Answer :
Final answer:
The neurons directly responsible for the increase in heart rate in response to fear are the preganglionic sympathetic fibers, also known as cardiac accelerator nerves. These neurons initiate a signal in the brain's cardiovascular center, leading to the release of norepinephrine. The norepinephrine then binds to the heart's adrenergic receptors, causing the heart rate to increase.
Explanation:
The type of neurons directly responsible for increasing heart rate in response to stress or fear, such as a trapeze artist falling, are the sympathetic neurons. More specifically, these are the preganglionic sympathetic fibers or cardiac accelerator nerves.
When the fear response is triggered in such a situation, these neurons initiate a signal in the cardiovascular center in the medulla oblongata of the brain. This signal leads to the release of the neurotransmitter norepinephrine. When norepinephrine binds to the adrenergic receptors in the heart, the heart cells depolarize faster, leading to an increased heart rate. In summary, the increase in heart rate during a fear response is primarily mediated by the sympathetic nervous system, which releases norepinephrine to speed up the heart cells' depolarization process.
Learn more about Sympathetic Neurons here:
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