Question

The heart rate is increased by:

• A. an increase in the level of adrenaline in circulation
• B. an increase in the activity of the sympathetic nerves that supply the heart
• C. a decrease in the activity of the parasympathetic system
• D. all of the above

Answer 1

The correct option is D all of the above

• Normal heart rate is about 60-90 beats per minute. It depends on the balanced activity between the sympathetic and parasympa­thetic nerve influence that are acting on it.
  
• Heart rate can be increased because of either an increased activity of sympathetic nerve fibers or a decreased activity of parasympathetic nerve fibers and vice versa for a decrease in heart rate.
  
• Adrenaline and noradrenaline released from adrenal glands stimulate the adrenergic receptors and SA node increasing the heart rate.
  

So, the correct option is 'All of the above'.