4.1 Resting Membrane Potential

Summary

Chapter 4 delves into the intricacies of neural conduction, focusing on the resting membrane potential, a critical concept for understanding how neurons transmit signals. Despite being 'at rest,' neurons exhibit dynamic activity, characterized by a negative charge of approximately -70 millivolts. This potential is maintained through the sodium-potassium pump, which actively transports ions across the cell membrane, creating an electrochemical gradient. The chapter clarifies that resting potential is not a state of inactivity but rather a complex balance of ion movement and energy expenditure, essential for neural communication.

Takeaways

• 🧠 Chapter 4 focuses on how neurons conduct and transmit signals through the nervous system.
• 🔋 Understanding resting membrane potential is crucial for grasping neural conduction and synaptic transmission.
• 💧 The neuron's membrane is composed of lipid and protein, including channel proteins and signal proteins.
• 📡 Resting membrane potential is the electrical charge difference between the inside and outside of the neuron, typically around -70 millivolts.
• 🔬 Microelectrodes are used to measure membrane potential without damaging the neuron.
• 🔄 Ions, such as sodium (Na+), potassium (K+), and chloride (Cl-), play a key role in determining the neuron's charge.
• 🌊 At rest, there are more sodium ions outside and more potassium ions inside the neuron, contributing to the negative resting potential.
• 🔁 The sodium-potassium pump actively transports ions across the membrane, maintaining the resting potential.
• ⚡ Depolarization occurs when the cell loses its charge, which is a necessary step for neural conduction.
• 🔄 The neuron is constantly active even at rest, with a dynamic exchange of ions maintaining the resting potential.

Q & A

What is the main focus of Chapter 4 in the context of the nervous system?

Chapter 4 focuses on understanding how neurons conduct and transmit signals through the nervous system, specifically covering resting membrane potential.

Why is understanding resting membrane potential important for neural conduction and synaptic transmission?

Understanding resting membrane potential is crucial because it provides the baseline electrical state of a neuron, which is essential for comprehending how neurons can generate and propagate action potentials during neural conduction and synaptic transmission.

What is the composition of the neuron's membrane as discussed in the script?

The neuron's membrane is composed of lipids and proteins, specifically a bilayer of lipids with various types of proteins, including channel proteins and signal proteins.

How is the resting membrane potential measured?

The resting membrane potential is measured by using microelectrodes, with one tip positioned inside the cell and the other in the extracellular fluid, to record the voltage difference.

What is the typical resting membrane potential of a neuron?

The typical resting membrane potential of a neuron is approximately -70 millivolts, indicating a negative charge inside the cell relative to the outside.

What role do ions play in determining the charge of a neuron?

Charged ions, which are atoms or molecules with a net electric charge due to the loss or gain of electrons, determine whether a neuron is positively or negatively charged. The ions of interest here are sodium (Na+), potassium (K+), and chloride (Cl-).

Why are there more sodium ions outside the cell and more potassium ions inside during the resting potential?

During the resting potential, there are more sodium ions outside the cell and more potassium ions inside due to the action of the sodium-potassium pump, which actively transports sodium out of the cell and potassium into the cell, maintaining the resting potential.

What is the function of the sodium-potassium pump in maintaining the resting potential?

The sodium-potassium pump actively transports three sodium ions out of the cell for every two potassium ions it transports in, using energy to maintain the concentration gradients of these ions across the membrane, which is essential for the resting potential.

How does the resting potential relate to the concept of polarization in neurons?

Polarization refers to a neuron carrying a charge. At rest, a neuron is polarized, meaning it has a negative charge inside relative to the outside, which gives it the potential to generate an action potential.

What is the significance of the distribution of sodium, potassium, and chloride ions across the neural membrane?

The distribution of ions across the neural membrane is significant because it creates the necessary electrochemical gradients that underlie the neuron's ability to transmit electrical signals. Sodium and potassium ions are actively pumped against their concentration gradients to maintain the resting potential, while chloride ions help maintain charge balance.

Outlines

00:00

🧠 Understanding Neurons' Communication

This paragraph introduces the topic of how neurons conduct and transmit electrochemical signals within the nervous system. It emphasizes the importance of understanding the resting membrane potential, which is a prerequisite for grasping the complexity of neural conduction and synaptic transmission. The concept of resting potential is explained as the difference in electrical charge between the inside and outside of a neuron, typically around -70 millivolts. The paragraph also discusses the composition of the neuron's membrane, highlighting the presence of lipids and proteins, including channel proteins that facilitate signal transmission. The role of charged ions, such as sodium (Na+), potassium (K+), and chloride (Cl-), in determining the charge of the neuron is also covered, setting the stage for further exploration of neural communication.

05:02

🔋 The Dynamics of Resting Potential

This paragraph delves deeper into the concept of resting potential, clarifying that it is not a static state but involves continuous activity. It describes the sodium-potassium pump, a specialized protein that actively transports ions across the cell membrane, maintaining the resting potential. The pump exchanges three sodium ions out of the cell for every two potassium ions it brings in, using energy to do so. This process is crucial for the neuron's ability to polarize and depolarize, which is essential for signal transmission. The paragraph also illustrates the movement of ions along their concentration gradients and the role of anions like chloride in maintaining charge balance. The sodium-potassium pump's action is highlighted as a key mechanism that keeps the neuron at rest, ready to fire when needed.

