You measure levels of Ca2 in various locations within a moto

You measure levels of Ca²⁺ in various locations within a motor neuron and a skeletal muscle fiber when the motor neuron is depolarized, and the muscle fiber is actively shortening. Where do you expect to find higher levels of Ca²⁺? (Select all that apply.)

Btw there is more than one answer! Thanks in advance!

diffusing into the axon terminus of a motor neuron through specialized channels in the plasma membrane

bound to troponin

within the sarcoplasmic reticulum

in vesicles within the motor neuron

binding to the receptors at the motor endplate of the muscle cell

within the T-tubules

bound to myosin

bound to tropomyosin

Solution

The neurotransmitters released from the presynaptic neuron transmit a message to the dendrites of the postsynaptic neuron. When the action potential reaches the terminal buttons, the depolarization causes voltage-dependent calcium (Ca²⁺) channels on the presynaptic membrane to open and allows Ca²⁺ to enter into the cell. Ca²⁺ binds with the membrane of the synaptic vesicles, which causes the vesicles to break and release the neurotransmitter into the synaptic cleft.

Troponin is attached to the protein tropomyosin and lies within the groove between actin filaments in muscle tissue. ... Some of this calcium attaches to troponin, which causes it to change shape, exposing binding sites for myosin (active sites) on the actin filaments.

sarcoplasmic reticulum to release calcium ions into the muscle interior where they bind to troponin, thus causing tropomyosin to shift from the face of the actin filament to which myosin heads need to bind to produce contraction.

Thus sarcoplasmic reticulum consists high concentrations of calcium ions