What causes membrane potential changes?
- Gated channels
- Open/close in response to stimuli
- Affect mvmt of ions - electrical signal
What are the 3 types of gated channels?
1. Voltage gated - change in elec
2. Ligand (chemically) gated - messenger
3. Mechanically gated - sensory perception
What are the 4 different polar states of a neuron?
- Resting potential (reference pt)
What are the 2 types of potential changes?
1. Graded Potentials
2. Action Potentials
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
What is the purpose of graded potentials?
Determine whether or not an action potential will occur
What is the threshold voltage needed for an action potential?
What causes excitation of a neuron? ...inhibition?
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
What is an Action Potential?
Rapid, large depolarization of membrane potential for communication
What are the phases of an Action Potential?
- Phase 1. Depolarization
- Phase 2. Repolarization
- Phase 3. After-hyperpolarization
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
What does the Threshold trigger?
- Rapid opening of Na+ channels ( + feedback)
- Slow closing of Na+ channels
- Slow opening of K+ channels
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
What are the properties of voltage-gated K+ channels?
- One gate
- Voltage and time dependent
- (-) feedback
Minimum depolarization necessary to induce the regenerative mechanism for the opening of sodium channels.
What is a Refractory Period?
Period of time following an action potential, marked by decreased excitability.
What are the 2 types of Refractory Periods?
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.
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.
What are the consequences of refractory periods?
- Frequency coding
- Unidirectional propagation of actions potentials
What does the speed and distance of conduction depend on?
Diameter and Mylenation
How is neural stability maintained?
Na+ and K+ pump prevents dissipation caused by graded potentials