Which of the following correctly describes a graded potential?
It can have amplitudes of various sizes.
It travels long distances.
It is initiated by voltage changes in the membrane.
It has a depolarization, repolarization, and hyperpolarization phase.
The Correct Answer And Explanation is:
Correct Answer: It can have amplitudes of various sizes.
Explanation:
Graded potentials are a type of electrical signal used by neurons and other excitable cells to process and transmit information. Unlike action potentials, which are all-or-none events, graded potentials vary in size (amplitude) and are therefore described as graded.
Key Characteristics of Graded Potentials:
- Amplitude Varies with Stimulus Strength
The correct choice, “It can have amplitudes of various sizes,” is the defining characteristic of graded potentials. The strength of the stimulus determines the size of the graded potential. A stronger stimulus opens more ion channels, resulting in a larger change in membrane potential. This is in contrast to action potentials, which have a fixed size regardless of stimulus strength (as long as the threshold is reached). - Localized and Short-Distance Travel
Graded potentials occur locally, typically on dendrites or the cell body of a neuron, and do not travel long distances. They diminish in strength as they spread away from the site of origin, a process known as decremental conduction. This is why the option “It travels long distances” is incorrect; that description fits action potentials. - Initiated by Chemical or Mechanical Stimuli, Not Just Voltage
Graded potentials are usually triggered by ligand-gated or mechanically-gated ion channels, often in response to neurotransmitters or sensory stimuli, rather than by changes in membrane voltage. Therefore, “It is initiated by voltage changes in the membrane” is not correct—this describes action potentials, which involve voltage-gated channels. - Do Not Exhibit Depolarization-Repolarization-Hyperpolarization Sequence
Unlike action potentials, graded potentials do not have distinct depolarization, repolarization, and hyperpolarization phases. They can be depolarizing (more positive) or hyperpolarizing (more negative), depending on the type of ions involved, but they lack the characteristic three-phase sequence of an action potential.
Summary:
Graded potentials are variable, localized changes in membrane potential whose amplitude depends on the strength of the stimulus. They are crucial for integrating synaptic inputs and initiating action potentials if the threshold is reached at the axon hillock.