IMAT Biology Lesson 6.8 | Anatomy and Physiology | Nervous System I
Summary
TLDRIn this video, Andre from Med School EU delves into the human nervous system, explaining its organization into the central and peripheral nervous systems, and further into the autonomic and somatic nervous systems. He discusses the roles of the parasympathetic and sympathetic systems in rest and fight-or-flight responses. The anatomy of neurons, including dendrites, axons, and Schwann cells, is explored, highlighting their function in signal transmission. The video also covers the reflex arc, demonstrating how the nervous system reacts quickly to stimuli for survival.
Takeaways
- 🧠 The nervous system is divided into the central nervous system (CNS) and the peripheral nervous system (PNS).
- 🌐 The CNS includes the brain and spinal cord, which are the primary control centers for the body.
- 🌿 The PNS extends outside the CNS and includes the autonomic nervous system (ANS) and the somatic nervous system (SNS).
- 🔄 The ANS is further divided into the parasympathetic and sympathetic nervous systems, which regulate rest and digest versus fight or flight responses, respectively.
- 🏃♂️ The SNS controls voluntary movements and is under conscious control, unlike the ANS which is involuntary.
- 🌱 Neurons are the basic units of the nervous system, consisting of a cell body, dendrites, and an axon.
- 🚀 Axons are insulated by Schwann cells, which help transmit electrical signals quickly through nodes of Ranvier.
- 🔌 There are three primary types of neurons: motor neurons (transmit impulses from CNS to effectors), sensory neurons (transmit impulses from receptors to CNS), and interneurons (relay impulses between sensory and motor neurons).
- 🔁 The reflex arc is a rapid response mechanism that involves sensory neurons, interneurons, and motor neurons to protect the body from harm.
- 🏃♀️ Reflex actions occur quickly, often before conscious awareness, as demonstrated by the example of pulling your hand away from a hot stove.
- 🌟 The nervous system's ability to react and transmit signals at incredible speeds is crucial for survival and everyday functions.
Q & A
What is the primary topic of the video?
-The primary topic of the video is the nervous system, focusing on its anatomy and physiology in humans.
How is the nervous system divided into different types?
-The nervous system is divided into the central nervous system (CNS) and the peripheral nervous system (PNS). The CNS includes the brain and spinal cord, while the PNS includes the autonomic nervous system (ANS) and the somatic nervous system.
What are the two subdivisions of the autonomic nervous system?
-The autonomic nervous system has two subdivisions: the parasympathetic nervous system, which is involved with rest and digest, and the sympathetic nervous system, which is involved in the fight or flight response.
What is the role of the parasympathetic nervous system?
-The parasympathetic nervous system is responsible for slowing down the body's functions, conserving energy, and promoting a state of rest and digestion.
How does the sympathetic nervous system differ from the parasympathetic nervous system?
-The sympathetic nervous system is activated during times of stress or physical activity, increasing heart rate and energy expenditure, in contrast to the parasympathetic system which conserves energy and promotes rest.
What is the somatic nervous system and how is it different from the autonomic nervous system?
-The somatic nervous system is voluntary and under conscious control, primarily involved in the movement of skeletal muscles. Unlike the autonomic nervous system, which is involuntary and operates without conscious awareness.
What are the basic components of a neuron?
-A neuron consists of a cell body (soma), dendrites for receiving signals, an axon for transmitting signals, and terminal branches that connect to other neurons or parts of the body.
What is the function of Schwann cells in a neuron?
-Schwann cells provide insulation for the axon, allowing electrical signals to jump from one node of Ranvier to the next, which helps in the rapid transmission of signals.
What are the three primary types of neurons?
-The three primary types of neurons are motor neurons, which transmit impulses from the CNS to effectors; sensory neurons, which transmit impulses from receptors to the CNS; and interneurons, which relay signals between sensory and motor neurons within the CNS.
Can you explain the concept of a reflex arc?
-A reflex arc is an automatic response to a stimulus that involves a sensory neuron, interneuron, and motor neuron. It allows for a quick reaction, such as pulling your hand away from a hot stove, before conscious awareness of the stimulus occurs.
What is the significance of the reflex arc in terms of survival?
-The reflex arc is a survival mechanism that enables the body to react quickly to potentially harmful stimuli without the delay of conscious processing in the brain, ensuring rapid protective actions.
