(5) Neuron Physiology: Action Potentials

If a graded potential is _______ the threshold when it reaches the trigger zone, nothing happens

Below

Action potential

Brief, rapid, large changes in membrane potential

Action potential mV

~100mV

Graded potential mV

~15mV

Action potentials are a what process?

All or nothing

Explain Step 1 of the action potential sequence

Resting membrane potential (neuron -70mV)

Explain Step 2 of the action potential sequence

Depolarizing stimulus (going from -70mV to -50mV) another name could be graded potential arriving at trigger zone

Explain Step 3 of the action potential sequence

Membrane depolarizes to threshold; voltage gated Na+ and K+ channels start to open

Explain Step 4 of the action potential sequence

Rapid Na+ entry depolarizing cell (sudden rapid rise in membrane potential from -50mV to 30mV)

Explain Step 5 of the action potential sequence

Na+ channels close and slower K+ channels open

Explain Step 6 of the action potential sequence

K+ moves out of the cell, repolarizing the membrane

Explain Step 7 of the action potential sequence

K+ continues to leave the cell, hyperpolarizing it

Explain Step 8 of the action potential sequence

K+ channels close, less K+ leaks out of the cell

Explain Step 9 of the action potential sequence

Cell returns to resting potential

Resting membrane is more permeable to what ion?

K+

Voltage gated Na+ channels have an activation gate that opens ______ and an inactivation gate that closes ________

Rapidly, slowly

At rest, voltage gated Na+ channels have what open and what closed?

Activation gate is closed , inactivation gate is open

Absolute Refractory Period

Period of time after an action potential has begun when another action potential absolutely cannot be stimulated

Relative Refractory Period

The next 1-2 ms where some Na+ channels have reset. A stronger than normal stimulus could trigger another action potential

Voltage Gated K+ channels have only an activation gate that opens ________ respose to ________

slowly, depolarization stimulus

Na+ - K+ ATPase Pump

Actively pumps 3 Na+ out of the cell and 2K+ into the cell. Helps restore ions to proper compartment after action potential

When one region of the membrane depolarizes, charges flow to

Adjacent regions

Action potentials can only propogate forward, which means they are

Unidirectional

What happens if myelin is damaged or destroyed?

Action potential conduction can fail as the current leaks out of cells

The farther from the threshold,

The stronger the stimulus needed

K+ is the most important determinant of the

Resting membrane potential

Hyperkalemia

the state of having too much K+ in the blood, increasing membrane potential.

Makes cells too easy to stimulate, numbness, tingling, then muscle weakness

Hypokalemia

The state of having not enough K+ in the blood

Makes cells hard to stimulate, muscle weakness, cramps, or spasms