Force generation Flashcards
What are the striations in the cardiac muscle caused by?
Regular arrangement of contractile proteins- the alternating of action and myosin.
What are gap junctions?
Protein channels that form low electrical communication pathways between neighbouring monocytes.
What do the intercalated discs contain?
Desmosomes
What do the desmosomes do?
Provide mechanical adhesion between neighbouring cells and spread tension from one cell to the next.
What do muscle fibres contain?
Myofibrils
What are myofibrils?
Contractile unit of the heart
What protein filaments are contained in myofibrils?
Actin (thin and light)
Myosin (dark and thick)
What are myosin and actin arranged in?
Sarcomeres
What is a sarcomere?
Functional unit of the heart
What causes muscle tension?
The sliding of action and myosin
What is force generation dependent on?
ATP interaction between actin and myosin.
What must be present before interaction?
Calcium.
What does calcium do to allow myosin to bind to actin?
Bonds to troponin which causes the troponin tropomysin complex to slide away exposing the myosin binding site on the actin.
Where is calcium stored?
In the lateral sacs of the sacroplasmic reticulum.
What is required for calcium to be released from the lateral sacs?
Extra cellular calcium.
In the plateau phase how does calcium enter the cardiac muscle cell?
Through l type Ca channels.
What is intrinsic mechanisms?
Within the heart muscle itself
What are extrinsic mechanisms?
Nervous and hormonal control
What is the refectory period?
The period following an action potential in which it is not possible to produce another action potential.
What is the importance of the refractory period?
It is protective of the heart, preventing the generation of tetanic contractions in the cardiac muscle.
What is the stroke volume?
The volume of blood ejected by each ventricle per heart beat.
How is the SV regulates?
By intrinsic and extrinsic mechanisms.
How are changes in the SV brought about?
By changes in the diastolic length of the myocardial fibres. The more the heart is stretched the greater the SV.
What does the end diastolic volume determine?
The cardiac preload and it’s determined by the venous return to the heart.
