Force generation by heart - lecture 4 Flashcards
What type of muscle is the cardiac muscle,what causes it and what is absent from it?
- Striated
- caused by regular arrangement of contractile protein
- no neuromuscular junctions in the cardiac muscle
What is the all or none law of the heart and how is this carried out?
- either electrical activity is initiated in the whole heart or none at all
- Cardiac myocytes are electrically coupled by gap junctions which forms low resistance electrical communication pathways between neighbouring myocytes and so all electrical excitation reaches all cardiac myocytes
What provides mechanical adhesion between cardiac cells and why is this important?
Desmosomes within the intercalated discs and this ensures that the tension developed by one cell is transmitted to the next
What causes muscle tension ?
Produced by sliding of actin filaments (thin) on myocine filaments (thick)
What does force generation depend on?
ATP- dependant interaction between myosin and actin filaments (without ATP- will not occur)
What is troponin?
During a relaxed stat, binding sites of myosin to actin are covered by troponin
Why is Ca++ required?
Required to bind with troponin to uncover binding site and to switch on cross bridge binding which allows contraction
What is released from the sacroplasmic reticulum ands what is it dependant on?
Ca++ - this release is dependant on presence of extra-cellular Ca++
Where is the concentration of Ca++ high when ventricular muscle relaxes?
High in sacroplamisc reticulum but low in cytoplasm
What happens to Ca++ during ventricular muscle contracts ?
Induced Ca++ release from sarcoplasmic reticulum
What is the refractory period?
A period following an action potential in which it is not possible to produce another action potential
Why is long refractory period important?
Protective for the heart by preventing generation of tetanic contractions in the cardiac muscle
What is stroke volume?
The volume of blood ejected by each ventricle per heart beat
How can Stroke volume be calculated?
SV= end diastolic volume -end systolic volume
What does intrinsic mean?
Within the heart muscle itself