Nervous System

Summary

The video script delves into the diversity and specialization of cells in the human body, with a focus on the nervous system. It outlines the structure of the nervous system, including the central nervous system (CNS) and peripheral nervous system (PNS), and highlights the roles of the brain's regions. The script emphasizes the importance of neurons and glial cells in the nervous system and explains the concept of action potentials and neurotransmitters, which facilitate communication between neurons. The video aims to dispel common myths about the brain and explores the intricacies of the nervous system's function and structure.

Takeaways

• 🧬 Cell diversity is vast, with specialized cells performing unique functions in different body systems.
• 🧠 The nervous system is divided into the central nervous system (CNS) and the peripheral nervous system (PNS).
• 🌟 The CNS consists of the brain and spinal cord, while the PNS includes all other components like nerves throughout the body.
• 💡 The brain is divided into the hindbrain, midbrain, and forebrain, each with distinct functions such as regulation, alertness, and higher cognitive processes.
• 🏃‍♂️ The somatic nervous system (SNS) is involved with voluntary motor functions and somatic reflexes.
• 🔄 The autonomic nervous system (ANS) regulates the body's internal environment and can be further divided into the sympathetic and parasympathetic systems.
• 🌐 Neurons and glial cells are the two major types of cells in the nervous system, with neurons being the primary communicators and glial cells providing essential support.
• 🚀 Action potentials allow neurons to communicate rapidly by changing the electrical charge along the axon in a process that is 'all or none'.
• 🔌 Synapses are the junction points where neurons communicate, and neurotransmitters are released from synaptic vesicles to bind specific receptors on neighboring neurons.
• 🧠 The brain's structure and function are complex, with myths like 'we only use 10% of our brain' being debunked.
• 🔍 Ongoing research in neurology aims to better understand and treat diseases and conditions of the nervous system.

Q & A

What is the main topic of the video?

The main topic of the video is the nervous system, its structure, function, and the cells that comprise it.

What are the two general regions the nervous system can be divided into?

The nervous system can be divided into the central nervous system (CNS), which includes the brain and spinal cord, and the peripheral nervous system (PNS), which includes all other components of the nervous system such as nerves throughout the body.

What are the three general regions the human brain is divided into?

The human brain is divided into the hindbrain, midbrain, and forebrain.

What are the primary functions of the medulla in the hindbrain?

The medulla has many regulatory functions such as the regulation of breathing, blood pressure, and heart rate.

How is the peripheral nervous system (PNS) functionally divided?

Functionally, the PNS is divided into the somatic nervous system (SNS), which is involved with motor functions of skeletal muscle, and the autonomic nervous system (ANS), which deals with the internal environment and involuntary functions.

What are the two major types of cells that make up nervous tissue?

The two major types of cells that make up nervous tissue are neurons and glial cells.

What is the role of glial cells in the nervous system?

Glial cells, or glia, play critical roles in the nervous system, including structural support, maintaining the blood-brain barrier, producing myelin to insulate axons, and participating in immune functions within the nervous system.

What is an action potential and why is it important for neurons?

An action potential is a rapid change in the electrical charge of a neuron that allows it to communicate with other cells. It is important because it enables the fast transmission of signals along the neuron's axon, which is essential for the neuron's function in communication and processing information.

What happens when an action potential reaches the end of an axon?

When an action potential reaches the end of an axon, it signals synaptic vesicles to release neurotransmitters into the synapse, the space between two neurons. These neurotransmitters then bind to specific receptors on the next neuron, potentially initiating a new action potential in that neuron.

What is the significance of the 'fight or flight' response in the sympathetic nervous system?

The 'fight or flight' response in the sympathetic nervous system prepares the body for rapid action in response to a perceived threat or stressor. It increases heart rate, blood flow to muscles, and alertness, while temporarily reducing functions like digestion that are not immediately necessary for survival in the short term.

How does the parasympathetic nervous system contrast with the sympathetic nervous system?

The parasympathetic nervous system is often referred to as the 'rest and digest' system. It works to conserve resources, reduce heart rate, promote digestion, and generally maintain homeostasis in the body, in contrast to the activating effects of the sympathetic nervous system.

What is the myth about the brain that the video aims to dispel?

The video aims to dispel the myth that 'humans only use 10% of their brain.' This is incorrect, as we use virtually every part of our brain, though not all areas are active at the same time.

