Membrane Potential Dynamics in Cardiac Muscle Cells

The video tutorial explains the changes in membrane potential within heart cells, focusing on the phases of depolarization, plateau, and repolarization. It highlights the absolute refractory period and compares action potentials in cardiac and skeletal muscles. The role of pacemaker cells, particularly the sinoatrial (SA) and atrioventricular (AV) nodes, in generating action potentials is discussed. The video concludes with an explanation of pacemaker activity and its impact on cardiac muscle contraction.

What is the peak membrane potential during depolarization in cardiac muscle cells?

• Negative 60 millivolts

• Zero millivolts

• Positive 30 millivolts

• Negative 90 millivolts

During the plateau phase of a cardiac action potential, which ions primarily move into the cell?

• Sodium ions

• Calcium ions

• Potassium ions

• Chloride ions

What is the absolute refractory period in cardiac muscle cells?

• A period when no action potential can be generated

• A period when the membrane potential is at its peak

• A period when the muscle is fully contracted

• A period when a second action potential can be generated immediately

How do cardiac muscle cells receive action potentials?

• From the brain

• From skeletal muscles

• From pacemaker cells

• From neurons

Which node is considered the main pacemaker of the heart?

• Sinoatrial node

• Atrioventricular node

• Purkinje fibers

• Bundle of His

What happens if the sinoatrial node is damaged?

• The bundle branches take over

• The Purkinje fibers take over

• The atrioventricular node takes over

• The heart stops beating

What is the threshold potential for pacemaker cells in the sinoatrial node?

• Zero millivolts

• Negative 40 millivolts

• Negative 20 millivolts

• Negative 60 millivolts

During the pacemaker potential phase, which channels are open?

• L-type calcium channels

• T-type calcium channels

• Sodium channels

• Potassium channels

What occurs during the depolarization phase of pacemaker cells?

• Chloride ions exit the cell

• Sodium ions enter the cell

• Calcium ions enter the cell

• Potassium ions exit the cell

What is the role of pacemaker cells in the heart?

• To supply blood to the heart

• To contract the heart muscle directly

• To receive action potentials from neurons

• To generate action potentials independently