Outlines
🧠 Nervous System Overview and Structure
The video script introduces the nervous system, highlighting its organization into two main branches: the central nervous system (CNS) and the peripheral nervous system (PNS). The CNS is further divided into the brain and spinal cord, while the PNS is split into the autonomic nervous system (ANS), which is involuntary and includes the sympathetic and parasympathetic divisions, and the somatic nervous system (SNS), which is voluntary and controls skeletal muscles. The autonomic nervous system is responsible for automatic responses like 'fight or flight' and 'rest and digest,' whereas the somatic nervous system allows for conscious control over body movements.
🌐 Neuron Anatomy and Signal Transmission
This section delves into the anatomy of a neuron, the fundamental unit of the nervous system, which includes the nucleus, dendrites, cell body, and axon. Dendrites receive signals from environmental stimuli or other neurons, while the axon transmits these signals to other neurons or effectors. Schwann cells provide insulation for the axon, allowing for rapid signal transmission through a process known as saltatory conduction, which involves jumping between nodes of Ranvier. The terminal branches of the axon form synaptic connections, which are crucial for signal transfer between neurons.
🔍 Types of Neurons and Their Functions
The script discusses the three primary types of neurons: motor neurons, sensory neurons, and interneurons. Motor neurons transmit impulses from the CNS to effectors, such as muscles, to cause action. Sensory neurons carry stimuli from the body or environment to the CNS. Interneurons, also known as relay or connector neurons, facilitate the transmission of signals between sensory and motor neurons within the CNS. The structure of each neuron type is tailored to its specific function, with motor neurons having long axons to reach distant effectors and sensory neurons having cell bodies that may lie near the receptors or within the CNS.
🏃♂️ Reflex Arcs and Rapid Response Mechanisms
The concept of the reflex arc is explored, which is a neural pathway that facilitates quick, automatic responses to stimuli without conscious thought. An example given is the withdrawal of a hand from a hot stove, which occurs as a reflex action before the brain processes the sensation of heat. The reflex arc involves receptors that detect stimuli, sensory neurons that transmit signals to the CNS, interneurons that process the information within the CNS, and motor neurons that send commands to effectors, such as muscles, to execute the response. This mechanism is essential for survival, providing rapid reactions to potential threats.
🚀 Conclusion and Preview of Upcoming Topics
The script concludes by summarizing the nervous system's remarkable ability to react swiftly to various signals and emphasizes that the topic is vast, with only the basics covered in this script. It teases the next video, which will focus on action potentials, explaining how the nervous system is stimulated and how signals are transmitted between neurons. This sets the stage for a deeper exploration of the underlying mechanisms of neural communication.
Mindmap
Keywords
💡Nervous System
💡Central Nervous System (CNS)
💡Peripheral Nervous System (PNS)
💡Autonomic Nervous System (ANS)
💡Somatic Nervous System (SNS)
💡Neuron
💡Dendrites
💡Axon
💡Schwann Cells
💡Reflex Arc
💡Action Potentials
Highlights
Introduction to the nervous system and its anatomy and physiology in humans.
Explanation of the nervous system's organization into the central nervous system (CNS) and peripheral nervous system (PNS).
Differentiation between the CNS, which includes the brain and spinal cord, and the PNS that extends to the limbs and organs.
Subdivision of the PNS into the autonomic nervous system (ANS) and somatic nervous system (SNS).
Description of the autonomic nervous system's role in automatic control of body functions without conscious awareness.
Detailing of the ANS's parasympathetic and sympathetic divisions and their respective roles in rest and fight-or-flight responses.
Importance of the equilibrium maintained by the parasympathetic and sympathetic systems for body regulation.
Overview of the somatic nervous system's voluntary control over skeletal muscles.
Neuron anatomy, including the nucleus, cell body, dendrites, and axon.
Function of dendrites in receiving signals from environmental stimuli or other neurons.
Role of Schwann cells in insulating axons and facilitating rapid signal transmission.
Explanation of nodes of Ranvier and their significance in speeding up electrical signal transmission.
Types of neurons: motor, sensory, and interneurons, and their specific structures and functions.
The reflex arc concept and its role in automatic, rapid responses to stimuli.
Description of the reflex arc's components, including receptors, sensory neurons, interneurons, and motor neurons.
Importance of the reflex arc as a survival mechanism allowing for quick muscle activation before conscious realization of harm.
Upcoming discussion on action potentials and signal transmission between neurons in the next video.
