Cardiac Muscle Structure & Function Flashcards
Cardiac muscles have a much longer ________ phase than skeletal muscle (to prevent tetanus).
repolarization
About ______ percent of cardiac myocytes cell volume is occupied by myofibrils and mitochondria.
85
What two proteins prevent actin-myosin interaction in the resting state of the myocyte?
Troponin and tropomyosin; when calcium is released into the cytoplasm, calcium binds troponin and troponin then pushes tropomyosin out of the way, allowing for myosin to walk along actin.
Cardiac output is given by __________.
stroke volume x heart rate
Like skeletal muscle, cardiac muscle is also ________.
striated
Cardiac muscle cells are connected both ________ and ______.
electrically; mechanically
Cardiac myocytes occupy about _____ the space of the heart, but they comprise only ______ of the number of cells.
2/3; 1/3
_________ forms an elastic spring, allowing for resting tension.
Titin
The ______ isoform of titin is more stiff.
N2B
What are some features that distinguish cardiac myocytes from skeletal myocytes?
Cardiac myocytes are striated and mono-nucleated, like skeletal myocytes, but cardiac myocytes are shorter, autonomous (i.e., they don’t need neural stimulation), and they are thin-filament regulated.
Only the ______ isoform of tropomyosin is found in cardiac muscle.
alpha
List the steps of sarcomere contraction.
(1) An action potential, originally from the sinoatrial node, causes calcium to release inside the cell; (2) calcium binds troponin; (3) troponin changes conformation and pushes tropomyosin out of the way; (4) once tropomyosin is out of the way, myosin can bind to actin and contraction proceeds.
Explain preload.
Preload is one of the factors that determines how much blood is ejected from the heart during systole; put simply, the heart muscles contract more depending on their initial length, so if more blood enters the heart during diastole, then more will exit it in systole.
Myocyte response can also be influenced by ___________.
calcium sensitivity–the more sensitive, the more force in response to a given amount of calcium
What is afterload?
It is the systemic pressure; the heart must pump over the baseline arterial pressure, so the stroke volume will increase in response to a decreased afterload.
