S1B4 - Cardiac Muscle Flashcards
1
Q
Describe atrial myocytes and ventricular myocytes.
A
Atrial Myocytes
- Smaller than ventricular myocytes
- Contract before ventricular myocytes to permit final pumping of blood from atria into ventricles
Ventricular Myocytes
- The myofibrils run longitudinally and contain well-organized sarcomeres which gives the muscle a “striated” appearance.
- Each muscle fiber contains a single central nucleus (in contrast to skeletal muscle which has many peripheral nuclei).
- Ventricular muscle fibers are interconnected in a branching array and joined by specialized junctions known as intercalated disks. The disks contain gap juntions (connexons) that are low resistance paths between cells, and desmosomes (macula adherens) which are structural attachments.
2
Q
Describe the mycardial connective tissue matrix.
A
- interconnects myocytes and blood vessels
- provides structural support for the heart
- prevent cardiac damage due to over-filling or during contractions.
- composed of collagen (secreted by fibroblasts) and elastin
- The connective tissue matrix is the major pathway for force transmission through the heart
- The connective tissue matrix is also responsible for the passive elasticity of the heart which determines the resting tension (i.e., diastolic pressure) in the heart
- The matrix forms the structural skeleton of the heart
- Collagen links adjacent myocytes and blood vessels and may help maintain vessel patency
- The collagen matrix prevents the heart from being overstretched and damaged due to over-filling during diastole
- It is also possible that collagen struts between myocytes and vessels may help hold vessels open during systole (contraction).
3
Q
What modulates myocardial contractility?
A
Contractility is modulated by the concentration of intracellular free Ca2+.
4
Q
What are two important proteins assossiated with the SR of cardiac myocytes? What do they do?
A
Phospholamban
- in SR membrane
- major regulator of the SR calcium pumps sequestering calcium
Calsequestrin
- within the terminal cisternae of the SR
- binds Ca2+ and further increases the capacity of the SR to concentrate and store Ca2+.
