1. Goals: - How do muscles contract. Cell electrical potential (p. 373)
Goals: - How do muscles contract Cell electrical potential (p. 373) Sliding filament model (p. 284) - Apply muscular contraction to the heart - How is electrical activity propagated through the heart - Cardiovascular physics -Cardiac output -Resistance to blood flow

2. The microstructure of the myocardium allows for a coordinated heart beat
Cardiac muscle characteristics:
Small cells
Single nucleus
Branching, specialized connections between cells
Aerobic, have rich oxygen supply and store oxygen via myoglobin

3. Chapter 9! Skeletal muscle: 1 functional unit = a sarcomere
Myofilaments are surrounded by a sacroplasmic reticulum
Sarcoplasmic reticulum stores Ca+
Sarcoplasmic reticulum absorbs Ca+ from within the cell

4. An electric “potential” exists across muscle cell membranes
T tubules connect the sarcoplasmic reticulum to the outside of the cell
The sarcoplasmic reticulum stores Ca+
Electric impulses (provided by nerves) travel along muscle cell membranes and induce Ca+ release into the cell

5. Myofilaments are overlapping in a sarcomere and slide past each other during muscle contraction - dependent on Ca+ and ATP

6. The sliding filament model of muscle contraction
Calcium is required to expose actin binding sites
ATP is required to reset the myosin head

7. Chapter 18 - The microstructure of the myocardium allows for a coordinated heart beat
Cardiac muscle characteristics:
Small cells
Single nucleus
Branching, specialized connections between cells
Aerobic, have rich oxygen supply and store oxygen via myoglobin

8. The conducting system of the heart coordinates contraction
Cardiac “skeleton” between atria and ventricles prevents signal propagation from the atria to the ventricle except through the SA
The sino atrial node (SA) acts as a pace maker - cells spontaneously depolarize
The internodal pathways loop around both atria, trigger contraction in multiple places simultaneously
The stimulus is delivered to the apex of the heart, where contractions begin in the ventricles, and are passed to other locations in the ventricles
Internodal pathways converge at the atrioventricular node (AV), which conducts to the ventricles (and can also function as a pacemaker)

9. The relative timing of signal propagation along the conducting system and contraction in the atria and ventricles

10. Skeletal muscles can be over stimulated and undergo tetanus seizure…….

11. ….Long recovery (refractory) in the SA node pacemakers prevents this in the heart

12. Cardiac output (amount of blood moved by the left ventricle/minute) fluctuates to meet demand
Can increase heart rate by 250%
Can double stroke volume

13. Nervous control of heart rate
Acetylcholine slows heart rate by opening K+ channels
Norepinephrine increases heart rate by opening additional ion channels

14. Ach and NE are delivered to the heart by the nervous system

15. Normal resting heart rates
What factors could influence an individuals resting heart rate?

16. Stroke volume also contributes to cardiac output

17. Resistance to blood flow results from friction
Blood cells (and molecules) rub against vessel walls. Resistance is proportional to length of vessel
Friction results from blood rubbing against blood. Wide vessels have less resistance then thin vessels
Diameter effects resistance more than length. Diameter influence resistance by R = 1/r^4, the effect of length is directly proportional

18. Velocity of blood flow changes throughout the cardiovascular system

19. Factors influencing heart rate

20. Factors influencing stroke volume
Stroke volume + Heart rate = cardiac output

21. There is a net loss of fluid to the interstitial spaces over time