Module 1 Lesson 2 Flashcards
What type of muscle is cardiac muscle most similar to in structure?
Skeletal muscle
What specialized structures allow cardiac muscle cells to function as a syncytium?
Intercalated discs, desmosomes, and gap junctions
What property allows the heart to generate action potentials without external stimuli?
Autorhythmicity
What are the two main types of cardiac muscle cells?
Contractile cells and conducting/autorhythmic cells
What equation is used to calculate the resting membrane potential based on ion permeability?
Goldman-Hodgkin-Katz Equation
What phase of the cardiac action potential is associated with calcium channel opening?
Plateau phase
What is the primary pacemaker of the heart?
Sinoatrial (SA) node
What prevents summation and tetanus in cardiac muscle?
Long absolute refractory period
What is the sequence of electrical conduction in the heart?
SA node → Internodal pathways → AV node → Bundle of His → Bundle branches → Purkinje fibers
Why do cardiac muscle cells function as a coordinated unit?
Because of gap junctions, which allow electrical signals to pass directly between cells.
How does the SA node differ from ventricular muscle cells in action potential generation?
The SA node has an unstable resting membrane potential, while ventricular cells have a steady resting phase and are only activated by Na⁺ channel opening.
What is the functional significance of the plateau phase in cardiac action potentials?
It extends the contraction time to allow efficient blood ejection and prevents tetanus.
Why don’t atrial and ventricular muscle cells share gap junctions?
They are separated by a non-conductive fibrous skeleton to ensure proper timing of contraction.
How does the opening of K⁺ channels contribute to repolarization in cardiac cells?
K⁺ exits the cell, restoring the negative membrane potential after depolarization
What role does calcium influx from extracellular fluid play in cardiac muscle contraction?
It triggers calcium release from the sarcoplasmic reticulum, initiating contraction.
If a patient has an abnormally fast heart rate, which part of the electrical conduction system is likely overactive?
The SA node, as it controls the heart rate.
How would blocking calcium channels affect cardiac action potentials?
It would shorten the plateau phase, reduce contraction strength, and impair heart function.
If a person has a damaged AV node, how would this affect heart function?
The electrical signal may not properly reach the ventricles, leading to heart block and irregular contractions.
How does the long refractory period in cardiac muscle prevent arrhythmias?
It ensures that each contraction is followed by relaxation before another action potential can be generated
How would an increase in extracellular K⁺ affect the resting membrane potential of cardiac cells?
It would make the resting potential less negative, possibly leading to arrhythmias or abnormal excitability.
