Tricky Topics: Synaptic Transmission

Summary

This script delves into the intricacies of neuronal communication via synaptic transmission. It explains how neurons, with their billions of connections, communicate using electrical signals and chemical messengers like neurotransmitters. The process involves graded potentials and action potentials, with neurotransmitters playing a crucial role in message transmission across synapses. The script also distinguishes between excitatory and inhibitory postsynaptic potentials, triggered by different ion channel receptors, ultimately leading to action potentials if a threshold potential is reached.

Takeaways

• 🧠 The nervous system is composed of billions of neurons that communicate constantly, even during sleep.
• 🔌 Neuronal communication is facilitated by electrical signals and chemical messengers called neurotransmitters.
• 📡 Neurons have two primary functions: transmitting messages across a synapse and carrying messages along their axon.
• 🔄 Graded potentials are electrical signals that can be either excitatory or inhibitory, depending on the type of ion channel receptor activated.
• 🔬 If graded potentials are of the right size and type, they can trigger action potentials, which are necessary for message transmission along the axon.
• 🔴 The presynaptic neuron sends signals, while the postsynaptic neuron receives them, with synapses forming the connection points.
• 💧 Synaptic vesicles contain neurotransmitters that are released into the synaptic cleft to communicate with the postsynaptic neuron.
• 🔄 Binding of neurotransmitters to receptors on the postsynaptic neuron can lead to either depolarization (excitatory) or hyperpolarization (inhibitory).
• 📈 Glutamate is an example of an excitatory neurotransmitter that, when bound to its receptor, allows sodium ions to enter the neuron, causing depolarization.
• ⛔ GABA is an inhibitory neurotransmitter that, when bound to its receptor, allows chloride ions to enter the neuron, causing hyperpolarization.
• 🚀 If the sum of EPSPs and IPSPs reaches a threshold, voltage-dependent sodium channels open, initiating an action potential and allowing the neuron to transmit its message.

Q & A

How do neurons communicate with each other?

Neurons communicate with each other through a process called synaptic transmission, which involves the use of electrical signals and chemical messengers called neurotransmitters.

What is the role of neurotransmitters in synaptic transmission?

Neurotransmitters act as messengers that transmit messages across a synapse from the presynaptic neuron to the postsynaptic neuron.

What are the two important jobs of a neuron?

A neuron's two important jobs are to transmit a message to a target across a synapse using neurotransmitters and to carry the message along the length of its axon to its target using an action potential.

What is a graded potential?

A graded potential is a type of electrical signal that results when neurotransmitters bind to receptors on the postsynaptic neuron, causing a change in the neuron's membrane potential without necessarily generating an action potential.

What is an action potential?

An action potential is a type of electrical signal that allows the neuron to send its message to its targets when the membrane potential reaches a threshold, typically around -55 millivolts.

What is the difference between a presynaptic and a postsynaptic neuron?

The presynaptic neuron is the sending neuron that releases neurotransmitters into the synapse, while the postsynaptic neuron is the receiving neuron that has receptors for these neurotransmitters.

What are synaptic vesicles and what do they contain?

Synaptic vesicles are small bubbles within the presynaptic neuron that contain neurotransmitter molecules, which are released into the synaptic cleft to transmit signals.

How do neurotransmitters create a graded potential in the postsynaptic neuron?

Neurotransmitters create a graded potential by binding to receptors on the postsynaptic neuron, which can be gated to ion channels. This binding allows ions to flow across the membrane, creating a change in potential.

What is the role of ion channels in generating graded potentials?

Ion channels play a crucial role in generating graded potentials by allowing certain ions to flow across the neuronal membrane when they are opened by neurotransmitter binding, thus changing the neuron's membrane potential.

What is an excitatory postsynaptic potential (EPSP)?

An EPSP is a type of graded potential that occurs when neurotransmitters, such as glutamate, bind to their receptors and cause positive ions like sodium to enter the neuron, making it less negative and more likely to fire an action potential.

What is an inhibitory postsynaptic potential (IPSP)?

