Final answer:
Positive ion movements across a cell membrane influence cell charge: the cell becomes more negative when they move out and more positive when they move in, affecting the resting membrane potential which is crucial for neuron signaling.
Step-by-step explanation:
Movements of ions can indeed change the membrane potential of a cell. If a positive ion moves out of a cell, the cell will become more negative. Conversely, if a positive ion moves into a cell, the cell will become more positive. This is due to the electrochemical gradient across the cell membrane that affects ion movement.
The resting membrane potential is typically around -70 mV inside a neuron due to the higher concentration of potassium ions inside and sodium ions outside the cell, as well as the activity of the sodium-potassium pump which expels more cations than it allows in. When positively charged ions such as sodium (Na+) enter the cell, they reduce the negativity of the cell's interior, resulting in depolarization. This action moves the membrane potential closer to zero. On the other hand, when potassium ions (K+) leave the cell, it enhances the negative charge inside, which is referred to as hyperpolarization.
The balance of these ionic movements is crucial for the generation and propagation of electrical signals in neurons and muscle cells, enabling them to communicate and respond to various stimuli.