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A few weeks ago I began wondering what is going on in the brain and nervous system when people fall asleep in class.  I had a friend who could not stay awake in one of the classes that we had together.  There was something about the room such that about half an hour into every class she couldn’t keep from falling asleep (one might argue that it was the lecturer, not the classroom, but the lecturer changed from class to class; although this doesn’t rule out other options such as the course subject…).  She would do the typical head bob where she would just barely be asleep and then her head would slowly roll forward, and then more quickly jerk back, usually partially waking her up.  Of course, I have also had this experience and I know how annoying, yet natural this bobbing behavior is.

It only occurred to me now that it can possibly be explained as the brain and the I-function shutting down (in the sense of going to sleep) while the nervous system is still awake, ready to receive external stimuli.  In fact, I began to wonder if it was actually corollary discharge (related to balance?) that was causing the head to jerk back in the opposite direction of the way that it is falling.  Another question this raises in my mind is whether the nervous system really ever goes to sleep because it seems that nerves get plenty of time to rest when they are not firing, although the idea of corollary discharge suggests that there may be some neurons that are working or are ready to work all the time.

An observation that I have with respect to the nervous system going to sleep: I am a light sleeper, so my response to external stimuli is usually that my brain wakes up, while my sister is a much sounder sleeper and if I were to poke her while she was sleeping, she might respond without her brain being fully awake, or not respond at all.  I also know that there are times when I have really been out, and probably haven’t responded to stimuli, so that suggests to me that there are different degrees to which the nervous system shuts down to sleep.  I wonder what the advantages between these differing degrees or levels might be and why someone might be more inclined than another to sleep at a certain level?  (Some mildly related questions: why do we need to sleep?  What needs to sleep?  And of course: what is sleeping?)