Final answer:
Opposition to the buildup of graded potentials in a neuron's soma is supported by the opening of chloride (Cl-) and potassium (K+) channels, low density of channels, and voltage dissipation, which negate depolarization that otherwise occurs due to the opening of sodium (Na+) channels during excitatory events.
Step-by-step explanation:
Factors that oppose the buildup of graded potentials in the soma include the opening of chloride channels, the opening of potassium channels, low density of sodium channels and potassium channels, and voltage dissipation across the membrane and cytosol. Not mentioned is the opening of sodium channels, which actually contributes to depolarization and supports the buildup of graded potentials. During neuron depolarization, the neuron's membrane potential becomes more positive due to the influx of Na+ ions. Conversely, hyperpolarization occurs when K+ exits the cell or Cl- enters, making the inside more negative relative to the outside. The entry of Cl- works against the formation of depolarizing graded potentials by stabilizing or hyperpolarizing the membrane potential.
During an action potential, Na+ channels first open to depolarize the membrane, and then, following the peak depolarization, K+ channels open to allow positive ions to leave, returning the membrane potential to a more negative state, often even more negative than the resting potential before returning to it. This sequence of ion channel activities enables neurons to reset and be ready for subsequent action potentials. Opposing forces such as the entry of Cl- or the exit of K+ during graded potentials help regulate this process and prevent the indiscriminate buildup of excitatory signals.