Lecture 29 - Cardiac Muscle Physiology Flashcards
what are the cardiac muscle cells
o Mono-nucleated
o Striated
o Branching
o Intercalated discs
skeletal muscle
striated and voluntary
cardiac muscle
striated and involuntary
smooth muscle
unstriated and involuntary
Cardiac histology and physiology
o Very similar to skeletal muscle
o Increase calcium concentration muscle contraction
o Muscle contraction due to action/myosin cross bridge cycling
gap junctions
Allow adjacent cardiac myocytes to communicate chemically and electrically
SA node
o Located in heart right atrium
o Cells spontaneously depolarise
o At threshold they initiate muscle contraction
o Depolarizing current is transmitted from one cell to the adjacent cell through gap junctions
depolarization of cardiac myocyte
o Leads to opening of Vca and Ca2+ influx
o ANS innervates hear
o Sympathetic
Cardio acceleration (positive chronotropy)
Increased force of contraction (positive inotropy)
o Kinase activity on LTCC prolongs opening
cardiac conduction system
Made up of SA node, AV node, Bundle of His, Bundle of branches, Purkinje fibres
autorhythmicity
o Cells in the SA and AV nides spontaneously depolarize to threshole
o Due to slow Na+ leak across the membrane
pacemakers of the heart
o SA node
o AV node
o Purkinje fibres and ventricular myocytes
Conduction velocity through the heart and cardiac conduction system
o Slow conduction through the AV node
o Very fast conduction through bundles
what is the ECG
o A measure of the sum of all electrical activity of the heart
o It indirectly measures the propagation of action potential through the heart
Comparison of action potentials in different tissue
o Neurons = 1ms
o Muscles (arm) = 3ms
o Heart = 200ms
how is the shape of AP determined
o By the exact ion channels that are being activated
o Therefore different areas of the hear have slightly different cellular physiology
