Electrical function

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ectopic-- out of place

electrical transmission

intercalated discs- enable communication of action potentials between cells

--movement of ions

functional syncytium-- cells act as one

heart nerves modulate heart activity DONT cause heart beat

myocytes stable at resting potential

nodes generate action potential of them selves

SAN depolarises more quickly than AVN -- overrides it

AVN much slower but can take over if damage to SAN

SAN wall of RA

acton potential cell to cell across atria then collects at AVN

prevented from ventricles by annulus fibrosis

passing through AVN slowed action potential

gap between ventricle contracting --why?

purkinje fibres-- L and R branch

- LV and RV contract as one

-anterior and posterior fascicle of L branch -- ensures contraction simultaneous STREAM

Innervation

--STREAM

-sympathetic inc heart rate, contractility, faster conduction, maximise diastole

-para does opposite

Action potential

-Heart must contract then relax-- not prolonged contraction

--graphs

--contraction occurs during and just after plateau phase

- not possible for another action potential during plateau phase

-- ensure ventricle fill will blood between beats

Cations-- positive

-more K inside cell than out

-More Ca and Na in

-STREAM

-Ca channels slow-- longer to open

-Na in

-K stopped from exiting

---Graphs STREAM

-sodium channels won't reopen before cell repolarised --refractory period

--prevents action potential on potental

-NO tetany or summation

Atrial cells beat faster than ventricular cells

-repolarise quicker

-Ap in atria shorter Slide 13

Pacemaker cells

Graph

-no resting potential

-constantly falling and rising

STREAM

-Na channels open then close

-Ca channels open then close

-slower upstroke Ca comping in

Two Pacemakers

-AVN narrower diamete , slower conduction , longer refractory period

EC coupling

-actin and myosin

-CA bind to troponin exposing binding site

- Ca from SR and EXTRACELLULAR

- ATP binds to myosin, hydrolyses causing power stroke

-once Ca channels closed-- Ca moved to SR or Extracellular

Electrolyte disturbance - in ECF

-Inc K - reduces gradient

-- slower repolarisation

---slower heart rate

-Cats that can't pee

-dec Na - slows depolarisation

--slower heart rate

--often seen with high K

-dec Ca - slower depolarisation?

-shorter plateau period?

-dec contractibility