CARDIAC MUSCLE

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SAN NODE - RMP = -55 MV ; less negative because cell mebranes of this special region is leaky to sodium and calcium ions which keep on entering the cell therby decreasing negativiity.

inherent leakiness of cell towards na and ca causes their excitation

slow action potential in cardiac muscle 0-

CONDUCTION IN AVNODE - 0.05 mt /sec

av node delay - refers to delay in conduction transfer to av node and the conduction of impulse from the av n to ventricular mass obviosuly due to larger size of ventricles.

significance of avn - emptying of blood into ventricle ; AV NODE CELLS HAVE LONG REFRACTORY PERIOD -LIMITING IMPULSES UPTO 180 BEATS /MIN;

YPU CAN REALY APRREACIATE THAT CARDIAC MUUSCLE FIBERS TAKE ABOUT 200-300MS OF AP.. WHEREAS OTHERS TAKE FEWS ECONDS

Significance of this point it ensures that

decreased potassium permeability in turn causes plateuing of the graph as a result of which the muscle fibre doesnt drop suddenly to its rmp .. this in turn is responsible for longer ap in cardiac muscle ... this is in turn responsible for as to why cardiac muscle cannot be tetanised...

see the moment ca2= enters , contraction occurs (ca induced ca release) becuase of which that graph given in guytne in pg 172 is given .. therfore it cant be tetanised

SAN - 60-100 BEATS/MIN; AV NODE- 40-60 ; PURKINJE FIBRES- 15-40 BEATS/MINUTES

HOW DOES SYMPATHETIC INCREASE/DEC HEART RATE- ? BY ALTERING PREPOTENTIAL ...

HEART RATE - ALTERED BY PREPOTETNIAL WHIHC IN TURN MAY BE AFFECTED BY - ACHE /EPINEPHRINE/TEMP/IONS /CA /NA

calcium rigor - too much of calcium in ecf - too uch of heart contractility - this decreases time for diastole - less cbf - keads to less cbf- heart arrested in systole..

all energy provided by fats

SUMMATION = ADDING OF CONTRACTION

Increases frequency of contraction / multible fibre stimulation

FREQUENCY SUMMATION AND TETANUS - as the frequency of impulse is increasing , new contraction occurs before the preivous one ; as a result the first contraction is added to the first and so on ... when frequency becomes unimaginably high all these muscular contractions fuse with one another to form a straight line -whole muscle appears to be in the fully contracted state- teetannisation i incomplete tetanisation and completet tetanus (straight saturated line )

TREPPE - not the same as summation ; at the end of relaxation immediately another imulse is given ; each subsequent action / response is stronger than the previous one due to more amount of ca ions present in icf.. can occur in cardiac

incomplete tetanus vs staircse effect

staircase effect vs treppe

extrasystole - caused due to stimulation of ventricel with an impulse stronger than normal during rrp....

EXPLANATION OF SAN GRAPH

SAN NODAL TISSUES are leaky to both sodium and calcium -accounts for pacemaker potential ; phase 4

na influx doesnt matter because the na gated channels are in inactivated state - this can be understood from the fact that - membran potential is less negative than -50 mv for more than a few seconds - as a result of which they get closed automatically .

hyperpolarisation - potassium channels open for prolonged time ; doesnt proceed indefinetly as potassium channels close when ap is over

na and ca channels automatically close after 100 seconds post openign

explanation of ventricular muscle graph

fast sodium gated channels open up

na - ca channels

decreased permeability of heart muscle towards potassium which occurs in the begining of action potential due to sudden influx of ca

when influx of na and ca decreases after designated time ; k permeabiltiy automatically increases