L6 Flashcards
what does intrinsic control effect
HR and SV
this is preload, afterload, and contractility
what is extrinsic control
hormonal and nervous controls
why do we need to be able to regulates our hearts excitability
because of the 4 F’s
fight, flight, feeding and fucking
where do the autonomic nerves come from
the brain stem
what is the parasympathetic nerve that innovates the heart called
the vagus nerve
where do the parasympathetic nerve fibers go to in the heart
the SA and AV node
what effect do parasympathetic fibers have on the heart
they only extend to the nodes and not the mussel itself therefore it only has an effect on the rate that the heart beats
what is the sympathetic nerve called that innovates the heart
the cardiac nerve
where do the sympathetic nerve fibers extend to
therefore leading to what effect
the nodes and the mussel therefore it has an effect on the HR and the contractility
what is contractility
changing the function of the heart without changing the EDV
what phases of excitation does autonomic nerve innovation effect
phase 4 and 3
explain the effect of sympathetic stimulation on pacemaker cells
noradrenaline is released onto the pacemaker cells, this binds to the b-adrenoceptors which through intracellular signaling causes more +ive charge to come into the cell
more +ive charge is coming into the cell making the slope of phase 4 steeper (reaching threshold of LTCC (-50, -40mV) faster
therefore the spontaneous rate of the SA node depolerisation is increased
what is it called when you increase the heart rate
tachycardia
describe the intracellular signalling pathway for sympathetic stimulation in pacemaker cells
noradrenaline binds to the b1-adrenoceptor which is coupled to adenylyl cyclase. when NA binds it activates adenylyl cyclase which then generates cAMP
cAMP directly regulates the funny Na+ channels therefore an increase in cAMP increases funny Na+ current
cAMP also activates protein kinase A which phosphorylate TTCC. this causes them to become more active meaning more Ca2+ comes into the cell
PKA also increases activity of K+ channels meaning that K+ is better able to leave the cell meaning that the cell is able to repolarise faster
what is the overall effect of parasympathetic stimulation of the heart
the spontaneous rate of the SA node depolerisation decreases
what is bradycardia
when the HR decreases
describe the intracellular signalling pathway for parasympathetic stimulation
ACh binds to muscarinic receptors (M2), this inhibits adenylyl cyclase causing a fall in intracellular cAMP
this decreases the flow of Na through the funny Na channels and reduced PKA activity
less PKA = less Ca2+ through TTCC and reduced K+ current
HOWEVER the M2 receptor is coupled to a ACH sensitive K+ channel, therefore when ACH binds this channel opens causing hyperpolarisation
the overall effects of para and sympathetic stimulation are…..
sympathetic = stronger and faster
parasympathetic = slower and weaker
how come the SA node is known as the pacemaker of the heart when all of the cells are callable of generating action potentials
this is because the SA spontainiously fires at the highest rate
this means that although the other cardiac cells spontaneously fire, they never get the chance for those AP’s to be fired because they are always conducting the APs from the SA node
what what rate does the AV node spontaneously fire
40-50BPM
what what rate do the purkinje fibers spontaneously fire
20-30BPM
what are chronotropic factors
factors that affect heart rate (things that cause tachycardia and bradycardia)
what is proof that the sympathetic and parasympathetic systems are always tonically active in the heart
because the SA node fires at 110 BPM therefore if these weren’t tonically active resting heart rate would be 110BPM
factors that affect contractility are called…..
inotropic factors
