How we think, feel, sense and act comes from our mind, and while there has always been this belief that our minds and bodies are separate, all is actually spurred by our body’s internal biochemistry.
When you hear a startling noise, you jump, your heart starts to beat and your mind races to decide the best course of action. Internally, what is really happening is that noise is stimulating an electrochemical signal. These signals travel through the billions of neurons (nerve cells) that make up our nervous system, crossing synapses using chemicals known as neurotransmitters, making their way up to our brain, where a fight or flight response occurs.
So realistically, everything happening in our minds is because of chemical reactions in the body, and these are triggered by the brain. They rely on each other more than we could imagine.
From Crash Course: Psychology on YouTube presented by Hank Green