Heart Muscle Flashcards
How many litres of blood does the heart pump a day?
8000L
What causes striations in cardiac muscle?
Actin- light and myosin-dark
Why is cardiac muscle branched and ordinated in different directions?
The heart must pull in many different directions to become as small as possible when contracting.
How are neighbouring cells in the heart bonded together physically and electrically?
Intercalated discs and desmosomes
Mechanical - folds, Electrical - gap junctions
How do we know that the heart is good at oxidative metabolism ?
Many mitochondria
What are the main cations inside and outside of the cells?
Inside - K+ (Leaks out)
Outside Na+
What is the chief characteristic of the non pacemaker action potential ?
Long period of depolarisation AP (0.25s)
Normal AP (<10msec)
Contains RMP of -92mV
What is the chief characteristic of pacemaker action potential ?
It is self excitable and doesn’t have a RMP.
Rises and falls.
Describe the phases of non pacemaker AP?
Phase 0 - Na + channels open at -70mv and has a slower slowing gate at -30 - -40 mv allowing the mV to get to 20mV before the channel is fully closed
Phase 1 - Closer of Na+ channels, small opening of K+ channels and opening of Cl- channels allows some chlorine into the cell
Phase 2 - Slow prolonged opening of Ca++ channels which allow calcium into the cell very slowly, responsible for the plateau
Phase 3 - 2K+ channels (Ikr and Iks) Ikr allows K+ into the cell until half way through phase 2 and then allows K+ to leave the cell. Iks allows K+ to leave the cell during phase 2. Causes large drop in MP back to -90mV
Phase 4- RMP
Describe the phases of pacemaker AP?
Phase 0 - Long lasting Ca++ channels open at -40 mV.
No phase 1 or 2
Phase 3 - K+ channel allows K+ to flow out of the cell causing MP to drop.
Phase 4 - (creep potential) slow rise in Ca++ flowing out of the cell and K+ leaks out of the cell at a reduced amount. I’f’allows Na+ into the cell but K+ out of the cell but less K+ leaves the cell than Na+ enters.
What type of stimulus can activate a muscle during the relative refractory period?
Supra Normal Stimulus
Can a muscle be stimulated during absolute refractory period?
No
Why would you not want to be able to activate a muscle many times a second on the heart?
The heart would be in spasm and wouldn’t function effectively as the heart beat is a muscle twitch in many fibres at the one time. We do not want summation because we do not want a sustained contraction.
When does contraction of the heart muscle begin in relation to calcium concentration?
When calcium concentrations go from 10-7 to 10-4 inside of cells
Why would lengthening the cardiac muscle fibres be useful?
When the muscle gets longer it gets bigger
