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Communication and homeostasis

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Question 33

A physiological study investigated the nervous regulation of heart rate in a mammal. Under normal conditions, the resting heart rate is 75 bpm75\text{ bpm}75 bpm. The following experimental observations were recorded:

  • When the parasympathetic cardiac (vagus) nerve is severed, the resting heart rate increases to 115 bpm115\text{ bpm}115 bpm.
  • When the sympathetic cardiac nerves are severed, the resting heart rate decreases to 65 bpm65\text{ bpm}65 bpm.
a.

Suggest two conclusions about the nervous control of resting heart rate in this mammal that can be drawn from these observations. Use quantitative evidence from the data to support your conclusions.

[4]
b.

Identify:

  1. The specific structure in the heart wall (the pacemaker) where these autonomic nerves terminate to modulate heart rate.
  2. The neurotransmitter released by the postganglionic parasympathetic nerve terminals at this site.
[2]

Communication and homeostasis Questions

  1. A Level
  2. /Biology
  3. /Communication and homeostasis