Outlines

00:00

🌟 Diversity of Body Cells and Overview of the Nervous System

This paragraph introduces the concept of cell diversity within the human body, emphasizing that cells are not all uniform but have specialized functions. It highlights examples such as parietal cells in the stomach that produce stomach acid, mast cells in the immune system that release histamine, and skeletal muscle cells that facilitate muscle contraction. The paragraph then transitions to the main focus of the video, the nervous system, and provides a general tour of its structure, including the central nervous system (CNS) and peripheral nervous system (PNS), and briefly touches on the functions of the brain's regions like the hindbrain, midbrain, and forebrain.

05:02

🧠 Neurons and Glial Cells: The Building Blocks of the Nervous System

The second paragraph delves into the two primary cell types of the nervous system: neurons and glial cells. It describes the structure of a neuron, including the cell body, dendrites, and axon, and explains the concept of synapses where neurons communicate. The paragraph also reiterates the importance of glial cells, which were once thought of as merely supportive but are now understood to have critical roles in maintaining homeostasis, producing myelin, and participating in immune responses within the nervous system. Additionally, the paragraph introduces the concept of action potentials, which are essential for rapid communication between neurons, and explains the resting potential of a neuron and the process of depolarization during an action potential.

10:06

🚀 The Nervous System's Functioning and Communication

The final paragraph wraps up the discussion on the nervous system by recapping the main points covered in the previous sections. It reiterates the division of the nervous system into the PNS and CNS, the latter including the brain and spinal cord, and the functional differences between the somatic and autonomic nervous systems. The paragraph also summarizes the roles of glial cells and neurons, the process of action potentials, and the release of neurotransmitters in synaptic communication. It concludes by acknowledging the complexity of the nervous system and the ongoing research in neurology, encouraging viewers to stay curious and explore careers in this field.

Keywords

💡Body Cell Diversity

The concept of body cell diversity refers to the wide variety of cell types in the human body, each with unique structures and functions. In the video, this is introduced to contrast the common misconception that all cells are similar, emphasizing the specialization of cells like parietal cells in the stomach that produce stomach acid, or mast cells in the immune system that release histamine.

💡Nervous System

The nervous system is the body's complex network of nerves and neurons that transmit signals between different parts of the body. It is divided into the central nervous system (CNS), consisting of the brain and spinal cord, and the peripheral nervous system (PNS), which includes all other nerves throughout the body. The nervous system is responsible for processing sensory information, initiating motor responses, and regulating body mechanisms.

💡Neurons

Neurons are the primary cells of the nervous system, responsible for transmitting information through electrical and chemical signals. They have a unique structure with a cell body, dendrites that receive signals, and an axon that carries signals to other cells. Neurons communicate with each other through synapses, where neurotransmitters are released.

💡Glial Cells

Glial cells, also known as glia, are non-neuronal cells in the nervous system that provide critical support and protection for neurons. They help maintain the extracellular environment, produce myelin to insulate axons, and play roles in the immune response within the nervous system.

💡Action Potential

An action potential is a rapid, temporary change in the electrical potential across the membrane of a neuron, allowing for the rapid transmission of signals along the neuron's axon. It is initiated when a stimulus received by the dendrites reaches a certain threshold, causing a wave of depolarization and repolarization that travels to the axon terminals.

💡Synapse

A synapse is the junction between two neurons where information is transmitted from one neuron to another. It consists of the axon terminals of the presynaptic neuron and the dendrites or cell body of the postsynaptic neuron, separated by a small gap called the synaptic cleft. Neurotransmitters are released into this gap to bind to receptors on the postsynaptic neuron, continuing the signal.

💡Central Nervous System (CNS)

The central nervous system (CNS) is composed of the brain and spinal cord. It serves as the control center of the nervous system, processing sensory information, initiating motor responses, and regulating body mechanisms. The CNS is responsible for higher cognitive functions and is divided into regions like the hindbrain, midbrain, and forebrain, each with specific functions.

💡Peripheral Nervous System (PNS)

The peripheral nervous system (PNS) includes all the nerves outside the central nervous system, extending throughout the body. It is responsible for transmitting sensory information to the CNS and carrying motor commands from the CNS to the muscles and glands. The PNS is further divided into the somatic nervous system (SNS) and the autonomic nervous system (ANS), each with distinct functions.

💡Somatic Nervous System (SNS)

The somatic nervous system (SNS) is part of the peripheral nervous system that controls the voluntary movement of skeletal muscles. It is involved in motor functions and somatic reflexes, which are actions that can be consciously controlled and are essential for interacting with the environment.

💡Autonomic Nervous System (ANS)

The autonomic nervous system (ANS) is a part of the peripheral nervous system that regulates the body's internal environment, including involuntary functions such as heart rate, digestion, and respiration. It is divided into the sympathetic and parasympathetic systems, which often have opposing effects on the same organ, managing the body's 'fight or flight' and 'rest and digest' responses, respectively.

