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Stuart Farrimond

Stuart Farrimond has written 249 posts for Guru Magazine

Local and general anaesthetics: what’s the difference and how do they work?

be pro: the chief is watching... by Cyril Vallée, on FlickrAnaesthesia itself means ‘without sensation’, and drugs that cause anaesthesia are commonly prescribed by medical staff to relieve pain. As you rightly point out, there are two main classes of drug that can bring about this state; these are known as local and general anaesthetics.

A local anaesthetic causes a small area of the body to feel numb whilst the person remains fully conscious. An example of this may be a numbing injection given by a dentist before they try to yank a tooth out. However, with a general anaesthetic, the patient will be totally unconscious and unaware of what is going on. This type of anaesthesia is usually reserved for major operations.

These pain-relieving drugs bring about these effects in different ways, and for many of them we’re not 100% sure how they work.

Local anaesthetics work by reducing the ability of nerve fibres in a small area to transmit electrical signals toward the brain. There aren’t just pain-sensing nerves in the skin, however. There are various different types of nerves – temperature, touch and pressure and joint position nerves. The thinnest of these nerves are pain fibres, and these are most susceptible to the local anaesthetic. Other nerve types (such as touch and pressure nerves) aren’t affected – meaning that you can still feel pressure and tugging throughout your tooth extraction. (If only they could stop that!)

General anaesthetics are very mysterious. They are either injected or inhaled and quickly pass from the blood into and throughout the brain. They temporarily stop various parts of the brain working normally, but in particular they act on an area called the reticular activating system (at the base of the brain) – a region that makes us awake and alert.

Each general anaesthetic, however, seems to work in a different way, making it even more difficult for researchers to figure out how they work. There are lots of complex theories that you can read about, but be advised – trying to get your head around them all could send you asleep.

Hope this helps!

Answer by Emily Hughes and Dr Stu

Image: Cyril Vallée, on Flickr

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Tig or Tag?

Tig Tag Playground“Euax!” shouts Appia as she taps the shoulder of Hadrianus. “Non sum!” Hadrianus screams, running away. Just then, Gallus emerges from his tent to tell the kids to pipe it down and play something quieter. The children ignore their uncle and continue to bicker over who is “it”…

Such is how a game of ‘tag’ would probably have been played in ancient Rome. (Assuming my Google-powered Latin translations are accurate.) For chasing games are some of the oldest games still played in today’s playgrounds. We all know the rules: one person is ‘it’, who must chase the other children and ‘tag’ them by touching them. The ‘tagged’ child then becomes ‘it’ and so must take their turn in chasing the other children.

Tig Tag UK MapThe game has had various names and variations throughout history. In ancient Greece, for example, kids played ostrakinda – a version of “tag” similar to dodgeball. In today’s English, however, the chasing game is called “tag” or “tig”; neither name is more correct as both originate from the Anglo-Saxon words for touch or strike.

Unsurprisingly enough, which name you go for correlates pretty strongly with where you grew up: in the UK, northerners are more likely to call the game ‘tig’, while southerners will call it ‘tag’. There are actually dozens of weird and wonderful names for the game used in different regions of the UK (including “tip” in North Wales, “tuggy” in Newcastle and “dobby” in Nottingham).

American children are a lot less creative with their game naming, with “tag” used pretty much unanimously across the 50 states.

Interestingly, Gorillas also play tag. So when the children’s game really does get out of hand, you can justifiably tell them that they’re behaving like little monkeys*.

*Gorillas are actually apes, but the kids won’t know that.

Answer by Dr. Stu

Image credit: Philip Howard on flickr, map via usvsth3m.com

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Why does sour cream have a ‘use by’ date? Can it go off?

Yummy! via FlickrUnwittingly pouring gone off milk over the breakfast cereal is one of the worst ways to start a day. Milk that has gone bad tastes sour and smells revolting. There is no salvaging it, and there is no salvaging the corn flakes (please don’t try washing them, it doesn’t work – I tried).

Saying that soured cream has a use-by date, therefore sounds ridiculous – how can something that has already ‘gone off’ possibly ‘go off’ any more? Well it can, because there is a big difference between a milk product ‘souring’ and a milk product spoiling.

Sour cream, like crème fraiche, is a fermented milk product made in a similar way to yoghurt. It is made by mixing cream with certain types of bacteria, called ‘lactic bacteria’. These bacteria feed off the sugars in the cream (lactose) producing lactic acid as a biproduct. It is the acid (lactic acid) that gives sour cream its tangy taste and changes the structure of the proteins in the cream (casein), causing it to thicken.

Spoiling is different to souring and happens when a variety of bacteria (and possibly molds) grow in the milk – breaking down the fats, protein and sugars in the milk, changing its taste completely and producing some very unpalatable biproducts. And even though your shop-bought sour cream has been pasteurised to eliminate harmful bacteria, it is not completely sterile – very low levels of bacteria will be in there. After about two weeks from milking, these bacteria will have multiplied enough to spoil the sour cream. So ignore the use-by date at your peril.

The best way to have a dairy product that won’t go off easily is to buy it UHT processed – that is, heated to a very high temperature making it sterile of essentially all bacteria. The downside, as you probably know, is that UHT milk products tend to taste a bit naff.

That said, even UHT milk on your cereal is better than crying over soured milk.

Question sent from ‘Val’ via Facebook

Image source: James LeVeque, Flickr

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