Video Transcript
In this video, we’ll learn about
the organizational structure of the human nervous system. We will learn how to describe the
components of both the central and peripheral nervous system. Then, we’ll learn about the
differences between the motor and sensory division of the peripheral nervous
system. Finally, we’ll discuss how the
motor division is further organized into the somatic and autonomic nervous
systems.
As a human, we have the ability to
feel, think, sense, and respond to the world around us. The system that makes this possible
is the human nervous system. From basic reflexes to more
complicated behaviors like courting potential mates, the nervous system is the
electrical wiring that runs throughout the human body and allows us to interact with
the world. The human nervous system has three
main functions: gathering sensory input, processing the sensory input, and
responding appropriately via motor output.
To efficiently collect, process,
and respond to information, the nervous system has a highly organized structure. This means that while the human
nervous system is a very large integrated network of cells, it can be divided into
subdivisions, each with their own specific structural and functional
characteristics. The first division of the nervous
system splits the network into two subdivisions: the central nervous system, which
is often abbreviated to CNS, and the peripheral nervous system, which is abbreviated
to PNS.
Let’s take a closer look at the
central nervous system. The central nervous system consists
of two main components: the brain and the spinal cord. A major function of the brain is to
control complex functions, like thinking, emotional feeling, and maintaining
homeostasis, which is a constant internal environment in the body. The brain is also responsible for
processing and interpreting sensory information. After sensory information has been
processed and interpreted, the brain will then coordinate a motor response. In order for the brain to command
and control the functions of the body, it sends signals through the nerves of the
spinal cord. You can think of the spinal cord as
an information superhighway. This is because a major function of
the spinal cord is to relay messages between the brain and the body. So the central nervous system,
which comprises the brain and the spinal cord, is responsible for integrating
sensory information and responding to it.
But how does sensory information
arrive at the central nervous system? And how are motor responses carried
out by the body? These are jobs of the peripheral
nervous system. Use of the root word “periphery” in
peripheral nervous system is meant to indicate any nervous system structures beyond
the brain and the spinal cord. The primary function of the
peripheral nervous system is to transmit information towards and away from the
central nervous system. But nerve cells can only transmit
information in one direction. So, to achieve these functions, the
peripheral nervous system can be subdivided based on its directional flow of
information.
One set of nerve cells carries the
information towards the central nervous system, while another set of nerve cells
carries information away from the central nervous system. Nerves that carry information
towards the CNS are called afferent nerves. The word “afferent” is Latin for
bringing towards. This is to indicate that
information that moves from the periphery towards the CNS is sensory
information. So afferent nerves collect sensory
information from our body and the external environment and bring it towards the CNS
for processing and integration. These afferent nerves make up the
sensory division of the peripheral nervous system.
Within the sensory division, nerves
are activated by physical or chemical inputs from the environment, like sounds,
sights, odors, flavors, or textures, all inputs that correspond to the five major
senses. This sensory information about the
stimuli in our environment or changes in our internal organs is sent through the
spinal cord to the brain in order to relay the state of our body and the external
environment.
Nerves that carry information away
from the CNS are called efferent nerves. The word “efferent” comes from the
Latin for carrying away. Information that moves from the CNS
back out to the periphery is motor information. So efferent nerves carry motor
information from the brain and spinal cord away to the muscles, organs, and glands
found in the periphery. This also means that efferent
nerves make up the motor division of the peripheral nervous system.
Within the motor division, nerves
are activated by the motor commands sent from the CNS to various muscles and organs
to execute a specific response. So the peripheral nervous system is
subdivided into the sensory division, which is composed of afferent sensory nerves
that bring information towards the CNS, and the motor division, which is composed of
efferent motor nerves that carry information away from the CNS. The subdivisions of the peripheral
nervous system don’t end there. As we just learned, the motor
division handles all motor responses, like the contraction of skeletal muscles or
cardiac muscles. But the control of skeletal muscles
and cardiac muscles is very different. So this means we can further
subdivide the motor division based on the types of motor responses.
There are two types of motor
responses handled by the motor division. They are voluntary motor movements
and automatic motor movements. Voluntary motor movements are made
by choice and require awareness. Voluntary motor movements can be as
simple as flipping on a light switch to turn on a light when you’re unable to see in
a dark room. These types of motor responses are
carried out by skeletal muscles, which are generally attached to the skeleton and
controlled by our conscious awareness. Actions executed by the skeletal or
voluntary muscles use somatic nerves, which connect the brain and spinal cord to
skeletal muscles. So voluntary muscles are controlled
by the somatic nervous system.
