Membrane potentials lecture 3

Question 1

Go over the cross-bridge lecture from cell biology

Question 2

What is the peripheral nervous system made up of?

Answer 2

sympathetic branch and the parasympathetic branch

Question 3

What law dictates the gradients of the ions?

Answer 3

laws of physical chemistry
-gradients also require energy to be maintained

Question 4

What is a cell in reference to an ion gradient?

Answer 4

a biological structure that accumulates proteins

Question 5

What charge do proteins generally have? And what property other property do they have?

Answer 5

have a negative charge and cannot cross cell membranes

Question 6

What makes cell membranes generally semi-impermeable to common ions?

Answer 6

cell membranes that have no input of energy

Question 7

What is the permeability of potassium and sodium ions for semi-permeable membranes?

Answer 7

K+ is permeable
Na+ is not permeable

Question 8

Where does the permeable cation accumulate? why?

Answer 8

where the impermeable anion is located- this means that there will be a high intracellular potassium concentration

Question 9

Why does the impermeable ion need to be pumped out of the cell against the gradient?

Answer 9

because it leaks into the cell so is pumped out of the cell via an Na pump (this is called primary active transport) with other molecules

Question 10

How is energy provided to allow for the active pumping of Na?

Answer 10

via ATP

Question 11

Is the concentration of the K ion higher inside or outside the cell?

Answer 11

inside the cell so potassium tends to diffuse out of the cell

Question 12

What does the loss of K+ do to the inside of the cell membrane?

Answer 12

it leaves a small risidual negative charge on the inside of the cell; manufacturing an electrochemical equilibrium- this is how a membrane potential develops

Question 13

What are the consequences of a extracellular K+ concentration increasing?

Answer 13

the amount of K ions diffusing begins to slow down as the extracellular concentration increases as there is less space and equilibrium is being attained and so the required membrane potential to balance the movement is less

Question 14

What are the consequences of a high intracellular K+ concentration?

Answer 14

K ions will start to diffuse out down the electrochemical gradient

Question 15

What do we need to assist Na+ into the cell?

Answer 15

a sodium pump

Question 16

What does the sodium pump require to move Na across the membrane?

Answer 16

ATP

Question 17

What equation allows for the calculation of the relationship between membrane potential and extracellular K+ concentration?

Answer 17

nernst equation

Question 18

What does a rise in extracellular K+ do to the membrane potential?

Answer 18

it will make the membrane potential less negative than the resting membrane potential and so the membrane will end up depolarising

Question 19

If potassium concentration inside a cell is higher than outside the cell, what direction is the potassium likely to move in?

Answer 19

outside the cell

Question 20

How does the movement of the k+ result in a membrane potential being formed?

Answer 20

when it leaves the cell it leaves a small risidual negative charge on the inside of the cell; manufacturing an electrochemical equilibrium- this is how a membrane potential develops

Question 21

Why is the relationship between membrane potential and extracellular potassium not linear

Question 22

do all cells have resting membrane potentials?

Answer 22

yes it is a property of all cells, it reflects the difference in charge inside and outside the cell
the cytoplasm side is usually negative in relation to the extracellular fluid
resting membrane potential ranges between -20 and -95 mv

Question 23

What does the nernst equation refer too? Explain this

Answer 23

the relationship between the membrane potential and extracellular concentration

Question 24

What happens if the extracellular potassium increases?

Answer 24

it makes the membrane potential less negative than the resting membrane potential- this leads to depolarisation

Question 25

Why is the relationship between membrane potential and extracellular potassium not linear

Answer 25

because of the nernst equation

Question 26

why does membrane potential change?

Answer 26

the availability of ion channels
- the movement of charged ions across the membrane

Question 27

what happens if potassium ions leave the cell what does this do to the membrane potential?

Answer 27

it will make the inside of the cell more negative

Question 28

How do ions move in and out of the cell?

Answer 28

through ion channels which are protein pores that span the phospholipid bilayer

Question 29

How are ion channels classified?

Answer 29

via the gating stimulus to which they are responsive

Question 30

What are the different types of ion channels?

Answer 30

voltage gated channels- which are activated by a small change in membrane potential (by an electrical stimulus)

ligand gated channels
-an extracellular chemical binds to receptors on a membrane

signal gated ion chanels

Question 31

What are ligand-gated channels?

Answer 31

when a ligand bind to a site on the ion channel causing the channel to open up

-found in muscle and merve cells and secretory cells

• are cation selective (mainly Na+ flows into the cells)
• when activated they cause depolarisation and make the cell more excitable
  -some are anion-selective (so allow Cl- to inter the cell)- this causes hyperpolarisation and makes the cell less excitable

Question 32

What is an action potential?

Answer 32

a transient depolarisation of a cell
-cells that generate action potentials are excitable cells
-action potentials are within close limits, of a fixed magnitude and duration

Question 33

What does an action potential look like in peripheral nerves, cardiac muscles and skeletal muscles?

Answer 33

draw it