Cardiac Muscle Cell Channels

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What type of channels participate in depolarization at the membrane of cardiac muscle cells?

Fast voltage-gated K+ channels

Slow voltage-gated Ca2+ channels

Voltage-gated Na+ channels (correct)

Non-voltage gated Cl- channels

Which ion is significant in the normal function of cardiac muscle cells?

Potassium (K+)

Chloride (Cl-)

Calcium (Ca2+) (correct)

Sodium (Na+)

What happens to the membrane potential during depolarization of cardiac muscle cells?

It changes from -90 mV to +30 mV

It remains at +30 mV

It remains at -90 mV

It changes from +30 mV to -90 mV (correct)

What triggers the opening of fast voltage-gated Na+ channels in the sarcolemma of cardiac muscle cells?

Depolarization Signup and view all the answers

In which direction does Ca2+ move in response to the opening of voltage-gated Ca2+ channels in cardiac muscle cells?

Into the cell Signup and view all the answers

Which ion channel is involved in the repolarization of the membrane of cardiac muscle cells?

Voltage-gated K+ channels Signup and view all the answers

What is the main difference between the refractory period of skeletal and cardiac muscle cells?

Skeletal muscle has a shorter refractory period. Signup and view all the answers

What condition is characterized by sustained muscle contraction without any relaxation?

Tetany Signup and view all the answers

Why can skeletal muscle be restimulated at a frequency that does not allow for complete relaxation?

Due to its short refractory period. Signup and view all the answers

In skeletal muscle fibers, what occurs while sarcomeres are still contracting?

Repolarization at the sarcolemma. Signup and view all the answers

What event delays repolarization in cardiac muscle cells, leading to a longer refractory period?

Plateau event at the sarcolemma. Signup and view all the answers

How long does it take for muscle contraction and relaxation associated with sarcomeres in cardiac muscle cells to occur?

Approximately 250 milliseconds. Signup and view all the answers

What are the three variables that may influence stroke volume?

Venous return, presence of inotropic agents, and afterload Signup and view all the answers

What is the typical end-diastolic volume (EDV) in a resting adult?

130 mL Signup and view all the answers

What is the typical end-systolic volume (ESV) in a resting adult?

60 mL Signup and view all the answers

How is stroke volume (SV) calculated?

SV = EDV - ESV Signup and view all the answers

What is the primary mechanism by which sympathetic stimulation increases heart rate?

Sympathetic stimulation increases Ca2+ influx into SA nodal cells, causing them to reach threshold more quickly Signup and view all the answers

Which of the following factors can influence end-diastolic volume (EDV)?

Preload Signup and view all the answers

Which of the following factors can influence end-systolic volume (ESV)?

Afterload Signup and view all the answers

Which of the following is NOT a positive chronotropic agent mentioned in the text?

Dopamine Signup and view all the answers

How does thyroid hormone increase heart rate?

Thyroid hormone increases the number of $\beta_1$-adrenergic receptors on SA nodal cells Signup and view all the answers

What is the role of protein kinase enzymes in the sympathetic regulation of heart rate?

Protein kinase enzymes phosphorylate Ca2+ channels, causing them to open and increasing Ca2+ influx into SA nodal cells Signup and view all the answers

Which of the following is a direct effect of sympathetic stimulation on the AV node?

Sympathetic stimulation increases Ca2+ influx into AV nodal cells, decreasing the delay and increasing the conduction rate Signup and view all the answers

Which of the following is a mechanism by which chemical compounds can increase heart rate?

Chemical compounds increase Ca2+ influx into SA nodal cells, causing them to reach threshold more quickly Signup and view all the answers

What causes the atrioventricular (AV) valves to close and the semilunar valves to open during ventricular ejection?

Increased pressure in the ventricles and decreased pressure in the aorta and pulmonary artery Signup and view all the answers

What is the end-diastolic volume?

The total amount of blood in the ventricles at the end of ventricular relaxation Signup and view all the answers

What is the relationship between end-diastolic volume, end-systolic volume, and stroke volume?

Stroke volume = end-diastolic volume - end-systolic volume Signup and view all the answers

What is the primary function of the cardiac output?

To transport respiratory gases, nutrients, and other substances throughout the body Signup and view all the answers

Which phase of the cardiac cycle is associated with ventricular contraction?

Ventricular systole Signup and view all the answers

Which of the following statements about the cardiac cycle is true?

The AV valves close during ventricular relaxation Signup and view all the answers