Muscle VII Flashcards
What is cardiac muscle made of
- cardiac myocytes (myocardial muscle cells)
- all cells interconnected by intercalated disks
- larger t-tubules
- smaller amounts of SR
- ## abundance of mitochondria (1/3 cell volume)
What is main role of cardiac muscle
Generates force to move blood throughout whole blood
What are cardiac myocytes
Shorter, branched cells and usually contain single nucleus
What are two types of intercalated disks
- desmosomes link mechanically (uniform contraction)
- gap junctions link them electrically (uniform propagation)
What type of calcium does cardiac muscle require more than skeletal
Extracellular calcium
What type of metabolism for cardiac muscle for ATP production
Oxidative metabolism
How many cardiac muscle cells contract in average life span
- almost 3 billion times without resting
- 70x/min
What is cardiac contraction initiated by
Autorhythmic cells (pacemakers)
What are autorhythmic cells
1% of myocardial cells are specialized non-contracting cells
- generate APs spontaneously
- smaller and contain few contractile fibers
- pass conduction out to contractile cells
Where does depolarization occur in heart
Sinoatrial node (main pacemaker of heart)
What are gap junctions for in heart
AP travels through
- calcium and sodium diffuses to adjacent cell causing depolarization
- auto-rhythmic cells are electrically coupled to auto-rhythmic cells and then coupled to contractile cells and contractile to each other
Why do APs in autorhythmic cells occur spontaneously
Hyperpolarization-activated cyclic nucleotide-gated (HCN) channels
- depolarize at negative membrane potential
Where are HCN channels
Only in autorhythmic cells
What is plateau of cardiac muscle AP for
Prevents summation
- voltage gated Na+ channels in inactive state
- creates long refractory period
- don’t want summation, rest so chamber can fill and then twitch again
How much calcium from SR and from ECF in cardiac cells
SR 90%
ECF 10%
