Final answer:
The change from -70 mV to +50 mV in a neuron's membrane potential during an action potential is caused by depolarization, where sodium ions enter the cell upon stimulation, and repolarization, where potassium ions exit the cell.
Step-by-step explanation:
What causes the membrane potential to change from -70 mV to +50 mV is the process known as depolarization, which occurs during the action potential in nerve cells. Initially, a resting membrane potential is established at about -70 mV, mainly due to the negatively charged ions inside the cell and positively charged sodium ions outside.
Upon stimulation, voltage-gated sodium channels open, allowing sodium ions to rush into the cell, making the inside less negative and eventually positive, reaching up to +30 mV. As the depolarization reaches its peak, potassium channels open, and potassium ions leave the cell, carrying positive charges with them, which starts the process of repolarization—bringing the membrane potential back towards the resting level.