Explain the role of inorganic ions in the body.

The resting membrane potential of cells is maintained by the actions of Na+ and K+. A resting cell is impermeable to Na+ so the concentration of Na+ is greater outside the cell than in it. However the cell is permeable to K+ so there is a greater concentration of K+ inside the cell than out. This generates an electrochemical gradient caused by the movement of + ions. The resting membrane potential is also maintained by the Na+/K+ pump which transports 3 Na+ out of the cell for every 2 K+ it transports in. Resting membrane potential is maintained at -70mV. Action potentials of cells are also determined by the movement of Na+ and K+ ions. On arrival of an action potential in a neuron voltage gated Na+ channels open causing an influx of Na+ into the neuron rapidly raising the membrane potential of the neurone. At 30mV the Na+ channels close and voltage gated K+ channels open causing an efflux of K+ which hyperpolarises the cell. This hyperpolarisation prevents tetanus as it prevents any further action potentials for a short period of time allowing discrete signals to be send along the neurone. Ca2+ has a role in muscle contraction. On arrival of an action potential to a sarcomere (muscle cell) Ca2+ is released from the sarcoplasmic reticulum. Ca2+ then binds to troponin on tropomyosin causing it to move and expose the binding sites on actin filaments allowing myosin to bind to actin and allow muscle contraction.