Lecture 6 Flashcards
Describe the ON mechanisms for calcium
Voltage gated calcium channels/L-type channels brings in trigger calcium, Type 2 RyR in SR membrane which cause CICR.
Where does trigger calcium come from?
Extracellular matrix through VOC.
Where does the calcium released in CICR come from?
the SR
Describe some OFF mechanisms
SERCA pump regulated by phospholambam, PMCA, Na/Ca exchanger which needs an inwards sodium gradient which is maintained by Na/K ATPase.
What are beta-1 receptors coupled with?
Adenyl cyclase which generates cAMP from ATP which activates PKA.
What are some PKA substrates?
Phospholambam, VOCC, RyR.
Where does the heart beat initiate?
The SA node
Where does the depolarisation spread rapidly to?
The AV valve. there is a delay where while the atrial muscular tissue is depolarised more slowly
Describe the SA node
Autorhythmic, set own rate of depolarisation, frequency sets the heart beat. pacemaker tissue constantly firing action potentials to heart muscle.
Describe phase 0 of ventricle muscle action potential
Rapid depolarisation due to inward sodium current
Describe phase 1
Overshoot due to small outward potassium movement starting to repolarise
Describe phase 2
Plateau phase where calcium/trigger calcium is coming in which keeps membrane potential high.
Describe phase 3
Repolarisation due to outward potassium current
Describe phase 4
resting
How long does the action potential in ventricular muscle last?
300ms (compared to 4ms in neuronal AP).
What is the key difference between muscle cell AP and neuronal AP?
Muscle cell has inward calcium which creates plateau phase.
At what point of the cycle does peak contraction occur?
Just before repolarisation.
What part of the cycle is the absolute refractory period?
From the start of the depolarisation to the end of repolarisation.
What prevents tetany?
The long refractory period.
How does atrial plateau phase differ?
Not as pronounced because there are fewer VOC channels as the atria do not need as strong a contraction as the ventricles.
How does the SA node AP differ?
Slower rate of depolarisation, reduced overshoot, no plateau because no calcium and no contraction. smaller amplitude
Why is the SA node a slower response?
The resting membrane is less negative because there is less potassium channels. Progressive spontaneous depolarisation of the cell to threshold occurs due to slow inward movement of sodium. depolarisation occurs due to inward calcium current which is slower than sodium.