An IPSP is a type of graded potential that occurs when neurotransmitters, such as GABA, bind to their receptors and cause negative ions like chloride to enter the neuron, making it more negative and less likely to fire an action potential.

How does the type of ion channel receptor activated determine the type of graded potential?

The type of ion channel receptor activated determines whether the graded potential is excitatory (depolarizing) or inhibitory (hyperpolarizing), based on whether positive or negative ions are allowed to enter the neuron.

Outlines

00:00

🧠 Understanding Neuronal Communication

This paragraph explains the fundamental process of synaptic transmission, which is crucial for neuronal communication. It highlights that the nervous system contains billions of neurons that communicate through synapses. Neurons have two main functions: transmitting a message across a synapse using neurotransmitters and carrying the message along the axon using an action potential. The paragraph introduces the concepts of graded potentials and action potentials, which are electrical signals that facilitate communication. It also describes the roles of presynaptic and postsynaptic neurons and delves into the structure of synapses, including synaptic vesicles and neurotransmitter release. The paragraph concludes with an overview of how neurotransmitters initiate graded potentials by binding to receptors on the postsynaptic neuron.

05:01

🔬 Excitatory and Inhibitory Graded Potentials

This paragraph delves into the specifics of excitatory and inhibitory graded potentials. It explains how different types of ion channel receptors can lead to either depolarization (excitatory) or hyperpolarization (inhibitory) of the postsynaptic neuron. An excitatory neurotransmitter, like glutamate, causes sodium ions to enter the neuron, leading to a depolarization and an excitatory postsynaptic potential (EPSP). Conversely, an inhibitory neurotransmitter, like GABA, allows chloride ions to enter, causing hyperpolarization and an inhibitory postsynaptic potential (IPSP). The paragraph also discusses the role of voltage-dependent sodium channels, which, when activated by the sum of EPSPs and IPSPs reaching a threshold, initiate an action potential. This potential is critical for the neuron to transmit its message to its targets, illustrating the complexity and importance of synaptic transmission in neuronal communication.

Keywords

💡Neurons

Neurons are the fundamental units of the nervous system, responsible for transmitting information through electrical and chemical signals. In the video, it is emphasized that the human nervous system contains billions of neurons, each capable of having hundreds or thousands of contacts, highlighting their critical role in communication within the nervous system.

💡Synaptic Transmission

Synaptic transmission refers to the process by which neurons communicate with each other via synapses. The video script describes synaptic transmission as the mechanism that allows neurons to transmit messages across a synapse using neurotransmitters, which is central to the video's theme of neuronal communication.

💡Graded Potential

A graded potential is a type of electrical signal in a neuron that varies in magnitude with the strength of the stimulus. The script explains that when neurotransmitters bind to receptors on the postsynaptic neuron, they can cause an influx of ions, leading to either depolarization (excitatory) or hyperpolarization (inhibitory), which are forms of graded potentials.

💡Action Potential

An action potential is a large, rapidly propagating electrical signal that travels along the length of a neuron's axon. The video describes how, if the sum of graded potentials reaches a certain threshold, voltage-dependent sodium channels open, creating an action potential that allows the neuron to send its message to its targets.

💡Presynaptic Neuron

The presynaptic neuron is the neuron that sends signals across a synapse. In the script, the axon terminals of the presynaptic neuron are described as forming synapses with the dendrites of another neuron, releasing neurotransmitters into the synaptic cleft to initiate communication.

💡Postsynaptic Neuron

The postsynaptic neuron is the neuron that receives signals across a synapse. The video explains how neurotransmitters released by the presynaptic neuron can bind to receptors on the postsynaptic neuron, leading to the generation of graded potentials.

💡Neurotransmitters

Neurotransmitters are chemical messengers that transmit signals across a synapse from the presynaptic neuron to the postsynaptic neuron. The script mentions that neurotransmitters are released from synaptic vesicles into the synaptic cleft, where they can bind to receptors on the postsynaptic neuron.

