a bit of trivia: compared to insects, spiders have a more centralized nervous system and more clearly defined and evolved vitals, having an respiratory system and 'heart' though not anywhere near as complex and functional as ours. This is why they could be so much bigger than insects at times. However, none of those are in it's head.
So if you go to another world or just Australia and end up fighting man sized spiders, remember:
thorax and upper legs = brain
upper underside of abdomen = lungs
entire top side of abdomen = heart