6.1.3 Control of heart rate

Question 1

how does the cardiac conduction system work

Answer 1

• SAN spontaneously depolarises, producing wave of excitation across atria, causing atrial contraction
• Non-conductive tissue in atrio-ventricular septum prevents wave of excitation passing directly to ventricles
• AVN causes pause in conduction, allowing time for atria to empty
• Wave of excitation passes from AVN down bundle of His and out into purkinje fibres
• Causing contraction of ventricles from apex upwards

Question 2

what is involved in the ANS

Answer 2

sympathetic and parasympathetic nervous systems

Question 3

what does the sympathetic nervous system do

Answer 3

increases bodily activity e.g. heart rate, fight or flight

Question 4

what does the parasympathetic nervous system do

Answer 4

reduces bodily activity e.g. heart rate, breathing rate

Question 5

what controls the heart rate

Answer 5

medulla oblongata

Question 6

how does the medulla oblongata increase heart rate

Answer 6

increase action potentials along the accelerator nerve which increases the rate of SAN depolarisation

Question 7

how does the medulla oblongata decrease heart rate

Answer 7

increases action potentials along vagus nerve causes decreased rate of SAN depolarisation

Question 8

where are chemoreceptors found

Answer 8

walls of aorta and carotid arteries (sensitive to changes in pH)

Question 9

what do chemoreceptors detect

Answer 9

decreased pH (caused by lactic acid and CO2)

Question 10

how do chemoreceptors work during exercise

Answer 10

• Fall in pH, due to increased CO2 concentration
• Increase in action potentials along sensory neuron to medulla oblongata
• Increase in action potential along accelerator nerve
• Increased cardiac output and excretion of CO2
  As pH increases, the frequency of action potentials along sensory neuron decreases

Question 11

what do baroreceptors detect

Answer 11

changes in blood pressure

Question 12

where are baroreceptors found

Answer 12

walls of aorta and carotid artery

Question 13

what do baroreceptors do if pressure increases

Answer 13

increase in action potentials to decelerator region of medulla oblongata - results in more parasympathetic activity, decreased heart rate and cardiac output

Question 14

what do baroreceptors do if pressure decreases

Answer 14

increase in action potentials to accelerator region of medulla oblongata - results in more sympathetic activity, increased heart rate and cardiac output