cardiac muscle

hydrostatic pressure

pressure of non-moving fluid- equal in all directions (ICF)

hydraulic pressure

pressure of moving fluid
driving pressure: forward moving, push to area of low pressure
lateral pressure: sideways pressure on vessel

pressure gradient

bigger gradient= faster flow

resistance from friction

low resistance=faster flow; depends on diameter, length, viscosity

what determines mean arterial pressure

cardiac output x peripheral resistance
cardiac output determined by stroke volume and heart rate; peripheral resistance determined by length, diameter, viscosity

myocardial contractile cells

membrane only have voltage gated ion channels; many sarcomeres (striated), contractions change size of valves to produce pressure

connected by intercalated discs
-desmosomes: connected to transfer force
-gap junctions: electrical synapse, allow flow of Ca2+
need lots of mitochondria for sustained ATP production and no fatigue → less sarcoplasmic reticulum → need more Ca2+ from ECF → large branched t-tubles for more contact to ensure easy Ca2+ entrance

why does the action potential last as long as the contraction

to prevent mechanical summation *cannot have tetnus in the heart

how can cardiac twitches be graded

by tonic sympathetic control; more Ca2+ entry = more Ca2+ release and stronger contraction, more blood volume increases stretch increasing force generated when contracted