Transcripts
[Music]
hi everyone my name is andre welcome to
med school eu and the topic of today's
video is going to be the nervous system
and this is something we talked about in
our animal tissues unit however we're
going to revisit this in greater detail
and talk about the anatomy and
physiology in humans on the nervous
system so the first thing i'm going to
discuss is the organization of the
nervous system how it is organized
and what are the names of the different
types of nervous systems as they are
divided into
several different types so first we got
at the very top of the hierarchy we got
of course the nervous
system if we are following downwards it
breaks off into two separate systems
it's called the central nervous system
and the peripheral nervous nervous
system so the central nervous system i'm
going to label here because it divides
into two other
branches so it's called central nervous
system i'm just going to label it as cns
and we got the peripheral nervous system
that is going to be labeled as pns so
that's the two subdivisions
of the greater nervous system altogether
now the peripheral nervous system is
something that is outside
the spinal cord and the brain so the
brain is considered to be the central
nervous system that's the commands that
are given to the entire body and then
those commands are passed on by the
peripheral nervous system that is
situated in the limbs
in the uh
in your
organs
in your inter internal body
except for the spinal cord as well as
the brain
and so the central nervous system has
two other subdivisions which we just
mentioned it would be the brain
and the spinal cord
so the peripheral nervous system has two
other subdivisions one is called
autonomic nervous system and i'm going
to label it here a n s
and the other one is called somatic
nervous system we're going to discuss
both in
briefly so somatic
nervous
system sns
the autonomic nervous system
is the nervous system that is controlled
automatically
by our brain and the spinal cord so this
nervous system is is controlled without
our
us being aware of it
and so it has two subdivisions it's got
the parasympathetic nervous system and
sympathetic nervous systems so
parasympathetic is involved with
rest and digest
so it's involved with slowing down your
your body so it does not waste resources
it's all about concentrating the energy
and sympathetic nervous system is
involved in fight
or flight response so it is involved in
doing the work expanding energy in times
of stress so if there's a
something physical that's going on or
something that's internal that would be
activated by the sympathetic nervous
system that's the thing that raises your
heart rate raises your breathing in case
you're doing exercise and then once you
stop exercising the parasympathetic
nervous system kicks in
and
it would regulate it in order to slow
down the heart rate because you no
longer need your heart to be putting out
a bigger cardiac output when you're
resting 30 minutes after your workout or
or whatever happens to be so the
parasympathetic system is extremely
important just like the sympathetic they
play a role
of an equilibrium system
so when you are
exercising it does not mean the
parasympathetic system is not involved
anymore
it means that it's involved a lot less
than the sympathetic system so it's it
forms sort of an equilibrium however
when the demands of the body are changed
that's when the equilibrium is going to
shift towards sympathetic or it will
shift toward parasympathetic depending
on what the body is doing and what the
environment is like finally from the
somatic nervous system sns so it's
somatic
the somatic nervous system is voluntary
so this system is something that we can
control it's something that we are aware
of and that's
more involved in terms of your
movement of your limbs
your muscles you have complete control
of your skeletal muscle
in most areas of the body
and so the automatic nervous system is
not going to be controlling any of that
because you are in complete awareness
and control of when the muscle is going
to contract
which muscle will contract and how
you're going to move that is all
controlled by the somatic
nervous system it is
voluntary
whereas the autonomic nervous system is
involuntary now it is broken down into
two segments it is called sensory
and motor
moving on we're going to talk a little
bit about the neuron anatomy and this is
something that i brought up earlier
in our previous lectures however here i
wanted to go a little bit further detail
about this
so first of all the part that's right in
in the center here with the
light blue that is the nucleus
of our cell
so of course this is anatomy of a neuron
a neuron
is the
basic unit
of the nervous system so it is the
single cell and these cells could be
very long or they could be
shorter
however they they can range depending on
which type of neuron this is so they're
composed of this nucleus that's in in
the middle of the cell body so this
entire thing here is the cell
body
and that's the
the kind of tree-like circle over here
and then these projections that are
sticking out of it they are called
dendrites so i'll label it here
and these dendrites they're responsible
for receiving signal from either
environmental stimuli that's on the
surface of the skin
or maybe from pressures onto the skin
or
they are
responsible for receiving signal from
other neurons that are interconnected to
them and i i will
i'll talk about what that means
now also the it's important to note that
the cytoplasm of these neurons
they have these uh
various structures just like a regular
cell would and the cytoplasm contains
mitochondria so many mitochondria
that would provide energy for the cell
and they would have an extensive a rough
