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Stimulus and Response

In Signal Path, you have to set the order to sensory neuron → association neuron → motor neuron yourself before a signal can travel all the way to a response — get the order wrong and it stops partway. You'll also see that a reflex skips the brain, bouncing straight back from the spinal cord, which is why it's faster. In Nerve vs. Hormone, compare how a nerve signal is fast but reaches only one place, while a hormone is slow but spreads through the blood to many places at once — growth hormone, insulin, glucagon, and thyroxine all work this way. In Blood Sugar, raise and lower blood sugar by eating, exercising, and letting time pass, then switch off insulin or glucagon and watch blood sugar get stuck away from its normal level of 100. Keeping the body steady turns out to be teamwork between nerves and hormones.