Video Transcript
In this video, we’ll learn how to
describe the structure and function of the different parts of the central nervous
system. We’ll start by learning to describe
the different divisions of the brain, including the three membranes that surround
and protect the brain and spinal cord. Then, we’ll explore the basic
structure of the brain divisions, how to identify the different lobes of the
cerebrum, and discuss the different function of each of these brain divisions. We will also outline the components
of the spinal cord and learn to identify the structures of the spinal cord when
shown in cross section. Finally, we’ll briefly discuss how
the structure of the spinal cord supports the transmission of nerve impulses to and
from the brain.
The human nervous system has three
main functions: gathering sensory information, processing the gathered sensory
information, and coordinating a motor response to the process sensory
information. The central nervous system, or CNS,
is a part of the human nervous system that is responsible for receiving sensory
information, processing sensory information, and coordinating an appropriate motor
response. To carry out all of these actions,
the CNS uses its two major components, the brain and the spinal cord.
Since the brain and spinal cord
perform some of the most critical functions of our bodies, they are heavily
protected. The first layer of protection for
the brain and spinal cord are the bones that encase these two structures. The brain is surrounded by the
skull, whereas the spinal cord is surrounded by many small bones called the
vertebrae. Underneath the bone, there are
three more layers of protection in the form of membranes called the meninges. These three membranes each have a
specific function and name. The outermost membrane that lines
the bones is called the dura mater. Dura mater is Latin for tough
mother and helps describe the texture of this membrane, which is very thick and
durable.
Underneath the dura mater is the
arachnoid mater. If the word “arachnoid” reminds you
of spiders and cobwebs, great catch! The term is derived from the Greek
word for spider. The arachnoid mater gets its name
because it has the consistency and appearance of a spider web. And much like a spider web, while
it is thin, it’s very strong and able to stabilize the movement of the brain within
our skull.
The membrane closest to the brain
and spinal cord is called the pia mater. Pia mater is Latin for tender
mother. This is meant to describe the
delicate structure of this membrane. However, while delicate, the pia
mater adheres tightly to the surface of the brain and spinal cord like a plastic
wrap. This forms a resistant barrier
around these structures, making it difficult for foreign bodies to act upon the
brain and spinal cord.
Now that we know how the brain and
spinal cord are protected from physical damage, let’s take a look at each component
of the CNS in detail, starting with the brain. From a developmental perspective,
the brain has three divisions, the forebrain, the midbrain, and the hindbrain. Each of these divisions contains
multiple parts. The forebrain is mainly composed of
the cerebrum and deeper brain structures like the thalamus and the hypothalamus. The midbrain is the smallest of the
three brain divisions and is mainly composed of the tectum, the cerebral aqueduct,
the tegmentum, and the cerebral peduncles. The hindbrain, which is the lowest
of the three brain divisions, has three main parts: the pons, the cerebellum, and
the medulla oblongata.
Let’s take a deeper dive into the
function of the different brain components found within the forebrain, midbrain, and
the hindbrain. The forebrain is the largest and
most developed part of the human brain. And as mentioned, the forebrain
consists primarily of the cerebrum and deeper brain structures, including the
thalamus, hypothalamus, hippocampus, optic nerves, and the olfactory bulb. These structures of the forebrain
are responsible for reasoning, memory, language, sensory perception, and emotional
responses.
The cerebrum comprises the bulk of
the forebrain and is split into two halves or hemispheres. The hemispheres communicate and
transmit information to one another through a thick track of nerve fibers. The outermost layer of the cerebrum
is called the cerebral cortex and is easily identified by its characteristic
wrinkled appearance. The term “cortex” is derived from
the Latin term for bark, which helps describe this thick piece of tissue that
comprises the cerebral cortex.
The wrinkled appearance of the
cerebral cortex is created by folds in the brain tissue. These folds help increase the
surface area of the brain, which allows for a greater number of neurons to fit
within the skull. Therefore, the more folds or
wrinkles there are in the brain, the greater number of neurons and the higher
intelligence of the animal. And the largest wrinkles are used
as landmarks to help researchers distinguish the four distinct sections of the
cerebrum.
