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What causes membrane potential changes?
- Gated channels
- Open/close in response to stimuli
- Affect mvmt of ions - electrical signal
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What are the 3 types of gated channels?
1. Voltage gated - change in elec
2. Ligand (chemically) gated - messenger
3. Mechanically gated - sensory perception
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What are the 4 different polar states of a neuron?
- Resting potential (reference pt)
- Depolarization
- Repolarization
- Hyperpolarization
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What are the 2 types of potential changes?
1. Graded Potentials
2. Action Potentials
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What are the properties of graded potentials?
- Initiated by stimulus
- Small changes in MP
- Magnitude varies with strength of stimulus
- Short distance, decremental
- Spread by electrotonic conduction
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What is the purpose of graded potentials?
Determine whether or not an action potential will occur
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What is the threshold voltage needed for an action potential?
-55 mV
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What causes excitation of a neuron? ...inhibition?
Depolarization
Hyperpolarization
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What are the 2 types of summation in graded potentials?
1. Temporal Summation - same stimulus, repeated close together in time
2. Spatial Summation - different stimuli, overlap in time
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What is an Action Potential?
Rapid, large depolarization of membrane potential for communication
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What are the phases of an Action Potential?
- Phase 1. Depolarization
- Phase 2. Repolarization
- Phase 3. After-hyperpolarization
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What causes rapid depolarization of the membrane?
Permeability change from K+ > Na+ to Na+ >> K+
Voltage gated Na+ channels open, Na+ rushes in, results in positive Vm
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What does the Threshold trigger?
- Rapid opening of Na+ channels ( + feedback)
- Slow closing of Na+ channels
- Slow opening of K+ channels
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What are the 2 gates associated with voltage-gated Na+ channels and what are their properties?
1. Activation Gate - voltage dependent, opens at threshold, (+) feedback
2. Inactivation Gate - voltage & time dependent, close/open during depolarization
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What are the properties of voltage-gated K+ channels?
- One gate
- Voltage and time dependent
- (-) feedback
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Define Threshold.
Minimum depolarization necessary to induce the regenerative mechanism for the opening of sodium channels.
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What is a Refractory Period?
Period of time following an action potential, marked by decreased excitability.
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What are the 2 types of Refractory Periods?
- Absolute
- Relative
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What are the properties of absolute refractory periods?
- Spans all of depolarization and most of the repoarizatioin phase.
- Second action potential cannot be generated.
- Na+ gates are inactivated.
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What are the properties of relative refractory periods?
- Spans last part of repolarization phase and hyperpolarization.
- Second action potential can be generated by stronger stimulus.
- Some Na+ gates closed, some inactivated, some open.
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What are the consequences of refractory periods?
- All-or-none
- Frequency coding
- Unidirectional propagation of actions potentials
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What does the speed and distance of conduction depend on?
Diameter and Mylenation
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How is neural stability maintained?
Na+ and K+ pump prevents dissipation caused by graded potentials
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