The Central Nervous System: The Brain and Spinal Cord

Summary

This script offers an introductory exploration of the human brain's structure and function, highlighting the central nervous system's complexity. It details the brain's development from a neural tube into primary and secondary vesicles, leading to the adult brain's distinct regions. The focus is on the cerebral cortex's role in conscious thought, and the brain's various sensory and motor areas. The summary also touches on the diencephalon, brainstem, cerebellum, and protective structures like meninges, concluding with a brief mention of the spinal cord and its functions.

Takeaways

• 🧠 The human brain is considered the most complex object in the known universe, with its structure and function, especially consciousness, not yet fully understood.
• 🌱 The development of the brain begins with the neural tube in an embryo, which differentiates into primary and secondary brain vesicles, eventually forming the adult brain regions.
• 🏰 The central nervous system (CNS) includes the brain and spinal cord, with the brain being divided into the cerebrum, diencephalon, brainstem, and cerebellum.
• 🧬 Neurons and various types of neuroglia, such as astrocytes, microglial cells, and oligodendrocytes, play crucial roles within the CNS.
• 🧐 The cerebral cortex, part of the cerebrum, is responsible for conscious mind functions and is divided into motor, sensory, and association areas.
• 🤲 The motor homunculus illustrates the body parts' size in proportion to the number of neurons controlling them, highlighting the complexity of motor control.
• 👁️ The sensory areas of the brain process information from various senses, including touch, vision, hearing, smell, taste, and balance.
• 🔄 The diencephalon, located at the brain's center, includes the thalamus and hypothalamus, which are vital for learning, memory, and autonomic functions.
• 🌐 The brainstem, consisting of the midbrain, pons, and medulla oblongata, connects to the spinal cord and manages essential life functions.
• 🏋️‍♂️ The cerebellum is responsible for muscle coordination and smooth motion, playing a key role in motor control.
• 🛡️ The brain is protected by the meninges, including the dura mater, arachnoid mater, and pia mater, which provide a protective layer between the brain and skull.

Q & A

What are the two main divisions of the nervous system?

The two main divisions of the nervous system are the central nervous system (CNS), which consists of the brain and spinal cord, and the peripheral nervous system (PNS).

What is the human brain considered to be in terms of complexity?

The human brain is considered to be the single most complex object in the known universe due to its vast number of neuronal connections and the not yet fully understood mechanisms of consciousness.

What is the process called that allows the brain to occupy the available space within the skull?

The process is called gyrification, which involves the formation of many folds in the brain to best occupy the available space within the skull.

What are the four main regions of the brain?

The four main regions of the brain are the cerebral hemispheres, diencephalon, brain stem, and cerebellum.

What is the function of the ventricles in the brain?

The ventricles are hollow cavities in the brain filled with cerebrospinal fluid and lined with ependymal cells, which help circulate the fluid.

What are the roles of the different types of neuroglia in the central nervous system?

Neuroglia in the CNS include astrocytes, which perform regulatory functions; microglial cells, which monitor neuron health; and oligodendrocytes, which form myelin sheaths.

What is the primary function of the cerebral cortex?

The cerebral cortex, made of gray matter, is the most recently evolved section of the animal brain and is where the conscious mind is found. It is responsible for higher mental functions such as memory and language.

What does the term 'motor homunculus' represent?

The term 'motor homunculus' represents an image of the human body where each body part is depicted in a size proportional to the quantity of neurons that control it, showing the disproportionate amount of cortex devoted to fine motor control areas like the face, tongue, and hands.

What are the main functions of the diencephalon in the brain?

The diencephalon, consisting of the thalamus, hypothalamus, and epithalamus, is involved in directing information to the cerebral cortex, controlling the autonomic nervous system, regulating body temperature, hunger, thirst, sleep cycles, emotional responses, and housing the pituitary and pineal glands.

What is the cerebellum responsible for in terms of motor control?

