Action Potentials

AP 1

1

A __________ ___________ determines whether or not an action potential is generated.

graded potential

2

Even if the stimulation voltage is increased above threshold, the amplitude of the action potential remains _____________.

constant

5

Graded potentials decay with distance due to:

• Current leak

• Cytoplasmic resistance

AP 2

1

Where is the trigger zone?

Axon hillock and initial segment

2

________________ postsynaptic potentials lead to a local depolarization of the postsynaptic membrane.

Excitatory

5

How does hyperkalemia (excessive extracellular K⁺ concentration) affect the resting membrane potential?

Depolarization because less K⁺ ions diffuse out of the cell due to higher [K⁺] outside of the cell; this makes the inside of the membrane less negative.

AP 3

1

A ______________ stimulus produces depolarizations that are not large enough in magnitude to produce an action potential in excitable cells.

subthreshold

2

A period after firing when a neuron is returning to its normal polarized state and will fire again only if the incoming message is much stronger than usual

Relative Refractory Period

5

In the PowerPhys, increasing frequency of stimulation to the trigger zone resulted in a decrease in the number of action potentials. This is because there is overlap between the stimulus and ________________________________.

Absolute refractory period

AP 4

1

The membrane potential which, if reached, leads to the all-or-none initiation of an action potential

Threshold

2

In the PowerPhys, where was membrane potential measured?

Axon hillock and axon

5

For the experiment on the effect of stimulus strength on action potential generation, what was the dependent variable? Independent variable? Controlled variables?

• Membrane potential

• Stimulus strength (voltage)

• Frequency of stimulation

• Type of neuron

Dependent variable: membrane potential

Independent variable: stimulus strength (voltage)

Controlled variables: Frequency of stimulation, Type of neuron

AP 5

1

A ______________ stimulus creates a graded potential that is still above threshold by the time it reaches the trigger zone.

suprathreshold

2

In repolarization, voltage-gated Na⁺ channels are ________________, and voltage-gated K⁺ channels ___________.

inactivating, open

5

How does hypokalemia (low extracellular K⁺ concentration) affect the resting membrane potential?

Decreased potassium levels in the extracellular space will cause hyperpolarization of the resting membrane potential.