The other type of motor responses
occurs automatically and does not require relaying a message to the brain. This means that automatic motor
responses are involuntary and do not require awareness in order to be carried
out. An example of automatic behaviors
would be breathing or digestion. While we know we need to perform
these actions, they occur without our awareness. Many of these involuntary automatic
actions are executed by smooth muscles and can never be under voluntary control. So these types of motor responses
are handled by the autonomic nervous system.
The word autonomic comes from the
root word “autonomy,” which means self-governing. This is to indicate that the motor
responses controlled by the autonomic nervous system are actions that occur under
the governance of that organ, like our heartbeats, digestion, or respiration. The automatic function of the
autonomic nervous system helps regulate our ability to perform the most basic
survival functions of being a human.
So the peripheral nervous system is
first subdivided into the sensory and motor divisions. Then, the motor division is further
subdivided into the types of different motor responses. Motor responses that are voluntary
are handled by the somatic nervous system, while involuntary motor responses are
handled by the autonomic nervous system. Now that we have a better
understanding of the organization of the human nervous system, let’s try some
practice questions.
What part of the nervous system is
made up of the nerves that extend from the brain and spinal cord into the external
limbs and other organs? (A) Peripheral nervous system. (B) Central nervous system.
This question is asking us to
recall parts of the human nervous system. So, to answer this question, let’s
start by reviewing the organizational structure of the human nervous system. This is the human nervous
system. The human nervous system has three
main functions: gathering sensory information, information processing, and
transmitting motor responses. These functions are accomplished by
the different parts of the human nervous system, which is a highly organized
integrated network of nerve cells. So the human nervous system can be
divided into subdivisions, each with their own specific structural and functional
characteristics.
The first division of the nervous
system subdivides it into the central nervous system and the peripheral nervous
system. The central nervous system consists
of two main components: the brain and the spinal cord. The central nervous system is
responsible for processing and interpreting sensory information, as well as
coordinating motor responses. The peripheral nervous system
refers to all of the nerves beyond the brain and the spinal cord. These nerves extend from the spinal
cord all the way out to the external limbs and other organs. This helps the peripheral nervous
system achieve its primary purpose of transmitting information towards and away from
the central nervous system. With this information, we can now
answer the question. The part of the nervous system that
is made up of nerves that extend from the brain and spinal cord into the external
limbs and other organs is the peripheral nervous system.
The diagram provided shows how the
peripheral nervous system and its motor division are divided into their component
parts. What is the primary function of the
somatic nervous system? (A) To transmit information to
muscles that are under voluntary or conscious control and to mediate reflex
actions. (B) To transmit information to
muscles and glands that are not under voluntary or conscious control.
This question is asking us to
recall the function of the somatic nervous system. To answer this question, let’s
review how the motor division of the peripheral nervous system is organized. The motor division of the
peripheral nervous system can be subdivided based on the types of motor
responses. The motor division handles two
types of motor responses: voluntary motor responses and involuntary motor
responses.
Voluntary motor responses are made
by choice and require awareness. These motor movements can be as
simple as flipping on a light switch in a dark room. Voluntary motor responses are
carried out by skeletal muscles and use somatic nerves in order to connect the brain
and spinal cord to the skeletal muscles. So voluntary muscles are controlled
by the somatic nervous system.
Involuntary motor responses are
automatic and do not require awareness in order to be carried out. Many of the involuntary motor
responses are executed by smooth muscle and therefore can never be under voluntary
control. An example of this would be
breathing or digestion. While we know we need to perform
these actions, they occur without our awareness. So involuntary muscles are
controlled by the autonomic nervous system.
With this information, we can now
answer the question. The primary function of the somatic
nervous system is to transmit information to muscles that are under voluntary or
conscious control and to mediate reflex actions.
Let’s wrap up by taking a moment to
review some key points we’ve learned in this video. The nervous system is divided into
two main parts: the central nervous system and the peripheral nervous system. The central nervous system includes
the brain and the spinal cord. The peripheral nervous system is
further subdivided into the sensory and motor divisions. The sensory division transmits
sensory information, while the motor division transmits motor information. The motor division is further
subdivided into the somatic and autonomic nervous systems. The somatic nervous system controls
voluntary motor responses and reflex actions. The autonomic nervous system
regulates involuntary motor responses like breathing or digestion.
