Cardiac Action Potential Flashcards
specialise types of cardiac cell
contractile cells and autorhythmic cells are the two types specialised types of cardiac cell
what is pacemaker potential
autorhythmic cell membrane slow drift threshold is called pacemaker potential
how are autorhythmic cells initate action potential
autorhythmic cells cyclically initiate Action potential which then spread through the heart to trigger contraction without any nervous stimulation
the four specific site
the four specific site are Sinoatrial node , atrioventricular node , bundle of His , Purkinje fibres
SA node
SA Node is the pacemaker of the heart
AV node
AV causes a delay that allows depolarisation
Bundle of His
bundle of his transmits the impulse to the left and right bundle branches and into the ventricles
Purkinje Fibres
Purkinje fibres play role in electrical conduction and propagation of impulse to the ventricular muscle
only conducting pathway
AV node forms the only conducting pathway between the atrial muscle and Bundle of His and hence the ventricles
what is the latent power
AV node cells have well developed latent powers of rhythmicity and can take over pacemaking if impulses from the SA node fail to reach them
membrane potential
Slow depolarisation towards threshold, reaches potential action potentail in which pacemaker potential is fires causing stimulation of the contractile cells allowing heart rate
permability of the membrane channels
Increase when membrane channels open
Decrease when membrane channels close
Pacemaker potential
the two stages of pacemaker potential is specific sodium gated voltage channels and funny channels close
end of pacemaker potential action potential is initiated
Action potential in a cardiac contractile cell
transient potassium channels open and then slow I type long lasting channels open
what is refractory peroid
transient potassium channels open and then slow I type long lasting channels open
recording
No wave is recorded for SA nodal depolarisation
ECG seperate
Normal ECG no seperate wave for atrial repolarisation is visible. the electrical activity associated with atrial repoalrisation occurs simultaneously with ventricular depolarisation is masked by the QRS complex
p wave
the p wave is smaller than the QRS complex because the atria have much smaller muscle mass than the ventricles
what is cardiac output
Cardiac output is the volume of blood pumped by each ventricle per minute
CO = HR X SV
what is stroke volume
Stroke volume is the volume of blood ejected per contraction
SV = EDV - ESV
what is CO controlled
CO is controlled according to physiological requirements via control of HR and SV
strength of cardiac muscle contraction
Strength of cardiac muscle contraction by
varying the initial length of the cardiac muscle fibres which in turn depends upon EDV
Varying the extent of sympathetic stimulation
intrinsic control of SV depends on what
Intrinsic control of SV depends on the direct correlation between EDV and SV
what does intrinsic control depend on
Intrinsic control depends on the length-tension relationship of cardiac muscle, which is similar to that of skeletal muscle
increased EDV the more the heart is stretched
the more the heart is stretched the longer the initial cardiac fibre length before contraction
the increased length results in a greater force on the subsequent cardiac contraction and thus in a stroke volume
what is Frank Starling Law
the intrinsic relationship between EDV and SV is known as the Frank Starling law of the heart
summary of frank starling
Frank Starling law is the heart normally pumps out during systole the volume of blood returned to it during diastole, increased venous return results in increased stoke volume
the advantages of SV is
equalising output between the left and right sides of the heart
when a larger CO is required - during exercise venous return is increased through action of sympathetic NS. the resulting increase EDV automatically increases SV
exercise also increases HR so these two factors act together to increase CO so more blood can be delivered to the excising skeletal muscle
cellular basis of the franks starling mechanism
the frank starling mechanism
greater initial length increases the sensitivity of contractile proteins in the myofibrils to Ca2+
increased initial fibre length may also increase Ca2+ release from the SR
SV is also subject to extrinsic control by
sympathetic stimulation and adrenaline
both enchance the heart contractility
increase contraciltiy is due to
This increased contractility is due to increased Ca2+ entrytriggered by NorAd/Ad
plateau phase
Increase in inward Ca2+ flux during the plateau phase of the action potential enhances the intracellular calcium store
what is required excitation contraction coupling
Ca2+ is required for excitation-contraction coupling in cardiac muscle cells
increase the rate of relaxation of cardiac muscle cells by
increase the rate of relaxation of cardiac muscle cells by stimulating Ca2+ pumps take up Ca2+ from cytoplasm more rapidly - shortening systole
frank starling curve to the left
Shift of the frank starling curve to the left by sympathetic stimulation - increase in stroke volume at same end diastolic volume
what is after load
The arterial blood pressure is called the afterload because it is theworkload imposed on the heart after the contraction has begun
increase in afterload
The heart may be able to compensate for a sustained increase in afterload by enlarging (hypertrophy)
measurement of myocardial
the simplest measurements of myocardial contractility use analyses of the pressure waveform during the isometric contraction phase
strength of cardiac muscle contraction SV
varying the initial length of the cardiac muscle fibres which in turn depends upon EDV
Varying the extent of sympathetic stimulation
what are the arteries
arteries have low resistance conducting blood to the various organs with little loss in pressure
acts as pressure reservoirs for maintaining blood flow between ventricular contraction
what is artrioles
arterioles are major sites of resistance of blood flow
responsible for the pattern of blood flow distribution
participate in the regulation of arterial blood pressure
what is capillaries
capillaries - site of exchange between blood and tissue
what is veins
Veins are low resistance vessels for blood to flow back to the heart , their capacity for blood is adjusted to facilitate flow
vascualr system and flow
the vascular system blood is always from a region of higher pressure to one of lower pressure
the pressure exerted by a fluid is often termed the hydrostatic pressure
flow rate
the pressure difference between two points and also the resistance to flow is flow rate
what is resistance
resistance a measure of how difficult it is for blood to flow between two points at any given pressure difference
a measure of the friction impeding flow
what is blood flow
Blood Flow through vessels depends upon the pressure gradient and vascular resistance
driving force is the pressure generated by contraction of the heart
Flow = Pressure gradient/resistance of blood vessels
what is parabolic distribution
parabolic distribution of the speeds of flow across a circular tube shows how flow through arteries work
resistance to blood flow depends upon 3 factors
viscosity of the blood (n)
vessel length (L)
vessel radius (r) - major role
Calculation for flow rate
Flow Rate = pi ^ Pr4 / 8 n L
Posuille’s law
A two fold change in radius will produce a 16 fold change in flow
a slight change in radius brings about a notable change in flow
what happens to arterial pressure
arterial pressure fluctuates in relation to ventricular systole and diastole
what do the arteriolar walls include
Arteriolar walls include a thick layer of smoothmuscle that is richly innervated by nerves of thesympathetic nervous system
what is smooth muscle is sensitive
This smooth muscle is also sensitive to many local chemical changes and certain circulating hormones
smooth muscle runs circularly around the arteriole
contraction = decreased radius , increase resistance, decrease local blood flow = vasoconstriction
Relaxation = increased radius, decrease resistance = increased local blood flow = vasodilation
What is vascualr tone
vascular tone is the arteriolar smooth muscle displays a state of partial constriction
what are the two factors responsible for vascular tone
two factor are responsible for vascular tone is myogenic and sympathetic activity
what happens if there is any change in contractility of arteriolar smooth muscle
Any change in contractility of arteriolar smooth muscle will substantially change resistance to flow in these vessels
