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F. of Physiology and Anatomy Cardiovascular System £2.99   Add to cart

Lecture notes

F. of Physiology and Anatomy Cardiovascular System

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Includes detailed notes on: Lecture 8: Electrical and mechanical events of the cardiac cycle - (Prof Mike Shattock) Lecture 9: Control of Cardiac output - (Prof Mike Shattock) Lecture 10: Structure and function of blood vessels/control of blood pressure - (Dr Greg Knock) Lecture 11: Regional ...

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  • June 1, 2021
  • 14
  • 2020/2021
  • Lecture notes
  • Dr. greg knock
  • All classes
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joharyantra
FUNDAMENTALS
OF PHYSIOLOGY
AND ANATOMY
4BBY1060




Cardiovascular
Physiology & Anatomy

, LECTURE 8:

The cardiac pacemaker
All cardiac pacemaker tissues have
intrinsic activity, Therefore contracts
without external stimuli. If a pacemaker
fails to shoot an action potential, the
following node will take over. (from fastest
beating to slowest beating)
 There primary pacemaker of the
heart is the SA node (sinoatrial).
(Top right)
 Then it spreads down to
atrioventricular node (AV node).
 Moved down towards the Bundle of
Hiss, that then branches through the septum
 Then branches out towards Purkinje fibers
The cardiac pacemaker also has a slow diastolic depolarization (funny current),
from –70mV to –40mV when the action potential fires.
 The steeper the rate of the funny current the faster the depolarization and
therefore the faster the heart rate.
o May be modified by:
 Sympathetic stimulation (faster bpm), steeper gradient,
tachycardia
 Parasympathetic stimulation (slower bpm), more gentle,
brachycardia
The ∑ of stimulations (in proportions) , tachycardia + brachycardia = bpm
 Until 90bpm – vagus tone is in charge
 To raise < 90bpm – you must activate the sympathetic tone


Spread of excitation
Conduction from SA to AV is slow, as there is no specialized path from one to the
other. Once there is a is a delay, known as the ‘AV pause’. This stops high rates
of excitation being conducted to the ventricles.
 This serves to fill the ventricles, and conditions where the AV pause does
not occur are known as atrial fibrillation – could become lethal arrythmia


ECG – electrocardiogram explained
By using electrodes at each side of the heart we can measure an electrical
dipole. Must be thought in a 3D context as the electrical impulse moves down
the apex and then around the back of the heart.
 Wave of positiveness – delay – wave of
negativeness
o + wave is upstroke of the action potential
spreading down towards apex of heart
o – wave is due to the repolarization
 Must be set in Einthoven's Triangle

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