The cerebellum is responsible for regulating muscle contraction to generate smooth and coordinated motion.

What are the protective structures for the brain and spinal cord called?

The protective structures for the brain and spinal cord are called meninges, which include the dura mater, arachnoid mater, and pia mater.

Outlines

00:00

🧠 Central Nervous System Structure and Development

Professor Dave introduces the central nervous system (CNS), emphasizing the brain's complexity and its division into the brain and spinal cord. The script delves into the embryonic development of the CNS, detailing the formation of primary and secondary brain vesicles, leading to the adult brain's regions. It explains the process of gyrification, the creation of cerebral hemispheres, and the distinction between different brain areas such as the cerebrum, diencephalon, brainstem, and cerebellum. The importance of neuroglia in the CNS is highlighted, including ependymal cells, astrocytes, microglial cells, and oligodendrocytes. The cerebral cortex's structure and function are explored, noting its role in conscious mind activities and the presence of motor, sensory, and association areas.

05:04

🔍 Brain Function and Lateralization

This paragraph discusses the functional specialization of the cerebral cortex, identifying motor, sensory, and association areas, and how higher mental functions like memory and language are distributed across the cortex. It clarifies the concept of brain lateralization, dispelling the myth of distinct 'left-brain' and 'right-brain' personalities. The paragraph describes the primary motor cortex and its representation through the motor homunculus, the role of the premotor cortex in movement planning, and the function of Broca's area in speech production. Sensory areas are detailed, including somatosensory, visual, auditory, olfactory, gustatory, visceral, and vestibular cortices, along with multimodal association areas. The diencephalon's components—the thalamus, hypothalamus, and epithalamus—are explained in terms of their roles in sensory relay, autonomic nervous system control, and sleep regulation. The brain stem and cerebellum's functions in muscle coordination and balance are also summarized.

10:06

🌿 Spinal Cord and Protective Structures

The final paragraph provides an overview of the spinal cord, its location within the vertebral column, and its protective mechanisms, including cerebrospinal fluid and meninges. It describes the spinal cord's structure, highlighting the gray matter's butterfly shape composed of multipolar neurons and the white matter's role in communication between the brain and the body. The paragraph explains the spinal nerves' organization and the gray matter's zones responsible for sensory and motor functions. Ascending, descending, and transverse nerve fibers in the white matter are mentioned, setting the stage for further exploration of the nervous system's pathways.

Keywords

💡Nervous Tissue

Nervous tissue is a specialized type of tissue that makes up the nervous system, including the brain, spinal cord, and nerves. It is composed of neurons, which are the primary functional cells, and glial cells, which provide support and protection. In the video, nervous tissue is foundational to understanding the structure and function of the brain and the entire nervous system.

💡Neuron

A neuron is the fundamental unit of the nervous system, responsible for transmitting information through electrical and chemical signals. The script discusses the structure of a neuron, which includes dendrites, cell body, and axon, and how these components contribute to the complex communication within the brain.

💡Central Nervous System (CNS)

The central nervous system, composed of the brain and spinal cord, is the control center of the body. It processes information and coordinates activities. The video script delves into the CNS's development and its critical role in the overall functioning of the nervous system.

💡Peripheral Nervous System (PNS)

The peripheral nervous system consists of all the neural elements outside the CNS, including nerves and ganglia. It connects the CNS to the rest of the body, allowing for sensory input and motor output. Although not the main focus of the video, the PNS is mentioned in contrast to the CNS.

💡Brain Vesicles

Brain vesicles refer to the early developmental stages of the brain's structure, which eventually differentiate into the prosencephalon, mesencephalon, and rhombencephalon. These vesicles are crucial for understanding the embryonic development of the brain as described in the video.

💡Cerebrum

The cerebrum is the largest part of the brain, consisting of two cerebral hemispheres. It is responsible for higher cognitive functions such as thought, decision-making, and memory. The script explains how the cerebrum develops from the telencephalon and its importance in the brain's structure.