💡Myth of Brain Usage

The myth of brain usage refers to the popular but incorrect belief that humans only use 10% of their brain. This misconception has been debunked by neuroscience, showing that most of the brain is active and involved in various functions, often simultaneously.

Highlights

Body cell diversity and the specialized functions of different cell types.

Parietal cells in the stomach produce stomach acid, showcasing cell specialization within the digestive system.

Mast cells in the immune system contain histamine, critical for the inflammatory response.

Skeletal muscle cells, or muscle fibers, have a unique cylindrical structure with multiple nuclei and thin and thick filaments for muscle contraction.

The nervous system is composed of the central nervous system (CNS) and the peripheral nervous system (PNS).

The CNS includes the brain and spinal cord, serving as the command center of the body.

The PNS consists of all other components, providing sensory information to the CNS and executing motor responses.

The human brain is divided into the hindbrain, midbrain, and forebrain, each with distinct functions.

The hindbrain includes the medulla, pons, and cerebellum, regulating essential functions like breathing and balance.

The midbrain is involved in alertness, sleep/wake cycles, and motor activity.

The forebrain, including the cerebrum, is responsible for speech, thinking, reasoning, sensing, and emotions.

The PNS can be further divided into the somatic nervous system (SNS) and autonomic nervous system (ANS), based on their functions.

The SNS is involved with motor functions of skeletal muscle, including voluntary actions and somatic reflexes.

The ANS regulates the internal environment, including the gastrointestinal, excretory, endocrine, and smooth and cardiac muscle functions.

The ANS is divided into the sympathetic and parasympathetic systems, responsible for the fight or flight response and rest and digest functions, respectively.

Neurons are the primary cells of the nervous system, with structures including the cell body, dendrites, and axon.

Glial cells, or glia, are essential supporting cells in the nervous system, involved in maintaining homeostasis, producing myelin, and immune functions.

Action potentials are rapid electrical signals that allow neurons to communicate, involving the movement of ions across the neuron's membrane.

The resting potential of a neuron is characterized by a negative charge inside the cell, maintained by the sodium-potassium pump.

Depolarization occurs during an action potential as sodium ions flood into the neuron, changing the electrical charge along the axon.

The action potential is an 'all or none' event, meaning it either occurs fully or not at all, similar to a light switch.

Neurotransmitters are released from synaptic vesicles at the end of an axon, crossing the synaptic cleft to bind to receptors on the next neuron.

Transcripts

You know – sometimes we forget how  different the cells in the body can  

be – we kind of imagine them as all as  little circle blobs when in reality,  

there is so much body cell diversity.  Parietal cells in the stomach as part  

of the digestive system – they can make stomach  acid! Thankfully, cells in other systems do not.

Mast cells as part of the immune system  – they contain substances like histamine  

that they can release which is critical  for the inflammatory response. Skeletal  

muscle cells -which are also called muscle  fibers – as part of the muscular system,  

they’re shaped like cylinders with  multiple nuclei – and their structure  

includes thin and thick filaments which  are essential for muscle contraction.

We could on with all the specialized  cells in all the body systems and  

the cells themselves structurally sure  are different – specialized for their  

function. And if I had to pick my favorite  specialized body cell – it’d be a neuron  

–a cell that is part of the nervous system.  The system that is the topic of this video.

But before we talk about neurons  or other cells in the nervous  

system because it’s not just neurons – let’s give  a little general tour of the nervous system. Then  

we’ll get to cells of the nervous system  and briefly mention the action potential!

First, structure wise, you can divide the nervous  system into 2 very general regions: the central  

nervous system (CNS) – which consists of the brain  and spinal cord - and peripheral nervous system  

(PNS) –which consists of all other components of  the nervous system -such as nerves throughout the  

body. The PNS can provide sensory information for  the CNS while the CNS can process that information  

and act as a command center – the CNS can execute  motor responses or regulate body mechanisms.

So, we said the CNS consisted of the spinal  cord and brain. Let’s talk a bit about the  

amazing human brain – although realize we  are being very general here – as we are  

going to divide it into 3 general regions:  the hindbrain, midbrain, and forebrain.

Let’s look at the hindbrain first.  It includes the medulla, pons,  

and cerebellum. The medulla has many regulation  functions such as the regulation of breathing,  

blood pressure, and heart rate. The pons is  involved with some of these type of functions  

as well and also coordinating signals with  this area to the rest of the brain. And the  

cerebellum? Balance and movement coordination  are some functions of the cerebellum.

