P: Cardiac muscle Flashcards
How does the AP spread from the SA node
The sinoatrial node is capable of its own spontaneous depolarisations, which causes APs
It spreads through coupled cells, gap junctions through the atria and via the atrio ventricular node to the ventricles
Describe contraction + relaxation of cardiac muscle
Voltage-gated Ca channel (DHPR receptor) facilitates calcium entry from ECF –> induces calcium release from SR
During relaxation, SERCA takes up calcium in SR, but calcium must also be extruded to ECF via:
- Na/Ca transporter (3 Na+ in, 1 Ca2+ out)
- ATP (pumps out Ca)
How is force of contraction in cardiac muscle increased
An increase in intracellular Ca2+
Increased stretch on CM as an intrinsic mechanism for increasing force of contraction
What is isoproterenol
A β-agonist which increases the intracellular calcium transient which in turn increases the force of contraction
Effect of SNS on heart
Release of adrenaline/noradrenaline
Binds to receptors on the cell membrane
Increase in cAMP levels –> increases PKA
Leads to phosphorylation of several proteins in the muscle cell e.g. voltage-gated Ca channel + SR phospholamban
This means more Ca2+ released from SR so more actin-myosin cross-bridges –> greater force of contraction
Ultimately during SNS stimulation, time for diastole and systole decreases
Intrinsic mechanism to increase contraction
Increased stretch:
By effect of titin to increasing no. of actin/myosin interactions And by increased sensitivity to any available Ca2
What is titin?
Because titin is attached to both myosin and actin, stretching of titin brings them closer together, increasing the chances of contact between both filaments. Anchors actin to Z discs
