Electrical activity of the heart Flashcards Preview

CVS > Electrical activity of the heart > Flashcards

Flashcards in Electrical activity of the heart Deck (10):

what is a syncytium

The heart is a syncytium
A cell which is made up of different cells fused together


How are cells in the heart connected and what does this allow

Physically; desmosomes
electrically: gap junctions
this forms an intercalated disc
allows the cells in the heart to communicate and contract in sync.


How are action potentials in cardiac muscle different to skeletal muscle

Last longer- 250ms vs 2ms
Have a longer resting potential- they do not have tetanic potentials as the refractory period is much longer


What are the different types of resting potentials in heart cells and where are they found

Resting potential
-found in non-pacemaker potential cells
-maintained by leaky potassium channels

Fluctuating resting potential :
-found in pacemaker cells
-due to decreased permeability of potassium channels, increased permeability to sodium and T-type calcium channels being opened


Trend of an action potential in a pacemaker cell- explains AUTORHYTHMICITY

-fluctutating R.P.
-calcium channels open (T-type)
-calcium flows into the cell and depolarises it to threshold
-Calcium channels close and potassium channels open


Trend of an action potential in a non-pacemaker cell

-resting R.P.
-cell becomes depolarised as the sodium channels open and the L-type calcium channels open
- Plateau- the sodium channels close but the calcium channels stay open, permeability to potassium decreases
-Repolarisation- potassium channels open and calcium channels close


How can electrical activity be modulated

-calcium channel blockers: decreases calcium entering the heart, decreases the forces of contraction
-cardiac glucosides: opposite
HYPERKALEMIA- high potassium in the plasma
- decreases the gradient so less potassium flows out of the cell
-resting potential cannot be maintained which leads to fibrillation
-increases amount of calcium in the plasma
-increases amount of calcium flowing into the cell
-increases heart rate and force of contraction
HYPOCALCEMIA: does opposite
TEMPERATURE: heart rate increases by 10bpm for every 1 degree celsius- increased force of contraction


Describe the special conducting system of the heart

sinoatrial node:
-found In right atrium
-fastest depolariser -0.5 ms
-spreads electrical activity through both atria
Annulus fibrosus:
-layer of non-conducting tissue
-prevents the ventricles from conducting before the atria
AV node: delays spread
Bundle of his and purkinje fibres:
-electrical activity spreads down bundle of his through to purkinje fibres at the apex of the heart
-ventricles contract from bottom up


what is the pacemaker of the heart

the SA


explain the excitation-contraction coupling theory?

1- A.P. enters transverse TUBULE ( folds in membrane)
2- calcium is released from LATERAL SAC and binds to sarcoplasmic reticulum
3-increased calcium ions in sarcoplasmic redticulum bind to troponin.
4-troponin is bound to tropomyosin and holds it in place. tropomyosin partially covers the myosin cross-bridge heads. when calcium binds to troponin, it causes it to change shape and detach from tropomyosin. cross-bridge moves

How does the cross-bridge work?
1- cross-bridge binds to actin
2-cross-bridge moves- ADP and Pi detach from cross-bridge head
3- ATP binds to myosin- cross-bridge breaks
4-cross-bridge head is activated by ATP hydrolysis