Final answer:
The control of heart rate is mediated by adrenergic receptors, which respond to norepinephrine to increase heart rate, and muscarinic receptors, which respond to acetylcholine to decrease heart rate.
Step-by-step explanation:
The two types of receptors involved in the control of heart rate (HR) are adrenergic receptors and muscarinic receptors. These receptors are influenced by the autonomic nervous system, which consists of sympathetic and parasympathetic divisions. When norepinephrine is released, it binds to adrenergic receptors causing cardiac cells to depolarize faster, which increases HR.
Conversely, when acetylcholine (ACh) is released, it binds to muscarinic receptors, causing cells to hyperpolarize, making it harder to reach the threshold, thus slowing HR. The sympathetic nervous system increases HR during stress or exercise, while the parasympathetic nervous system slows HR down during rest