Questions for this column may be submitted via e-mail to sci.net@campus .bt.com
Q 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.

Q How did Uranus's satellites get their strange names?

In 1787 William Herschel thought he had discovered several Uranian satellites (though only two were later confirmed). In accordance with the custom of the time, he only gave them numbers. In 1851 William Lassell discovered two more. Because of the confusion over Herschel's unconfirmed satellites, Lassell consulted Herschel's son John and decided to the confirmed satellites proper names. John Herschel wrote: "Proceeding from without, inward in succession, the names Oberon, Titania, Umbriel and Ariel, of the fairies, sylphs and gnomes of Shakespeare and Pope have been assigned respectively". The subsequent Uranian satellite discoveries (Miranda by Gerald Kuiper in 1948 and the 10 satellites discovered by the Voyager 2 spacecraft in 1986) have been named from the same sources.

Q 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), which makes you look pale. But your nose helps to 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.

Q 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.

Q How far can ants see?

There is no simple answer to this question. Some worker ants have well- developed eyes and can leap from branch to branch. Others have greatly reduced vision and some have no eyes at all.

Q 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.

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