Questions and Answers
What are graded potentials?
Depolarizations or hyperpolarizations that occur in dendrites, soma, or near the axon terminals.
Graded potential occurs when?
When ion channels open or close causing ions to enter or leave the neuron.
Why are they called graded potentials?
Because their size or amplitude is directly proportional to the strength of the triggering event.
Give an example of large or small graded potential.
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Give an example of a graded potential.
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What is the wave of depolarization that moves through the cell known as?
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What is current flow in biological systems defined as?
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The strength of the initial depolarization in a graded potential is determined by?
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Why do graded potentials lose strength as they move through the cytoplasm?
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What is current leak?
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What is cytoplasmic resistance?
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Graded potentials that are strong enough eventually reach the?
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Where are the trigger zones in motor neurons?
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Where are the trigger zones in sensory neurons?
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What is the integrating center of the neuron?
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What does a trigger zone contain in its membrane?
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What is the threshold voltage?
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What happens if graded potentials reaching the trigger zone depolarize the membrane to the threshold voltage?
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The resting membrane potential of the trigger zone is -70mv. To initiate an action potential, what must the influx of sodium change the membrane potential to?
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What happens if the depolarization does not reach -55mv (threshold voltage)?
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A depolarizing graded potential is known as?
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Depolarization is necessary to?
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What is a hyperpolarization graded potential?
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Hyperpolarizing graded potentials are called?
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Study Notes
Graded Potentials Overview
- Graded potentials are changes in membrane potential (depolarizations or hyperpolarizations) initiated in dendrites, soma, or near axon terminals.
- They occur due to the opening or closing of ion channels, leading to the movement of ions into or out of the neuron.
Characteristics of Graded Potentials
- The amplitude of graded potentials is proportional to the strength of the triggering event, hence the term "graded".
- Strong stimuli result in larger graded potentials, while weak stimuli lead to smaller ones.
Mechanism of Graded Potentials
- A chemical or mechanical stimulus can open sodium channels on a postsynaptic neuron's membrane, allowing sodium ions to flow into the neuron.
- This influx generates a wave of depolarization known as local current flow, propagating through the cytoplasm.
Factors Influencing Strength and Propagation
- The initial strength of depolarization in a graded potential depends on the amount of charge entering the cell.
- Graded potentials lose strength as they travel through the cytoplasm due to current leak and cytoplasmic resistance.
- Current leak occurs when positive charges escape through open (leak) channels in the membrane.
- Cytoplasmic resistance impedes the flow of electricity within the cell.
Trigger Zone and Action Potential
- Graded potentials that are sufficiently strong to reach the trigger zone can initiate an action potential.
- In motor neurons, the trigger zone is located at the axon hillock and initial segment.
- For sensory neurons, the trigger zone is near the receptor where dendrites connect to the soma.
- The trigger zone serves as the neuron's integrating center and contains a high concentration of voltage-gated sodium channels.
Threshold Voltage and Action Potential Initiation
- The threshold voltage for initiating an action potential is -55 mV, with a resting membrane potential of -70 mV in the trigger zone.
- If graded potentials depolarize the membrane to the threshold voltage, voltage-gated sodium channels open, leading to the initiation of an action potential.
- If depolarization does not reach -55 mV, no action potential occurs, and the graded potential dissipates.
Types of Graded Potentials
- A depolarizing graded potential, which makes the neuron more likely to fire, is termed an Excitatory Post Synaptic Potential (EPSP).
- Depolarization is essential for neuron activation and firing of an action potential.
- A hyperpolarizing graded potential moves the membrane potential further from the threshold, making it more negative and less likely to fire an action potential.
- Hyperpolarizing graded potentials are referred to as Inhibitory Post Synaptic Potentials (IPSP), as they decrease the likelihood of action potential generation.
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Test your understanding of graded potentials with these flashcards. Explore the definitions, occurrences, and significance of graded potentials in neurons. This quiz will strengthen your grasp on key concepts related to neuronal signaling.