Each hemisphere of the cerebrum has
four lobes: a frontal lobe, a parietal lobe, an occipital lobe, and a temporal
lobe. The frontal lobes are important for
managing higher level cognitive functions that support our ability to achieve a
goal. These functions cover a wide range
of actions, such as the control of voluntary movements, language production,
decision-making, reasoning, and memory formation. So when you plan a schedule, pay
attention to instructions, imagine the future, hold two different ideas in your
mind, or use reasoned arguments, it’s the frontal lobe in action.
The parietal lobe contains a
somatosensory map of the body. So the lobes are critically
important for integrating sensory information and using that information to move us
through space. These two functions are called
somatosensation and proprioception. Somatosensation uses areas of the
parietal lobe to process touch sensations like pressure, pain, and temperature. This helps us understand what
sensory information we are encountering. Proprioception uses areas of the
parietal lobe to sense the orientation and location of our body parts. This helps us understand where our
bodies are located in space.
The occipital lobe is the visual
processing center of the human brain. It contains the visual cortex,
which processes information from the eyes and interprets this information into
images that create our perception of the world. These lobes also contain the visual
receiving and association areas, which process visual images of language, making
them critical for reading and comprehension. So whenever you can recognize the
words of another language but have difficulty understanding them, you’re only using
the visual receiving areas of the occipital lobe.
The temporal lobes are dedicated to
processing auditory information, memory, and emotion. A large portion of the temporal
lobes contain the auditory cortex, which supports auditory perception and
processing. This helps us not only understand
what we’re hearing when it comes to speech and emotions, but it also helps us
appreciate complex sounds like music. The temporal lobes are also
specifically responsible for supporting the retention of visual memories and
integrating them with sensations of taste, sound, sight, and touch. Finally, the inner middle portion
of the temporal lobes contain the hippocampus and the amygdala, which are crucial
for memory formation and emotional processing.
The forebrain also contains a fifth
lobe called the insula. These lobes are best visualized if
looking at the brain in cross section as the insula is hidden beneath the four other
lobes of the cerebrum. The insula acts as a sort of
receiving zone that reads the state of the entire body and generates feelings that
can bring about actions like eating or decision-making. It also contains the gustatory
complex, which is responsible for our perception of taste.
Now that we’re well acquainted with
the forebrain, let’s discuss the midbrain. The midbrain is the smallest of the
three brain divisions and is located at the topmost part of the brain stem. As a part of the brain stem, it
helps connect the brain and the spinal cord. As mentioned, the structures found
within the midbrain include the tectum, the cerebral aqueduct, the tegmentum, and
the cerebral peduncles.
Since the primary role of the
midbrain is to act as a sort of relay station, these structures contain important
centers for many of the functions of the midbrain, functions such as relaying visual
and auditory information, contributing to reflexes, supporting motor control, as
well as contributing to sleeping, waking, alertness, and temperature regulation. The diversity of functions
supported by the midbrain helps the central nervous system in calculating responses
to sensory information, changes in the environment, as well as carrying out actions
that do not require conscious awareness, like coughing or startling upon hearing a
large sudden sound.
Beneath the midbrain is the
hindbrain, which is the lowest brain division and comprises the lower structures of
the brain stem. Structures of the hindbrain include
the pons, the cerebellum, and the medulla oblongata. Together, these structures support
and coordinate functions that are crucial to human survival.
The word “pons” is derived from the
Latin term for bridge, which helps to describe one of the major roles of the
structures, that is, to connect the midbrain to the medulla. Other functions of the pons include
serving as an origin point for four out of 12 cranial nerves and supporting
involuntary actions like the intensity and frequency of breathing.
