Heart

• The conducting system of the heart

  1.Pacemaker/SAN contains auto rhythmic cells/is where the heart beat originates/is found in the wall of right atrium.

  2. Impulse/wave of excitation spreads across the atria/cause the atria to contract/cause atrial systole.

  3. (Impulses) reach/stimulate the atrioventricular node/ AVN.

  4. AVN located in centre of heart

  5. Impulses from AVN travel down fibres in the central wall of the heart and then up through the walls of the ventricles

  6. (Causing) contraction of ventricles/ventricular systole.

  7. This is followed by diastolic phase/diastole.
• Nervous control of the cardiac cycle

  1.Medulla regulates the rate of the sino-atrial node (SAN)

  2. Through the antagonistic action of the autonomic nervous system (ANS)

  3. Sympathetic nerve increases the heart rate.

  4. Sympathetic nerve releases noradrenaline/norepinephrine.

  5. Parasympathetic nerve slows down the heart rate.

  6. Parasympathetic nerve releases acetylcholine.