How a synapse works

Summary

This script delves into the electrical properties of neurons, explaining how they generate membrane potentials and action potentials. It highlights the importance of understanding the neuronal membrane and the collective behavior of interconnected neurons in the brain. The lesson focuses on synapses, distinguishing between electrical and chemical synapses, and their roles in neuronal communication and brain function. It also touches on synaptic involvement in neurological disorders and the significance of synaptic plasticity in learning and memory.

Takeaways

• 🧠 Understanding the electrical properties of neurons is fundamental to neuroscience, but it's not enough to explain the collective behavior of billions of neurons in the brain.
• 🔋 Membrane potentials arise from electrical forces and diffusion, and neurons can generate action potentials or 'spikes' to propagate signals along the membrane.
• 🌐 Neurons are polarized cells with dendrites for receiving inputs and an axon for sending outputs, which are crucial for signal transmission.
• 🤝 Neurons connect with one another through synapses, which can be either electrical or chemical, facilitating communication between cells.
• ⚡ Electrical synapses allow for fast and synchronous signal transmission between cells through pores that let ions pass through.
• 🧪 Chemical synapses involve a more complex process where an action potential triggers the release of a chemical into the synaptic cleft, which then affects the downstream neuron.
• 💊 The chemical step in chemical synapses is slower than electrical transmission but enables a wide range of signaling mechanisms and synaptic functions.
• 🧬 Synaptic function is critical for the computations performed by neurons and will be further explored in the course.
• 🛑 Defective synaptic physiology can lead to neurological and psychiatric disorders, highlighting the importance of synapse health.
• 💊 Synapses can be targeted by psychoactive drugs and poisons, which can modulate neuronal signaling and behavior.
• 📚 Synapses can change over time in response to external stimuli, which is fundamental to learning and memory processes.

Q & A

What are the electrical properties of individual neurons?

Individual neurons have electrical properties that include the generation of membrane potentials due to electrical forces and diffusion, and the ability to generate and propagate action potentials or 'spikes' along their membrane.

Why is understanding the properties of the neuronal membrane essential?

Understanding the properties of the neuronal membrane is essential because it forms the basis for how neurons function at an individual level, but it is not sufficient to understand the collective behavior of billions of connected neurons in the brain.

What is the significance of approaching neuroscience at different scales and levels of analysis?

Approaching neuroscience at different scales and levels of analysis allows for a gradual understanding of the complexity of the nervous system, from single molecules like ion channels to the collective behavior of neurons in large functional regions of the brain.

What is the basic cellular anatomy of neurons?

The basic cellular anatomy of neurons includes dendrites, which are specialized for receiving inputs from other cells, and an axon, which carries action potentials to other neurons.

What is the term for the portion of a neuron that receives inputs from other cells?

The portion of a neuron that receives inputs from other cells is called 'dendrites'.

What is the term for the part of a neuron responsible for sending outputs?

The part of a neuron responsible for sending outputs is the 'axon'.

What happens at the boundary between two neurons?

At the boundary between two neurons, an interface called a 'synapse' allows for the transmission of signals from one neuron to another.

What are the two general types of synapses?

The two general types of synapses are electrical synapses and chemical synapses.

How do electrical synapses function?

Electrical synapses function by having pores between two cells that allow ions to pass through, effectively passing the electrical signal to a neighboring cell without much delay.

How do chemical synapses differ from electrical synapses?

Chemical synapses differ from electrical synapses in that they involve the release of a chemical into the synaptic cleft, which is then taken up by the downstream neuron, converting the chemical signal back into an electrical one or having other effects on the cell.

What role do synapses play in the computations performed by neurons?

Synapses play a critical role in the computations performed by neurons by enabling diverse and complex signaling, which is crucial for the brain's ability to process information.

How can defective synaptic physiology be related to neurological and psychiatric disorders?

Defective synaptic physiology can lead to neurological and psychiatric disorders by disrupting the normal functioning of synapses, which can affect the transmission of signals between neurons and lead to abnormal brain function.

What is the significance of synaptic change over time in response to external stimuli?

Synaptic change over time in response to external stimuli is significant because it plays a foundational role in learning and memory, allowing the brain to adapt and store information.

