How does the body move?

Answer 1

Wow - tricky question because it goes at so many levels. I'll just keep increasing the detail and you read till you have enough.

Okay - at the most obvious level:

your brain makes a decision to move (and that one is "why does the body move?") for whatever reason

your brain passes the message down through parts of the brain the relate to coordination and movement, memory etc and then the message goes down the spinal cord and winds up in the nerves to the sets of muscles. Then the muscles do it.

It's actually a little more complicated than just "bend my elbow" or "move your big toe" (Kill Bill fans - anyone?) because your brain sends the message to the biceps (in the front of your arm) to bend your elbow and also to the triceps (in the back of your arm) to pay out slack and let the elbow bend. You CAN send messages for both to contract and the elbow to stay rigid (isometric exercises).

Certain parts of our brain are dedicated to coordination of these push/pull effects and allow one group of muscles to relax while the opposing group pull.

The muscles then pull on their attachment to the bones (the tendons) and then the bones move at the joints. This causes the body parts to move.

Okay - let's learn about the muscle fibres and see how they actually do the movement. There's a good wiki page. Specifically, it has a good close up picture showing the actin and myosin proteins that make up the contractile elements of the muscle fibre.

SLIDING FILAMENT MODEL

If you look at the close up picture, you will see that each contractile element is made up of long chains of ACTIN and MYOSIN. The Myosin being made up of a long chain of tropomyosin and a little troponin head.

This is, if you will imagine, a sort of a ratchet mechanism.

It forms a couple of sliding chains with lots of little troponin heads connecting the tropomyosin to the actin. In the picture of the sarcomere showing actin, myosin and titin you can see that the myosin is sort of double ended and pulls on two sets of actin.

When stimulated by the nerve impulse (we'll get to that later) the myosin troponin heads waggle and "pull" the actin in and shorten the whole apparatus (the sarcomere).

In the normal resting state - the actin and the troponin heads are not actually bound together. It requires the presence of molecules of calcium to cause a change in the shape of the myosin head. This change in shape causes it to bind the actin filament and then "bend" thus pulling the actin and the myosin along each other. Remember that there are millions of the little blighters all binding at slightly different spots and all pulling along. The more of these you activate (again, controlled by the nerves) the more bind and pull you have and the stronger the contraction of your muscle.

Okay - so how do you trigger it and where does the calcium come in? The calcium is stored in the muscle fibre in a spot called the "sarcoplasmic reticulum". These are arrange at each end of the sarcomere in conjunction with the transverse tubules ("T-Tubules") which penetrate the spaces between sarcomeres and allow electrical signal to flow rapidly all over the muscle fibre.

The trigger mechanism to cause the muscle to move comes from the NERVES. So let's take a look here to find out how this comes about.

The nerves which carry the signal from the brain, via the spinal cord, to the muscles all have a long process called the AXON which joins on to the muscle at a place called the Neuromuscular junction.

The axon makes and stores special chemicals called Neurotransmitters (usually Acetylcholine). When they get the signal to say "make this muscle go" they release the neurotransmitters which float across the teenie tiny space and land on the muscle fibre part (called an End Plate) and pass the signal on to the muscle.

The presence of the neurotransmitter molecules causes a change in the end plate so that channels open in the muscle cell membrane and let sodium in to the cell and potassium out of the cell. This causes a change in the electricity of the muscle cell and this in turn opens more channels allowing calcium to flow from the sarcoplasmic reticulum to where the actin and myosin fibres are - causing them in turn to contract. The mechanism of this last set of channels is not entirely known yet.

There - I hope this is of some help!

Answer 2

The brain sends out electronic instructions through nerves to the muscles. The muscles then interpret these instructions contract, pulling on tendons which are connected to bones or cartilage, this subsequent movement is transmitted as a message back to the brain, which responds accordingly with further instructions though the nerves... etc etc.

Answer 3

Contractions of muscles caused by brain impulses. And by God's providence, of course :)

Answer 4

Vias messages from your brain to your nerves/muscles/tendons/joints etc.

All movement stems from the brain. That is why brain damage can make you paralysed.

Answer 5

Carefully.

Answer 6

contraction of muscles attached to the bones

Answer 7

Cotter pins.

Answer 8

you move your left leg/right leg your body will follow
it's called walking.

Answer 9

We are like marrionettes with our tendons, muscles and bones.

Answer 10

With the motion that is kinetic energy.