Does snow cool the world by reflecting light?

Does snow cool the world by reflecting light?

Well, the thing about snow is that it’s quite reflective compared to bare ground. A good thick snow cover will reflect back up to 80 percent or even more of the sunlight that’s falling on it. Whereas bare ground or grasslands might only reflect 10 or 20 percent of the sunlight falling on it and so, the sunlight warms it up considerably. So, if you replace that bare ground by snow cover, then a lot of the sunlight that would’ve heated the ground just gets reflected back into space. So, if you remove a snow cover by ploughing it up or sweeping it away or whatever, revealing the bare ground underneath, then the ground is going to absorb a lot more sunlight, and will warm up a lot more quickly than if the snow were there. We are having an effect on the reflectivity, the albedo of the planet by changing land use for instance; cutting down forests and replacing them with grasslands. But that generally has the opposite effect, forests absorb quite a lot of sunlight, grassland is less reflective. People have suggested that we could partially offset global warming by painting the roofs of all of our buildings white. I think some calculations have been done that have showed that this will be a good thing, but it wouldn’t have a very large effect because you're only talking about a rather small area of the planet that you'll be changing the reflectivity of.

Why is chocolate toxic for dogs?

Why is chocolate toxic for dogs?

Yes. Chocolate, unfortunately, is toxic to dogs. And the reason for that is because it contains a compound called theobromine. Theobromine and caffeine are both present in chocolate but theobromine is the problem. They’re both methyl xanthines. In dogs, theobromine is very long lasting. So it’s got a very long half-life of about 18 hours. Whereas in people, the half-life is only two or three hours. And people readily absorb the theobromine.

It’s just a fact that every species has a different metabolism. We see differences between dogs and cats. With certain drugs, say for example, you shouldn’t give a cat paracetamol whereas dogs can tolerate paracetamol. So it’s just a species difference; probably down to different enzymes that are present in the system.

So how much theobromine is toxic, you might ask yourself. So if a dog eats a couple of M&Ms, that’s not going to cause any problem. The toxic levels vary from 20 mg per kilogram of theobromine to about 150 mg per kilogram of theobromine. So what does that mean in reality?

Well, putting into a typical scenario, if you got a labrador and that ate a 200 gram bar of dark chocolate, that, potentially, is enough to kill your dog. So it’s actually not very much. And the big problem this time of year is someone gives you a box of chocolates, wrapped up, and you put it under the Christmas tree, and the dog eats the box of chocolates. If that happens you certainly should call your vet as soon as possible.

Can we create artificial nerve signals?

Can we create artificial nerve signals?

Yes we can. We actually know quite a lot about how nerve information travels. If you can imagine a nerve cell as a bit like a long straw, with sides and a space in the middle - what nerves do is to move positively charged ions, in this case sodium ions, from the inside of the nerve, to the outside world. So the inside of the nerve is a bit negative compared to the surroundings.

When a nerve impulse travels along a nerve, what happens is that some "positive" (some sodium) goes back inside the nerve through tiny pores, which are on the surface of the nerve. This is called de-polarising the nerve, and it makes that section of the nerve become, transiently, a bit positive.

Now this does two things; it starts an electrical signal rather like a Newton’s Cradle running inside the nerve, but it also activates other little channels and pores on the surface of the nerve a bit further downstream. They open and let in some more "plus" to sustain and maintain the propagation of the signal. In a big nerve, this signal is actually travelling along at something like 100m/s.

The impulse (or action potential) only goes in one direction though because, in the opposite direction - where it’s just come from, the nerve pumps the "plus" back out again, so it goes back to being net minus and the nerve resets itself.

This process happens in milliseconds, so you can literally conduct hundreds if not thousands of these impulses down a nerve in less than a second. The information can travel very, very fast.

You can also make this happen by artificially stimulating the nerve. If you apply a little bit of electricity to the wall of the nerve fibre itself you can actually make that process trigger off, and then it self-sustains. The signal will propagate along the nerve to wherever it goes – in both directions.

Scientists use this for a number of reasons; one is that you can artificially activate muscles that way – so if you've been paralysed, for example, you can use techniques like this to restore movement to certain muscle groups by electrically stimulating certain nerves that supply those muscles. Another reason is to use brain stimulation – this has been done quite effectively in Parkinson’s disease. Scientists implant a little electrode in a part of the brain which makes movements and is involved in the same circuit as is affected by Parkinson’s disease. If you stimulate those bits of the brain electrically, you can trigger off impulses in the right way and the right rate to help people who have Parkinson’s symptoms to overcome their symptoms and move a bit more easily.

So, it is possible to re-create nerve signals. At the moment it's fairly low resolution: you’re not stimulating individual nerve cells, you’re stimulating clusters of nerve cells. But at the same time, you can do that.

Also, if you listened to last week’s programme, you’ll know that we talked about cochlear implants, which are things that basically stimulate the nerve that conveys hearing information into the brain stem. They’re doing effectively the same thing – stimulating nerve cells directly to send sound information into the brain.