Heart

Question 1

Cardiac muscle?

Answer 1

• Myogenic - it contracts on its own accord, but rate of contraction is controlled by wave of electrical activity (nervous system)

Question 2

Sinoatrial node (SAN)?

Answer 2

• located in right atrium
• known as the pacemaker

Question 3

Atrioventricular node (AVN)?

Answer 3

• located between right atrium and left ventricle within atria still

Question 4

What tissues run down the septum?

Answer 4

Bundle of His

Question 5

What fibres are in the walls of the ventricles?

Answer 5

Purkyne fibres

Question 6

Control of heart rate?

Answer 6

• SAN releases wave of depolarisation across the two atria, causing it to contract
• AVN releases another wave of depolarisation when first wave reaches it. Non-conductive layer between atria and ventricles prevents wave of depolarisation travelling down to ventricles
• instead, bundle of His conducts the wave of depolarisation down the septum and the purkyne fibres
• as a result, apex and walls of ventricles contract - short delay before this happens whilst AVN transfers second wave of depolarisation - allows enough time for atria to pump all blood into ventricles
• finally, the cells depolarise, and the cardiac muscle relaxes

Question 7

Medulla Oblongata?

Answer 7

• in brain
• controls heart rate via the autonomic nervous system
  Two parts:
• a centre linked to SAN to increase heart rate via sympathetic nervous system - releases wave of depolarisation more frequently
• another that decreases heart rate via parasympathetic nervous system - release waves of depolarisation less frequently

Question 8

Homeostatic control of heart rate?

Answer 8

• heart rate changes in response to pH and blood pressure - stimuli detected by chemoreceptors and pressure receptors