Cardiac Myocytes and Action Potentials

The video explains the heart's function as a muscle that contracts and pumps blood, driven by electrical impulses. It details the role of pacemaker cells in generating these impulses and the conduction system's function in spreading them. The video also covers the action potentials in cardiac cells, highlighting differences between pacemaker and contractile myocytes. It describes the ionic mechanisms involved in depolarization and repolarization, the role of calcium in muscle contraction, and the importance of the plateau phase in cardiac action potentials.

What is the primary function of cardiac myocytes?

• To regulate body temperature

• To generate nervous impulses

• To store calcium

• To contract and pump blood

Which part of the heart is responsible for initiating all heartbeats?

• Purkinje fibers

• SA node

• Bundle of His

• AV node

What is the resting membrane potential typically like in a cell?

• Variable

• Negative

• Neutral

• Positive

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

• -60mV

• -50mV

• -30mV

• -40mV

What is the role of 'funny' currents in pacemaker cells?

• To allow rapid influx of calcium

• To trigger potassium efflux

• To enable slow influx of sodium

• To maintain a stable resting potential

What is the stable resting potential of contractile myocytes?

• -90mV

• -70mV

• -30mV

• -50mV

What phase is characteristic of cardiac action potentials due to calcium influx?

• Depolarization phase

• Repolarization phase

• Resting phase

• Plateau phase

What triggers the release of calcium from the sarcoplasmic reticulum?

• Potassium efflux

• Calcium-induced calcium release

• Magnesium influx

• Sodium influx

Why is the refractory period in cardiac muscle longer than in skeletal muscle?

• To allow for faster contraction

• To prevent tetanus and ensure relaxation

• To increase heart rate

• To enhance calcium storage

What is the main purpose of the plateau phase in cardiac muscle contraction?

• To shorten the contraction duration

• To allow rapid repolarization

• To decrease calcium influx

• To ensure prolonged contraction for blood expulsion