endoplasmic
reticulum rough er and it's extensive it
is typically
more
complex than the
the regular cell that we've discussed
previously
now if we take a look at the long
projection that comes off the cell body
it is called the axon
and we've talked about the axon a little
bit before so it's the axon that goes
all along here now all these yellow
structures
that are around the axon
these ones are called schwann cells in
between the schwann cells there's these
little gaps and all of these gaps
they're going to be called nodes
of ranvier these are the the primary
structures of the axon the schwann cells
they provide insulation for the axon in
order to have the signal passed on much
quicker as you might imagine the neuron
is
is providing signals electrical signals
that are is basically a means of
communication between one part of the
body and another part of the body so the
brain is going to communicate with your
bicep muscle in order to raise your arm
or or raise your forearm
and and flex the muscle and it's going
to be done almost instantaneously and
the reason for that is because the way
it's passed on these cells these neurons
are able to pass on the signal extremely
fast in milliseconds and so this occurs
primarily due to these schwann cells
because the schwann cells provide
insulation so the electrical signal will
be able to jump from one node of ranvier
to the next instead of going through the
entire thing
much much slower and not every uh neuron
has schwann cells schwann cells have
this importance in terms of transmitting
signal so that it is the system
in general works very efficiently and
very quickly
now the ends of the axon here
and and these projections kind of look
like the dendrites these are called
terminal branches and these terminal
branches typically connect to the
dendrites or other parts of the body so
they could connect to dendrites of
another neuron and the signal will be
passed on this way and if they do
then they form these synaptic knobs and
we're going to talk about that
a little bit later and before we move on
i wanted to come back to this schwann
cell
just to kind of provide a better anatomy
of it so you could imagine what these
schwann cells look like because the the
insulation that they provide they're
actually
cells they're not some material that's
around the axon that's that's doing this
they're actual cells that
do their
specialized function so here the center
of it this is basically a cross section
of the axon that we just saw previously
so this would be the axon and there's
the cross section of it
and here this spiral structure is
called schwann cell and this would be
the body the cell body or the nucleus
here
and this bigger yellow structure this
would be the cell
body of the schwann cell so this is the
way it is structured and as you can see
it would provide this sort of insulation
for the axon so that the electrical
signal cannot escape and it would have
to jump over and really transmit much
faster through that part
of the axon
next i wanted to revisit the concept of
the types of neurons so we're going to
take a look at the three different
structures the three different
primary types of neurons of course
there's a couple of other subsections
but they all kind of fall into these
three categories
and so we have
our motor neuron up at the top here so
this is going to be the motor
neuron and you can know how they're
shaped the reason why the cell body and
the dendrites are located in this sort
of orientation is because the cell body
of the motor neuron lies within the
spinal cord or the brain so it lies
within the central
nervous system this is where
this cell body and the dendrites are
located and so that they're in this sort
of orientation and then the nucleus of
the neuron is always in the cell body
and often dark specks can be seen in the
cytoplasm if you're looking through the
microscope and typically these axons of
the motor neuron tend to be extremely
long they tend to run very long
distances
because their cell body is located in
the spinal cord typically and its axon
is going to be running all the way up to
your toes for example in terms of
stimulation of the muscles
in in the toes so you can imagine how
long this cell could really be because
it the axon is still part of this one
single cell and then these terminal ends
are going to be attached to
the receptors on the skeletal muscle
which will activate the muscle and will
cause contraction so the
the motor neuron
so the motor neuron in summary transmits
impulses from the central nervous system
to the effector
now for looking at the sensory neuron
it transmits impulses from receptors
to the central nervous system and this
is what i've mentioned in the previous
slide
the correlation between sensory and
motor neuron
is that the sensory is going to sense
any stimuli coming from the environment
or from the body itself and then it's
going to transmit that impulse to the
central nervous system and the central
nervous system will give a command
to the effector through the motor neuron
that's the kind of relationship it's a
circular path
that this goes on to
and
as you can see the sensory neuron
because this this would be
labeled as the sensory and the sensory
neuron has a different structure than
the motor neuron its
cell body is going to lie somewhere in
the middle of the axon
and so it is just important to know
that it's going to have this different
structure
now if we're talking about the inner
neuron it's also uh called the relay or
the connector neurons so the inner
neurons function is to transmit impulses
from the
sensory neuron
so from the impulse from the environment
to the motor neuron and so these would
be located in the central
nervous system so there's this
relationship going on first you get
