Final answer:
The voltage in a mammalian cell is established by separation of charge across the membrane, resulting in a potential difference. Ion channels play a key role, allowing ions to move in and out, creating voltage pulses for neural signaling and muscle contraction.
Step-by-step explanation:
In a typical mammalian cell, the voltage or membrane potential is established by the separation of charge across the cell membrane. This creates a potential difference usually between -60 to -90 mV (millivolts), with the inside of the cell being negative relative to the outside. The process involves a dynamic balance of ions, particularly sodium (Na+) and potassium (K+), which are moved in and out of the cell by ion channels and pumps in the cell membrane. Furthermore, the electric field generated across the thin membrane, about 7 to 10 nm thick, is substantial, on the order of 11 MV/m, indicating a strong separation of charge. Energy expenditure is significant as well, with up to 25% of a cell's energy used to maintain these potentials.
When a neuron is activated, Na+ ions rush into the cell through channels, causing depolarization and subsequently a reversal of the membrane potential, leading to an action potential. This voltage pulse is fundamental for nerve signal transmission. Post-depolarization, K+ ions help return the cell to its resting potential in a process called repolarization. These cellular mechanisms are crucial for neural signaling and muscle contraction, also known as Excitation-Contraction Coupling.