Outlines

00:00

🧠 Neuron Communication Basics

This paragraph introduces the fundamental concepts of how neurons communicate through electrical properties. It explains the importance of understanding membrane potentials and action potentials for signal generation and propagation. The script emphasizes the need to study neurons at various scales and levels of complexity, starting from single molecules to large brain regions. It also poses the question of how two neurons connect, leading into a discussion about neuron anatomy, specifically the roles of dendrites and axons in receiving and sending signals, respectively.

🔌 The Synaptic Interface

This section delves into the specifics of how neurons interact at the synapse, the junction between two neurons. It differentiates between two types of synapses: electrical and chemical. Electrical synapses are simpler, allowing ions to pass directly between cells, facilitating fast and synchronous communication. In contrast, chemical synapses involve a more complex process where an action potential triggers the release of a chemical into the synaptic cleft, which then influences the downstream neuron. The paragraph highlights the diversity and complexity of signaling made possible by chemical synapses and their critical role in neuronal computations.

Keywords

💡Neuron

A neuron is the fundamental unit of the nervous system, responsible for receiving, processing, and transmitting information through electrical and chemical signals. In the video, neurons are the central focus as the script delves into their electrical properties and how they communicate with one another, which is essential to understanding brain function.

💡Membrane Potential

Membrane potential refers to the voltage difference across the cell membrane, which is crucial for neuronal function. The script explains how electrical forces and diffusion give rise to membrane potentials, setting the stage for the generation of action potentials, a key concept in the video's exploration of neuronal communication.

💡Action Potential

An action potential, also known as a 'spike,' is an electrical signal that travels along the neuron's membrane. The video discusses how cells can generate and propagate these signals, which are vital for communication between neurons and the collective behavior of neural networks.

💡Polarized Cells

Polarized cells, such as neurons, have distinct regions specialized for different functions. The script mentions that neurons have dendrites for receiving inputs and an axon for sending outputs, highlighting the importance of cellular polarity in neuronal communication.

💡Dendrites

Dendrites are the tree-like structures of a neuron that specialize in receiving input from other cells. The script uses the term 'dendrites' to describe the parts of the neuron that collect signals, which are then passed to the cell body for potential action potential initiation.

💡Axon

The axon is the long, slender part of a neuron that carries electrical signals away from the cell body to other neurons or target cells. In the script, the axon's role in transmitting action potentials to other neurons is emphasized, illustrating the propagation of signals in the nervous system.

💡Synapse

A synapse is the junction between two neurons where information is transmitted. The video focuses on the synapse as the interface for neuronal communication, distinguishing between electrical and chemical synapses and their roles in the brain's complex signaling processes.

💡Electrical Synapses

Electrical synapses are direct connections between cells that allow the passage of electrical signals. The script simplifies the concept by comparing them to pores, emphasizing their speed and the synchronicity they provide in neuronal communication.

💡Chemical Synapses

Chemical synapses are the more complex and common type of synapse, involving the release of a chemical neurotransmitter into the synaptic cleft. The script explains how this chemical signal is received by the downstream neuron, converting it back into an electrical signal, and highlighting the diversity and complexity of signaling in the brain.

💡Neurotransmitter

A neurotransmitter is the chemical substance released at a chemical synapse that transmits signals across the synaptic cleft. The script describes the process by which neurotransmitters are released and received, underlining their critical role in neuronal signaling and synaptic function.

💡Synaptic Cleft

The synaptic cleft is the small gap between the axon terminal of one neuron and the dendrite of another where neurotransmitters are exchanged. The script uses the term to describe the location where chemical signaling occurs, which is essential for understanding how neurons communicate via chemical synapses.

Highlights

Understanding the electrical properties of individual neurons is crucial for grasping the collective behavior of billions of connected neurons in our brains.

Neuroscience can be approached at various scales and levels of analysis, allowing for a gradual understanding of complexity.

The course will explore the progression from single molecules to large functional regions of the brain.

Neurons are 'polarized' cells with distinct regions for receiving inputs (dendrites) and sending outputs.

Dendrites have a branching, tree-like structure, facilitating the reception of signals from other cells.

Sufficient depolarization of the cell body can initiate an action potential that travels down the axon to another neuron.

The 'synapse' is the interface between the axon of one neuron and the dendrite of another, critical for neuronal communication.