💡Synaptic Cleft

The synaptic cleft is the small gap between the presynaptic and postsynaptic neurons where neurotransmitters are released and travel to reach the postsynaptic neuron. The video uses the term to describe the space across which neurotransmitters travel to continue the cycle of communication.

💡Depolarization

Depolarization is the process by which the inside of a neuron becomes less negative, often leading to an excitatory response. The script gives the example of glutamate binding to its receptor, allowing sodium ions to enter the neuron and cause depolarization, which can lead to an excitatory postsynaptic potential (EPSP).

💡Hyperpolarization

Hyperpolarization is the process by which the inside of a neuron becomes more negative, often leading to an inhibitory response. The video describes how the neurotransmitter GABA can cause chloride ions to enter the neuron, leading to hyperpolarization and the generation of an inhibitory postsynaptic potential (IPSP).

💡Ion Channels

Ion channels are proteins embedded in the cell membrane that allow ions to pass through. The script explains that neurotransmitters can bind to receptors that are gated ion channels, opening them to allow ions to flow across the neuronal membrane, which is crucial for generating graded potentials.

Highlights

Neurons communicate through synaptic transmission.

The nervous system has billions of neurons.

Each neuron can have hundreds or thousands of contacts.

Neurons are in constant communication even during sleep.

Neuronal communication is facilitated by electrical signals and chemical messengers.

Neurons have two key functions: transmitting messages across synapses and carrying messages along their axons.

Graded potentials are electrical signals resulting from neurotransmitter release.

Action potentials are electrical signals that carry messages along the axon.

The axon terminals of one neuron form synapses with the dendrites of another.

Neurons can act as both presynaptic (sending) and postsynaptic (receiving) cells.

Synaptic vesicles contain neurotransmitter molecules.

Neurotransmitters are released into the synaptic cleft and bind to receptors on the postsynaptic neuron.

Binding of neurotransmitters opens ion channels, generating graded potentials.

Graded potentials can be either depolarizing (excitatory) or hyperpolarizing (inhibitory).

Glutamate is an example of an excitatory neurotransmitter.

GABA is an example of an inhibitory neurotransmitter.

Depolarization makes the neuron's inside more positive, while hyperpolarization makes it more negative.

Excitatory postsynaptic potentials (EPSPs) and inhibitory postsynaptic potentials (IPSPs) sum up to determine neuronal activity.

If the membrane potential reaches a threshold, voltage-dependent sodium channels open, creating an action potential.

Synaptic transmission is a fundamental process for neuronal communication.

Transcripts

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to understand how neurons communicate

