Final answer:
Tim's reaction to seeing a mountain lion was caused by sympathetic stimulation of the heart, which is part of the body's 'fight or flight' response to perceived threats. This increases the heart rate and prepares the body for action, contrasting with the parasympathetic system's 'rest and digest' functions.
Step-by-step explanation:
When Tim saw the mountain lion, his reaction was triggered by sympathetic stimulation of the heart. This response is part of the 'fight or flight' response system, which prepares the body to react to perceived threats. The sympathetic nervous system increases heart rate, dilates pupils, and directs blood flow to muscles, preparing the body for quick action.
The parasympathetic system, in contrast, is responsible for 'rest and digest' activities and would not be the primary trigger in a situation requiring immediate reaction. Somatic motor stimulation controls voluntary movements, and while Tim's muscles may have been primed for action, it is the sympathetic activation that specifically targets the heart's response in this scenario. Hence, options b and c are not applicable in this context, and while both the sympathetic and parasympathetic systems can influence heart function, in the case of a threat like seeing a mountain lion, it is mainly the sympathetic nervous system that is activated.