The midbrain: deep in the brain, this area is  involved in alertness and the sleep/wake cycle,  

motor activity, and more. If you’ve heard  the term “brainstem,” this includes some  

of the structures we just mentioned: the  medulla, pons, and midbrain specifically.

Finally, the forebrain. Most notably, this  includes the cerebrum, which itself is  

divided into two hemispheres: right and left. So many functions are done by our amazing  

cerebrum depending on specific location whether  it’s our speech, our thinking and reasoning,  

our sensing, our emotions – check out  the further reading to explore this!  

The forebrain also technically includes some  structures in it like the thalamus – which is  

involved with sensory and motor information-  and hypothalamus – which if you remember  

from our endocrine system video, has  major control of the endocrine system.

There are a lot of myths about the brain. One  quick myth I heard all the time as a kid that  

I’d like to put to rest. It’s the myth that  “humans only use 10% of their brain” – it’s  

not correct. We have a great reading suggestion on  that as well as some others that circulate around.

Now, that was all the central nervous system  (CNS). What about the peripheral nervous  

system or PNS? Functionally speaking, we can  further divide the PNS based on what it does.  

The somatic nervous system (SNS) and autonomic  nervous system (ANS). The SNS is involved with  

motor functions of skeletal muscle. This will  include voluntary actions under conscious  

control but also somatic reflexes that involve  skeletal muscle. The ANS is all about what’s  

going on in the internal environment in  regard to gastrointestinal or excretory  

or endocrine or smooth and cardiac muscle  and it also includes autonomic reflexes.

And the ANS itself can be further divided –  I know, I know, there’s a lot of dividing but  

stay with me – the ANS can be divided into the  sympathetic and parasympathetic systems. The  

sympathetic system – the shorter word of the two–  helps me remember it’s part of the quick fight  

or flight response. I know the whole running  from a bear is a very popular example. For me,  

it’d be more realistic if I was face to face with  my personal nemesis: the copy machine which I may  

or may not have had some very bad experiences  with before – and the warning bell just rang  

so you now know you have 60 seconds to get your  copies – but it’s making crazy machine noises  

and giving you vague warnings– this also could  activate your fight or flight response. A response  

that can cause your heart to race and breathing  rate to increase and some things to not be active:  

like the digestive system. Because if you’re  desperately trying to run from a bear or take  

on the copy machine, you don’t really need to be  digesting your food at that very moment…right?

The parasympathetic system – longer word  – this is often called rest and digest.  

Heart rate will decrease, digestion will  occur – again, rest and digest. Many times,  

these two systems can therefore have  opposite effects on the same organ.

So let’s talk about two major types  of cells in the nervous system that  

makes up nervous tissue. That means  these are cells that you’ll find in  

the central nervous system and  the peripheral nervous system.

Most of the time, neurons are what come to mind.  There are different types of neurons but to focus  

on general neuron structure: you have the cell  body – the nucleus and most other organelles  

are here. There are dendrites, generally  these branched structures are where signals  

are received. And you have an axon – I like  to think away axon! – because axons are the  

fiber where normally a signal will be carried  away to some other cell. The junction area  

where the neuron will be communicating  with another cell is called a synapse.

And the other major cell type? Glial cells. Or  you can call them glia. When I was a student  

and read that they were supporting cells – I  don’t think the word “supporting” emphasized  

to me at the time how essential they really  are. Structurally, there was a lot of emphasis  

on how they actually help the neurons connect  in place – the word “glia” comes from a Greek  

word that means glue. But glia have huge roles  and they are SO much more than that. Some glial  

cells keep a balance of certain chemicals  in the space between cells – essential for  

signaling – and maintain the blood-brain barrier  which keeps a lot of substances in the body from  

getting into the nervous system. Some glial  cells make myelin – which goes around the  

axons of neurons as something called a myelin  sheath - insulates the axon and transferring  

of the signal. Some glial cells produce  cerebrospinal fluid which is protective  

to the brain and essential for homeostasis -  as well as many other critical functions. Some  

glial cells have important immune function in the  nervous system. These are all just a few examples.

As amazing as glial cells are, it’s time to  move on to the action potential. Generally,  

action potentials are recognized as something  neurons do – but we did link some interesting  

reads about certain glial cell types and  action potentials. We’re just going to touch  

on what an action potential is but we may have  a future video to go into more detailed steps.

