Question

Provide a rationale as to how a single ion such as calcium is able to mediate such diverse responses. In other words—how is it that Ca2+ serves to communicate different signals in neurons, versus muscle cells, versus egg cells, etc.?

Answer 1

Answer: Transmission at chemical synapses occurs when a nerve impulse arrives at the terminal of the presynaptic neuron. This lead to the change in membrane potential caused by the arrival of the action potential leads to the opening of voltage-gated calcium channels in the presynaptic membrane. Because the concentration of calcium ions are more in the extracellular fluid, calcium flows inward through the opened channels. An increase in the concentration of calcium inside the presynaptic neuron serves as a signal that triggers exocytosis of the synaptic vesicles. Neurotransmitter diffuses across the synaptic cleft and binds to receptors present in postsynaptic neurons. Binding of neurotransmitter to receptor generates postsynaptic potential.

The signal from nerve triggers an action potential in the sarcolemma. The action potential propagates through T-tubules. The t-tubule membrane contains voltage-sensitive proteins, which are activated by an incoming action potential. Activated voltage-sensitive proteins trigger the opening of calcium release channels in the sarcoplasmic reticulum. Increase in cytosolic calcium initiates the contraction of each myofibril.

The skeletal muscle contraction is regulated by the tropomyosin-troponin complex bound to the thin actin filament switching between the contraction-inducing state in the presence of calcium and relaxed in its absence.

In living organisms, the rise in intracellular calcium level is responsible for releasing unfertilized eggs in meiosis and triggering the embryonic development, called as egg activation. Endoplasmic reticulum regulates calcium signalling and also maintain homeostasis.

Calcium severs as a signal for guard cells, free calcium enters the cytosol from outside the cell thereby reversing the concentration gradient of K+ ions which cause loss of solutes that make cell flaccid and closes the stomatal pores.

Calcium also required for the formation f mitotic spindle, without which cell division will not take place.

Answer 2

I think the simple answer is two-fold:

- what if all our cells use calcium ions to communicate with each other?

- Dr. Carey Reams believed hundreds or thousands of calcium compunds existed in the body, both precursers and metabolites.  This exapnds the logic of what teh question asserts.