What does it mean if cardiac muscles are myogenic?
It can contract and relax without receiving electrical impulses from nerves
What is the sino-atrial node? (SAN)
The hearts natural pacemaker
Sends our regular waves of electrical activity to make the heart beat
The rate at which the SAN fires is controlled by the brain (medulla oblongata)
What is the atrio-ventricular nose? (AVN)
After a delay, the AVN conveys a wave of electrical excitation to the ventricles
What is the bundle of His?
Conducts the wave through the septum to the apex of ventricles
How does the body initiate a heart beat?
SAN sends our regular waves of electrical activity to atrial walls
Causes the right and left atria to contract at the same time
Reaches AVN where a delay occurs to allow for the atria to empty before ventricles contract
AVN sends the wave of electrical activity down the Bundle of His to purkinje fibres
Causes the right and left ventricles to contract simultaneously up the apex
Where and what is the role of chemoreceptors?
Wall of carotid arteries
Sensitive to changes in pH (o2 levels)
Where and what is the role of baroreceptors?
Wall of carotid arteries and aorta
Sensitive to changes in blood pressure
What is normal blood pressure?
120
——
80
Describe what happens when blood pressure is too high
Baroreceptors detect rise in bp and transmits impulses to the medulla oblongata
Medulla oblongata sends a signal to decrease the heart rate (via the parasympathetic nervous system)
Acetylcholine is secreted and binds to receptors on the SAN
Causes less frequent impulses so decreased stimulation of AVN
Describe what happens when blood pressure is too low
Baroreceptors detect low bp and transmits impulses to the medulla oblongata
Medulla oblongata sends a signal to increase heart rate (via the sympathetic nervous system)
Noradrenaline is secreted and binds to receptors on the SAN
Causes more frequent impulses so increased stimulation of AVN