Keywords

💡Neurons

Neurons are the fundamental units of the nervous system, responsible for receiving, processing, and transmitting information through electrical and chemical signals. In the context of the video, neurons are the primary focus as they communicate via electrochemical impulses, which is essential for understanding the nervous system's function. The video script discusses how neurons conduct and transmit these signals, which is central to the theme of neural communication.

💡Electrochemical impulses

Electrochemical impulses are the means by which neurons communicate, involving the movement of charged particles across the neuron's membrane, creating an electrical signal. The video script emphasizes that understanding how neurons conduct and transmit these impulses is crucial for grasping the overall function of the nervous system.

💡Resting membrane potential

Resting membrane potential refers to the difference in electrical charge between the inside and outside of a neuron when it is not transmitting signals. The video script explains that this potential is maintained at around -70 millivolts, which is a key concept in understanding how neurons function even when they are not actively firing.

💡Membrane

The membrane, as described in the video, is the lipid and protein layer surrounding the neuron. It plays a critical role in the neuron's ability to transmit signals by selectively allowing certain ions to pass through. The video script highlights the importance of understanding the membrane's composition and function for grasping neural conduction.

💡Channel proteins

Channel proteins are a type of protein found in the neuron's membrane that forms channels for ions to pass through. The video script discusses how these proteins facilitate the transmission of signals in the nervous system by allowing the flow of ions like sodium and potassium, which is essential for maintaining the resting membrane potential and enabling neural communication.

💡Signal proteins

Signal proteins are another type of protein in the neuron's membrane that are involved in receiving and interpreting signals. While the video script does not delve deeply into signal proteins, it mentions them as part of the membrane's composition, suggesting their role in the broader context of neural communication.

💡Sodium (Na+)

Sodium ions, denoted as Na+, are positively charged ions that play a key role in the neuron's electrical activity. The video script explains that sodium ions are more concentrated outside the neuron at rest, contributing to the resting membrane potential. Their movement across the membrane is crucial for the generation of action potentials.

💡Potassium (K+)

Potassium ions, denoted as K+, are also positively charged and are more concentrated inside the neuron at rest. The video script discusses how potassium ions help maintain the resting membrane potential and are involved in the process of repolarizing the neuron after an action potential.

💡Chloride (Cl-)

Chloride ions, denoted as Cl-, are negatively charged and contribute to the overall charge balance across the neuron's membrane. The video script mentions chloride ions in the context of the resting membrane potential, indicating their role in maintaining the electrical gradient that is necessary for neural signaling.

💡Sodium-potassium pump

The sodium-potassium pump is a specialized protein that actively transports sodium out of the cell and potassium into the cell, using energy from ATP. The video script describes this pump as a critical mechanism for maintaining the resting membrane potential by constantly exchanging ions against their concentration gradients.

💡Depolarization

Depolarization is the process by which the neuron's membrane potential becomes less negative, often leading to an action potential if the threshold is reached. The video script explains that the sodium-potassium pump helps to depolarize the cell by moving ions across the membrane, which is a necessary step for neural communication.

Highlights

Neurons communicate through electrochemical impulses.

Chapter 4 focuses on how neurons conduct and transmit signals.

Understanding resting membrane potential is crucial for grasping neural conduction and synaptic transmission.

The neuron's membrane is composed of lipid and protein, including channel and signal proteins.

Resting membrane potential is the difference in electrical charge between the inside and outside of the neuron.

Microelectrodes are used to measure membrane potential without damaging the neuron.

Resting potential is approximately -70 millivolts, indicating a polarized neuron.

Charged ions, such as sodium (Na+), potassium (K+), and chloride (Cl-), determine the neuron's charge.

At resting potential, there are more sodium ions outside and more potassium ions inside the neuron.

The sodium-potassium pump actively transports ions to maintain resting potential.

The sodium-potassium pump exchanges three sodium ions out for two potassium ions in.

The term 'resting potential' is misleading as there is significant activity even when the neuron is not firing.

The neuron's membrane plays a role in the distribution of ions through passive and active transport.

Ions move down their concentration gradients, influenced by the neuron's membrane.

The negative internal charge creates a pressure for sodium and potassium to enter the neuron.

The sodium-potassium pumps are specialized channels that help maintain the neuron's charge balance.

