Lecture #21: Cardiac Muscle Cells

A collection of flashcards covering key concepts and details related to cardiac muscle cells, their structure, function, and physiology as discussed in Lecture #21.

What is the primary difference in the shape of cardiac muscle cells compared to skeletal muscle cells?

Cardiac muscle cells are branched, while skeletal muscle cells are long cylinders.

What structures synchronize heart contraction?

Intercalated discs and gap junctions.

What type of control describes skeletal muscle, cardiac muscle, and smooth muscle?

Skeletal muscle is under voluntary control, cardiac muscle is under involuntary control with intrinsic excitation, and smooth muscle is also involuntary.

What is the function of pacemaker cells in the heart?

Pacemaker cells generate impulses that initiate heart contractions and maintain rhythm.

What is the significance of the plateau phase in the action potential of cardiac muscle cells?

The plateau phase prolongs depolarization preventing tetanic contractions.

What ion influx is responsible for the rapid depolarization phase in pacemaker cells?

Calcium ion (Ca²+) influx.

What is the role of norepinephrine in cardiac muscle contraction?

Norepinephrine increases contraction force by enhancing Ca²+ influx and release.

What physiological effect does the vagus nerve have on heart rate?

The vagus nerve decreases heart rate.

Why is there a longer absolute refractory period in cardiac muscle compared to skeletal muscle?

To prevent tetanic contractions, allowing the heart to fill and pump efficiently.

What is the inherent firing rate of the sinoatrial (SA) node in the absence of autonomic input?

The inherent firing rate is approximately 100 beats per minute.

What effect does acetylcholine have on cardiac pacemaker cells?

Acetylcholine slows down the heart rate.

What feature distinguishes the action potential of cardiac muscle cells from neuronal and skeletal muscle action potentials?

Cardiac action potentials have a plateau phase due to prolonged Ca²+ influx.

What happens to cardiac muscle action potentials in the presence of hypoxia?

Anaerobic respiration occurs, leading to increased H+ concentration which can block gap junctions and cause fatal arrhythmias.

What is the function of desmosomes in cardiac muscle cells?

Desmosomes anchor the cardiac muscle cells together to prevent separation during contraction.

How does the autonomic nervous system influence cardiac muscle contraction?

The autonomic nervous system alters heart rate and force of contraction through sympathetic and parasympathetic pathways.