sections -- the telencephalon and the diencephalon.

The rhombencephalon forms into another pair, called the metencephalon and the myelencephalon.

And in between, the mesencephalon, thanks to evolution, remains undivided.

The real action starts as these five secondary vesicles start developing into the major adult

brain regions that you might be more familiar with -- the brainstem, the cerebellum, the

diencephalon, also known as the interbrain, and finally the cerebral hemispheres.

But, in order to go from a simple tube into that classic, wrinkly icon we think of as

the “brain,” each of these five vesicles grows in different ways. Basically, some develop

a lot more than others.

The least dramatic changes occur in the three most caudal or lower sections: the mesencephalon,

the metencephalon, and the myelencephalon.

They go on to form the cerebellum, which mostly helps coordinate muscular activity, and the brainstem,

which plays a vital role in relaying information between the body and the higher regions of the brain.

The brainstem actually has three main components -- and I know this is getting to be a lot

of vocabulary here -- you have the midbrain, the pons, and the medulla oblongata. Together

they regulate many of the most basic, vital involuntary functions, like keeping your heart on pace, keeping

your lungs working, and controlling things like sleep, and appetite, and pain sensitivity, and awareness.

But of the three brainstem parts, it’s your midbrain that carries out the higher-level functions.

Like, when your eyes track a fast moving object, or when you look behind you after hearing

some sudden loud sound, it’s the midbrain that receives and processes that sensory information

and sends out the reflexive motor signals, so you react without thinking.

The midbrain also passes that data to regions like the cerebral cortex, which do the actual

conscious thinking about the stimuli, like “What is that thing whizzing across the sky?”

or “WHAT JUST EXPLODED BEHIND ME?!”

So with the brainstem and cerebellum covering your basic life and motor functions, you start

to see somewhat more complex tasks being carried out in the next major brain structure, the diencephalon.

This is where you find the thalamus, hypothalamus, epithalamus, and the mammillary bodies, which

regulate things like homeostasis, alertness, and reproductive activity. Here we also find

part of the limbic system, which is a center for strong emotions, like fear.

This area is sometimes called the “reptilian brain” because we share it with some of

our less philosophical animal brethren like lizards and fish.

I’m not putting these guys down, but by our standards, they don’t think so much

as focus on the more instinctual pursuits that are ruled by the caudal regions of the

brain -- eat, drink, sleep, mate, stay safe.

All those things are awesome. But it wasn’t until the appearance of birds and mammals

that some animals’ brains came to be dominated by the last of the five vesicles, the telencephalon.

During your brain’s growth, the telencephalon undergoes the biggest changes of all, as it

develops into the most brainy part of your brain -- the two classic, walnut-looking hemispheres

we collectively call the cerebrum, that cover the rest of your brain like a mushroom cap on its stalk.

That’s the cerebrum -- not to be confused with Cerebro, which is Professor X’s telepathy-enhancing

device -- and it is the largest region of the brain and performs the highest functions.

It’s made up of the wrinkled, outer layer of “gray matter” called the cerebral cortex,

and the inner squishy layer of “white matter” beneath it.

And it’s the cerebrum that rules our voluntary movements and our most advanced tricks, like thinking,

and learning, and regulating and recognizing emotions, and experiencing consciousness in general.

You’ll remember that higher processing requires lots of synapses, which require lots of nervous tissue.

So as the cerebrum grew through evolutionary time, it got more massive but our skull didn’t exactly keep up.

So in order to squeeze all that material into your skull, the brain forms little creases,

called gyri, and larger grooves, or sulci, giving it more folds than than an origami pineapple.

And although a big fissure separates the left and right hemispheres, the two halves communicate,

through a series of myelinated axon fibers called the corpus callosum.

And each hemisphere has other, smaller fissures that divide it into lobes -- each with a different

set of major functions.

The frontal lobe, for example, governs muscle control and cognitive functions like planning

for the future, concentration, and preventing socially unacceptable behaviors.

In most people, this area doesn’t finish developing until after the teenage years,

which tells you a lot about the teenage years. Since Broca’s area lives in this lobe in

the left hemisphere, it also is important in language comprehension and speech.

If you’re enjoying a beautiful sunset, you can thank your occipital lobe at the back

of your head for processing those bright visual cues.

And the next time you step on a lego, you can curse your parietal lobe, which processes

the sensations of touch, pain, and pressure.

Meanwhile the temporal lobe helps sort out auditory information, including language.

It contains Wernicke’s area -- another important region of the brain associated with the production

of written and spoken language.

This part of the limbic system includes your short-term memory keeper, the hippocampus,

and the emotional amygdala, which controls sexual and social behavior. So, if you damage

the wrong part of your temporal lobe, you may never again be able to remember what you

ate for lunch… or you might suddenly become a total jerk who kicks kittens and cuts in line.

We could do a whole course on the finer-grained functions and consequences of malfunction

in every bit of brain in your gourd, but, well, we can’t do that today.

And you got to remember that, when it comes to your body, no organ or system is an island.

Your brain would be pretty useless if it weren’t hooked up to the outside world. That’s where

the peripheral nervous system comes in, which we’ll be spending the next few lessons exploring.

Meanwhile, you learned today about the central nervous system and how important location

is to brain function. We looked at how the brain develops from an unassuming neural tube

into three primary vesicles, and then five secondary vesicles, and finally into our complex

set of four adult structures and their basic functions.

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This episode was written by Kathleen Yale. The script was edited by Blake de Pastino,

and our consultant, is Dr. Brandon Jackson. It was directed by Nicholas Jenkins and Michael

Aranda, and our graphics team is Thought Café.