💡Gyri and Sulci

Gyri are the ridges, and sulci are the grooves on the surface of the cerebrum. These structures increase the surface area of the brain, allowing for a greater number of neurons to fit within the skull. The video script uses the terms to describe the physical appearance and functional significance of the brain's surface.

💡Cerebral Cortex

The cerebral cortex is the outer layer of the cerebrum, composed mainly of gray matter. It is involved in higher brain functions, including perception, thought, and language. The script highlights the cortex's role in conscious mind activities and its layered structure.

💡Motor Homunculus

The motor homunculus is a distorted representation of the human body that illustrates the areas of the primary motor cortex responsible for voluntary movements. The video script uses this concept to explain the disproportionate allocation of cortical space to different body parts based on their motor complexity.

💡Lobe

Each cerebral hemisphere is divided into five lobes: frontal, parietal, temporal, occipital, and insula. These lobes are named after the bones of the skull they are adjacent to and are associated with different cognitive functions. The video script describes the lobes to provide a comprehensive understanding of the brain's anatomy.

💡Diencephalon

The diencephalon is a region of the brain situated between the cerebral hemispheres and the brainstem, including structures like the thalamus and hypothalamus. It plays a vital role in sensory integration, motor control, and autonomic functions. The script explains the diencephalon's central position and its various functions.

💡Brain Stem

The brain stem, consisting of the midbrain, pons, and medulla oblongata, connects the brain to the spinal cord and regulates many essential life functions such as breathing and heart rate. The video script discusses the brain stem's role in maintaining these critical processes.

💡Cerebellum

The cerebellum is responsible for coordinating muscle activity and maintaining balance. It is located at the back of the brain and plays a key role in fine motor control and coordination. The video script describes the cerebellum's function and its structural relationship to the rest of the brain.

💡Meninges

The meninges are the protective layers of tissue that surround the brain and spinal cord. They include the dura mater, arachnoid mater, and pia mater, which serve to cushion and protect the delicate neural structures. The video script mentions the meninges as part of the brain's protective structures.

💡Neurotransmitters

Although not explicitly mentioned in the script, neurotransmitters are the chemical messengers that transmit signals across synapses between neurons. They are essential for communication within the nervous system and are implied in the discussion of neuronal connections and brain function.

Highlights

The two main divisions of the nervous system are the central nervous system (CNS) and the peripheral nervous system (PNS).

The CNS consists of the brain and spinal cord, with the brain being the most complex object in the known universe.

Brain development begins with a single neural tube that eventually differentiates into various brain vesicles.

The cerebral hemispheres form the cerebrum, while the midbrain and hindbrain segments collectively become the brainstem.

The brain undergoes gyrification, producing folds to occupy the available space within the skull.

The adult brain is divided into four main regions: cerebral hemispheres, diencephalon, brainstem, and cerebellum.

Ventricles are hollow cavities in the brain filled with cerebrospinal fluid and lined with ependymal cells.

Neuroglia in the CNS include astrocytes, microglial cells, and oligodendrocytes, which perform various supportive functions.

The cerebral cortex is the most recently evolved section of the brain and is responsible for conscious mind functions.

The cerebral cortex is divided into motor, sensory, and association areas, each responsible for specific bodily functions.

The motor homunculus is an image depicting the human body parts proportional to the quantity of neurons controlling them.

The diencephalon includes the thalamus, hypothalamus, and epithalamus, playing key roles in sensory processing and bodily regulation.

The brainstem consists of the midbrain, pons, and medulla oblongata, connecting to the spinal cord.

The cerebellum regulates muscle contraction for smooth, coordinated motion and is involved in motor learning.

Meninges are connective tissue membranes that protect the brain, including dura mater, arachnoid mater, and pia mater.

The spinal cord is protected by cerebrospinal fluid and the same meninges as the brain, with 31 pairs of spinal nerves attaching to it.

