Cardiac Muscle Action Potential

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40 Questions

What is the approximate resting potential of a cardiac muscle cell?

-85mV

Which ion plays a crucial role in creating the resting potential of a cardiac muscle cell?

Potassium (K+)

In a theoretical cell with an initial equal number of positive and negative charges, what creates the charge imbalance for the resting potential?

Diffusion of positively charged potassium ions out of the cell

What is the primary form of negative charge inside cardiac cells contributing to the resting potential?

Organic phosphates

Which pump is responsible for maintaining the ionic concentration gradients in cardiac muscle cells for resting potential?

Na+/K+ ATPase

What happens to the sodium gates when the membrane potential reaches between +20 and +30 mV?

They are inactivated by the electric charge distribution.

During which phase of the action potential does the K+ permeability begin to increase significantly?

Phase 1

What role do L-type voltage gated calcium channels play in the action potential?

They create a plateau phase in phase 2.

Why does the membrane potential not immediately fall to the equilibrium potential for potassium despite increased K+ permeability?

Simultaneous opening of calcium channels and inward flow of calcium.

When does the myocyte contraction occur in relation to the action potential phases?

During phase 2

Which phase of the cardiac action potential is characterized by the opening of sodium gates and a hundred-fold increase in sodium permeability?

Phase 0

What ion has its concentration gradient reversed in the Goldman equation used to calculate the true resting potential?

Sodium (Na+)

During which phase of the cardiac action potential does the membrane potential depolarize to reach the threshold potential (-60 to -65mV)?

Phase 0

What is the primary characteristic of the plateau phase of the cardiac action potential?

Prolonged period of slow repolarization

Which type of muscle tissue is primarily responsible for generating the wave of excitation that triggers the opening of sodium gates in cardiac muscle membranes?

Pacemaker tissue

What is the main reason for the initial resting potential in the SAN being less negative compared to the rest of the heart?

Presence of 'inward rectifier' potassium channels

What causes the pacemaker potential or 'prepotential' to drift upwards towards depolarization?

Influx of Na+ through funny channels

Which ion channel type is responsible for the diastolic depolarization phase in pacemaker cells?

'Funny' sodium channels

During which phase is there an inward calcium current that accelerates depolarization towards the threshold potential?

Phase 0: Depolarization phase

What distinguishes the maximum depolarization level in the pacemaker cells from contractile myocardial cells?

+10 mV for pacemaker cells and +30 mV for contractile cells

What triggers the opening of sodium ion channel gates in cardiac muscle, leading to rapid ion permeability rise and the generation of another action potential?

Depolarization to threshold potential

Which parts of the heart exhibit automaticity, generating action potentials spontaneously?

Sinoatrial node

What is the term used to describe the ability of the sinoatrial node (SAN) to have the fastest intrinsic rhythm in the human heart?

Pacemaker tissue

Which type of muscle cells in the heart typically do not display automaticity?

Ventricular muscle cells

What determines the rate of contraction in cardiac muscle?

Rate of depolarization of resting potential

During which phase of the cardiac action potential do Na+ channels remain closed, leading to the 'absolute refractory' period of the myocytes?

Plateau phase

What is the primary consequence of the 'absolute refractory' period in cardiac myocytes?

Inability to generate another action potential

Where do some areas of the heart have particularly unstable 'resting potential'?

Pacemaker tissue

What happens to many Na+ channels during the repolarization phase of the cardiac action potential?

They partially reopen

Why is it harder to generate a subsequent action potential during the 'relative refractory period' of the cardiac action potential?

'Na' channels have partially recovered

What concept is the Nernst equation based on?

Balance between diffusive and electrical gradients

Why is the equilibrium potential for potassium in cardiac muscle cells slightly more negative than the resting membrane potential?

Influence from movements of ions other than potassium

What is the primary ion influencing the magnitude of the resting potential in cardiac muscle cells?

Potassium

Why is the membrane potential far from the Na+ equilibrium potential of +60 mV at rest?

Low permeability to sodium ions

What is responsible for maintaining the ionic concentration gradients in cardiac muscle cells?

Sodium-potassium pump

What contributes to the resting membrane potential being slightly more negative than the potassium equilibrium potential in cardiac muscle cells?

Movement of ions other than potassium

What is the role of the Na+/K+-ATPase pump in relation to ion gradients and membrane potential?

Creates and maintains ionic concentration gradients

Why is sodium far from electrochemical equilibrium at rest in cardiac muscle cells?

Low sodium permeability at rest

Why does potassium have a substantial influence on the resting membrane potential?

Low permeability to other ions

What determines the slightly more negative equilibrium potential for potassium in cardiac muscle cells compared to the RMP?

Other ion movements besides potassium

Learn about the process of depolarization and action potential in cardiac muscle, leading to rhythmic contractions. Explore the concept of myogenic activity in the mammalian heart.

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