Unit 3.6: Cardiac Muscle Flashcards
What are cardiac cells also called?
Myocardial cells
Are cardiac cells striated?
Yes.
How are cardiac cells different than skeletal cells in terms of
- size
- nucleus
- t-tubules
- how they’re connected to each other
Cardiac muscle cells are much smaller with single nucleus with 1/3 of cell occupied by mitochondria
T-tubules are much larger and branched and SR is smaller
adjacent cells are joined by intercalated discs with desmosomes
What are the 2 types of cardiac muscle cells?
Contractile cells and autorhythmic/pacemaker cells
What are autorhythmic/pacemaker cells?
They are involved in the electrical excitation of the heart
How are autorhythmic/pacemaker cells connected to other cardiac cells?
Through gap junctions
How are cardiac cells different than skeletal muscle cells in terms of contraction?
Ca2+ enters through Ca2+ channels on cell membrane and SR
- Calcium enters through cell membrane
- Calcium induced calcium release - release of calcium from SR
How are cardiac cells different than skeletal muscle cells in terms of relaxation?
Cardiac cells have Na+/Ca2+ antiport in addition to Ca2+-ATPase
True or False
Cardiac muscles cells exhibit all-or-nothing contractions.
False.
Cardiac muscles exhibit graded contraction
What are graded contraction proportional to?
Number of active crossbridges
What are factors influencing cardiac muscle contraction force?
- Changes in concentration of Ca2+
2. Sarcomere length
How do changes in concentration of Ca2+ influence cardiac muscle contraction force?
Regulated by epinephrine and norepinephrine
- binding then activates cAMP second messenger signalling pathway that leads to
- phosphorylation of voltage-gated Ca2+ channels which increases their probability to open which increases concentration of Ca2+ in cytosol
- phosphorylation of phospholambam which leads to increase SR Ca2+-ATPase activity which increases SR Ca2+
How do contractile cardiac muscle cells contract and generate action potentials?
See coursenotes p. 72
What is sustained depolarization due to in a contractile cardiac muscle cell?
Due to the slow opening of the voltage-gated Ca2+ channels
Why is sustained depolarization important?
Prevents tetanus and allows the heart to relax between contraction
Why don’t cardiac muscle cells undergo summation and tetanus?
Because of the longer refractory period, means that the cell has finished contracting before the next action potential
