Another dumb question...

Fremen

Right, another question that people probably won't have an answer to:
What is the biological reason for our brains being in our skulls?

It seems to me that the skull is a weird place to find the control center of the body. If a person falls, the skull had the furthest to drop and will therefore hit the ground hardest. The brain is at an extremity, so nerve impulses have further to travel.

It seems to me that if our brains were in our chest cavities, they would be better protected and more central, which would allow quicker transmission of impulses and therefore quicker reflexes. So why aren't they in our chests?

Capt'n Midnight

our brains evolved a long time ago back with the fishes

it's probably to keep the main sense organs close to the brain
the left side of the brain controls the right side of the body may be because if you are attacked from the left and your brain is damaged the right side of your brain will still be able to fight back with the left side of your body

octopuses have their brains wrapped around their guts so that brings it's own special problems

Kevster

I would answered this question in the same way as you just have, Capt'n Midnight. The 'primitive' brain consists of a bunch of ganglia in the head region of insects, because that is where the sense organs also located. Thus, there is less distance for the nerve-imuplses to travel; and when you're an insect, fractions of seconds count in the bid for survival.

Interestingly, some modern insects have large ganglionic swellings in their abdomens too, as far as I know.

Kevin

John

Fremen wrote: »

Right, another question that people probably won't have an answer to:
What is the biological reason for our brains being in our skulls?

As the others have pointed out, the brain is a lot older than humans or even mammals. The body plan (head, thorax, abdomen) evolved a long time ago (around the time of the Cambrian explosion which was about 530 million years ago) and mutations that have affected this body plan tend to be lethal. So basically all changes (such as the development of a brain compared to ganglia) have to conform to this body plan.

It seems to me that the skull is a weird place to find the control center of the body. If a person falls, the skull had the furthest to drop and will therefore hit the ground hardest.

Firstly, the body plan I mentioned above that appeared in the Cambrian era occurred at a time when all life was marine-dwelling. There was not the same effect of gravity as there is on land-dwelling animals. Secondly, in most animals on land, they have a low centre of gravity (four legged, head low to the ground, etc.) so a fall won't be so dramatic. Third, your head doesn't exist on its own, you have limbs to absorb the shock as you fall as you flail about to stop yourself crashing to the ground. Fourth, the skull is there to protect the brain in case of just such a situation. Fifth, biology is not fool proof and thing's like this can be used as arguments against intelligent design (i.e. why not put the brain somewhere really safe?).

The brain is at an extremity, so nerve impulses have further to travel.

Nerve impulses are frighteningly quick. If you think it's a big distance from your toe to your brain, think of what it's like for a giraffe! Nerve impulses travel roughly at 360km an hour, considering your body probably doesn't reach 0.002km, that's a huge speed.

Not only that, you have circuits of neurons outside the brain called interneurons that perform tasks like withdrawing a limb away from pain. Next time you stand on something sharp in your bare feet, look at the experience objectively. You step down, withdraw your foot and then think about the fact you've just experienced pain. These interneurons hardwire the pain recetor to its nearest muscle so you withdraw without thinking (a reflex).

It seems to me that if our brains were in our chest cavities, they would be better protected and more central, which would allow quicker transmission of impulses and therefore quicker reflexes. So why aren't they in our chests?

As I said, the sort of mutation needed to remodel the body plan in such a drastic way would be lethal. Many mutations of single genes are lethal, highly disruptive or maladaptive. Interestingly, at the time of the Cambrian explosion there were many different body plans (including some that could have given rise to a more central central nervous system) but only the current one was successful.

Ah my twin loves, developmental biology and neuroscience!

Capt'n Midnight

Kevster wrote: »

Interestingly, some modern insects have large ganglionic swellings in their abdomens too, as far as I know.

As did some of the dinosaurs , stegesarus had one in it's hips that was larger than it's brain , never impulses being so slow it's been suggested that it was for self defense so the animal could react before the nerve impulse got to the brain , 360Km/hr sounds fast but that's about 100m a second and if you are 50m long the signal would have to the brain get processed and send back from the brain . . .

Kevster

Capt'n Midnight wrote: »

As did some of the dinosaurs , stegesarus had one in it's hips that was larger than it's brain , never impulses being so slow it's been suggested that it was for self defense so the animal could react before the nerve impulse got to the brain , 360Km/hr sounds fast but that's about 100m a second and if you are 50m long the signal would have to the brain get processed and send back from the brain . . .

... ...Very interesting - Thank you for that.

Fremen

John wrote: »

Third, your head doesn't exist on its own, you have limbs to absorb the shock as you fall as you flail about to stop yourself crashing to the ground. Fourth, the skull is there to protect the brain in case of just such a situation.

I'm picking nits here, but I think you're mixing cause and effect with these points. These are adaptations designed to cope with the problems of having a high-up, vulnerable brain, rather than reasons why it's there in the first place.

Everything else makes perfect sense. Interesting post, cheers.

John

Fremen wrote: »

I'm picking nits here, but I think you're mixing cause and effect with these points. These are adaptations designed to cope with the problems of having a high-up, vulnerable brain, rather than reasons why it's there in the first place.

Everything else makes perfect sense. Interesting post, cheers.

Skulls predate land-dwelling animals (bony fish have skulls) and limbs were in existence long before man walked upright. I'm not saying that limbs exist because the brain is on our shoulders or vice versa but limbs are one reason why it's not a maladaptive trait having our brain where it is now.