Graded potentials:
arise when ion movement causes a minor change in the resting membrane potential.
usually propagate down the length of an axon.
occur when voltage-gated channels open.
are most often observed in axons.
are usually associated with ion movement through leakage channels.
To answer this question, we can break it down statement by statement.
1. "Graded potentials arise when ion movement causes a minor change in the resting membrane potential."
Graded potentials refer to localized changes in the membrane potential of a neuron, which can either depolarize (increase the membrane potential) or hyperpolarize (decrease the membrane potential). These changes occur in response to the opening or closing of ion channels in the neuron's membrane. For example, if positive ions (like sodium or potassium) enter the neuron, it will depolarize, while if negative ions (like chloride) enter, it will hyperpolarize. These changes can be small and localized, compared to the all-or-nothing action potentials.
2. "Graded potentials usually propagate down the length of an axon."
Unlike action potentials, which propagate down the entire length of the axon, graded potentials often do not propagate as far. Graded potentials tend to decrease in strength as they move away from the initial site of stimulation since these potentials are passive, meaning they dissipate as they spread. Therefore, graded potentials are primarily responsible for short-distance signaling within neurons.
3. "Graded potentials occur when voltage-gated channels open."
This statement is not entirely accurate. Voltage-gated channels are responsible for generating action potentials rather than graded potentials. Graded potentials primarily result from the opening or closing of ligand-gated channels, which are triggered by the binding of specific chemical messengers (ligands) such as neurotransmitters. These ligand-gated channels allow ions to enter or exit the neuron, leading to changes in the membrane potential.
4. "Graded potentials are most often observed in axons."
This statement is incorrect. Graded potentials are not specific to axons; they can occur in any region of the neuron's membrane, including the dendrites and soma (cell body). In fact, graded potentials are particularly prominent in the dendrites, where they play a crucial role in integrating synaptic inputs from multiple sources before generating an action potential.
5. "Graded potentials are usually associated with ion movement through leakage channels."
This statement is also inaccurate. Graded potentials are primarily associated with ion movement through ligand-gated channels, as mentioned earlier. Leakage channels, on the other hand, are continuously open and allow a small "leak" of ions across the membrane, contributing to the resting membrane potential, but they are not directly involved in generating graded potentials.
In summary, graded potentials are localized changes in membrane potential caused by the opening or closing of ligand-gated channels. They can depolarize or hyperpolarize the neuron but do not propagate as far as action potentials. Graded potentials are not specific to axons and are not associated with leakage channels.