a signal coming from the environment
that will be taken up by the sensory
neuron and brought to the
central nervous system from the central
nervous system
it will be passed on around to the motor
neuron and from the motor neuron in the
central nervous system which
which is where the
cell body lies it will go to the
effector and the final thing i wanted to
talk about today is called the reflex
arc and this is something i briefly
mentioned previously
in our of one one of our first videos on
this unit
however i wanted to again talk about
this concept and give a little bit more
detail to provide a better understanding
of it
and so the reflex arc the way it really
works i used previously the example of
the hot stove so when you put your hand
on the hot stove by accident and
you feel your hand is gonna is gonna
burn but before you get the sense that
the hand is burning your hand has
already come off so it will
automatically pull away before you even
realize it was hot and then maybe a
second later you will realize oh no wow
that was really hot
so
the way this works is that once you have
a stimuli
that goes and as you can see here
there's a there's a reception for pain
so
you you get you get pain and in the
sight of your finger
and the way you get a response is you
get two responses one that goes to the
spinal cord and one that goes further to
the brain of course to the brain is
going to travel further so it's going to
take a longer time there's going to be
more connections between neurons and the
inner neurons and so on
and it's just going to take a longer
time to to happen however when it goes
to the spinal cord there's going to be
an automatic reaction
for the muscle to activate and to pull
back this is why you're going to pull
back before you realize
what happened because it takes a little
bit longer for the brain to process
things before it can activate the muscle
however this is really a survival
mechanism that we have
and there's all types of different
reflexes that we have
to keep us alive for example when you're
when you're tripping you know you're
walking down or you're walking down the
stairs
and
and you slip so you're going to be
tripping
and you catch yourself but you catch
yourself not because you realized you
were tripping and then you gave yourself
commands on how to catch yourself this
happens automatically because of the
action of the spinal cord and then once
you do catch yourself and you you might
have
saved a bad accident
from happening
and
that is done by the spinal cord and only
later you realize they almost fell so
this is really a survival mechanism
for us to be able to activate the muscle
before you even realize
that there's any harm happening to the
body
and so i wanted to again go over some of
the anatomy of this reflex arc so first
we have our receptor now obviously we
just talked about that this would be the
sensory neuron
so that would be sensing the the pain
the signal and it's going to be
transmitting it to the spinal cord
there's going to be another neuron that
will be going off and transmitting it to
the brain as well however we're just
going to be focused on this
spinal cord the part of the spine where
the sensory neuron goes is called the
dorsal root
it's that's the
that's the part of the spinal cord that
this goes to and it's going to interact
and
this would be the cell body
of the sensory
neuron because the cell body of the
sensory neuron typically lies around
either the spinal cord or it's going to
lie closer to the receptor
now the signal is obviously going to be
passed on to the intermediate neuron as
we talked about before
this has already reached its central
nervous system because the spinal cord
is part of the central nervous system
and the the signal is going to be
transmitted
by the inner neuron so that's the cell
body
of
interneuron i n i'm gonna label it so
that's that's right here right
in the center
now this part uh here is called white
matter and in the gray matter we have
most of the
cell bodies so the cell bodies are
typically going to be located in the
gray matter of the spinal cord and in
the white matter we're going to have
mostly the axons
as you can see the axon is going to be
passing through
this white matter part
now then there's going to be a
connection between the inner neuron and
the motor
neuron
and that's uh that's going to be the
cell body of the motor neuron
because remember the cell body of the
motor neuron comes off the central
nervous system which is right here
comes right off the spinal cord and it's
going to follow through the ventral root
ventral root and you can you can look up
these terms they're pretty interesting
in terms of anatomy when you'll be
learning just to be able to qualify what
is the front what is the back of the
body and they would be labeled with the
dorsal and the ventral root so the motor
neuron will be going through this
ventral root right here instead of
the the dorsal root it will be going
through this side of the spinal cord and
it will be producing its output as you
can see here
on the muscle so be pulling
the finger away from harm
before
you even realize it which is pretty
phenomenal it is
absolutely incredible how the nervous
system works and the speed at which is
able to react to different signals
is is absolutely fascinating so we've
reached the end of today's video however
it's not going to be the end of the
topic of the nervous system as it is
extremely extensive and we're just going
to cover
the tip of the iceberg and so in the
next video we're going to talk about
action potentials we're going to talk
about how the nervous system is
stimulated and how signals are
transmitted
between one neuron and another
[Music]
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