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What two factors are critical in determining resting membrane potential?
- Ion concentraion gradients
- Membrane permeability to ions
How much of the resting potential is due directly to the Na+/K+ - ATPase?
Describe the movement of ions due to the Na+/K+ - ATPase pump.
The membrane of a neuron is _____ permiable to K+ than Na+.
25 x more
Describe the distriubtion of ions accross the membrane at resting membrane potential.
- Sodium and Chloride are outside the cell.
- Potassium and organic anions are inside the cell.
Describe the strength of netforce in relation to ion equilibrium potential.
The strength of the netforce of an ion increases the further away the membrane potential is from the equilibrium potential.
Describe the forces acting on Potassium during resting potential.
- Resting Potential : -70 mV
- Ek : -94mV
- Electrical force is into the cell
- Chemical force is out of the cell
- Net Force : is weak out of the cell
Describe the forces acting on Sodium during resting potential.
- Resting potential : -70mV
- ENa : +60mV
- Electrical force is into the cell.
- Chemical force is into the cell.
- Net force is strong into the cell.
What maintains the concentration gradient of a neuron at rest?
Describe graded potentials.
- They are intiated by a stimulus and cause a small change in membrane potential.
- Some are depolarizing, while others are hyperpolarizing.
What is Threshold?
The level of depolarization from graded potentials necessary to elicit action potential.
What is the difference between Temporal and Spatial summation?
- Temporal: same stimulus, repeated close together in time.
- Spatial: Different stimuli which overlap in time.
The opening of subsequent sodium channels after depolarization is do to what type of feed back loop?
Describe the two types of gates associated with voltage gated sodium channels.
- Activation gates : Voltage dependent; opens at threshold and depolarization; opens in response to positive feedback.
- Inactivation gates : Voltage and time dependent; Open during depolarization; Closed during repolarization.
Describe voltage gated potassium channels.
- There is one type of gate.
- It is voltage and time dependent.
- Opens in response to negative feedback.
What is a refractory period?
A period of time following an action potential, which is marked by a decreased excitability.
What is the difference between an absolute and relative refractory period?
- Absolute : No AP can be generated. Sodium gates are inactivated. Spans most of the repolarization phase.
- Relative : AP can be generated if stimulus is strong enough. Some sodium gates are closed, while others are still inactivated.
What is frequency coding?
The time between action potentials which allows the brain to interperate the strength of a stimulus.
In what type of fiber does saltatory conduction take place?
How does the diameter of an axon effect the speed of propagation?
- Larger : less resistance, faster
- Smaller : more resistance, slower