As you are driving to school, you feel a movement on your leg and suddenly realize there is a spider crawling up it. you stop the car, feeling panicky. given what is known about the indirect pathways for sensory information, it is likely that the moment you saw the spider, that information was first routed to the

thamalus

Explanation:

Based on studies conducted by various neurologists, it can be said that in this situation that information was most likely first routed to the thamalus. This is a part of the brain that relays motor and sensory information to the cerebral cortex. It is also responsible for regulating sleep, consciousness and even alertness. Which is what was triggered (alertness) when you saw the spider crawling up your leg.