As long as you explore slowly and lightly, you’ll find a new sense of length and comfort for your back after spending time with this lesson. It begins on the back and then leads you into experimenting with the same movements in different positions. This strategy – of making the familiar seem unfamiliar by varying positions- is something you will see often in Feldenkrais lessons.
Some of the movements will seem familiar to you, but resist the urge to do the movements automatically. Make each movement a variation and feel free to do the movement badly. Sometimes having the intention to move badly reveals new information and raises new, valuable questions to explore.
Of course, in every lesson we are learning about how our whole self is involved in the various movements, so local anatomy is not something you need to know. Often, knowing the anatomy of a particular area isn’t even helpful when doing a lesson. But if you are interested after you do this lesson, there are some nice pictures and animations of the spine here.
By the way, the link is to the Wiki article you get if you search “Flexion and Extension of the Spine.” I note that the article confines itself to one segment of the spine. Don’t you do the same!