The Neuronal Membrane at Rest
What is the resting membrane potential of a cell permeable only to K+? +62mV 0 mV -80mV +80 mV
-80mV
Be able to describe the concept of equilibrium potential and be able to apply it
-Equilibrium state occurs when diffusional and electrical forces are equal and opposite -Ionic equilibrium potential (equilibrium potential) is the potential difference that balances the ionic concentration gradient for any given ion -Each ion has own equilibrium potential
Understand the basic electrical concepts , resistance, conductance, voltage, current and how ion movement in controlled
-K+ is higher inside than out and Na+ and Cl-are higher outside than inside. -The lipid bilayer forms a high-resistance barrier to ion flow, until ion channels are opened -Electrical current (I)- movement of charge, positive in the direction of positive charge movement -How much current flows depends on (1) electric potential (voltage, V) and (2) electrical conductance. -Voltage is measure of the difference in charge between anode and cathode, more difference = more current -Conductance (g, siemens) is relative ability for a charge to move from one place to another, depends on number of particles available to carry the charge and how easily these can travel; if =0 then no current flows •Resistance (R, ohms) is the relative inability of an electric charge to migrate, R=1/g
Refresh knowledge of basic structure of cell membrane and proteins
-Membrane proteins-specific proteins localized to soma, dendrites, axon -20 amino acids, properties determined by R group -Proteins can be made of one or more polypeptides -Ion channels: Have both hydrophobic and hydrophilic regions, Selective, Can be controlled -Pumps: Transport ions across membranes against concentration gradients using ATP as the energy source
Describe the basic structure and function of potassium channels
-key to determining a neurons resting Vm -mutations in K+ channels lead t severe neurological problems or death
What are ion channels?
-proteins that create specific pathways for charged molecules -have both hydrophobic and hydrophilic regions *selective -can be controlled
Which of the following is FALSE? The cell membrane is thin enough that ions outside the cell can be attracted to ions inside the cell Resistance is inversely related to conductance Rate of diffusion is temperature dependent All responses are true
All responses are true
Using the Nernst equation, if the K+ concentration outside of the cell was increased by 10X, what would happen to the K+ equilibrium potential? Become more negative Become more positive Stay the same Become more negative, then more positive
Become more positive
What prediction can be made if the resting potential of a cell is +55Mv? Cell is mostly permeable to Na+ at rest Cell mostly permeable to K+ at rest Cell is equally permeable to Na+ and K+ at rest No predictions can be made
Cell is mostly permeable to Na+ at rest
Consider Ohm's Law I=gV. Which of the following statements is TRUE? Current would always be high if voltage was high Current would be high if membrane resistance is high Current would be high if conductance and voltage were high All are FALSE
Current would be high if conductance and voltage were high
Increasing the K+ concentration outside of a neuron would Hyperpolarize the neuron Depolarize the neuron Have no effect Hyperpolarize then depolarize
Depolarize the neuron
Changing the Na+ concentration outside the cell would change the K+ equilibrium potential because it would change the Vm of the cell. True False
FALSE
Considering Ohm's Law (I=gV), if V= 80mv and no channels are open, current flow will be high. True False
FALSE
Diffusion of Na+ ions into a neuron can still occur if all Na+ channels are closed. True False
FALSE
Opening more K+ channels will increase the K+ equilibrium potential. True False
FALSE
The resting potential of all neurons is -65mV. True False
FALSE
If ion X is negatively charged and has a negative equilibrium potential it is at: Higher concentration outside of cell Higher concentration inside of cell Equal concentration inside and outside of the cell
Higher concentration outside of cell
What is the difference between ion channels and ion pumps?
Ion pumps require ATP and ion channels do not
Which of the following is FALSE? Nernst equation is used to determine the equilibrium potential of an ion The Goldman equation is used to determine a neuron's Vm Ions such as K+ and Na+ are hydrophobic Resting potentials vary between different types of neurons
Ions such as K+ and Na+ are hydrophobic
What is ALWAYS higher inside the cell?
K+
What is the major ion channel determining a neuron's resting potential? Voltage-gated K+ channels Voltage-gated Na+ channels K+ leak channels Na+ leak channels
K+ leak channels
Which of the following statements is FALSE? Equilibrium occurs when diffusion and electrical forces are balanced in the cell Large numbers of ions (mMoles) must move to change the membrane potential of a cell from negative to positive Each ion has its own equilibrium potential Cells without a resting potential can't transmit action potentials
Large numbers of ions (mMoles) must move to change the membrane potential of a cell from negative to positive
Select all that apply. When a neuron is at rest, the... Membrane is more permeable to K+ than Na+ Membrane potential is closer to the K equilibrium potential than to the Na+ equilibrium potential Membrane is more permeable to Na+ Membrane does nothing
Membrane is more permeable to K+ than Na+ Membrane potential is closer to the K equilibrium potential than to the Na+ equilibrium potential
Using the Goldman equation, if a neuron became more permeable to Na+, how would this change the resting Vm? More positive More negative No change More positive, then more negative
More positive
What is ALWAYS higher outside of the cell?
Na+ Cl-
If ion X is high inside the cell, and has an EX which is positive, what is the charge of the ion? Positive Negative Cannot determine from the information given
Negative
Astrocytes are important in maintaining extracellular K+ concentrations. True False
TRUE
Resistance is inversely related to conductance. True False
TRUE
How will increasing the Na+ concentration outside of the neuron affect the K+ equilibrium potential? Make it more positive Make it more negative No effect More positive, then negative
No effect
If the membrane potential is -65mV, which direction would K+ flow when K+ channels are opened? Into cell Out of cell No net movement off would occur
OUT OF CELL
Which of the following is FALSE? Opening more ion channels will decrease conductance Equilibrium state occurs when diffusional and electrical forces are equal and opposite Each ion has its own equilibrium potential Identification of K+ channel structure helped determine the structures of other voltage-gated channels
Opening more ion channels will decrease conductance
If ion X is high outside the cell, and has an EX which is positive, what is the charge of the ion? Positive Negative Cannot determine from the information given
Positive
How does the Goldman equation differ from the Nernst equation? Concentrations of ions inside and outside of the cell is considered Temperature is factored into the equation Relative permeability to ions is considered Charge of the ions is considered
Relative permeability to ions is considered
Suppose a neuron was selectively permeable only to K+ ions (only K+ channels open). What happens to the membrane potential of this cell if Na+ channels were added to the cell and then opened? Vm will depolarize Vm will hyperpolarize No change in Vm
Vm will depolarize
Under what conditions would Na+ have the lowest driving force? Vm= +55 mV Vm=+62mV Vm=+65mV Vm=0
Vm=+62mV