This is definitely a strange sensation -- you get up out of your seat, and all you feel from one foot is an uncomfortable tingling. Or you wake up in the middle of the night, and you can't move your arm at all. And then, as your body part "wakes up," the strange tingling intensifies. Just what is going on here?

Usually, you feel this familiar sensation after you've been putting pressure on part of you­r body -- sitting on a foot, sleeping on an arm, etc. When you apply this pressure for a prolonged period of time, you actually cut off communication from your brain to parts of your body. The pressure squeezes nerve pathways so that the nerves can't transmit electrochemical impulses properly. Nerve impulses carry sensation information from nerve endings in the body to the brain, as well as instructions from the brain to the parts of the body. When you interfere with this transfer by squeezing the nerve pathways, you don't have full feeling in that body part, and your brain has trouble telling the body part what to do.

This pressure can also squeeze arteries, stopping them from carrying nutrients to body cells. Without these nutrients, the nerve cells may behave abnormally, which can further interfere with communicating bodily sensations.

Due to both these factors, the information transmitted from the body part becomes somewhat jumbled, and the brain receives strange messages. Some nerve cells don't transmit any information and others start sending impulses erratically. This causes you to feel a strange tingling sensation, which actually serves an important function. Your foot falling asleep for 10 minutes doesn't pose any health threat, but if you were to cut off circulation for an extended period of time -- several hours -- you could suffer serious nerve damage. The initial tingling sensation tells you that you might want to readjust your position.

Once you do move your foot, stretch your legs, or roll over off your arm, the nerve impulses begin to flow properly again. You don't regain feeling right away, however. There is a certain amount of re-adjustment time before the nerves transmit impulses correctly again. This increases the intensity of the tingling, causing the familiar "pins and needles" sensation.

If this has ever happened to you, you know that there are actually a few distinct sensations you go through as your body part "wakes up." The tingling may be followed by a more uncomfortable burning sensation, before your body part finally returns to normal. This happens because the nerves in your body are made up of separate long nerve cells that carry different sorts of impulses. These nerve fibers have different surrounding structures. Some nerve fibers have thicker "insulation" around them and so take longer to begin transmitting impulses properly after they've been squeezed. The fibers that transmit pain and temperature information are relatively thin, so you feel the tingling situations pretty quickly. Motor control fibers are thinner than the ones carrying touch information, so you can move the body part before you've regained complete feeling in it. Eventually, all the nerve fibers return to normal and you regain full use of the sleeping body part.

Your liver is your largest internal organ, and it performs many amazing and vital functions.

Weighing an average of 1.3kg (2.8lbs) in women and 1.8kg (4lbs) in men, the liver is located under the lower right hand side of your ribs. For comparison, the heart weighs an average of 255g (9oz) in women and 298g (10.5oz) in men.

The liver is large, and it has a large role in your everyday life. The liver is responsible for about 500 different functions, including aiding in digestion. The liver produces a substance called bile, which helps break down fat and it helps the body take up vitamins A, D, E, and K.

The liver also, famously, breaks down poisonous substances we consume, such as alcohol. A rough sketch of what happens when you drink alcohol:

When you drink alcohol, the alcohol is absorbed into your bloodstream from the stomach and the intestines. Your liver will break down the majority of the alcohol; the rest of the alcohol leaves your body in your urine, breath, and sweat. Your liver breaks down alcohol into acetaldehyde using an enzyme called alcohol dehydrogenase (ADH), then acetaldehyde is broken down into acetate with the enzyme aldehyde dehydrogenase (ALDH), and finally acetate is broken down into carbon dioxide and water. Your liver uses different enzymes to break down alcohol if there is a very large amount of alcohol in the bloodstream or, sometimes, if you drink regularly. (Side note: acetaldehyde is a nasty substance that can cause serious damage, so the accumulation of it can be harmful to your liver).

Interestingly, if you drink methanol (a type of alcohol not meant for consumption) it can kill you because the liver breaks down methanol into formaldehyde and formic acid. Methanol can be found in a variety of substances, such as antifreeze and copy machine fluid. If methanol is consumed, emergency care is necessary. Part of the emergency treatment for methanol poisoning involves giving the patient ethanol. Ethanol competes for ADH, preventing and slowing the breakdown of methanol.

The liver is also important in providing quick energy. Carbohydrates are broken down into glucose in the liver, and stored as glycogen in the muscles and liver if there is a surplus. If you suddenly find yourself running for your life, your muscles can use the stored energy, but when they run out, the liver provides more.

Your liver also stores iron, produces enzymes and other proteins responsible for blood clotting and tissue repair, and, as if the liver wasn’t awesome enough, it can also regenerate itself after serious damage.

If you've ever laced your fingers together, turned your palms away from you and bent your fingers back, you know what knuckle popping sounds like. Joints produce that CRACK when bubbles burst in the fluid surrounding the joint.

Joints are the meeting points of two separate bones, held together and in place by connective tissues and ligaments. All of the joints in our bodies are surrounded by synovial fluid, a thick, clear liquid. When you stretch or bend your finger to pop the knuckle, you're causing the bones of the joint to pull apart. As they do, the connective tissue capsule that surrounds the joint is stretched. By stretching this capsule, you increase its volume. And as we know from chemistry class, with an increase in volume comes a decrease in pressure. So as the pressure of the synovial fluid drops, gases dissolved in the fluid become less soluble, forming bubbles through a process called cavitation. When the joint is stretched far enough, the pressure in the capsule drops so low that these bubbles burst, producing the pop that we associate with knuckle cracking.

It takes about 25 to 30 minutes for the gas to redissolve into the joint fluid. During this period of time, your knuckles won't crack. Once the gas is redissolved, cavitation is once again possible, and you can start popping your knuckles again.

As for the harms associated with this habit, according to Anatomy and Physiology Instructors' Cooperative, only one in-depth study regarding the possible detriments of knuckle popping has been published. This study, done by Raymond Brodeur and published in the Journal of Manipulative and Physiological Therapeutics, examined 300 knuckle crackers for evidence of joint damage. The results revealed no apparent connection between joint cracking and arthritis; however, habitual knuckle poppers did show signs of other types of damage, including soft tissue damage to the joint capsule and a decrease in grip strength. This damage is most likely a result of the rapid, repeated stretching of the ligaments surrounding the joint. A professional baseball pitcher experiences similar, although obviously heightened, effects in the various joints of his pitching arm. But assuming you haven't signed a multimillion dollar contract to constantly pop your knuckles, it hardly seems worth the possible risk to your joints.

On the positive side, there's evidence of increased mobility in joints right after popping. When joints are manipulated, the Golgi tendon organs (a set of nerve endings involved in humans' motion sense) are stimulated and the muscles surrounding the joint are relaxed. This is part of the reason why people can feel "loose" and invigorated after leaving the chiropractor's office, where cavitation is induced as part of the treatment. Backs, knees, elbows and all other movable joints are subject to the same kind manipulation as knuckles are.