Summary 02 10663 Control of Heart Rate Review

Cardiac output (CO) - total volume of blood ejected by the heart in one minute
CO = heart rate (HR) x stroke volume (SV)
CO = HR x (EDV – ESV)
- EDV – end diastolic volume
- ESV – end systolic volume
- SV = EDV – ESV

Control of heart rate
- Cardiac muscle cells depolarise & contract rhythmically without nerves – myogenic
rhythmicity or autorhythmicity
- Specialised cells in the heart spontaneously produce electrical activity, this electrical
activity originates in the Sino-atrial (SA) node
o SAN is in the wall of the right atrium, near the entrance of the superior vena
cava, made up of around 1000 cells
o SAN – pacemaker, as it dictates the rate of which the heart beats
- Electrical activity is conducted throughout the heart in a highly coordinated way to
ensure the events of the cardiac cycle occur in order




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Autonomic control of the CVS
- Resting heart rate and changes in heart rate are primarily controlled by the ANS
- Autonomic control of heart and blood vessels

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- There is both parasympathetic and sympathetic innervation of the heart and they
work antagonistically
- The parasympathetic nerve, the Vagus, leaves the brainstem and travels to the SA
node – it alters heart rate
- The Vagus also innervates the atrioventricular node and some innervation of
ventricles
- Sympathetic fibres travel from the brainstem down in the spinal cord
- the short sympathetic preganglionic neurons leave the spinal cord and synapse in a
chain of ganglia running down the spinal cord
- the long post ganglionic sympathetic neurones innervate the SA node, AV node and
the ventricles
SA node
- Increased sympathetic activity increases hr
- Blue line shows there is a steady depolarisation that takes the membrane potential
up to threshold
- The ANS alters the slope of this depolarisation and  the time it takes for the cell to
reach threshold