The spinal cord's gray matter is butterfly-shaped, consisting of multipolar neurons that connect with skeletal muscles and other body structures.

White matter in the spinal cord contains nerve fibers for communication between the cord and the brain, with various pathways.

Transcripts

Professor Dave here, let’s look at some brains.

We just learned about nervous tissue, and the structure of a neuron, as well as the

divisions of the nervous system.

The two main divisions are the central nervous system and the peripheral nervous system,

so let’s go over the first of these in more detail now.

As we said, the central nervous system consists of the brain and spinal cord.

The human brain is the single most complex object in the known universe.

With a dizzying number of neuronal connections, and the mechanism by which it produces consciousness

not yet well-understood, we will have to be satisfied with a mere introduction to this organ.

Rest assured, the brain and cognition will be discussed in far greater detail in the

upcoming biopsychology course, but for now, we will just cover the basics.

The best way to approach learning the structure of the brain is to examine early brain development.

Within an embryo, the brain and spinal cord begin as a single neural tube.

The anterior or rostral end begins to expand and constrictions soon demarcate the three

primary brain vesicles.

These are the prosencephalon, or forebrain, the mesencephalon, or midbrain, and rhombencephalon,

or hindbrain.

The posterior or caudal end of the neural tube will eventually become the spinal cord,

which we will discuss later.

From the primary brain vesicles, the secondary brain vesicles eventually develop.

The forebrain becomes the telencephalon, or endbrain, and the diencephalon, or interbrain.

The midbrain stays as it is, and the hindbrain becomes the metencephalon, or afterbrain,

and myelencephalon, or spinal brain.

These will then all develop further to become the regions of the adult brain.

The telencephalon sprouts two lateral regions called cerebral hemispheres, which together

form the cerebrum, and the midbrain and hindbrain segments collectively become the brain stem.

Confined to the volume of the skull, the fast-growing brain produces many folds, a process called

gyrification, in order to best occupy the available space.

This eventually results in the representation of the brain we are all familiar with, which

we typically divide into four main regions.

Those are the cerebral hemispheres, diencephalon, brain stem, and cerebellum.

There are also hollow cavities called ventricles, which are filled with cerebrospinal fluid

and lined with glial cells called ependymal cells.

Many of these have cilia to help circulate the fluid.

The other types of neuroglia we will find in the central nervous system include astrocytes,

with lots of branches to perform a variety of regulatory functions, microglial cells,

which monitor neuron health, and oligodendrocytes, which form myelin sheaths.

Getting back to brain structure, the majority of the mass of the brain sits in the cerebral

hemispheres.

The spongy appearance is produced by ridges called gyri that are separated by grooves

called sulci, while deeper grooves are called fissures, like the longitudinal fissure that

separates the hemispheres.

Each hemisphere is divided into five lobes, those being frontal, parietal, temporal, occipital,

and insula, the first four of which are named after the cranial bones that are adjacent

to them.

We can also describe each hemisphere as exhibiting three regions.

There is a cerebral cortex made of gray matter, consisting mainly of nerve cell bodies and

nonmyelinated fibers, an internal region of white matter, which is a dense collection

of myelinated fibers, and basal nuclei, or regions of gray matter within the white matter.

As it’s the most complex, let’s focus on the cerebral cortex.

This is the most recently evolved section of the animal brain, and as such it is where

the conscious mind is found.

It is made of gray matter comprised of six layers of interneurons, as well as glia and

blood vessels, and there are specific regions in the cortex called domains, which are responsible

for particular motor and sensory functions.

In other words, certain parts of the cortex are in charge of certain aspects of bodily

function.

We call these motor areas, sensory areas, and association areas.

The highest mental functions, however, like memory and language, are spread around much

of the cortex, and overlap numerous domains.

In addition, each hemisphere is responsible for the sensory and motor functions of the

opposite side of the body, so the left side of the brain controls the right side of the

body, and vice versa.

