IMAT Biology Lesson 6.8 | Anatomy and Physiology | Nervous System I

Summary

In 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

00:00

🧠 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.

05:00

🌐 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.

10:01

🔍 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.

15:02

🏃‍♂️ 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.

20:04

🚀 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.

Keywords

💡Nervous System

The nervous system is a complex network of nerves and cells, or neurons, that transmit signals between different parts of the body. It is central to the functioning of all living organisms, particularly in response to sensation and movement. In the video, the nervous system is divided into the central nervous system (CNS) and the peripheral nervous system (PNS), highlighting its role in communication and control within the body.

💡Central Nervous System (CNS)

The CNS is composed of the brain and spinal cord and serves as the control center of the body. It processes information received from the peripheral nervous system and sends signals to various parts of the body. In the script, the CNS is described as the part of the nervous system that gives commands to the entire body, emphasizing its critical role in decision-making and response.

💡Peripheral Nervous System (PNS)

The PNS consists of nerves that originate from the CNS and extend to the rest of the body, including the limbs and organs. It is responsible for transmitting sensory information to the CNS and carrying out commands from the CNS to the muscles and glands. The script mentions that the PNS is outside the spinal cord and brain, indicating its extensive reach and function in the body.

💡Autonomic Nervous System (ANS)

The ANS is a part of the PNS that controls involuntary actions such as heart rate, digestion, and respiration. It is divided into the sympathetic and parasympathetic systems, which regulate the body's fight-or-flight response and rest-and-digest functions, respectively. The script discusses how the ANS operates automatically and is crucial for maintaining homeostasis in the body.

💡Somatic Nervous System (SNS)

The SNS is another subdivision of the PNS and is responsible for voluntary movements controlled by the conscious mind. It controls the skeletal muscles, allowing for deliberate actions such as walking or picking up objects. The script explains that the SNS is under conscious control, contrasting with the involuntary nature of the ANS.

💡Neuron

Neurons are the basic units of the nervous system, responsible for receiving, processing, and transmitting information through electrical and chemical signals. The script describes the anatomy of a neuron, including its nucleus, dendrites, and axon, highlighting how these components work together to facilitate communication within the nervous system.

💡Dendrites

Dendrites are branched extensions of a neuron that receive signals from other neurons or sensory receptors. They play a crucial role in the integration of information and are essential for the neuron's function. In the script, dendrites are described as receiving signals from environmental stimuli or other neurons, illustrating their role in sensory input.

💡Axon

The axon is a long, often single, projection of a neuron that conducts electrical impulses away from the neuron's cell body. It is essential for transmitting signals to other neurons, muscles, or glands. The script mentions the axon's role in sending signals, emphasizing its importance in communication within the nervous system.

💡Schwann Cells

Schwann cells are glial cells that provide support and insulation for axons in the peripheral nervous system. They facilitate the rapid transmission of electrical signals by creating a myelin sheath around the axon. The script describes how Schwann cells help in the efficient and quick transmission of signals, contributing to the nervous system's speed and efficiency.

💡Reflex Arc

A reflex arc is a neural pathway that mediates a reflex action in response to a specific stimulus. It involves a sensory neuron, an interneuron, and a motor neuron, allowing for a quick and automatic response. The script uses the example of pulling away from a hot stove to illustrate how the reflex arc operates, demonstrating its role in immediate, protective responses.

💡Action Potentials

Action potentials are the electrical signals that travel along neurons, allowing for the transmission of information. They are generated by changes in the electrical charge across the neuron's membrane. The script mentions action potentials in the context of future discussions, indicating their fundamental role in the functioning of the nervous system.

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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