Transcripts

we've learned about neurons and some of

the major anatomical parts of the

nervous system we also know that neurons

are able to communicate an

electrochemical impulses what we don't

know is how neurons are able to conduct

and transmit these signals through the

nervous system chapter 4 will introduce

us to this this is an overview of the

topics that we'll cover in chapter 4 for

this specific module we will limit

ourselves to understanding resting

membrane potential

the complexity of neural conduction and

synaptic transmission can only be

understood if we understand membrane

potential you will learn in this module

that although the term resting potential

is used there really is nothing restful

about everything that's going on in the

background even when a neuron is off or

not firing to understand membrane

potential we have to understand what

membrane is and as you may remember from

Chapter three we looked at the membrane

being the surrounding tissue around the

neuron you see we have the dendrites

here and the membrane would be on the

outside of the neuron insight would be

the nucleus and various other organelles

you may also remember that the membrane

is composed of lipid and protein more

specifically a by lipid layer you may

remember the dead is made up of or it

has two different types of protein

channel protein and signal protein in

this chapter we will learn about how

those walls those protective coatings in

here facilitate for the transmission of

signals in the nervous system membrane

potential is the difference in

electrical charge between the inside and

the outside of the cell to record the

membrane potential one tip of electrode

is positioned inside the cell whereas

another tip of another electrode is

positioned outside the neuron and that

what we call the extracellular fluid to

avoid severely damaging the membrane

micro electrodes are used to record

inter cellular charge the tips of micro

electrodes are less than 1,000 of a

millimeter in diameter much too small to

be seen by the naked eye when both

electrode tips are in the extracellular

fluid the voltage difference between

them is zero however whenever we put one

micro electrode inside and the other one

outside then we're able to read what we

have as a negative

charge and it is what we call the

resting potential that has a steady

potential of approximately 70 millivolts

negative 70 millivolts this would occur

when this is what we would call as a

polarized neuron and every time you hear

the word polarize it means that it

carries a charge it has the potential to

then act on and demonstrate its force

we'll talk about this a little bit more

in future slides as you already know

when a neuron is off it has a negative

charge approximately negative 70

millivolts and charged ions which are

atoms or molecules with a net electric

charge due to the loss or gain of one of

more electrons are what determine

whether something is positively charged

or negatively charged

the ions that we'll be looking

specifically at here are sodium which

are positively charged and that's what

you'll see as na+ potassium k+ chloride

you can see that this is an anion which

is a negatively charged ion and then

other organic anions here in resting

potential we know that exists because

the ions are concentrated on different

sides of the membrane and we know that

when the cell is off meaning it's not

firing there are more sodium ions

outside the cell than they are inside

you have fewer fewer sodium ions inside

the cell and we also have more potassium

ions inside the cell than we have

outside cell please note that in my

attempt to provide this for you here we

have the membrane this would be one of

the lipid layers and this would be the

other lipid layer and here we would

start seeing pumps what we call pumps

these pumps are specialized proteins

channel proteins through which sodium

and potassium respective

we come in and out of the cell here we

can appreciate an artistic rendition of

a typical cell membrane and you can see

and appreciate the signal proteins which

are here you may remember that and if

not they may look back to chapter 3 to

understand this further and here you can

see the channel proteins through which

ions enter and exit the cell so on one

side would be the outside and on the

inside would be the inside of the cell

the term resting potential is quite

misleading as there is a lot of activity

going on when the cell is off

we know that sodium ions are actively

transported to maintain a resting

potential and these are transported

through specialized channels channel

proteins where we see a constant

exchange of three sodium ions from

inside of the cell for two potassium

ions that are outside of the cell so you

will constantly see this one going out

you have these going out three at a time

and then for every three that come out

you put two of these inside and this is

all occurring through what we call the

sodium potassium pump please note that

this actively uses energy force that

exchanges these ions and this is

basically what depolarizes the cell you

may remember from just two slides before

that polarization basically means that

the cell carries a charge when you

depolarize a cell that means that the

cell no longer carries a charge please

note it is important for us to know that

which is described in this slide is a

neuron at rest

meaning resting potential where the cell

is polarized and it is capable of

charging and in firing this is all

that's happening all while the cell is

off

here we see a nice rendition also of the

neural membrane as it passively and

actively is influencing the distribution

of sodium potassium and chloride which

is the negative they charged ion here in

an ion and this is all occurring across

the neural membrane you can see the

first step here where ions and motion

move down their concentration gradients

thus sodium will tend to enter and

potassium will tend to exit you may

remember we talked about this and that

there are three sodium ions inside the

cell that are exchanged from the inside

for two potassium ions outside the cell

as you would have experienced with

magnets before you know that positive

and positive tend to repel one another

whereas opposites attract and so when

you have too much positivity in one they

will constantly be moving out in and out

of the cell to maintain the balance in

there and in step number two we see the

negative internal charge creates

pressure for both sodium and potassium

to enter so whenever you have a negative

presence inside from anions that would

be the negatively charged and typically

we see chloride maintaining equilibrium

with these two then these would be

attracted because there's negativity

inside then you'd see both sodium and

potassium entering inside to try to

balance things out in the third step we

would see sodium potassium pumps which

are specialized channels notice that

each of these right here sodium has

there its own channel potassium has its

own potassium has its own and sodium has

its own but this right here demonstrates

what we call the big pump the big

channel protein and that is the sodium

potassium pump this transports three

sodium outside for every two potassium

that they transport in and just like

that we've described the resting

membrane