Cerebral Hemispheres

Summary

In this educational video, Dr. Mike explores the cerebral hemispheres, the largest and most developed part of the brain. He explains their role in motor and sensory functions, conscious awareness, and higher cognitive processes. The script delves into the structure of the cerebrum, including the cortex for integration and consciousness, and the deeper white matter for information transfer. It also touches on the importance of the limbic system for emotions and memory, and the significance of the corpus callosum in connecting the two hemispheres.

Takeaways

• 🧠 The brain is composed of the cerebrum, cerebellum, and brainstem, with the cerebrum being the largest and most developed part.
• 🔍 The cerebrum is divided into two hemispheres by a fissure, each with distinct functions and areas of specialization.
• 🏗️ The cerebral cortex, the outer layer of the cerebrum, is where integration and processing of information occur, containing gray matter and white matter.
• 🏋️‍♂️ The primary motor cortex, located in the frontal lobe, is responsible for initiating voluntary movements.
• 🔎 The primary sensory cortex in the parietal lobe processes sensory information from the environment for conscious awareness.
• 🤝 Association areas in the cerebral hemispheres help link previous and current information, aiding in complex analysis and planning.
• 💡 Conscious experience arises from the cerebral cortex; without it reaching this layer, awareness does not occur.
• ❤️ The limbic system, part of the cerebral hemispheres, plays a key role in memory and emotional aspects of behavior.
• 🧠 The prefrontal cortex in the frontal lobe is the highest aspect of cognitive function, involved in planning, judgment, and appropriate behavior.
• 🔄 Commissural fibers, like the corpus callosum, connect the two hemispheres, allowing information transfer between them.
• 🧬 Deeper structures within the cerebrum, including white matter, serve as pathways for projecting information to other brain areas and the body.
• 📏 The cerebral hemispheres are anatomically demarcated by sulci and gyri, which increase the brain's surface area for more neuron integration.

Q & A

What are the three main parts of the brain?

The three main parts of the brain are the cerebrum, the cerebellum, and the brainstem.

What is the function of the fissure in the cerebrum?

The fissure in the cerebrum separates it into two hemispheres: the left hemisphere and the right hemisphere.

What are the primary motor and sensory cortices located in?

The primary motor and sensory cortices are located in the cerebral hemispheres.

What does the term 'cortex' refer to in the context of the brain?

In the context of the brain, 'cortex' refers to the outer one to five millimeters of the cerebrum, which contains gray matter.

How does the gray matter in the brain differ from white matter?

Gray matter consists of cell bodies and areas of synapsing, serving as the site of integration. White matter, on the other hand, is composed of axons and serves as the highways for signal transmission.

What role do the association areas of the cerebral hemispheres play?

Association areas help the primary motor and sensory cortices by associating previous information with current information, allowing for the analysis of complex information.

How is the sensory cortex related to our conscious awareness of external and internal stimuli?

The sensory cortex is where information from the external and internal environment is processed for us to become consciously aware of it.

What is the role of the cerebral cortex in conscious experience?

The cerebral cortex is the substrate for conscious experience; it is where we become consciously aware of anything that reaches this outer layer of the cerebral hemispheres.

What is the limbic system and what is its importance in the brain?

The limbic system is important for memory and the emotional aspects of behavior, such as feeding, relationships, reproduction, and fight or flight responses.

What cognitive functions are primarily associated with the frontal lobe of the cerebrum?

The frontal lobe, specifically the prefrontal cortex, is associated with higher-order cognitive functions such as planning, judgment, emotion, and ensuring appropriate behavior for different scenarios.

What are the different types of fibers found in the cerebrum and their functions?

There are commissural fibers that connect the two hemispheres, projection fibers that carry information from the cerebrum to the brainstem and spinal cord, and association fibers that connect different parts of the cortex for integration and understanding.

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

The corpus callosum is the connection between the two cerebral hemispheres, allowing for the exchange of information between them. In some cases of severe epilepsy, it may be surgically cut to prevent the spread of seizure activity.

What are the anatomical features that give the brain its wrinkled appearance?

The brain's wrinkled appearance is due to the presence of gyri (bumps) and sulci (dips), which increase the surface area of the brain, allowing for more neurons and integration sites.