Electrical synapses allow for fast and synchronous transmission of electrical signals between cells.

Chemical synapses involve the release of a chemical into the synaptic cleft, which can be taken up by the downstream neuron.

Chemical synapses enable a diverse range of signaling mechanisms and are central to neuronal computations.

The unit will delve into the inner workings of chemical synapses and their role in interconnected neuronal networks.

Defective synaptic physiology can contribute to neurological and psychiatric disorders.

Synapses can be targeted by psychoactive drugs and poisons, affecting neuronal function.

Synaptic changes over time in response to stimuli are fundamental to learning and memory processes.

The course will examine how synapses adapt and their implications for cognitive functions.

The diversity of synaptic function is integral to the complexity of brain function and behavior.

Understanding synaptic mechanisms is key to unlocking the mysteries of brain disorders and treatments.

Transcripts

In the last module, we took first steps towards understanding

the electrical properties of individual neurons.

We learned how electrical forces and diffusion give rise

to membrane potentials,

and we learned how cells can generate and propagate signals called action

potentials, or 'spikes', along the membrane.

Understanding the properties of the neuronal membrane is essential,

but understanding just these properties isn't sufficient to give us insight

into collective behavior of the billions of connected neurons in our brains.

Luckily for us, we can approach neuroscience at many different scales

and levels of analysis, and we don't have to confront the full complexity

of everything all at once.

That's what we'll be exploring throughout the rest of this course

as we slowly go from our understanding of single molecules such as ion

channels'

...to the electrical behavior of neurons

...to their collective behavior in small circuits

...and finally onto how they become organized in large functional regions

of the brain.

Let's start simple, though.

Since we've examined one neuron, a logical next question is how do two

neurons connect with one another?

We'll first examine some basic cellular anatomy of neurons.

So far, we haven't made too much of the fact that the majority of neurons

are 'polarized'

cells.

That is, they have one portion of the cell

for receiving inputs and another portion for sending outputs.

The parts of the cells that are specialized for receiving inputs from

other cells are called 'dendrites.'

The word 'dendrite' comes from the Greek word 'dendron', meaning tree,

and as you can see the dendrites have a branching, tree-like shape.

A signal received by a dendrite is passed to the cell body.

If there is a sufficient depolarization of the cell body membrane

to initiate an action potential, then an action potential is sent down the axon.

The axon then carries the propagating action potential to another neuron.

So what actually happens at the boundary between two neurons,

between the axon of one neuron and the dendrite of another?

This interface is called a 'synapse',

and it'll be the focus of this lesson.

There are two general types of synapses that we'll cover in depth later:

electrical synapses, and chemical synapses.

Electrical synapses are less common in our own nervous systems,

but they're simpler to think about, so let's start with them.

Electrical synapses are basically pores between two cell

that allow ions to pass through.

They allow the passage of that electrical signal

through to a neighboring cell without much fuss.

It's not so different than just combining two cells into one larger

cell.

There are lots of reasons that nature might need synapses like this from time

to time -- they're fast, and they allow cells to couple together with

a high degree of synchronicity.

But most neurons are connected together by a much more complicated structure

called a chemical synapse.

In a chemical synapse, rather than simply passing along an electrical

signal from one cell to another, the action potential travels to the end

of the axon and causes a chemical to be released into a very small space

between the two neurons called the 'synaptic cleft'.

This chemical is taken up by the downstream neuron,

on the other side of the cleft.

This chemical signal can cause the downstream neuron

to depolarize its membrane, converting the chemical signal back

into an electrical one, or it can have other effects on the cell.

This chemical step is slower than transmission

across an electrical synapse, but it opens up

an enormously diverse repertoire of different and more complex

kinds of signaling, and synaptic function

plays a critical role in computations performed by neurons.

We'll spend the the rest of this unit exploring the inner workings

of chemical synapses, on our way to beginning to look at how networks

of interconnected neurons give rise to behavior.

We'll also look at the role of defective synaptic physiology

in neurological and psychiatric disorders,

and we'll see how synapses can be targeted by various psychoactive drugs

and poisons.

Finally we'll wrap up by looking at how synapse can change with time,

in response to external stimuli, playing a foundational role in how we learn

and remember.