The main idea is that neurons need to be able  to communicate with each other. And to do that  

they’ve got to be able to receive a signal in the  dendrite and carry it down the axon. And they need  

to do that fast – like less than 2 milliseconds  fast. The action potential makes that possible.  

We can’t talk about an action potential without  talking about when the neuron is at rest – meaning  

when there is no signal being carried – at  rest, a neuron has something called a resting  

potential. The resting potential of a neuron is  more negative than its surroundings – in fact  

it can be measured – it generally is around  -70 mv. Yes, mv, which is millivolts- it has  

an electrical charge. That’s because there are  ions involved inside and outside of the cell:  

ions like chloride (Cl-), sodium (Na+), potassium  (K+), certain anions (A-). Specifically,  

sodium (Na+) and potassium (K+) play huge roles  in keeping the resting potential – they should  

sound familiar because we talk about the sodium  potassium pump in another video and that is a pump  

that helps maintain a neuron at resting potential.  At rest, generally the sodium (Na+) concentration  

is higher outside of the cell and the potassium  (K+) concentration is higher inside the cell.  

How can we remember that? How about it’s Kool  to be K+ resting in the cell. But overall,  

at rest, the neuron is more negative  inside compared to its surroundings.

So let’s say the dendrite of the neuron receives  a signal. This can generate an action potential  

along the axon. An action potential is going to  rapidly change the charge in the neuron along  

the axon - the signal carries from one area  of the axon to the next. Ion channels open  

allowing Na+ to flood inside the first region  of the axon. Recall Na+ is a positive ion. This  

event is called depolarization – as the electric  charge is becoming more positive in the axon as  

Na+ floods in and most K+ channels at that moment  stay closed. This spreads to the next region of  

the axon and carries along. But as the action  potential spreads to a new region of the axon,  

the old region where the action potential  already occurred will start to be restored  

back - to learn more about the different channels  that open and close to achieve this amazing  

feat – or specific events like the undershoot or  refractory period- check out the further reading  

links in the video description. Eventually we  hope to have an entire video on this process.

Two things to point out about this  action potential. 1. If neurons are  

myelinated – meaning they have myelin  sheaths that insulate the axon and  

assist with the transfer of the signal  – the action potential can actually jump  

from node to node – the nodes being  areas of where it’s not myelinated.

2. Important to realize, the action  potential is considered an “all or  

none” thing. What we mean by that is that it  either happens or it doesn’t – like a light  

switch it’s either on or off – there isn’t a  dimmer switch, there aren’t different levels,  

it’s either off or it reaches a threshold  of when it’s on and if it’s on, it’s going.

So that’s all good but what happens next? Let’s  say you have an action potential and it’s going  

to signal another neuron – how? Well that’s one  way to introduce neurotransmitters. So the action  

potential goes down the axon and gets to the axon  terminals – the ends of the axon. We had mentioned  

there is this space called a synapse which  consists of the area between the two neurons.  

The action potential can signal synaptic vesicles  in that neuron to release something called  

neurotransmitters. There are different types  of neurotransmitters and they can be derived  

from different substances: for example, amino  acids or amino acid precursors. Or even a gas  

such as nitric oxide although the release  is different than other neurotransmitters.

Generally, when neurotransmitters are  released from the synaptic vesicles,  

the neurotransmitters only need to travel  a small space between the neurons specified  

as the synaptic cleft. Then they can  bind specific receptors of the next  

neuron – specific receptors to the type of  neurotransmitter that binds it. The dendrite  

area of the other neuron receives the signal and  can start an action potential across its axon.

When we cover a lot of things, we  think it’s important to recap: so,  

we’ve talked about the peripheral  nervous system (PNS) and the central  

nervous system (CNS). Since the CNS  includes the spinal cord and brain,  

we also talked some about major areas of the  brain. Then we focused on the PNS- how it can  

be divided into the somatic nervous system (SNS)  and autonomic nervous system (ANS) and then how  

the autonomic nervous system (ANS) can be divided  into the sympathetic and parasympathetic system.

We then explored major cell types in the  nervous system: glial cells and neurons.  

And since neurons can communicate with  each other using an action potential,  

we gave a brief overview of the action  potential. We then mentioned that once  

the action potential occurs, this can signal  the release of neurotransmitters in the synapse  

between neurons. Those neurotransmitters bind  specific receptors of a neighboring neuron. Phew!

So, with such a complex system that could be  so many videos long –there continues to be a  

lot of research done to help diseases and  conditions of the nervous system. If you  

have an interest in this field– there  are many careers involved in neurology  

to explore. Well that’s it for the Amoeba  Sisters, and we remind you to stay curious.