Which of the following correctly describes a graded potential?
A) it has a depolarization, repolarization and hyperpolarization phase
B) it can have amplitudes of various sizes
C) it is initiated by voltage changes in the membrane
D) it travels long distances
The Correct Answer and Explanation is:
The correct answer is B) it can have amplitudes of various sizes.
Explanation:
Graded potentials are a type of electrical signal that occur in the dendrites and cell body of a neuron. They are local changes in the membrane potential that vary in size depending on the strength of the stimulus. Unlike action potentials, which are all-or-nothing events, graded potentials have amplitudes that can vary—hence the term “graded.” This means they can be small or large, depending on the intensity of the stimulus that triggered them.
Let’s break down each option:
- A) It has a depolarization, repolarization, and hyperpolarization phase: This statement describes the phases of an action potential, not a graded potential. While graded potentials can be either depolarizing or hyperpolarizing (depending on whether the membrane potential becomes more positive or more negative), they do not follow the typical three-phase pattern (depolarization, repolarization, and hyperpolarization) seen in action potentials. Graded potentials are not characterized by a fixed sequence of phases.
- B) It can have amplitudes of various sizes: This is the correct statement. Graded potentials vary in magnitude depending on the stimulus. For example, a stronger stimulus will produce a larger graded potential, while a weaker stimulus will generate a smaller potential. The amplitude of a graded potential is directly proportional to the strength of the stimulus.
- C) It is initiated by voltage changes in the membrane: Graded potentials are typically initiated by sensory stimuli (e.g., pressure or light) or neurotransmitters binding to receptors, not by voltage changes in the membrane. In contrast, action potentials are initiated by a threshold depolarization that opens voltage-gated ion channels.
- D) It travels long distances: Graded potentials decay over distance. They are localized changes in membrane potential and do not travel long distances like action potentials. The signal weakens as it spreads away from the site of initiation.
In conclusion, graded potentials are local changes in membrane potential that vary in size and decrease in strength with distance, making option B the correct answer.