Muscle: cardiac muscle

Question 1

ventricular cardiac action potentials

Answer 1

• rapid polarisation due to fast voltage gates Na channel
• plateau due to slow voltage gates Ca channel
• repolarisation from closing of Ca channels and opening of K channels

Question 2

intercalated disc

Answer 2

desmosomes to prevent separation during contraction
gap junctions to allow action potentials to be carried from one cell to next
coordinated contraction of all myoctes

Question 3

Regulation of cardiac output (CO = SV x HR)

Answer 3

Heart rate: set by pacemaker cells in sinoatrial note. Modifiable - autonomic nerves releases neurotransmitters
Stroke volume: tension developed by cardiac muscle fibres in one contraction (volume of blood with each beat)
- increased by heart rate
- ventricle stretch
- neurotransmitters like noradrenaline

Question 4

automaticity

Answer 4

increasing heart rate increases contractile force (stroke volume)

Question 5

neural control of stroke volume

Answer 5

noradrenaline acting on beta receptors via second messengers leads to calcium channels opening and more calcium enters cell = bigger/shorter contraction. also SR Ca pumps active so removes calcium faster