Explain how graded potentials and action potentials are different. On which part of a neuron would you expect a graded potential to occur? An action potential? Explain what an EPSP and IPSP are? How would you generate an IPSP?
The Correct Answer and Explanation is:
Correct Answer:
Graded potentials differ from action potentials in their strength, duration, and location. Graded potentials are small, local changes in membrane potential that vary in size and decay over distance. They typically occur on the dendrites and cell body (soma) of a neuron. Action potentials, in contrast, are large, uniform electrical impulses that do not decrease in strength as they travel. These occur along the axon and begin at the axon hillock.
An EPSP (excitatory postsynaptic potential) is a graded depolarization that brings the neuron closer to the threshold for firing an action potential. An IPSP (inhibitory postsynaptic potential) is a graded hyperpolarization that moves the membrane potential farther from the threshold, decreasing the likelihood of an action potential. An IPSP can be generated when neurotransmitters such as GABA or glycine bind to receptors that open channels for negatively charged ions like Cl⁻, or cause the efflux of K⁺ ions.
300-Word Explanation:
Graded and action potentials represent distinct electrical phenomena in neurons, with specific characteristics and roles. Graded potentials arise in the dendrites and soma when chemically gated ion channels open in response to neurotransmitters. These potentials are variable in magnitude and direction depending on the strength and type of stimulus. If multiple graded potentials summate to reach a threshold level, they can trigger an action potential at the axon hillock.
Action potentials, by contrast, are uniform, all-or-none electrical events that occur along the axon. Once threshold is reached, voltage-gated Na⁺ channels open, causing a rapid depolarization. This is followed by repolarization due to the opening of voltage-gated K⁺ channels. Unlike graded potentials, action potentials do not diminish with distance and are propagated down the entire length of the axon.
EPSPs and IPSPs are types of graded potentials. An EPSP is caused by the influx of positive ions, usually Na⁺, making the inside of the neuron more positive and closer to threshold. An IPSP results from either the efflux of K⁺ or the influx of Cl⁻, making the membrane more negative and less likely to fire an action potential.
To generate an IPSP, a neurotransmitter like GABA can bind to a receptor on the postsynaptic neuron, opening Cl⁻ channels. The resulting influx of Cl⁻ causes hyperpolarization, stabilizing the membrane and reducing excitability. This plays a key role in controlling and balancing neural activity.
