Graded Potentials Flashcards

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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.

A large stimulus causes a strong graded potential and a small stimulus causes a weak graded potential. Signup and view all the answers

Give an example of a graded potential.

A chemical or mechanical stimulus opens sodium channels on the postsynaptic neuron membrane, causing positive charge carried by sodium to spread as a wave of depolarization through the cytoplasm. Signup and view all the answers

What is the wave of depolarization that moves through the cell known as?

Local current flow. Signup and view all the answers

What is current flow in biological systems defined as?

The net movement of positive electrical charge. Signup and view all the answers

The strength of the initial depolarization in a graded potential is determined by?

How much charge enters the cell. Signup and view all the answers

Why do graded potentials lose strength as they move through the cytoplasm?

Due to current leak and cytoplasmic resistance. Signup and view all the answers

What is current leak?

Some of the positive charges leak back across the membrane via open (leak) channels. Signup and view all the answers

What is cytoplasmic resistance?

Cytoplasm provides resistance to the flow of electricity. Signup and view all the answers

Graded potentials that are strong enough eventually reach the?

Trigger zone. Signup and view all the answers

Where are the trigger zones in motor neurons?

They are comprised of the axon hillock and initial segment. Signup and view all the answers

Where are the trigger zones in sensory neurons?

Immediately adjacent to the receptor where the dendrites join the soma. Signup and view all the answers

What is the integrating center of the neuron?

The trigger zone. Signup and view all the answers

What does a trigger zone contain in its membrane?

A high concentration of voltage-gated sodium ion channels. Signup and view all the answers

What is the threshold voltage?

Minimum level -55mv. Signup and view all the answers

What happens if graded potentials reaching the trigger zone depolarize the membrane to the threshold voltage?

The voltage-gated sodium channels open and an action potential is initiated. Signup and view all the answers

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?

-55mv. Signup and view all the answers

What happens if the depolarization does not reach -55mv (threshold voltage)?

No action potential has begun, and the graded potential dies out as it moves into the axon. Signup and view all the answers

A depolarizing graded potential is known as?

An Excitatory Post Synaptic Potential (EPSP). Signup and view all the answers

Depolarization is necessary to?

Excite the neuron to fire an action potential. Signup and view all the answers

What is a hyperpolarization graded potential?

It moves the membrane potential further from the threshold value, making the inside of the cell more negative and less likely to fire an action potential. Signup and view all the answers

Hyperpolarizing graded potentials are called?

Inhibitory Post Synaptic Potentials (IPSP). Signup and view all the answers

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.