How are the different lobes of the cerebrum anatomically demarcated?

The different lobes of the cerebrum are demarcated by sulci, such as the central sulcus separating the frontal lobe from the parietal lobe, and the lateral sulcus separating the temporal lobe from the frontal and parietal lobes.

Outlines

00:00

🧠 Introduction to Cerebral Hemispheres

Dr. Mike introduces the concept of cerebral hemispheres, explaining that the brain is divided into the cerebrum, cerebellum, and brainstem. The cerebrum, being the largest and most developed part, is further divided into two hemispheres by a fissure. The cerebrum is responsible for higher brain functions, including the primary motor and sensory cortices, which are involved in voluntary movements and conscious awareness of sensory information, respectively. The outer layer, or cortex, is composed of gray matter for integration and white matter for signal transmission. Association areas within the cerebral hemispheres help in analyzing complex information by associating past and present data.

05:01

🧠 Deeper Insights into Cerebral Functions

This paragraph delves deeper into the functions of the cerebral hemispheres, highlighting the importance of the cortex for conscious awareness and the role of the limbic system in memory and emotional behavior. The prefrontal cortex within the frontal lobe is identified as the area responsible for higher cognitive functions such as planning and judgment. The paragraph also discusses the structural components of the cerebrum, including the gray matter cortex for integration and the white matter for information projection. It explains the significance of commissural fibers like the corpus callosum, which connects the two hemispheres, and the implications of severing these fibers in cases of severe epilepsy. Additionally, the paragraph touches on the anatomy of the brain, including gyri and sulci, and how they contribute to the brain's complex structure and function.

10:04

🧠 Lobes and Fibers of the Cerebral Hemispheres

The final paragraph focuses on the anatomical aspects of the cerebral hemispheres, detailing the lobes and their respective functions. It describes the frontal, parietal, occipital, and temporal lobes, as well as the insular lobe, and how they are demarcated by sulci and gyri. The paragraph explains the role of different types of fibers: commissural fibers that connect the hemispheres, projection fibers that send information to deeper brain structures, and association fibers that facilitate communication between different cortical areas. It emphasizes the complexity and development of the cerebral hemispheres, which are crucial for conscious experience, cognitive functions, and emotional understanding.

Keywords

💡Cerebrum

The cerebrum is the largest part of the human brain, consisting of two hemispheres, the left and right, separated by a fissure. It is the most developed part of the brain and is responsible for higher cognitive functions such as thinking, understanding, and remembering. In the video, the cerebrum is discussed as the main focus, highlighting its role in motor and sensory functions, as well as its importance in consciousness and cognitive processes.

💡Hemispheres

Hemispheres refer to the two halves of the cerebrum, the left and right hemispheres, which are distinct in structure and function. The video script explains that these hemispheres are separated by a fissure and each has specialized roles in cognitive and sensory processing, emphasizing the complexity and development of the brain.

💡Cortex

The cortex, also known as the cerebral cortex, is the outer layer of the cerebrum, composed of gray matter. It is involved in higher-order brain functions such as perception, thought, and language. The script mentions the cortex in the context of primary motor and sensory cortices, which are essential for voluntary movement and conscious awareness of sensory information.

💡Gray Matter

Gray matter is a term used to describe the areas of the brain containing mainly the cell bodies of neurons, which appear gray due to the high concentration of these cells. The video script explains that gray matter is where integration and synapsing occur, making it crucial for processing information and is a key component of the cerebral cortex.

💡White Matter

White matter is the part of the brain composed of myelinated axons, which gives it a white appearance. It is responsible for transmitting signals throughout the brain. In the script, white matter is described as the 'highways' that connect different areas of the brain, facilitating communication between them.

💡Motor Cortex

The motor cortex is a region of the frontal lobe that is involved in the planning, control, and execution of voluntary movements. The video script specifically mentions the primary motor cortex as the area initiating voluntary or conscious motor movements, such as walking or playing the piano.

💡Sensory Cortex

The sensory cortex is the part of the brain that processes and interprets sensory information from the body and the environment. In the video, the primary sensory cortex is highlighted as the area where we become consciously aware of sensory information, such as feeling something in a pocket.

