18 Questions
What characterizes phase 1 of the action potential based on the provided text?
Increased Na+ permeability.
What phase is characterized by the plateau phase of the membrane potential as a result of an inward flow of calcium?
Phase 2
What causes the sodium gates to be 'inactivated' in phase 0 of the action potential?
Electric charge distribution across the cell membrane.
Which ion contributes to the rise in membrane potential in phase 0?
Sodium ions
What brings about the fall in membrane potential close to the potassium equilibrium potential in phase 3?
Decreased K+ permeability
Which event partly leads to the inactivation of calcium channels in phase 2?
Rise in intracellular calcium
During which phase of the cardiac action potential do the Na+ channels close?
Phase 0
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.
What occurs during phase 2 of the cardiac action potential?
Prolonged plateau phase due to Ca2+ influx.
Which statement best describes the 'relative refractory' period in cardiac myocytes?
Requires a greater than normal stimulation to generate an action potential.
What distinguishes cardiac muscle from skeletal muscle and most neurons in terms of resting potential?
'Resting potential' in cardiac muscle is particularly unstable.
How does the calcium current contribute to the action potential in cardiac muscle?
Ca2+ influx prolongs the plateau phase of the action potential.
What is the main cause of the diastolic depolarization (pacemaker pre-potential) in the SAN?
Inward movement of Na+ ions through funny channels
What is responsible for the relatively slow and smaller magnitude depolarization phase in the SAN?
Influx of Ca++ ions through T-type Ca++ channels
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
Which type of calcium channels contribute to the acceleration of depolarization towards the threshold potential in the SAN?
T-type Ca++ channels
What potential triggers an action potential in the SAN during phase 4?
-40 mV
Which ion is responsible for the depolarization phase in the SAN due to its influx through L-type Ca++ channels?
Ca++
Test your knowledge on the different phases of an action potential, including the changes in Na+ and K+ permeability and the resulting shifts in membrane potential. Understand the concept of sodium gate inactivation and the role of ion gradients in generating electrical signals in neurons.
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