• Heart:– Length-tension relationships– Starling’s law of the heart– reflex control of heart contraction

• Smooth muscle– Anatomy– Contraction mechanism– Contraction regulation

Length-tension relationships

• There is an optimal sarcomere length for generating a maximal force during contraction.

• As blood enters the ventricle, it expands and the sarcomere length increases

• The stroke volume increases when the force of contraction increases

Starling’s law of the heart

• The relationship between stretch and force in the intact heart.

• The force of contraction (stroke volume) is proportional to the end-diastolic volume.

• Within physiological limits, the heart pumps all the blood that returns to it.

Starling’s Law of the Heart

Understand:

• Integration of factors that regulate heart activity

Smooth muscle

• Blood vessels, G-I tract, urinary tract, reproductive tract,iris, etc.

• Slow, sustained contraction

• No sarcomeres

• Yes, contractile filaments

Example of smooth muscle

• Sphinctors

• Smooth muscle is tonically contracted

• Sphinctor relaxes when material leaves a hollow organ (eg. Esophagus stomach)

Smooth muscle cells

• Single nucleus

• Actin and myosin are located diagonally around periphery and single nucleus

Proteins associated with actin

• Actin

• Tropomyosin

• Actin filaments attach to dense bodies of protein

• Actin filaments terminate in protein plaques of cell membrane

Myosin

• Myosin thick filaments located between actin filaments

• Myosin heads line thick filament surface

• Slow ATPase activity

• Myosin light chain kinase phosphorylates myosin head (activates ATPase, stimulating cross-bridge cycling)

CaM is calmodulin

MLCK is myosin light chain kinase

Sometimes,dephosphorylatedmyosin remains attached to actinlatch state, contractionis maintainedMaintain contraction without ATP.

Source of calcium

• Pacemaker potentials

• Depolarization through Ca++ entry

• In single unit smooth muscle, gap junctions spread Ca++

• Ca++ induced Ca++ release

• Myogenic contraction