KEROCHI
Forum Guru
Topics: 60
Posts: 971
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The conduction of electrical impulses of His-purkinje system & SA node is based on its:
a. speed
b.velocity
c. arterial supply
d. energy
e.electrical charge
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| mildus
Forum Guru
Topics: 19
Posts: 614
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I haven't well understood the sense of the question.
What I know is which part will be a cardiac pacemaker depends on:
1. value of resting membrane potential
2. speed of spontaneous diastolic depolarisation
So, SA node is a pacemaker because it has the smallest value of resting membrane potential and the fastest spontaneous diastolic depolarization.
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| KEROCHI
Forum Guru
Topics: 60
Posts: 971
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sorry, didn't mean to ..
Answer given here was velocity.
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| KEROCHI
Forum Guru
Topics: 60
Posts: 971
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2 electrophysiological cat. of cardiac cells:
Fast fibers: atrial & ventricular muscle cells, Purkinje cells of the His-Purkinje system
Slow Fibers: SA node, AV node
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| Flying h4x0r
Forum Junior
Topics: 4
Posts: 51
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Slow fibers lack Na++ channels, which means the action potential is propogated by the slow Ca++ channels.
They also have smaller fiber diameter, which means that the action potential is slowed down.
....i don't understand how bigger fibers have faster conduction times, it seems counterintuitive, because smaller fibers have less surface area, which would make it seem like they can conduct faster....
what am i missing here?
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| twinkle
Forum Senior
Topics: 5
Posts: 44
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CONDUCTION VELOCITY is proportional to the size of inward current during the upstroke of the action potential....which means the larger the inward current ,the higher the conduction velocity.
Since pacemaker tissues lack fast Na+ channels, the inward current is much smaller in them resulting in lower conduction velocity.
Clinical Importance: Slow conduction thru AVN allows time for ventricular filling b4 ventricular contraction.( if conduction gets faster somehow....ventricular filling ud be compromised )
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| Flying h4x0r
Forum Junior
Topics: 4
Posts: 51
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i see
but my question is: is there any relationship to the diameter of the fibers?
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| twinkle
Forum Senior
Topics: 5
Posts: 44
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 i dont remember reading it anywhere....relationship with the diameter  ...cud it be..bigger fibers have bigger surface area...so fast Na+ channels produce bigger inward current???   ...KEROCHI pls correct me
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| mesh
Forum Guru
Topics: 77
Posts: 401
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conduction velocity increases with fibre size,because of decreased internal resistance.
resistance is inversely related to the radius of the fibre...
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