EEOB 2520 Lecture Notes - Lecture 32: Interventricular Septum, Atrioventricular Node, Purkinje Fibers
29 Apr 2016
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Heart Contraction Pattern figure 12-10
Need an action potential to get the heart to contract
• The signal we need for the myocardium cells to move = an AP = gets the contraction
started → ALWAYS!
• The pattern of contraction = movement of AP through your heart tissue → in a very
specific pattern
• First you need an initial AP to get everything started → happens as a result of your
nervous system impacting your heart
Central Nervous system AP → sinoatrial (SA) node (little yellow spot at top of
right atrium)
• Baseline heart rate = 70 bpm
• The bpm will be at 70 when at the SA node
• We know the neighboring atrial cells are connected by intercalated discs → which
include gap junctions → causes a domino effect of having our cells pass AP from one
to another
• The ones closest contract first, the ones furthest contract as the AP gets to them
• The AP transmitted through the gap junctions to the neighboring cells until all
atrial cells have gotten the AP and are doing their contraction
Atria’s ells
1. Contract
• “A odes effet surroudig atria ells ia doio effet AP’s, losest otrat first
2. Transmit AP via gap junctions
• Keep sending down the AP until all cells receive the AP and begin to contract
3. Atrioventricular (AV) node depolarizes
• Atrial tissue does not touch ventricular tissue because of the non-polar, lipid
boundary in between the atria and ventricle
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o Does’t allo APs to trael etee these to areas atria ad etrile due
to the big block
• The
• e AP can only continue to another node
• A node that is between our atria and our ventricles = AV node (atrioventricular
node)
o This is the only spot where we can continue to have the downward
movement of the AP into the ventricles
• There is no atrium cell that passes a message to a ventricular cell, must use the AV
node to pass the AP between the two
• The AV passes the AP along the Bundle of His
4. Bundle of His
• AP goes from AV node to here
• It is like an insulated wires → carry AP along its link down to the interventricular
septum but won’t pass it to ventriular tissue
• We do’t go straight to the etriular tissue eause e do’t at to otrat yet
• Bundle of His will move the AP to the bottom of the heart without seeing any
contraction in the interventricular septum
• Nothing is getting contracted right now
• They are taking the AP (this wire is running to) → Purkinje Fibers
5. Transfers the AP to additional, smaller wires, called the Purkinje Fibers
• The Purkinje fibers do interact with the ventricular tissue (unlike the Bundle of His)
→ we start seeing contraction happening
• → Depolarize ventricular cells
o They release the action potential so that we start seeing the action potential
happening in ventricular tissues
o We see movement of blood in the direction that we squeeze
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▪ We want blood in the atria to go through the cuspid valve into the
ventricles
o It is a top to bottom flow → we want the blood flow to be in this direction
from atria to ventricle
▪ e need to get the ventricles to contract from bottom to top →gets
us to squeeze from bottom to top, so then we get the blood to the
aorta and pulmonary artery, which is at the top gets us to squeeze
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Document Summary
We want heart to squeeze because that contraction causes pressure gradient blood goes to area of lower pressure. Blood pressure = contraction of space (pv=nrt: blood pressure = the pressure of blood going through the vessels, at an instant (cid:449)e are(cid:374)"t (cid:272)ha(cid:374)gi(cid:374)g a(cid:373)ou(cid:374)t of (cid:271)lood i(cid:374) there (cid:894)(cid:374)(cid:895), te(cid:373)perature (cid:894)t(cid:895)- In terms of heart we squeeze down volume = increase pressure = gets our blood to flow the way we want it to. Contraction is faster: what we care about is the blood moving, what we get out of this cycle is the stroke volume. Heart rate (hr) = cycles/min how many times do we put stroke volume out in a given time frame. Increase sv = increase co: the heart is not moving 4. 9 l/min at any given squeeze it"s (cid:271)e(cid:272)ause it is doing it so many times repeatedly, so we get a lot of blood.
