Physiology: Electrical Activity of the heart Flashcards
What are sum of the structures found in the myocardium?
Actin and Myosin Z line T-tubule Sarcoplasmic Reticulum Sarcolemma
What forms functional syncytium?
Intercalated Discs
What structures are involved in intercalated discs
Gap Junction Desmosomes
What are the functions of gap junctions?
Electrically connects intercalated discs
What are the functions of Desmosomes?
Physically connects intercalated discs
Describe the action potential of cardiac muscle?
Long action potential (250msec) with long refractory period
What does the the long refractory period of cardiac muscle?
No tetanic contraction can be observed
What is the effect of Ca2+ outside the cells on cardiac muscle?
Can be used to regulate the contraction of the muscle Ca2+ cannot saturate troponin Regulation of the release of Ca2+ can vary strength of contraction
Can you describe the resting membrane potential potential of pacemaker cells?
They are unstable
What does the action potential of Non-pacemaker cardiac muscle look like?
What does the action potential of Pacemaker cardiac muscle look like?
What ions are involved in the resting and action potential in non-pacemaker myocardium cells?
K+
Na+
Ca2+ (L-Type)
What ions have the highest concentration of resting potential in non-pacemaker cells?
K+
What happens within non-pacemaker for an action potential to occur?
Initial increase in PNa+ followed by and increase in PCa2+ and decrease in PK+
What occurs in non-pacemaker cells during repolarization?
There is a decrease in PCa2+ and an increase in PK+
What ions are involved in a pacemaker cell?
Ca2+ (L-Type)
K+
Na+
Ca2+
What happens to the pacemaker cell before an action potential?
There is a gradual decrease in K+ with an early increase in Na+ and late increase in Ca2+(T-type)
What happens to a pacemaker cell when an action potential occurs?
An increase in Ca2+ (L-type)
Name factors that modulate electrical activity of the heart
Sympathetic and Parasympathetic
Drugs
Temperature
Hyperkalaemia
Hypokalaemia
Hypercalcaemia
Hypocalcaemia
What are some drugs that effect electrical acitvity of the heart and what is there effect?
Ca2+ - Channel Blockers decrease the force of contraction
Cardiac Glycosides increase the force of contraction
What does hypekalaemia do to the electrical activity to the heart?
Can cause fibrillation and heart block
What does hypokalaemia do to the electrical activity to the heart?
Can cause fibrillation and heart block
What does hypercalcemia do to the electrical activity to the heart?
Increase HR and force of contraction
What does hypocalcemia do to the electrical activity to the heart?
Decreases the HR and force of contraction
