Final answer:
Graded potentials are changes in the membrane potential caused by the movement of ions through specific ion channels. Barriers to ion movement can prevent these potentials, affecting neuron excitability. The Coulomb force balances diffusion of ions with repulsion and attraction of charges, thereby establishing membrane voltage.
Step-by-step explanation:
When a barrier prevents the movement of opposite charges toward one another in neurons, it affects the local changes in the membrane potential known as graded potentials. These are crucial for the function of neurons as they determine whether or not a neuron will fire an action potential.
If positive charges such as Na⁻ or Ca²⁻ ions are prevented from moving into a neuron, a depolarizing graded potential will not occur, and the neuron will not be excited. Conversely, if negative charges such as Cl⁻ ions cannot enter or positive charges like K⁻ cannot exit the cell, a hyperpolarizing graded potential, which inhibits neuron firing, might not take place.
Graded potentials depend on specific ion channels in a cell membrane. These channels must open and close properly for ions to flow in or out, altering the voltage across the membrane. The Coulomb force plays a crucial role here by balancing the diffusion of ions with the repulsion and attraction of charges, which effectively creates a voltage across the membrane.