Final answer:
In response to succinylcholine, adults tend to experience tachycardia due to an increased sympathetic activity, while children may exhibit bradycardia due to parasympathetic dominance.
Step-by-step explanation:
The occurrence of tachycardia in adults as opposed to bradycardia in children following the administration of succinylcholine can be understood by considering the effects of neurotransmitters on heart rate. Succinylcholine is known to stimulate postganglionic fibers of the autonomic nervous system, which can result in different heart rate responses depending on the predominant system active in the individual.
Children often experience bradycardia with succinylcholine due to a more dominant parasympathetic system. In contrast, adults are more likely to experience an increase in heart rate or tachycardia, which would align with Option 1: Increased sympathetic activity. This sympathetic dominance causes norepinephrine release, leading to adrenergic receptor binding and increased heart rate.