What stage of sleep are you in under anesthesia, and why does it feel like no time has passed?
In: Biology
TL;DR: You’re not in a stage of sleep when under anaesthesia, you’re in a state of low brain activity throughout (which results in loss of consciousness, inability to respond to your environment and memory loss). When you’re asleep however, you are in an altered conscious state, and still very able to respond to things!
Effectively, being under anaesthetic is the deepest ‘sleep’ you can be in. A key part of talking about sleep or comas or anaesthetic is consciousness. Consciousness in a medical context is your ability to respond to stimuli (a detectable change)- so for example; if I shine a light into your eye, your pupil should constrict; if I strike just below your kneecap, your knee should jerk upwards and so on. These responses are important in assessing someone’s nervous system and brain responses- and you might often see them done on coma patients on medical dramas.
The fact is with sleep, you are still very much ‘aware’ of what is going on- you’re easily awoken and alerted if nudged or if yelled at, you still exhibit the above reflexes and so on. Sleep is very predictable, it has characteristic brain activity, metabolic activity etc.
Anaesthesia however is different, anaesthesia aims to cause unconsciousness, pain relief and amnesia. Someone under anaesthetic would not normally wake if you hit them or yelled at them, they wouldn’t react. If you shone a light in their eye, it wouldn’t constrict. Anaesthesia impairs your body’s natural nervous responses to these things by inhibiting along your central nervous system.
While you’re awake, your brain is sending excitation signals and inhibition signals all the time all around your brain. For a nerve cell to send a signal it needs to pass a ‘threshold’ of electrical activity to actually ‘fire’ the signal. Therefore, nerve cells themselves have components that excite them (yeah this signal is worth firing over!) or inhibit them (nah this signal isn’t worth firing over).
Anaesthetics, it is believed, work by increasing the strength of these inhibitory processes in the brain. One example of these inhibitory components is called the GABA receptor, a lot of people think anaesthetics make these GABA receptors more able to inhibit/depress the nerve cell so it won’t fire. By doing this all across the brain, the amount of excitation starts to drop.
The signals from your hearing drop, along with your eyes and nose. Signals from your skin telling you how warm or cold it is diminish. Your thoughts begin to quieten and silence, while your very wakefulness begins to fail. And all of a sudden you’re awake, with no memory of what happened, no pain and feeling a bit tired.
The exact mechanism how all this happens isn’t entirely known. But we do know there is a huge drop in brain activity due to anaesthetics. The quietening of these signals simply appears to put the whole central nervous system in a quiet standby state- your pain responses and memory systems just sort of say “meh” and don’t bother to fire to trigger pain or to make memories throughout.
So to sum up, anaesthesia isn’t normal sleep. Sleep is a natural thing many animals do, it is tied in to our natural healthy metabolism. Anaesthesia is effectively the application of drugs to try and ‘quieten’ the central nervous system, and it does it well. So well that it quietens your ability to make memories, feel pain and respond to any stimuli. These traits make it very unique and not as natural compared to sleep.
Here’s a few links about anaesthesia:
https://www.tuck.com/anesthesia/ (Easy to read quick overview)
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3162622/ (Academic overview of the nature and differences between coma, sleep and anaesthesia)
http://serious-science.org/difference-between-sleep-and-anesthesia-1160 (nice short article about the differences between sleep and anaesthesia, in reference to Michael Jackson’s death)
Latest Answers