💡Association Areas

Association areas are regions of the brain that integrate and process complex information from various sensory inputs. The script describes these areas as assisting the primary motor and sensory cortices by associating previous and current information, allowing for the sequencing and planning of complex tasks, and the analysis of sensory experiences.

💡Limbic System

The limbic system is a group of structures in the brain involved in emotions, behavior, and memory. The video script explains that the limbic system is important for the emotional aspects of various behaviors, including feeding, relationships, and the fight-or-flight response.

💡Cognitive Function

Cognitive function refers to the mental processes that include thinking, understanding, learning, remembering, judging, and problem-solving. The script identifies the cerebral hemispheres, particularly the prefrontal cortex, as the highest aspect of cognitive function, responsible for planning, judgment, and appropriate behavior.

💡Corpus Callosum

The corpus callosum is a band of nerve fibers that connects the two cerebral hemispheres, allowing for communication between them. The script discusses the importance of the corpus callosum in facilitating the transfer of information between hemispheres and mentions its surgical division in cases of severe epilepsy to prevent the spread of seizure activity.

💡Projection Fibers

Projection fibers are axons that carry information from the cerebral cortex to deeper brain structures, the brainstem, and spinal cord. The video script explains that these fibers are essential for the transmission of sensory and motor signals, and they typically cross to the opposite side of the body, reflecting the contralateral control of body movement.

Highlights

The brain is composed of the cerebrum, cerebellum, and brainstem.

The cerebrum is the largest and most developed part of the brain, featuring a fissure that divides it into left and right hemispheres.

Cerebral hemispheres contain primary motor and sensory cortices, which are crucial for voluntary movement initiation and conscious sensory awareness.

The cortex refers to the outer layer of the cerebrum, consisting of gray matter for neuron cell bodies and synapses, and white matter for axons.

Gray matter is the site of integration and consciousness, while white matter acts as the communication highways between brain regions.

Association areas in the cerebral hemispheres help analyze complex information by associating previous and current data.

The association areas for the motor cortex enable the planning and sequencing of complex movements.

Sensory association cortices assist in understanding sensory information by drawing from past experiences.

Conscious experience arises in the cerebral cortex, which is the outer layer of the cerebral hemispheres.

The limbic system, part of the cerebral hemispheres, is vital for memory and emotional aspects of behavior.

The prefrontal cortex within the frontal lobe is responsible for higher cognitive functions such as planning and judgment.

Damage to the prefrontal cortex can lead to issues in behavior, planning, and decision-making.

The cerebrum includes both the superficial cerebral cortex and deeper structures for information projection.

Commissural fibers, such as the corpus callosum, connect the two cerebral hemispheres, facilitating inter-hemispheric communication.

Corpus callosotomy, a procedure that severs the corpus callosum, can mitigate severe epilepsy by preventing neuron misfiring from spreading.

Split-brain experiments reveal fascinating insights into the separation of brain consciousness and functions.

Projection fibers connect the cerebral cortex to deeper brain structures, including the brainstem and spinal cord.

Association fibers are essential for inter-cortex communication, enabling complex task sequencing and sensory interpretation.

The cerebral hemispheres consist of distinct lobes, each with specific functions, including the frontal, parietal, occipital, temporal, and insular lobes.

Gyri and sulci are anatomical features that demarcate different brain regions and increase the brain's surface area for more neuron integration.

