My name is: ___________________and
_______________ will rock this coming midterm Time / Date of Section: Worksheet 2
Homeostasis, Eq & membrane potentials, and more
Membrane Potential / Equilibrium Potential
1. Which are the two most important factors determining the movement of ions across the cell membrane?
Chemical force and electrical force
2. Equilibrium Potential of an Ion
In each of the following situations, identify the direction of the 2 forces acting on the represented ion. (label
each force)
To note: The size of the letter representing the ion indicates the concentration. The “Vm” value, indicates how much more positive/negative the inside of the cell is compared to
the outside. So, if it says Vm=-70mV, this means that the inside of the cell is 70 mV more
negative than the outside (you can imagine negative signs on the inner side of the membrane) Situation 1: K K+ + K Vm= 0 mV K+ + K Na Situation 5: Na + Vm= 0 mV Situation
Situation
7:
8: Cl- - Cl Cl + K+ + Vm= +70 mV Vm= -70 mV Situation 4: - Situation 3: Situation 2: Na Situation 6: Na + Vm= -30 mV + Na + Na Vm= +30 mV Situation 9: Cl- Cl - 3. Equilibrium ClEquilibrium Potential
Potential
1 Vm= 0 mVVm= -50 mV Vm= +50 mV + My name is: ___________________and
_______________ will rock this coming midterm Time / Date of Section: a. What is the Equilibrium Potential of an Ion? Define in your own words. b. What is the name and expression of the Equation used to calculate the Equilibrium Potentials? c. True / False
When an ion is in equilibrium, there is no movement of that ion either into the cell or out of the cell. _________
d. Why is the equilibrium potential for K+ a negative value and the one for Na+ a positive value, if both ions
have positive charges? e. What happens to the equilibrium potential of Na+ if one doubles the external concentration of Na+?
(i) It stays the same.
(ii) It gets more positive (further away from zero).
(iii) It becomes less positive (closer to zero or even a negative value).
(iv) There isn’t enough information to answer this question.
f. What happens to the equilibrium potential of Na+ if one doubles the external concentration of K+?
(i) It stays the same.
(ii) It gets more positive (further away from zero).
(iii) It becomes less positive (closer to zero or even a negative value).
(iv) There isn’t enough information to answer this question.
g. What happens to the ENa+ if one doubles the external & internal concentration of Na+?
(i) It stays the same.
(ii) It gets more positive (further away from zero).
(iii) It becomes less positive (closer to zero or even a negative value).
(iv) There isn’t enough information to answer this question. Resting Potential
4. The resting potential depends on the leak channels and the equilibrium potential of the ions that they are
permeable to.
a. What ions do we have leak channels for? (You should have 3 ions in your answers) Which is the most
abundant leak channel in neuronal membranes? 2 My name is: ___________________and
_______________ will rock this coming midterm Time / Date of Section: b. What are the approx. Equilibrium Potentials for each of those ions? c. What would be the resting potential of a neuron if it were only permeable to K+? [Write down the aprox.
numeric value] d. What would be the resting potential of a neuron if it were only permeable to Na+? [Write down the aprox.
numeric value] e. What would be the resting potential of a neuron if it were equally permeable to Na+ & K+? [Write down the
aprox. numeric value. Explain.] f. In normal neurons, permeable to K+ and Na+ through leak channels, why is the resting potential ~ -70mV? e. True / False.
(i) When a neuron is at rest, the net combined movement of charges in / out of the cell through leak channels is
zero. ___True
(ii) At the resting potential, Na+ and K+ ions are each at their own equilibrium. False 3 My name is: ___________________and
_______________ will rock this coming midterm Time / Date of Section: Action Potential
5. Components of the Action Potential.
a. Complete the Leak K+
channels
open VG Na+ Channels VG K+ Channels A Leak Na+
channels
open Open/activated Closed/deactivated B open open inactivated Open/activated C open open Closed/deactivated Closed deactivated following table indicating whether the channels are open, closed or inactivated. A Leak Na+
channels
in Leak K+
channels
out VG Na+
Channels
in VG K+
Channels
No flow B in out No flow out C in
out
No flow
No flow
b. Complete the following
table
indicating whether the
ions going
through those channels are going into the cell or out of the cell. If the channels are closed, then write “no flow”.
6. Action Potential Conduction
a. What are the factors that can influence the conduction velocity of the AP? Indicate whether they increase or
decrease it. Multiple sclerosis is a demyelinating disorder. In patients that suffer from this disease, action potentials fail to
conduct and thus, they develop muscle weakness, memory problems, vision problems, etc. As the disease
progresses and more myelin is lost, the patients lose control of most of their body functions and mind.
b. Using the diagram of the axons below show what would happen to the ions that normally propagate the
action potential in axons from a normal subject and an axon from a MS patient. You must include: myelin, VG
Channels, Leak Channels, Nodes of Ranvier, and show the movement of ions. 4 My name is: ___________________and
_______________ will rock this coming midterm Time / Date of Section: 7. Refractory Period
a. What is the Absolute refractory period? What is the biophysical basis of it?
It is the time which another stimulus is given to the neuron. This would not lead to a second action potential. It
is the period after AP in which neuron cannot generate another action potential because Na+ channels are
innactive b. What is the Relative refractory period? What is the biophysical basis of it?
1. after firing when a neuron will not fire again no matter how strong the incoming message may be c. If the VG Na+ channel did not inactivate, how would this affect the Absolute and Relative refractory periods? 8. Compare Action Potentials vs Graded Potentials. Action Potentials Graded Potentials 5 My name is: ___________________and
_______________ will rock this coming midterm Time / Date of Section: Synaptic Transmission
9. Compare electrical and chemical synapses. Electrical Chemical 10. List the steps involved in synaptic transmission, from the arrival of the action potential to the presynaptic
terminal, to the response in the postsynaptic cell. 11. How are neurotransmitters eliminated from the synaptic cleft? 12. If a neuron does not fire an action potential, but instead you inject calcium into its presynaptic terminal, will
you see a response in the postsynaptic cell? (Assume chemical synapse) 6 My name is: ___________________and
_______________ will rock this coming midterm Time / Date of Section: 13. Define:
a. Excitatory Input b. Inhibitory Input. c. IPSP:
Is this a hyperpolarization or a depolarization?
d. EPSP:
Is this a hyperpolarization or a depolarization?
e. Temporal Summation: f. Spatial Summation: 14. Synaptic Integration
a. What would be the effect on Vm if equal numbers of excitatory and inhibitory postsynaptic channels were to
open simultaneously in a postsynaptic neuron, producing an equal amount of excitatory and inhibitory current? To the right is a plot of the responses observed in a postsynaptic neuron when a
input A and input B in different combinations. stimulus is given to b. Based on this data, draw the response to
stimulating B alone. Explain.
7 My name is: ___________________and
_______________ will rock this coming midterm Time / Date of Section: 15. Below you can find a blank I-V curve. You can add the units as you go.
a. Using a star, determine the point on the graph where a positively charged ion with Eq=-30 have no current.
b. Using a triangle, determine the point on the graph where a negatively charged ion with Eq=-30 have no
current.
c. Using a square, determine the area on the graph where the currant of a positively charged ion with [in]>[out]
will be when the electrical force is equal to zero.
d. draw the I-V curve for Sodium, and label the direction and amplitude of the electrical and chemical forces are
in relation to one another. 8Membrane Potential / Equilibrium Potential

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