Electrical Activity of the Heart Flashcards
In order for the whole heart to shorten on contraction, what two kinds of connections between the two membranes are needed?
- physical
- electrical
The arrangement of desmosome-gap junction-desmosome is known as
intercalated discs
Are action potentials in cardiac muscle longer or shorter than those in skeletal muscle?
Longer
The amount of calcium entering the heart from outside can be regulated by cardiac muscle, this allows what to be regulated?
- number of gap junctions
- strength of contraction
During what phase of the action potential does calcium enter the cardiac muscle cell?
Plateau phase
Through what channels does calcium enters cardiac muscle cells?
L-type voltage-gated calcium channels
Calcium sensitive calcium release channels in the sarcoplasmic reticulum release stored calcium into the cytoplasm though what process?
Calcium-induced calcium release
The combination of calcium release and calcium entry across the membrane causes a rapid increase in calcium concentration which
initiates contraction
What process is entirely responsible for calcium release from the sarcoplasmic reticulum?
Calcium-induced calcium release (CICR)
How are crossbridges formed?
Myosin heads protruding from the thick filament bind to sites on actin
At rest, the myosin binding sites on the actin are covered by what regulatory protein?
Tropomyosin
When calcium binds to troponin, there is a conformational change involving the dissociation of what?
Troponin from actin
What happens regarding tropomyosin when troponin dissociates from actin?
Tropomyosin shifts out of actin cleft, uncovering the actin binding sites for myosin
When myosin bridges form, what develops?
Tension
Tension is related to the number of
active crossbridges
What happens to calcium when ATP-dependent calcium pumps in the tubular part of the sarcoplasmic reticulum are activated?
Calcium is sequestered from the cytosol back into the sarcoplasmic reticulum
As the action potential repolarises what happens to the heart muscle?
Heart muscle relaxes
Cardiac muscle is electrically connected via
gap junctions
Cardiac muscle is physically connected by
desmosomes
Why does cardiac muscle not exhibit tetanic contraction?
It has a long refractory period
Cells with unstable resting membrane potential act as
pace makers
In a non-pacemaker action potential, there is a high resting membrane potential for what ion?
K+
What changes in permeability to ions occur in the plateau phase in a non-pacemaker action potential?
- increase in permeability to Ca2+
- decrease in permeability to K+
What changes in permeability to ions occur in the initial depolarisation of non-pacemaker action potentials?
Increase in permeability to Na+
