The Action Potential

Front 1

Rising phase

Back 1

Characterized by rapid depolarization of the membrane. This change in membrane potential continues until Vm reaches a peak value of about 40 mV.

Front 2

Overshoot

Back 2

The part of the action potential where the inside of the neuron is positively charged with respect to the outside.

Front 3

Falling phase

Back 3

Rapid repolarization until the membrane is actually more negative than the resting potential.

Front 4

Undershoot (After-hyperpolarization)

Back 4

Last part of the falling phase (repolarization to a more negative mV)

Front 5

Threshold

Back 5

Action potentials are caused by depolarization of the membrane beyond threshold.

Front 6

Firing frequency

Back 6

Reflects magnitude of the depolarizing current. Amt of action potentials.

Front 7

Absolute Refractory Period

Back 7

Once an action potential is initiated, it is impossible to intiate another for about 1 msec.

Front 8

Relative Refractory Period

Back 8

At end of absolute refractory period, still hard to intiate another AP. Thus, amt of current required to start AP is elevated.

Front 9

Define the steps of an AP

Back 9

1. Resting Potential reaches threshold (becomes depolarized i.e. less negative.
2. Na+ flows into the axon until the inside is more + than the outside.
3. K+ moves out of the axon.
4. Na+ ions flow into axon until polarization = 40mV
5. Na+ moved outside
6. Potential Difference drops to zero, then reaches slightly more negative than resting potential (e.g. more negative than -65mV)
7. Once inside becomes negative, K+ ions move back into the cell until -65mV restored.

Front 10

Relationship between ionic driving force, ionic conductance, and the amt of ionic current that will flow.

Back 10

Ex. using K+ ions:

I[ion] = g[ion] (V[m] - E[ion]

Front 11

Voltage clamp

Back 11

Enable researchers to clamp membrane potential of an axon at any value they chose. They could deduce the changes in membrane conductance that occur at different membrane potentials by measuring the currents that flowed across the membrane.

Front 12

Voltage-gated sodium channel

Back 12

The proteins form a pore in the membrane that is highly selective to Na+ ions, and the pore is opened and closed by changes in the electrical potential of the membrane

Front 13

Patch clamp

Back 13

Study ionic currents passing through individual ion channels. Sealing the tip of an electrode to a patch of membrane. Patch torn away, measure current.

Front 14

Tetrododoxin (TTX)

Back 14

Clogs the Na+ permeable pore by binding to a specific site on the outside of the channel. Blocks all sodium dependent action potentials and therefore = fatal

Front 15

Voltage-gated potassium channels

Back 15

Most open when the membrane is depolarized and function to diminish any further depolarization by giving K+ ions a path to leave the cell across the membrane.

Front 16

Spike-initiation zone

Back 16

The part of the neuron where an axon originates from the soma, the axon hillock.