The word “cerebellum” is derived
from the Latin term for little brain. This describes how this small,
dense, coral-shaped structure contains more neurons than both hemispheres of the
cerebrum. The large number of neurons found
within the cerebellum form an important hub that processes all of the information
arriving to the brain and all of the commands going out of the brain. This enables the cerebellum to
optimize the brain’s abilities and coordinate our voluntary movements to make them
smooth, precise, and perfectly timed. The large number of neurons within
the cerebellum also helps to interpret and process the brain’s intentions.
At the bottom of the brain stem is
the medulla oblongata. The medulla oblongata is important
for our survival because it contains all of the control centers for our autonomic
and involuntary functions like heart rate and blood pressure.
Beneath the hindbrain is the second
organ of the central nervous system, the spinal cord. The spinal cord is a thick bundle
of nerve fibers and nervous tissue that creates a two-way pathway between the brain
and the body. The spinal cord is divided into
four regions: the cervical region, the thoracic region, the lumbar region, and the
sacral region. These regions contain 31 segments
with 31 pairs of spinal nerves. Each region has a slightly
different set of spinal nerves. For example, there are eight
cervical spinal nerves, 12 thoracic spinal nerves, five lumbar spinal nerves, and
six sacral spinal nerves. Each of the 31 segments of the
spinal cord has roughly the same internal structure, which can be best visualized
when looking at the spinal cord in cross section.
When looking at the spinal cord in
cross section, there’s a distinctive letter H shape found at its core. The H shape is typically gray in
color, which is derived from the high concentration of neuron cell bodies that make
up the thick bundle of nerve fibers found in the spinal cord. The gray matter core is surrounded
by white matter, which is comprised of myelinated neuron axons. The meylin found on these axons is
what gives the adjacent space a whitish color.
This structure of the spinal cord
supports the flow of nerve impulses from the brain to the body and from the body to
the brain. Sensory information is carried by
the sensory neurons, traveling from the periphery to the spinal cord through the
dorsal root, crossing a structure called the dorsal root ganglion that hosts the
cell bodies of sensory neurons. Then, sensory information travels
towards the brain directly or, as shown here, towards neurons in the spinal gray
matter. Once inside the spinal cord, the
sensory neurons connect with relay neurons in one of the top arms of the H-shaped
gray matter core, which are called the dorsal horns.
After sensory information has been
processed in the brain, the brain will send a nerve impulse back out to the
periphery. To reach the appropriate effector
organs, the nerve impulse will travel through the ventral horn, which is one of the
lower arms of the H-shaped gray matter core. This highly structured circuitry is
used to transmit both voluntary commands sent from the brain as well as reflex arcs
that only involve communication with the spinal cord.
Now that we’ve reviewed all the
components and functions of the central nervous system, we’re ready to try a
practice problem.
What is the central nervous system
comprised of? (A) The brain and the spinal
cord. (B) The brain and the cranial
nerves. (C) The peripheral nerves in the
external limbs. (D) The spine and the spinal
nerves.
To answer this question, we’ll
review the structure of the human nervous system, paying close attention to the
components of the central nervous system. The human nervous system has three
main functions. They are gathering sensory input,
processing sensory input, and responding to sensory input via motor output. All of these functions are carried
out by the two main parts of the human nervous system.
The two main parts of the human
nervous system are the central nervous system and the peripheral nervous system. The central nervous system is
comprised of the brain and the spinal cord. These two components help to
process and interpret gathered sensory input as well as coordinate an appropriate
motor output response. The peripheral nervous system
refers to all of the nerves outside of the brain and spinal cord. These components help to gather
sensory input and execute the appropriate motor output. With this information, we’re now
ready to answer our question. The central nervous system is
comprised of the brain and the spinal cord.
Let’s review what we’ve learned in
this video. The central nervous system is
comprised of the brain and the spinal cord. The brain and the spinal cord are
surrounded by the meninges, which are the dura mater, the arachnoid mater, and the
pia mater. The brain is divided into the
forebrain, the midbrain, and the hindbrain. The four lobes of the cerebrum are
the frontal, temporal, parietal, and occipital lobes. The spinal cord is divided into
four regions: the cervical, thoracic, lumbar, and sacral regions.
