biology zoology blog sleeping hibernation

Hibernation : Sleeping Beauties’ Secrets

How to sleep away the bad times

Wouldn’t it be nice to be able to just sleep away a bad phase of one’s life, to hibernate until things would get better, to be like a bear in its den in the midst of winter? But hold it, the bear is not a good example. Physiologically it does not truly hibernate; it only rests.

The denning bear’s heart and breathing rates may slow down to 10% of their normal values, but even during its winter rest a bear responds to stimuli such as loud noises, to smells and smoke, to physical interferences and it can actually get up to replenish an empty stomach or to find a cozier place to continue its snooze. Yet, amazingly the denning bear does not have to drink or eat during the many months that it rests and (in case of the female bear) gives birth to its cubs and then starts producing milk for them to grow. Not needing to urinate, the denning bear in its wintersleep uses the retained urine physiologically in its metabolism.

What is critical when discussing true hibernation is the core body temperature and that, in the winter-sleeping bear, goes down only marginally during the long months of the bear’s winter rest. However, in ground squirrels, hedgehogs, bats of temperate countries and even the spiny anteater in Australia, the core body temperature usually drops to a few degrees above freezing. Hibernating bats may not take a breath for an hour; the heartbeat of a hibernating hedgehog may be as low as 2-3 per minute; the number of white and red blood cells may decrease to 50% of their original value and sensitivity of their sense organs, is almost non-existent. Even the perception of painful stimuli is reduced to almost non-existence.

In this state of torpor, the hibernating animal’s metabolism runs on the body fat accumulated during feeding phase prior to hibernation in summer and autumn when food was plentiful. Significantly, even in the deepest sleepers the spontaneous electrical activity of the brain never ceases completely; it seems that thermoregulation is not totally switched off, only adjusted to a much lower than usual level. On waking up, which is triggered by a warming of the environment, breathing increases in frequency, blood sugar levels are raised from stores in the liver and the musculature of the limbs at the front end and later those of the posterior appendages as well begin to tremble and contract periodically. At that time the region of the so-called “brown fat” deposits in the neck and the shoulder blades become more active in generating heat and a temperature gradient between the rectum and the neck develops.

The whole waking-up from hibernation to full wakefulness takes only three hours in the hamster, and although the average hamster’s lifespan is one-fortieth that of a human and the relatively reactivation procedure, therefore, requires the equivalent of approximately five human days, I still wonder if it wouldn’t be wonderful if we humans could imitate the hamster. That is, of course, if you are not one of those winter sports fanatics, who love skiing and ice-skating.

© Dr V.B. Meyer-Rochow and, 2018.
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