Transcripts

hi everyone dr mike here in this video

we're going to take a look at the

cerebral

hemispheres so when we take a look at

the brain itself we know the brain is

made up of

the cerebrum which is everything colored

here the cerebellum which is that little

brain that sits underneath and towards

the back

and the brain stem underneath which sits

just above

the spinal cord today we're talking

about the largest part of the brain

which is

the cerebrum which has a fissure

or segmentation down the middle that

separates it into two hemispheres

a left hemisphere and a right hemisphere

so it's the largest part of the brain

but it's also the most developed part of

the brain now what do i mean by

developed well let's take a look at some

of the functions

of the cerebrum first of which is that

the cerebral hemispheres contain

the primary motor and sensory cortices

now when i say cortices i'm referring to

the cortex

and the cortex is simply the outer one

to five

millimeters of the cerebrum it contains

gray matter remember

when we look at a neuron you're going to

have the cell body of a neuron

you have the axon of the neuron and then

you're going to have the axon

terminals that axon terminal is likely

going to talk to another axon or neuron

i should say for example so importantly

the axon is surrounded by fat myelin

and fat in this case looks white

so when we look at gray matter gray

matter

are the cell bodies in the areas of

synapsing so that's gray matter

and the white matter is actually simply

the axons so that means that

when you see gray matter this is the

site of integration when we make sense

of

information the white matter is simply

just highways

this is simply where one signal is sent

to the next area

all right keeping that in mind when we

look at the primary motor

and sensory cortices that sit within the

cerebral

hemispheres this is the highest level

of activity for example when we look at

the motor cortex

cortex or the primary motor cortex which

actually sits

in this part of the frontal lobe this is

the area where we want to

initiate some sort of voluntary or

conscious motor movement if i want to

begin

walking this is where it begins so

that's why it's the highest level in

which motor activity will function

when we look at the sensory cortex this

is where information coming from

the external environment or the internal

environment is coming

up for us to be consciously aware of it

again it's the highest

level of integration of sensor

information

this is where we become aware so think

about if you had your hand in your

pocket

when you feel something in your pocket

this is going

to the sensory cortex

all right now in addition to that i'm

going to skip this part here

we've got association areas that's part

of the cerebral hemispheres

now association areas they help the

primary motor and sensory cortices

by associating previous information and

current information

it's comparing and contrasting what it

already knows

so that you now have more information

it's basically a way to

to analyze complex information so

first of all the association areas for

the motor cortex

so i said you can have the motor cortex

here i want to initiate walking for

example

that's happening there at the primary

motor cortex but the association areas

allow for you to sequence and plan

more complex tasks so if i wanted to go

play the piano for example

or juggle some balls this is where we

have the association areas come into

play

for the motor cortex allows for us to

plan and

sequence complex movements when we look

at the sensory cortex which i didn't say

sits within that parietal lobe here the

association cortices

help it help you understand what piece

of sensory information

you are receiving so i said before that

primary sensory

cortex there you put your hand in your

pocket and you feel something

what the association cortex does is it

analyzes whether it's smooth or rough

whether it may be hot or cold have i

felt it before

what might this be from previous

experience so it's an association cortex

because

it's bringing associations from previous

experience

and throwing it to that of the primary

somatosensory cortex

so these are these association areas all

part of the cerebral cortex

the cerebral hemisphere is the substrate

for conscious

experience when we become consciously

aware of

anything it's because it's gone to the

cortex

of the cerebral hemispheres so if you

want to be consciously aware it needs to

get to

those one to five centimeter thick a

millimeter i should say layer of the

cerebral hemispheres

if you want to be consciously awake this

is where consciousness is going to arise

where you become aware of experience

more deeper areas of the brain

may receive sensory information but you

will not become aware

of it occurring or it may make a

decision about conscious

may make a decision about motor movement

but you're not going to be consciously

aware of that

for conscious awareness it must get to

that one to five centimeter

external layer that we call the cortex

of our cerebral hemispheres

the cerebral hemispheres also contain

the limbic system now the limbic system

is important for memory and emotional

aspects of

behavior so think of emotional aspects

of things that you do so the emotional

aspects of feeding

the emotional aspects of relationships

the emotional aspects of reproduction

the emotional aspects

of fight or flight this is the limbic

system

and you can see part of the limbic lobe

sitting here but there's deeper limbic

structures as well

right near the thalamus that you can see

here so we've got the limbic system

it's also the highest aspect of

cognitive function the cerebral