There are other aspects of the brain that are lateralized, meaning focused more on one

side of the cortex than the other, although that whole “left-brain/right-brain” personality

type is a complete myth.

Going back to the domains we mentioned, let’s discuss the motor areas first.

First is the primary cortex.

This region controls voluntary motion, and each part of the body is relegated to a particular

part of the primary cortex.

The most delicate voluntary motion occurs in the face, tongue, and hands, so a disproportionate

amount of this cortex is devoted to those areas.

The motor homunculus is an image that depicts the human body with all of its body parts

of a size that is proportional to the quantity of neurons that control them, which is why

some features seem dramatically oversized.

Then there is the premotor cortex.

This helps plan movements, and sequences them into complex tasks, like playing a musical

instrument.

Next is Broca’s area.

This controls muscles involved in speech production, among other things.

And then there is the frontal eye field, which controls voluntary eye movement.

Moving on, let’s list the sensory areas.

The primary somatosensory cortex receives information from receptors in the skin and

other areas.

This information goes to the somatosensory association cortex where it is integrated

to produce a rational understanding of an object that is being perceived.

The primary visual cortex and visual association area receive and integrate visual information,

the primary auditory cortex and auditory association area do the same for auditory information,

the olfactory cortex processes odors, the gustatory cortex perceives taste, the visceral

sensory area produces conscious perception of visceral sensations in the stomach and

other organs, while the vestibular cortex allows for our perception of balance or equilibrium.

There are also multimodal association areas that send and receive information to and from

multiple areas.

These are the anterior and posterior association areas, and the limbic association area.

Moving on from the cerebral hemispheres, we get to the diencephalon, which sits at the

very center of the brain.

This consists of the thalamus, hypothalamus, and epithalamus.

The thalamus receives and directs all of the information headed to the cerebral cortex.

This means it is intimately involved with learning and memory, among other things.

The hypothalamus sits immediately below the thalamus.

This controls the autonomic nervous system, regulates body temperature, hunger and thirst,

sleep cycles, physical response to emotions, and the endocrine system.

It also houses the pituitary gland.

Lastly the epithalamus houses the pineal gland, and helps regulate sleep.

After the diencephalon we get to the brain stem.

This consists of the midbrain, pons, and medulla oblongata, the last of which blends into the

spinal cord.

Finally, we get to the cerebellum.

This region, which consists of two hemispheres, regulates muscle contraction to generate smooth,

coordinated motion.

In addition, we should be aware of the structures that protect the brain.

Meninges are connective tissue membranes that sit between the brain and the skull.

On top is dura mater, consisting of a periosteal layer and a meningeal layer.

Immediately below is arachnoid mater, filled with blood vessels.

And lastly is pia mater, made of more delicate connective tissue.

That wraps up a basic survey of the brain.

We will go into more detail at another time, for now let’s finish off the central nervous

system with a quick look at the spinal cord.

We learned about the vertebral column when we looked at the skeletal system, and right

in the middle of the column sits the spinal cord, spanning from the base of the skull

to just past the ribs.

Other than the vertebral column, the spinal cord is protected by cerebrospinal fluid and

the same meninges that we saw for the brain.

Thirty one pairs of spinal nerves attach to the cord, and we can get a better look at

the cord by examining cross sections.

The gray matter towards the center takes on a butterfly shape, made of multipolar neurons.

From these dorsal horns and ventral horns, neurons connect with skeletal muscles and

other structures around the body, and these stem from four zones.

Somatic sensory, visceral sensory, visceral motor, and somatic motor.

Surrounding the gray matter is white matter, made of nerve fibers that allow for communication

between the cord and the brain.

These can be ascending, descending, or transverse, depending on their direction of travel.

These participate in an incredible number of pathways that we will investigate in more

detail later.

For now, let’s continue through a survey of the branches of the nervous system.