IF U WILL BASE UR QUESTION 2 SCIENCE AND NOT TO THE BIBLE THEN:
evolution has programmed man to survive and adapt from every obstacle, the nervous the system reacts with an immediate "fight or flight", the information doesn't have to the brain but will just act upon stimuli while the endocrine system has programed hormones to react immediately causing adrenaline so that we may be aware of our surroundings when we are in danger