Properties Of Cardiac Muscle Flashcards
What is the ability of cardiac muscle to respond to a stimulus called?
Answer: Excitability (Bathmotropism)
How does cardiac muscle respond to a stimulus?
Answer: By producing an action potential (AP)
What is the resting membrane potential of cardiac muscle?
Answer: -90 mV
What type of action potential does cardiac muscle have?
Answer: Plateau type
What is the refractory period of cardiac muscle?
Answer: The time during which a second action potential cannot be triggered
During what phases of the AP is the cardiac muscle absolutely refractory?
Phase ➡️0, 1, and half of phase 3
During what phase of the AP is the cardiac muscle relatively refractory?
Answer:
The rest of phase 3 until phase 4 begins
How long is the absolute refractory period in the atria and ventricles?
Answer:
Atria: 0.15 seconds;
Ventricles: 0.2 seconds
How long is the relative refractory period in the ventricles?
Answer: 0.05 seconds
What are two advantages of the long refractory period in cardiac muscle?
Answer:
1. Prevents tetanus, which could be harmful to the heart.
2. Allows for a compensatory pause after an extrasystole, helping to restore normal rhythm.
What is the ability of the heart to initiate its own impulse at regular intervals called?
Answer: Rhythmicity (Chronotropism)
What is the velocity of conduction in the ventricular muscle and the conducting system?
Ventricular muscle: 1 m/s;
Conducting system: 0.05-4 m/s
What is the ability of cardiac muscle to respond to a stimulus by contraction called?
Answer: Contractility (Inotropism)
What is the term for the intrinsic level of myocardial contraction?
Answer: Inotropic state
What is a positive inotropic stimulus?
Answer: Any factor that increases the force of contraction
What are some factors that have a positive inotropic effect on the heart?
Answer:
Sympathetic stimulation,
epinephrine and norepinephrine, increased ECF calcium concentration, caffeine,
theophylline
What is a positive inotropic stimulus?
Answer:
Any factor that increases the force of contraction
What is a negative inotropic stimulus?
Answer: Any factor that decreases the force of contraction
What are some factors that have a negative inotropic effect on the heart?
Answer:
Parasympathetic stimulation, acetylcholine,
hypercapnia,
hypoxia,
acidosis,
drugs like quinidine and barbiturates
Does cardiac muscle follow the all-or-none law?
Answer: Yes, it contracts with maximum force when a threshold stimulus is applied.
What factors can influence the force of contraction in cardiac muscle?
Answer: Initial length of muscle fiber and inotropic state
What is the treppe phenomenon?
Answer: The progressive increase in amplitude of contraction with increasing stimulation rate.
