I have the impression that sleep is a difficult subject.
Scientists give us this impression and perhaps they are right.
Professor Seth, on radio 4, 16.6.’15, asked himself how does consciousness happen. Sleep happens not consciousness. I think this is a better way of looking at things. Consciousness is the default state.
I contend sleep is simply ( I’m not suggesting the wiring is necessarily simple) a refined evolutionary device using, in general across the animal kingdom, the inevitable darkness of the diurnal day including what that means in the oxygenation of the air to best and most safely reverse the mostly oxidative (and other) processes of consciousness and activity. This is its prime function and any activities sensed during this period are simply by-products of this chemistry.
Consciousness is simply awareness of the animal to its environment and itself in the environment and to varying degrees, of itself: there is no implicit need for movement though it can happen if the mechanisms for this exist and are intact and it is needed.
The default safe state for all animals is consciousness, therein it can communicate, hunt or seek food, feed, mate, escape from predation and otherwise protect itself. The default state for any machine is the movement for which it was made.
The ordinary person knows that it is needed to function properly and not having an appropriate amount leads to an irritable and confused state.
A lot of time is spent looking at the minutia that occurs in sleep such as rapid eye movement and a various range of brain wave activities and patterns as determined by eeg and other encephalographic means.
When I see a person sleeping their eyes are shut, they usually look comfortable and they are barely breathing. (Except for their colour we all know how sometimes they can appear, for an instant, dead.)
The first two relate to reducing stimuli and the latter relates to the prime function of sleep and that is to deplete the body of oxygen and induce a reversal of the chemistry of fuel burning that sustains consciousness. It seems obvious that such reversal is of a redox nature and sleep is simply moving the reaction to the left.
consciousness
+/- activity >>>>
+ O2
Cell chemistry Cell chemistry ……………... CO2 (? v, ? isq, ? ^) in reduced state in oxidative stated
<<<< sleep
- O2
The depressed respiratory state of the sleeping person is complemented with a drop in blood pressure and an even lower oxygenated milieu at a cellular level. The increase in cellular PCO2 might be a catalyst though CO2 accumulation is ordinarily a respiratory stimulant.
So presumably this is blocked and/or the critical accumulation of CO2 to so act might not
occur from the reduced activity state.
The stillness in sleep or lack of movement is protective as is the likelihood that this occurs in darkness. The darkness of night also provides the lack of stimulus needed to ensure continuity of sleep. Movement of us or an animal in sleep is simply to reduce the effects of pressure
stimulating it and interfering with sleep.
The partial pressure of oxygen is low at night and lowers continually till around four in the morning.
The respiratory rate of the sleeping animal and the reduced partial pressure of oxygen in the air provide a protracted period wherein redox reactions in all the cells takes place renewing the vital catalysts and chemicals needed for energy providing reactions necessary for consciousness.
Poor or Interrupted sleep is reflected in how the animal performs after awakening simply because the quality and or the quantity of the chemicals for conscious activity are not appropriate.
The simplicity of this chemistry could be shown in animal twins by crossover transfusions where one is deprived of sleep and the other is not - rather tricky sadly as the needed anaesthesia would interfere with interpretation of events.
However this may not obfuscate as much as one would imagine.
It appears well known that after an anaesthetic patients do not feel as though they have slept and this rather fits nicely with the idea that they haven’t been asleep - a chemically induced ‘sleep’ yes and one wherein the patient has been exceptionally well ventilated with oxygen, the very opposite to that as happens with sleep. The reduced muscle activity of the anaesthetised patient, even assisted respiration if it is present is also contributant to a reduced oxidation state. That most patients by far are anaesthetised during ‘normal waking hours’ fits rather well.
As for the triggering of sleep this almost certainly is simply a build -up of oxidative/changed chemicals that fire the sleep inducing part of the brain to close us down.
It is hard to believe that from the thousands of head injuries that occur that few have the sequelae of sleep irregularities. It is possible that injuries to it infer injuries to local tissue from which survival is impossible or that area itself, if injured, could cause death. It is for the neurosurgeon and or the neuro-anatomist to reflect on those likely connections in the hypothalamus. Patently where or whatever they are they are sensitive to many drugs that aid sleep apart from the anaesthetist’s armamentarium.
Sterio-tactic ploys could be used, perhaps they are already, to determine this.
Many know that the final, the longest sleep for many with cardiac and respiratory issues
is that which occurs in the early hours of the morning. It shows how close the ordinary well person is deplete of oxygen to sub serve this chemistry of sleep.
