lecture 15 - resting membrane potential

what are membranes made of?

phospholipid bilayer

what is an important feature of the phospholipid bilayer

things can’t easily move through it (so you can control what goes in and out)

transport proteins

proteins that move specific ions/molecules across the membrane

what makes neurons electrically excitable?

they have a polarized membrane (charge difference on either side of the membrane)

the electrical properties of neurons result from what?

• ion gradient

• [ ] gradient

• permeability of membrane

concentration gradient

difference in concentration of a certain substance across a distance/membrane

with a concentration gradient, substances always want to move from areas of ____ [ ] to an area of ___ [ ]

high, low

how do we created a polarized plasma membrane?

separate +ve and -ve charges, making them want to get back together

the outside of the cell membrane is typically ___, while the inside is typically ___

+ve, -ve

membrane potential

potential difference b/w ions (charge + [ ]) on outside vs inside of the cell

oscilloscope

tool used to measure voltage

in a resting condition, the inside of an axon is more ___ than the outside

-ve

the voltage difference (membrane potential) at rest on the inside of an axon is ___mV

-70

resting membrane potential

voltage difference across membrane when cell is not active

ECF (outside of cell) has higher [ ] of:

• chloride (-ve)

• sodium (+ve)

• calcium (+ve)

cytosol (inside of cell) has higher [ ] of:

• potassium (+ve)

• proteins (-ve)

on the immediate inside/outside of the plasma membrane, there are clumps of what

+vely or -vely charged ions

2 ways in which ion gradient are created

1. sodium/potassium pump

2. membrane permeability

sodium-potassium (Na+/K+) pump

• helps create [ ] gradient for sodium and potassium

• actively transports 2 K+ into the cell and 3 Na+ out of the cell

sodium-potassium (Na+/K+) pump process

1. Na+ molecules on the inside of cell drawn to pump

2. ATP binds to pump

3. ATP → ADP + P_i

4. pump changes shape and moves the Na+ to the outside of cell

5. P_i stays with pump

6. site where K+ can enter into the pump is now open

7. K+ on outside of cell drawn to pump

8. P_i leaves pump, changing the pump back to its og shape and moving the K+ to the inside of the cell

active transport

requires ATP

if you are moving something against its [ ] gradient, do you need E?

yes

leak channels

• protein channels that allow the Na+ to ‘leak’ into the cell and K+ to ‘leak’ outside the cell

• would eventually allow equilibrium of Na+/K+ ions on either side of the cell

2 types of ion channels

1. leak (non-gated) ion channels

2. gated ion channels

leak (non-gated) ion channels

• type of ion channel

• always open

• each leak channel is specific to an ion (e.g. only K+ ions can move through K+ leak channels)

true or false: Na+ leak channels are more numerous than K+ leak channels

false

gated ion channels

• type of ion channel

• can open + close (have gates) on demand

• 3 types

3 types of gated ion channels

1. ligand-gated

2. mechanically-gated

3. voltage-gated

ligand-gated ion channel

• type of gated ion channel

• require a ligand/chemical signal to bind onto the ion channel to open the gates

mechanically-gated ion channel

• type of gated ion channel

• gates are physically opened

voltage-gated ion channel

• type of gated ion channel

• gates open in response to changes in membrane potential

what is important in determining permeability?

• how many channels are open at once

• size of ions + specificity of channels

the more ____ ion channels we have, the more on-demand changes we can make to the membrane potential

gated

establishing resting membrane potential

1. K+ move to the outside of the cell via K+ leak channels (bc of [ ] gradient)

2. net +ve charge on outside of cell and net -ve charge on inside of cell

3. -vely charged proteins are drawn towards cell membrane

4. K+ ions drawn back inside the cell (bc of ion gradient)

5. eventually get to a point where the amt of K+ ions being drawn in and out are the same

6. resting membrane potential reached

the -ve charge on the inside of the membrane is caused by what?

-vely charged proteins