Membrane potentials lecture 3 Flashcards
Go over the cross-bridge lecture from cell biology
What is the peripheral nervous system made up of?
sympathetic branch and the parasympathetic branch
What law dictates the gradients of the ions?
laws of physical chemistry
-gradients also require energy to be maintained
What is a cell in reference to an ion gradient?
a biological structure that accumulates proteins
What charge do proteins generally have? And what property other property do they have?
have a negative charge and cannot cross cell membranes
What makes cell membranes generally semi-impermeable to common ions?
cell membranes that have no input of energy
What is the permeability of potassium and sodium ions for semi-permeable membranes?
K+ is permeable
Na+ is not permeable
Where does the permeable cation accumulate? why?
where the impermeable anion is located- this means that there will be a high intracellular potassium concentration
Why does the impermeable ion need to be pumped out of the cell against the gradient?
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
How is energy provided to allow for the active pumping of Na?
via ATP
Is the concentration of the K ion higher inside or outside the cell?
inside the cell so potassium tends to diffuse out of the cell
What does the loss of K+ do to the inside of the cell membrane?
it leaves a small risidual negative charge on the inside of the cell; manufacturing an electrochemical equilibrium- this is how a membrane potential develops
What are the consequences of a extracellular K+ concentration increasing?
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
What are the consequences of a high intracellular K+ concentration?
K ions will start to diffuse out down the electrochemical gradient
What do we need to assist Na+ into the cell?
a sodium pump
What does the sodium pump require to move Na across the membrane?
ATP
What equation allows for the calculation of the relationship between membrane potential and extracellular K+ concentration?
nernst equation
What does a rise in extracellular K+ do to the membrane potential?
it will make the membrane potential less negative than the resting membrane potential and so the membrane will end up depolarising
If potassium concentration inside a cell is higher than outside the cell, what direction is the potassium likely to move in?
outside the cell
How does the movement of the k+ result in a membrane potential being formed?
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
Why is the relationship between membrane potential and extracellular potassium not linear
do all cells have resting membrane potentials?
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
What does the nernst equation refer too? Explain this
the relationship between the membrane potential and extracellular concentration
What happens if the extracellular potassium increases?
it makes the membrane potential less negative than the resting membrane potential- this leads to depolarisation
Why is the relationship between membrane potential and extracellular potassium not linear
because of the nernst equation
why does membrane potential change?
the availability of ion channels
- the movement of charged ions across the membrane
what happens if potassium ions leave the cell what does this do to the membrane potential?
it will make the inside of the cell more negative
How do ions move in and out of the cell?
through ion channels which are protein pores that span the phospholipid bilayer
How are ion channels classified?
via the gating stimulus to which they are responsive
What are the different types of ion channels?
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
What are ligand-gated channels?
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
What is an action potential?
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
What does an action potential look like in peripheral nerves, cardiac muscles and skeletal muscles?
draw it
