Where is Ca++ released during muscle contraction?

Once the motor neuron releases Ach it binds to the motor-end plate allowing an influx of sodium ions thus creating a depolarization...if threshold is reached an action potential is generated and will travel down the sarcolema into the transverse tubules and it will open the calcium channels here. The calcium then binds to troponin, changing the conformation, which in turn changes the conformation of tropomyosin that will reveal the active site on the actin. The myosin head releases phosphate and attaches to the active site and then releases ADP which causes the "power stroke." After this a new ATP comes along and removes the myosin head from the actin.

But I guess the answer you were looking for is transverse tubules (t-tubules) which are located in the infoldings of the sarcolemma (where calcium is stored).

Hopefully that helps some.

In a muscle movement, the motor neurons allow in Ca++ which releases acetylcholine, which gets bound and actively transported into a muscle cell. The active transport causes the actual movement. So I guess for a contraction, since the Ca++ is in the motor neuron during a muscle movement, it would get released from there too?

I know Ca++ interacts with the motor neurons, but I forget whether it entering the neuron is for expansion or contraction....

blood stream.