So it varies anywhere from four to one to one to four. And to see what we mean by that, let's compare the plasma membrane found on myelinated nerve cells to the membrane that encloses mitochondria. So what's the function of a neuron? Well, the function of a neuron is to basically carry an action potential to initiate an electrical signal and carry that signal the action potential along the axon. And so, in many of our neurons, on many of our neurons, the plasma membrane is actually myelinated by using these special lipids because it's the lipids that create this insulation layer that basically increases the rate at which that propagation actually takes place, because that signal can basically jump from one node to the next node. And so, because the function of the neuron and the plasma membrane on the neuron is to actually propagate, that signal will find a much higher amount of lipids compared to proteins.