Electrical activity of the heart Flashcards
(42 cards)
In skeletal muscle which are the thin vs thick filaments? WHich are attached to the Z line?
thin = actin thick = myosin
Actin are attched to the Z line
What is the membrane surrounding the muscle called? What is a T Tubule?
Sarcomere, T-tubules are transverse tubules run deep into muscle, allow calcium/ions to reach the whole muscle.
Where is the sarcoplasmic reticulum and what does it release? What Voltage do normal muscle cells remain at?
Membrane structure within the muscle. Calcium is released. Normal muscle cells remain at -90mV
What binds to troponin?
Calcium
Skeletal vs cardiac muscle
- connections and what do they allow through?
Skeletal muscle are muscle cells that have been merged together, whereas cardiac muscle have intercalated discs around the whole cell allowing signals to be distrubuted in every angle
What is a gap junction?
A protein channel connecting one cells cytopolasm to another, allowing small signalling molecules through.
What forms the intercalated disc? What is the advantage of hr intercalated disc?
Alternating gap junctions (allowing the signalling molecules through) and desmosomes (keeping cell-cell adhesion). Allows the whole heart to contact from one signal.
How long is the repolarisation in skeletal vs cardiac muscle? Why is there a difference?
Skeletal muscle = 1-2ms
Cardiac muscle = 250ms
Because cardiac muscle has the extra calcium channels and they take longer to repolarise. This means that the heart is unable to have tectantic contraction and so will contract and then relax.
How is the strength of contraction regulated?
By the amount of calcium channels that are open and so how much calcium is allowed to enter the cell from the outside which would depolarise the heart further leading to a faster and harder contraction.
What is a tetanus? Why is there no tetanus from cardiac muscle?
In skeletal muscle when the there are consecutive action potentials that summate and can maintain/increase force exerted by the muscle, eg useful whilst holding a baby,
In cardiac muscle we don’t want tetanus as we want the heart muscle to relax to allow it to fill with blood. Because it also has calcium channels this means that they take longer to repolarise and there is a longer refractory period, meaning that the heart muscle is almost fully relaxed before the next action potential can have an effect.
Do all cardiac muscle cells have an unstable resting potential? WHat do they act as?
No, not all, but those that do act as pacemaker cells.
resting skeletal muscle, which ions are where? which channels open upon an AP, and what is the rmp?
Skeletal muscle - K+ inside the cell mainly, leaky K+ channels open, Na+ outside the cell, it’s channel is closed, Ca2+ outside the cell, closed channel.
To depolarise, the voltage gated Na+ channels open.
Resting membrane potential is -70mV
in skeletal muscles, what is the main channel to depolarise a cell?
voltage gated sodium channels
Discuss the action potential in a non-pacemaker cardiac muscle
resting potential (approx. -90mV), caused by leaky potassium channels (high relative membrane permeability).
What keeps the plateau? And then what causes the repolarisation?
The calcium ion channels (L-type, L for LARGE, so lots calcium release and long lasting) and decrease in Potassium permeability (leaky potassium channels shut)
REpolarisation is caused by the Ca2+ channels shuttiing and the leaky potassium channels reopening.
The graphs from the powerpoint can be helpful if stuck (CVS 2.1)
Discuss pacemaker action potential
The action potential is due to the opening of Ca2+ (L-type)
Discuss pacemaker cells pacemaker potential (or pre-potential). What is the inerrant heart rate of the pace maker cells?
Gradual decrease in permeability to K+ (closing the leaky potassium channels)
The early increase in permeability of Na+ (aka PF - F for funny, because they open on repolarisation),
And lastly there is the late(r) opening of PCa2+ (T-type, T for transient, only let a little bit of Ca2+ into the cell).
These all gradually depolarise the cell to the threshold to create an action potential.
Heart rate is around 100bpm
What type of channel is a PF channel? what is it opend by?
Funny Sodium. Opened early on repolarisation from the previous action potential.
What are PCA2+ T-type gated channels?
Transient Ca2+ gated channels that are stimulated to open at mre hyperpolarised potentials, a late increase that finally pushes the potential over the threshold.
What determines heart rate?
The rate of the fastest pace maker cell
What is heart block? What can it be caused by?
Hyperkalemia. (High Potassium), this high potassium levels depolarises myocardial cells and triggers spontaneous and uncoordinated contraction (fibrillation).
Increase K+ outside cell. Reduced concentration gradient to pull K+ outside cell but bigger pull inside cell (from charges), so K+ conc increases inside cell, making inside cell more +ive and less negative and so closer to depolarise threshold.
Then also less +ive gradient for other +ive ions to enter cell, slowing down the condction of the action potential. Conduction through the AV node may fail and Atria depolarisation never reaches ventricles. This is what is known as HEART BLOCK.
A 1 degree rise in body temp leads to what in the heart?
Increase in heart rate by 10bpm
What effect does calcium channel blockers have on the rate and force of the heart?
So if you block the calcium channels (used for pacemaker pre potential and action potential or them), you will slow down the rate and strength of contraction of the heart.
Where are the fastest pacemaker cells found in the heart?
In the sinoatrial node