with one another it is vital to

understand the basics of synaptic

transmission the nervous system has

billions of neurons in each of them can

have hundreds or thousands of contacts

these neurons are in constant

communication even when we're sleeping

this sheer amount of activity is truly

remarkable

despite this neuronal communication is

made possible by couple different types

of electrical signals which are linked

by chemical messengers let's zoom in for

a closer look

neurons have two important jobs one is

to transmit a message to a target across

a synapse using neurotransmitters as

messengers the type of electrical signal

resulting from this is called a graded

potential if the graded potentials the

right size and type then it allows the

neuron to do its second important job

which is to carry the message along the

length of its axon to its target using a

type of electrical signal called an

action potential when an action

potential reaches the axon terminals it

triggers once again neurotransmitter

release which continues the cycle of

producing a graded potential and then

action potential and the next targeted

neurons this continuous cycle of

communication is running all the time in

your nervous system for this tricky

topic we'll focus on the events at the

synapse and learn how synaptic

transmission plays a role in neuronal

communication we're going to start our

journey to the synapse with a bird's eye

view the axon terminals of the neuron on

the Left shown here in red form synapses

with the dendrites of the neuron on the

right although most neuronal axon

terminals synapse on dendrites like you

see here keep in mind they can also form

synapses on other parts of the targeted

neuron

such as the soma and the axon the

sending neuron on the left is referred

to as the presynaptic neuron and the

receiving neuron on the right is

referred to

the postsynaptic neuron keep in mind

these are relative terms most neurons

act as senders and receivers of

information so they're both presynaptic

and postsynaptic depending on which

event were referring to let's pick this

particular synapse and zoom in for a

little more detail at this magnification

we can see little bubbles called

synaptic vesicles and inside these we

can see neurotransmitter molecules these

vesicles here are releasing their

neurotransmitter contents into the

synaptic cleft once released into the

synapse the neurotransmitters can travel

the short distance to the postsynaptic

neuron once they reach the other side

these neurotransmitters bind to

receptors on the postsynaptic neuron

there are lots of different types of

receptors but the simplest ones are

gated to ion channels like shown here

once the neurotransmitter binds it opens

the ion channel part of the receptor

allowing certain ions to travel across

the neuronal membrane along their

electrochemical gradient this influx a

positive current in the form of positive

ions is what generates graded potentials

in the postsynaptic neuron thus through

the binding of postsynaptic ion channel

receptors synaptic neurotransmitters

initiate postsynaptic graded potentials

let's review the steps so far first

neurotransmitter is released from the

presynaptic terminal second that

neurotransmitter binds to receptors

opening their ion channels on the

postsynaptic side what happens next in

the postsynaptic neuron depends on the

type of ion channel receptor that is

activated as different receptors are

permeable to different types of ions the

type of ion channel receptor that is

activated will then determine the type

of graded potential that is initiated if

the channel opens and positive ions

enter through the channel then the

inside of the neuron will become less

negative for example the potential of

the neuron might rise from its resting

potential of minus 70 millivolts to

minus 55 millivolts this is referred to

as a depolarization and is considered

excitatory if instead negative ions

enter through the channel then the

inside of the neuron will become more

negative

for example the potential of the neuron

might decrease from its resting

potential of minus 70 millivolts to

minus 90 millivolts this is referred to

as a hyper polarization and is

considered inhibitory let's look at some

examples of different types of receptors

which produce either excitatory or

inhibitory graded potentials first let's

look at depolarization a

neurotransmitter that is always

excitatory at the synapse is glutamate

so we can pretend that the orange

diamonds are glutamate molecules and the

white circles in the synapse are sodium

ions when glutamate binds to its

receptor the channels open in sodium

ions are driven by their electrochemical

gradient to enter the neuron when sodium

moves into the cell through the receptor

ion channel it brings its positive

charge with it making the cell more

positive which is called a

depolarization if the channel remains

open for longer more sodium will flow in

making the cell even more positive

this type of graded potential is called

an excitatory postsynaptic potential or

epsp for short what about

hyper-polarization a neurotransmitter

that's almost always inhibitory at its

synapse is gaba and it's receptor

channel is permeable to negatively

charged chloride ions shown here as

black circles when gaba binds to its

receptor the channel opens and chloride

ions are driven into the postsynaptic

neuron because of their concentration

when chloride moves into the cell

through the GABA receptor ion channel it

brings its negative charge with it

making the cell more negative which is

called a hyper polarization if the

channel remains open for longer more

chloride will flow in making the cell

even more negative

this type of graded potential is called

an inhibitory postsynaptic potential or

IPSP for short so why does this matter

well if the postsynaptic neuron adds up

all its epsps

and ipsps and the membrane potential

reaches a threshold of minus 55

millivolts a different type of ion

channel comes into play one that is

opened by a change in voltage the ion

channels we've learned about so far are

opened by neurotransmitter binding but

these voltage dependents sodium channels

are sensitive to changes in charge at

resting conditions say minus 70

millivolts these channels are closed and

sodium ions cannot pass through them

into the cell however when the sum of

all ipsps and ipsps raises the neurons

potential to are above minus 55

millivolts the voltage dependent sodium

channels open allowing sodium ions to

flow into the cell

when these voltage dependent sodium

channels open they create an action

potential which allows the neuron to

send its message to its targets overall

synaptic transmission may seem quite

tricky but it's actually quite simple

once you know the basics

you

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