Types of Crust
The layer immediately under the Earth's crust is called the lithosphere. The lithosphere is more capable of plastic deformation than the crust, and is warmer than the crust, but is still colder and more dense than the layer immediately below it, which is known as the asthenosphere. This picture to the left shows both ocean crust and continental crust.
The asthenosphere is a transitional region between the lithosphere and the upper mantle of the Earth. The asthenosphere does not have the properties of the mantle, but the lithosphere bends and descends into the asthenosphere under the forces which cause subduction. This implies that the lithosphere and crust can operate as a unit while the asthenosphere is a separate region altogether.