I'm amazed at the sheer speed the internals of our body work.

Let's say you want to move your arm. Your brain sends a signal to a neuron, the signal travels the length of the neuron, which can be up to a meter long, via electro-chemical signaling process whereby ions (such as chlorine, sodium, potassium, and calcium) are moved into/out of the cell. The neuron comes to a synaptic gap where it ends and another neuron, or muscle cell, begins. Again, electro-chemical signaling processes result in the release and uptake of various ions and neurotransmitters in the synaptic gap which in turn cause the release and uptake of ions in the muscle cell.

The muscle cell reaches it's action potential and releases calcium from the sarcoplasmic reticulum, the calcium binds to troponin, which causes a conformational change in the tropomyosin, which exposes the myosin binding sites on the actin. The myosin heads can now metabolize the ATP to undergo myosin-actin cross-bridging, literally pulling themselves along the actin, which contracts the muscle cell. Repeat this thousands and thousands of times for a single muscle.

Then, when it's done contracting, the myosin releases the actin, the ADP gets recycled into ATP, the calcium is released from the troponin, the tropomyosin goes back to it's previous position, the calcium is reabsorbed by the sarcoplasmic reticulum, the sodium, potassium, chlorine, and calcium levels in the cell and interstitial space return to normal via many ion channels (regulated by voltage, other ions, neurotransmitters, hormones, etc...) and the muscle is ready to contract again.

All of this is done in a fraction of a second.

Here is a neat little animation of a myosin head interacting with an actin thread...and yes, it really does look just like that:



Red thing is the myosin head, green sphere is the ATP, the little part that jettisons off is the Phosphate, so it's ADP that's left, the pink and blue thing is the tropomyosin complex, the yellow dot is calcium, and the orange is the actin.

Biology is so frigging complex.

Biology is so frigging complex.

Indeed it is. Organisms such as ourselves are so amazingly built.

And yet to flies and other fast-reacting organisms we move like slow lumbering skyscraper.

Flies have sensors that can detect sudden changes in air movement/pressure. If such an event has occurred, they perform air maneuver techniques not unlike those performed by fighter jet pilots.

It's cool.
Not into biology, but it's still interesting.

Indeed. It's surprising how a simple task such as moving your arm is actually an incredibly complex procedure.

Gives one a special appreciation of who and what we are no? A respect, for how durable and adaptable we are. But, also a care, for realizing that despite it all, sometimes we can be so very fragile.