Thursday, April 25, 2024
Resting membrane potential
Resting membrane potential is the charge difference across the membrane of a neuron when not firing an action potential or recovering during the refractory period. The membrane potential at rest is -70 mV.
(“Action potential graph” )
.isucomm.iastate.edu/314-4-kbcm/2016/11/13/resting-membrane-potential/
ATP function
The Na+K+-ATPase pump helps to maintain osmotic equilibrium and membrane potential in cells.
Quizz
In a cell permeable only to K+, the resting membrane potential would be called the___________________ potential for K+, which is ___________ mV.
a.extracellular fluid concentration of K+ (goes up)___________
b. ̄extracellular fluid concentration of K+ (goes down)___________
c.extracellular fluid concentration of Na+ (goes up)___________
d. ̄number of passive Na+channels (goes down) ___________
e.open voltage-gated K+channels ___________
f.open voltage-gated Na+channels___________
Guiding questions week 2
Guiding Questions:
The resting membrane potential
From last week:
Describe the mechanism of the Na+/K+ pump and explain how it contributes to the resting membrane potential of a cell.How does the sodium/potassium pump maintain the resting membrane potential? The resting membrane potential is maintained by the sodium-potassium pump. With each turn of the pump, 2 potassium ions are pumped into the cell and 3 sodium ions are pumped out of the cell.
What would happen to the resting membrane potential if the Na+/K+ pump was mutated and not working?
Describe several ways that intracellular fluid (ICF) differs from extracellular fluid (ECF).
What ions are higher in the ICF vs ECF?sodium ion high in ECF and Potassium ion High in ICF
water moves passively via osmosis, sodium and potassium ions move in and out of cells using active transport ion pumps.
Describe what a concentration gradient is and how it leads to diffusion and the establishment of a dynamic eHow do they contribute to the resting membrane potential of a cell? How do they contribute to membrane permeability?quilibrium.
How does a concentration gradient cause the diffusion of particles?
A concentration gradient occurs when the concentration of particles is higher in one area than another. In passive transport, particles will diffuse down a concentration gradient, from areas of higher concentration to areas of lower concentration, until they are evenly spaced.
Can you identify the flow of ions in/out of cells based on concentration gradients?
Describe the mechanism of Na+ and K+ leak channels. stimulus causes sodium channel to open
How do they contribute to the resting membrane potential of a cell? How do they contribute to membrane permeability?
What generates the resting membrane potential is the K+ that leaks from the inside of the cell to the outside via leak K+ channels and generates a negative charge in the inside of the membrane vs the outside. At rest, the membrane is impermeable to Na+, as all of the Na+ channels are closed.
What is the resting membrane potential? What voltage value is it typically for most cells in your body?
What is the voltage of the resting membrane potential?
Since the plasma membrane at rest has a much greater permeability for K+, the resting membrane potential (-70 to -80 mV) is much closer to the equilibrium potential of K+ (-90 mV) than it is for Na+ (+65 mV).
Altering the resting membrane potential
Opening and closing ion channels alters the membrane potential. In a neuron, the resting membrane potential is closer to the potassium equilibrium potential than it is to the sodium equilibrium potential.
If the concentration gradient of K+ decreases across the cell membrane, what happens to the membrane potential?when K+ concentration outside the cell decreases, the cell potential becomes more negative.
If the cell all the sudden became permeable (think gated membrane channels opening) to K+, what would happen to membrane potential? What about Ca2+? Na+?A set of voltage-gated potassium channels open, allowing potassium to rush out of the cell down its electrochemical gradient. These events rapidly decrease the membrane potential, bringing it back towards its normal resting state.
What is hyperpolarization vs depolarization of the membrane potential? What ion channels should be opened to cause either?
At rest, a typical neuron has a resting potential (potential across the membrane) of
-60 to -70 millivolts. This means that the interior of the cell is negatively charged relative to the outside.
Graded Potentials 
Draw and describe the structure of a neuron.
Identify each of the following structures on your drawing and describe their structures: dendrites, dendritic spines, cell body, axon, axon hillock, collateral, axon terminal, synapse, postsynaptic cell
Where are the sensory receptors located on a neuron? From where on the neuron are neurotransmitters released?
Where do graded potentials occur?
What type of stimuli causes a graded potential? How does the strength of the stimulus affect the amplitude of the graded potential? ( graded potential are generated by sensory input.)
As a graded potential travels through the cell body, they lose amplitude. Explain why. ***more on this next week
What is an EPSP? What is an IPSP? What ion channels contribute to each? Are each caused by depolarizations or hyperpolarizations?
How does an EPSP contribute to triggering an action potential? What about an IPSP?
Action Potentials***
Differentiate between graded potentials and action potentials.Graded potentials are important in short distances. Action potentials are the long distance signals of nerve and muscle membranes. ❖ Nerve and muscle cells as well as some endocrine, immune, and reproductive cells have plasma membranes capable of producing action potentials.
Where in the neuron do action potentials occur?
How does the strength of the stimulus effect the amplitude of the action potential? Why are they all-or-none?Third, nerve cells code the intensity of information by the frequency of action potentials. When the intensity of the stimulus is increased, the size of the action potential does not become larger. Rather, the frequency or the number of action potentials increases.
***more on this next week
Explain how ion permeability changes during the rising phase and falling phase of an action potential.
What is the stimulus for opening EACH of the channels used during an action potential?
What is the order of stimulus, opening and closing of all of these channels?
How is the resting membrane potential reestablished after an action potential?
Hint, we did this for our in-class activity! Can you visualize what’s happening with each of the channels?
Voltage gated Na+ channels in the axon contain two gates. What are they? How are they triggered?Voltage-gated sodium channels have two gates: an activating gate that is voltage-dependent and an inactivating gate that is time-dependent. The opening of the activating gate allows the influx of sodium and cell depolarization.
What are the absolute and relative refractory periods?There are two types of refractory periods; the absolute refractory period, which corresponds to depolarization and repolarization, and the relative refractory period, which corresponds to hyperpolarization.
How does the inactivation gate on the Na+ channel cause the absolute refractory period?
What causes the relative refractory period?
***I will update after lecture to see how much of APs we get through.
Diffusion :what is the goal of diffusion
-to reach equilibrium
-dissolved ions distribute evenly