Transcript control of Heart beat

The Heart
Control of the Heart Beat
The Heart Beat
 The heart is made up of cardiac muscle.
 Cardiac muscle is myogenic, which
means it naturally contracts and
relaxes.
 Therefore, it receives no impulse from a
nerve to make it contract.
The Heart Beat
 The cardiac cycle is initiated by a small
patch of muscle called the Sinoatrial
node (SAN) or pacemaker.
 This node sets the rhythm for all the
other cardiac muscle.
 Pacemaker cells have an inbuilt rhythm
that is faster than the other cells in the
heart.
The Heart Beat
 The SA node sends out an excitation
wave of electrical activity over the atrial
walls.
 The cardiac muscle responds to this
wave by contracting at the same speed
as the SAN.
 This results in both atria contracting
simultaneously.
The Heart Beat
 There is a delay between atrial contraction
and ventricular contraction.
 Fibres between the two chambers that do not
conduct the excitation phase cause this delay.
 Therefore, the wave is conducted through a
patch of fibres in the septum known as the
atrio-ventricular node or AVN.
The Heart Beat
 After about a delay of 0.1 seconds the
AV node passes the wave onto another
set of conducting fibres that run down
the centre of the septum between the
ventricles called the Purkyne fibres.
The Heart Beat
 The wave is then transmitted (very
rapidly) down to the bottom of the
septum, where it spreads through the
ventricles’ walls in an upward direction.
 This movement causes the muscle to
contract and the ventricles squeeze the
blood out of the heart.
The Heart Beat
 Fibrillation is the result of the
contractions of the atria and ventricles
becoming erratic and out of sync.
 Using electric shock treatment to restart
the SA node can rectify the problem.
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