What is Alzheimer’s disease and why does salt make you thirsty?

We explore some of the curious questions that science can answer

Joe was starting to regret eating all the salted peanuts (Getty)

Why does salt make you thirsty?

When salt crystals, which have a very orderly structure, get the chance to dissolve in water, they take it – because the level of disorder (or “entropy”) increases when the crystals become disordered ions in water. The drop in entropy when salt dissolves is much greater than for many other things – so salt preferentially takes water from other chemicals or states. Thus salt in your mouth or stomach sucks water from your bloodstream. This triggers sensors in the brain, which alert you that there’s less water in your blood circulation. In other words, you feel thirsty.

What is Alzheimer’s disease?

The disease was first described in 1907 by a German neurologist, Alois Alzheimer, and is a form of dementia that mainly attacks older people. About 4-5 per cent of over-65s have symptoms of Alzheimer’s, but it sometimes strikes those in their forties or fifties. It is the fourth-largest cause of death after heart disease, cancer and stroke. More than 850,000 people have dementia in the UK, but this is projected to rise to 1.6 million by 2040.

Citrus fruit does not grow in the Arctic, so how do Inuit people avoid scurvy?

The explorer Vilhjalmur Stefansson argued that European people could live for long periods on a traditional and entirely carnivorous Inuit diet, and that many Arctic explorers had developed scurvy (caused by lack of vitamin C) because they would not follow Inuit people and trust their instinct and experience.

He and a colleague volunteered to subsist on nothing but meat, under medical supervision in New York, for one year starting in February 1928. They each consumed between 100g and 140g of protein a day, with the remaining calories coming from fat. Both men remained in good health and showed no sign of scurvy. It has been estimated that a traditional, daily Inuit diet, even without any plant material, would contain 40mg of vitamin C, enough to avoid scurvy. But some flora – including rose hips, a good source of the vitamin – grow in areas where the Inuit live.

Why is it dangerous to wake a sleepwalker?

When we sleep, we go through different phases. Sleepwalking occurs in the “slow wave” part of sleep, during which our bodies use little oxygen and have basically shut down. During this form of sleep, the body cannot cope as well as usual with shock, so any sudden changes – such as being abruptly wakened – can be dangerous for people with heart problems.

Why does your nose go red when you are cold?

Cold causes your veins to shrink to cut down on the amount of blood near the skin (and so heat loss), making you look pale.

But your nose helps warm and humidify the air that you breathe and needs a good blood supply to work properly. So, the veins in your nose are adapted not to shrink in the cold, making your nose much redder than the rest of your face in low temperatures.

How does a nerve signal pass between cells?

When the nerve signal (in the form of an electrochemical “potential” between the inside and outside of the nerve) reaches the end of an axon, it is passed on to the next nerve cell, or on to an effector cell, such as a muscle. The axon of one neurone doesn’t usually make direct contact with the cell body of the next: the two cells are separated by a gap called a synapse. Information is transmitted across the synapse using chemicals called neurotransmitters, which cause electrical changes in the membrane of the next cell. The signal then passes along to the next nerve cell in the network. 

What is in a nerve besides nerve cells?

Packed between the neurones are the glial cells. These make up the neuroglia, tissue that supports the neurone network, protecting it and providing the neurones with nutrients. Glial supporting cells make up about half the weight of the human brain, outnumbering neurones by 50 to one. In other parts of the nervous system, the proportion is much lower – about 10 to one.

What’s the technical name for a freckle?

A freckle is called a lentigo. Freckles are caused by certain cells producing too much melanin, the chemical that gives our bodies colour.