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

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

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

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

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

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

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

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)

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

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

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

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

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

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

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

Stroke volume also contributes to cardiac output

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

Velocity of blood flow changes throughout the cardiovascular system

Factors influencing heart rate

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

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