Nervous System 2 - Action Potentials Flashcards
What Graded (Passive) potentials initiated by?
A stimulus that is either sensory or chemical
What is meant by Graded in Graded (Passive) potentials?
The magnitude can vary with the strength of the stimulus
What kind of polarization can Graded potentials give?
They can Depolarizing or Hyperpolarizing
How does the strength of the stimulus affect the membrane potential in Graded (Passive) Potentials?
A stronger stimuli will increase the Membrane potential more than a smaller stimuli. So the stronger a stimulus, the larger the passive potential
What do Passive Potentials arise from?
Current that flow into the membrane
What happens as the current moves down the axon in Passive Potentials?
It loses strength and falls in amplitude
What does Passive spread of current depend on?
It depends on the dendrite or axons resistance to flow of current
How do dendrites or axons affect the spread of current?
Smaller dendrite or axons have a higher resistance so current flows with difficulty down them
What are the characteristics of Nerve Action Potentials?
They are Rapid, transient and result in a large change in membrane potential resulting in a reversal fo polarity
What does a Nerve Action Potential consist of?
Rapid depolarization followed by rapid repolarization of the membrane
What is another name for an Action Potential?
A spike
What is a Spiking neuron?
One that is firing APs
What membrane potential must be met to produce an action potential?
Vm must reach threshold
What is Threshold?
The membrane potential at which a spike is initiated
Can graded potentials reach threshoid?
Graded potentials MAY bring Vm to threshold
How does the strength of the stimulus affect an membrane potential in an action potential?
As long as the stimulus reaches threshold the Membrane potential will reach the same amplitude every time
What does Threshold trigger in terms of channels?
Threshold triggers rapid opening of sodium channels, follow by slow closing of sodium channels and the slow opening of potassium channels
What is the order of the steps in membrane potential?
- Resting potential
- Rising Phase
- Overshoot
- Falling Phase
- Undershoot
What is the Equilibrium potential of Sodium?
+52mV
What does the transient inward current represent when the membrane is depolarized in an action potential?
The movement of sodium
What does the Delayed outward current represent when the membrane is depolarized in an action potential?
The movement of K+
What happens to the movement of sodium as the membrane potential is depolarized closer to +52mV?
Because the membrane potential is reaching the equilibrium potential of Na+ the driving force for Na+ to move into the cell decreases and the transient inward current decreases and eventually inverts as sodium moves outward
What happens to the movement of Potassium as the membrane potential is depolarized closer to +52mV?
The driving force of potassium increases as the membrane potential moves farther from its equilibrium
What does TTX (Tetrodotoxin) do?
Block voltage gated Na+ channels
What does TEA (Tetraethylammonium) do?
Blocks voltage gated K+ channels
How does TTX (Tetrodotoxin) affect current in an action potential?
It prevents the inward current of sodium
How does TEA (Tetraethylammonium) affect current in an action potential?
It prevents the outward current of K+
How does Conductance of channels change during an action potential?
Sodium channels increase conductance with the action potential and decrease conductance with the action potential
Potassium channels are delayed by time and conductance is prolonged
How can ions leak out of the axon?
Through leakage channels
What are leakage channels?
Channels through which K+ and Na+ can leak out of which are distinct from the voltage gated channels
What is the Refractory period?
The time during which the axon is resistant to generating a spike
What does a Refractory period result from?
Na+ channels being inactivated and unavailable
Where are Sodium channels concentrated?
At nodes of ranvier
What is the function of the Myelin sheath?
It reduces current loss across the membrane and acts as an electrical insulator
How do scorpion toxins affect action potentials?
They contain many active peptides that bind to Na+ channels to slow their inactivation and prolong their openings
How do many Anesthetic work?
They work by blocking voltage dependent Na+ channels which block action potentials or by hyperpolarizing the membrane by increasing Cl- influx
What occurs in multiple sclerosis?
The loss of myelin sheath slows spike conduction to eventually impair muscle contraction
