electrolytic muscle function, and disease

At rest : 

• [ neuron and muscle independently : sodium-potassium pump (slow) : pushes out 3Na+ for every 2K+ pulled in, maintaining negative voltage inside the cell ]

Firing : 

• [ neuron : ( due to upstream stimulation) opens sodium gate, Na+ inflow sends current to calcium gate, Ca2+ enters neuron, triggers acetylcholine release into synaptic cleft ] 
• -> [ muscle : acetylcholine from synaptic cleft, opens sodium gate, Na+ inflow sends current to sarcoplasmic reticulum, which releases calcium, which causes contraction of the cell : (fast) K+ leaves cell to restore negative voltage inside the cell ]

Muscle Diseases, and ordinary states which become diseases if not reversed within ordinary timeframes :

• - Ca2+ : 
• too much outside cells, "overshields" sodium gates of BOTH neurons and muscles, both become "understimulated" ... and subsequent to neuron stimulation, Ca2+ enters neuron slower, dumping acetylcholine slower, furthering muscle "understimulation"; 
• too little outside cells, "undershields" sodium gates of BOTH neurons and muscles, both become "overstimulated" ... and subsequent to neuron stimulation, Ca2+ enters neuron faster, dumping acetylcholine faster, furthering muscle "overstimulation"
• - Mg2+ :
• too much outside cells, block Ca2+ entry to neurons, reducing acetylcholine release, "understimulating" muscles
• too little outside cells, Ca2+ entry is less blocked, increasing acetylcholine release, "overstimulating" muscles
• - K+ : 
• too much outside cell, K+ cannot leave quickly, cell may become "overcontracted" - ditto "overexcitation" of neuron at early stages, but  at later stages, sodium gates fail, neurons and muscles both weaken; 
• too little outside cell, K+ leaves too fast, cell may become "hard to contract"
• - Na+ : 
• too much outside cell, Na+ enters quickly, cell may become "overexcited", ditto for neuron; 
• too little outside cell, Na+ cannot enter quickly, "underexciting" cell, ditto for neuron; nervous system may overcompensate with erratic voltages, causing "erratic excitation"