Action Potential Phases Quiz

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What characterizes phase 1 of the action potential based on the provided text?

Outward flow of calcium ions.

Decreased K+ permeability.

Increased Na+ permeability. (correct)

Simultaneous opening of L-type voltage gated sodium channels.

What phase is characterized by the plateau phase of the membrane potential as a result of an inward flow of calcium?

Phase 3

Phase 0

Phase 1

Phase 2 (correct)

What causes the sodium gates to be 'inactivated' in phase 0 of the action potential?

Favourable concentration and electrical gradient.

Electric charge distribution across the cell membrane. (correct)

Rise in intracellular calcium.

Outward flow of potassium ions.

Which ion contributes to the rise in membrane potential in phase 0?

Sodium ions Signup and view all the answers

What brings about the fall in membrane potential close to the potassium equilibrium potential in phase 3?

Decreased K+ permeability Signup and view all the answers

Which event partly leads to the inactivation of calcium channels in phase 2?

Rise in intracellular calcium Signup and view all the answers

During which phase of the cardiac action potential do the Na+ channels close?

Phase 0 Signup and view all the answers

What characterizes the 'absolute refractory' period of cardiac myocytes during the action potential?

Na+ channels are closed and stimulation cannot produce a further action potential. Signup and view all the answers

What occurs during phase 2 of the cardiac action potential?

Prolonged plateau phase due to Ca2+ influx. Signup and view all the answers

Which statement best describes the 'relative refractory' period in cardiac myocytes?

Requires a greater than normal stimulation to generate an action potential. Signup and view all the answers

What distinguishes cardiac muscle from skeletal muscle and most neurons in terms of resting potential?

'Resting potential' in cardiac muscle is particularly unstable. Signup and view all the answers

How does the calcium current contribute to the action potential in cardiac muscle?

Ca2+ influx prolongs the plateau phase of the action potential. Signup and view all the answers

What is the main cause of the diastolic depolarization (pacemaker pre-potential) in the SAN?

Inward movement of Na+ ions through funny channels Signup and view all the answers

What is responsible for the relatively slow and smaller magnitude depolarization phase in the SAN?

Influx of Ca++ ions through T-type Ca++ channels Signup and view all the answers

Why is the initial resting potential in the SAN less negative than in other parts of the heart?

Low K+ permeability due to absence of inward rectifier potassium channels Signup and view all the answers

Which type of calcium channels contribute to the acceleration of depolarization towards the threshold potential in the SAN?

T-type Ca++ channels Signup and view all the answers

What potential triggers an action potential in the SAN during phase 4?

-40 mV Signup and view all the answers

Which ion is responsible for the depolarization phase in the SAN due to its influx through L-type Ca++ channels?

Ca++ Signup and view all the answers