[Negin -(Universe) (OP)]

why exactly is it that the right side of the brain controls the left side of the body and the left side of the brain controls the right side of the body? why couldnt the left and right hemispheres control their corresponding body parts? i.e. right controls right and left controls left []

i would appreciate your thoughts and comments on this...

[Seany]

That's an interesting question. I never thought why, just thought it is. [] Hope you get an answer soon []

[Negin -(Universe) (OP)]

hope so to,
by the way if ur interested about my question on going back to the moon in the physics section ive given a short summary of what the program was about.

[Seany]

Ok, great thanks! []

[qazwart]

I have a theory. Vertebrates differ from other creatures like insects in their location of their nervous system. Vertebrates' spine is along the back, but insects have a network of nerves on their bellies. A recent study in Cell magazine (synopsis is here: newbielink:http://cordis.europa.eu/fetch?CALLER=EN_NEWS&ACTION=D&SESSION=&RCN=27545 [nonactive]) locates the common ancestor as the lowly marine worm.

The question becomes how did the nervous system switch from the front of the creature to the back. Detlev Arendt of the European Molecular Biology Laboratory in Heidelberg (who produced the paper in Cell) has a theory. Imagine a filter feeding worm that eventually became the ancestor to all vertebrates. Dr. Arendt envisions this creature half buried in the sea floor with its belly and nervous system protected by boney plates. One day, this creature leaves the safety of the sea floor to swim around -- upside down. Since the creature is in water, up and down has no real significance, so it simply adopted to its new posture where its former belly became its back and its back, its belly. (see newbielink:http://www.economist.com/science/displaystory.cfm?story_id=9033083 [nonactive] in the Economist near the end of the article).

If this happened, and the creature turned its head 180 degrees in order to adjust to this body plane, then the right side of the body is now controlled by the left side of the head and the left side of body is controlled by the right side of the head.

[LaurenaS]

The different brain hemisphere is required to communicate together in which they control the muscle and glands in the body on the opposite side of the body known as decussation.