hemispheres the highest aspect of

cognitive

function so when we look at cognitive

function we're thinking about

planning judgment

emotion making sense being

reasonable making sure that your

behavior is appropriate

for the scenario in which you're in

most of this sits within the frontal

lobe specifically an area called the

prefrontal

cortex if that area is damaged we have

issues when it comes to behavior

and planning and things like that all

right

so highest aspect of cognitive function

now like i said when we take the

cerebrum

it's going to have the one to five

millimeter layer and there's going to be

some deeper structures the one to five

millimeter layer like i said is the gray

matter that's the side of integration

and making sense and consciousness

but we've got deeper layers of the

cerebrum where we project information

these are the highways these

are the axons this is the white matter

all right now you can send information

from

one side

of one from this one cerebral hemisphere

to the other

and if you do this you're sending it

through white matter tracks or fibers

they're called

commisural fibers they are predominantly

going to be through what we call the

corpus callosum

that's the connection between those two

hemispheres some people

had a corpus callosum otomy otomy means

the cut it separates those hemispheres

these individuals

had very severe cases of epilepsy and

epilepsy is this misfiring of neurons

if you cut it it stops it from spreading

across the two hemispheres

and help mitigate the severity of their

epilepsy but it also separated the

hemispheres anatomically

and if you have a look at the split

brain experiment studies

you'll find some very interesting things

when it comes to splitting the

consciousness of the brain so you've got

the commissural fibers

from one hemisphere to the other we've

also got projection fibres

these fibres take it from more

superficial areas of the brain

to deeper aspects of the brain brain

stem

and spinal cord these are going to be

projection fibers you can see

that they're going to cross over to the

other side because the right hemisphere

controls the left hand side of the body

left hemisphere controls the right or

the right side of the body sends

information to the left hemisphere

and vice versa which means these

projection fibers must cross at some

point usually they're going to cross at

around about the medullary

region association fibers i spoke about

association

areas association fibers allow for one

part of the cortex to speak to another

part of the cortex

so that we can make more sense of what's

happening

in the situation if i want to sequence a

motor task i need these association

fibers

if i want to make sense of what i'm

feeling in my pocket

again we need these association fibers

so when we look

at the cerebral hemispheres it's made up

of

cerebral cortex one to five millimeter

layer this is the site of

what is it consciousness experience

integration

it's made up of lobes and these lobes

which you should probably look at before

we finish i'm going to focus

more attention on those lobes in future

videos these lobes are made up of the

frontal lobe the parietal lobe

the occipital lobe at the back the

temporal lobe

near the temple and we've also got an

insular lobe if i were to sort of pull

that temporal lobe away from the frontal

you could see the insula

underneath i'm going to do videos on

each of these lobes more specifically

but

final point is that when we look at the

superficial or surface

anatomy of the brain you're going to

find that there's areas which

have a bump up and a dip down

now the bump up is known as a gyrus

that's

singular if it's pleural it's gyri the

dip down is known as a sulcus

again that singular a sulci is plural

and this is what gives the brain its

wrinkled appearance

it just increases the surface area of

the brain which means

there's more room to fit more neurons

more sites of integration

all that type of fun stuff so

a couple of points because i said you've

got the frontal lobe the parietal lobe

the occipital lobe of the temporal lobe

how do we

separate them out how do we anatomically

know where

their demarcation points are well we use

gyri and sulci for example we separate

out the frontal lobe

from the parietal lobe with a sulcus

called the central

sulcus central

sulcus now wherever there's a sulcus

in front and behind is going to be a

gyrus right

so this central sulcus we've got a gyrus

in front called the pre-central

gyrus and that's that primary motor

cortex

we've got a gyrus behind it and that's

going to be called the postcentral

gyrus that's going to be the

somatosensory cortex that we spoke about

as well

when we look at the parietal lobe

separated out by the occipital

lobe we're going to have the parietal

occipital

sulcus parietal

occipital

sulcus and again separating out the

occipital to the parietal

lobe we've also got the temporal lobe

here how is that separated out from the

frontal and parietal lobe above it

we have a lateral sulcus here also known

as a lateral fissure or sylvanian

fissure situated there all right

in a future video i'm going to focus on

each of those lobes but to summarize

the cerebral hemispheres is the largest

and most complex

and most developed part of the brain it

allows for us to have

conscious awareness it has lobes and

these lobes have particular functions

it has cognitive higher order cognitive

function it has

limbic areas for emotional and

behavioral understanding

it has association areas primary motor

primary sensory areas

but more deeper to this it has fibers

axons that can project to other parts of

the cerebral

hemispheres but also deeper parts of the

brain as well