Grey matter and white matter. Here's a brain, here's a spinal cord. If we open up the brain we see grey matter around the outside and it's folded to give more room for the grey matter why well in the human brain we maybe have 80 or 90 100 billion neurons in the central nervous system but in the grey matter this is where we find the cell bodies of those neurons and this is where we find the connections and there are possibly a hundred trillion connections in the grey matter and that's what gives us our complexity. These neurons send information through their axons through the white matter in the middle of the brain and down to the spinal cord where we find the white matter on the outside. This is going to and from the brain.
And the grey matter in the centre of the spinal cord connects these neurons to nerves leaving and entering from the body.