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1. Introduction to Anatomy & Physiology5h 43m
2. Cell Chemistry & Cell Components12h 36m
3. Energy & Cell Processes10h 6m
4. Tissues & Histology10h 3m
5. Integumentary System2h 20m
6. Bones & Skeletal Tissue2h 16m
7. The Skeletal System2h 35m
8. Joints2h 17m
9. Muscle Tissue2h 33m
10. Muscles1h 11m
11. Nervous Tissue and Nervous System1h 35m
12. The Central Nervous System1h 6m
- Introduction to the Central Nervous System
  18m
- The Cerebrum
  48m
13. The Peripheral Nervous System1h 26m
14. The Autonomic Nervous System1h 38m
15. The Special Senses2h 41m
16. The Endocrine System2h 48m
17. The Blood3h 22m
18. The Heart2h 42m
19. The Blood Vessels3h 35m
20. The Lymphatic System3h 16m
21. The Immune System14h 37m
22. The Respiratory System3h 20m
23. The Digestive System2h 5m
24. Metabolism and Nutrition4h 0m
25. The Urinary System2h 39m
26. Fluid and Electrolyte Balance, Acid Base Balance37m
27. The Reproductive System2h 5m
28. Human Development1h 21m
29. Heredity3h 32m

11. Nervous Tissue and Nervous System

Properties of Graded and Action Potentials

11. Nervous Tissue and Nervous System

Properties of Graded and Action Potentials: Videos & Practice Problems

Video Lessons Practice Worksheet

Topic summary

Graded potentials are variable strength signals occurring when ion channels open or close in response to stimuli, typically on dendrites and the cell body. In contrast, action potentials are brief, identical depolarization events that propagate along axons, initiated only when the membrane reaches a threshold of approximately -55 mV. Graded potentials can be depolarizing or hyperpolarizing, while action potentials are always depolarizing. Understanding these differences is crucial for grasping neuronal communication and the all-or-none principle of action potentials.

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Graded and Action Potentials

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Graded and Action Potentials Video Summary

Graded and action potentials are fundamental concepts in neurophysiology, representing different types of electrical signals in neurons. Graded potentials are variable strength signals that occur when ion channels open or close in response to a stimulus. These potentials arise when a neuron receives a stimulus, leading to a change in membrane potential. They can be either depolarizing, making the membrane more positive, or hyperpolarizing, making it more negative, depending on the nature of the stimulus.

In contrast, action potentials are brief, all-or-nothing depolarization events that propagate along the axon of a neuron. The transition from graded to action potential occurs at the initial segment of the axon, where the axon meets the cell body. If the graded potential is strong enough to reach a threshold of approximately -55 millivolts, an action potential will be triggered. This threshold is crucial, as action potentials only initiate when this specific membrane potential is reached.

Graded potentials serve as input signals, typically occurring on dendrites and the cell body, and are designed for short-distance travel. Their strength varies with the magnitude of the incoming stimulus; a stronger stimulus results in a larger graded potential. Conversely, action potentials are output signals that occur along the axon and are designed for long-distance communication. Unlike graded potentials, action potentials are always identical in magnitude, regardless of the strength of the stimulus, which is why they are referred to as an all-or-none phenomenon.

In summary, graded potentials can vary in strength and do not require a minimum threshold to occur, while action potentials are uniform in strength and require reaching a specific threshold to initiate. Understanding these differences is essential for grasping how neurons communicate and process information.

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Properties of Graded and Action Potentials Example 1

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Properties of Graded and Action Potentials Example 1 Video Summary

Action potentials are critical for neuronal communication and are characterized as an all-or-nothing phenomenon. This means that once the membrane potential of a neuron reaches a specific threshold, an action potential will occur. The threshold for initiating an action potential is approximately -55 millivolts (mV). Understanding this threshold is essential, as it indicates the point at which the neuron can effectively transmit signals.

To grasp this concept, consider the resting membrane potential of a neuron, which is typically around -70 mV. For a neuron to fire an action potential, it must depolarize to -55 mV. This shift is manageable compared to a more significant change, such as moving from -70 mV to 0 mV or even +30 mV, which would require a substantial influx of ions and is less feasible. The proximity of the action potential threshold to the resting potential allows for a more efficient and rapid response, as only a moderate influx of sodium ions is needed to reach the threshold and trigger the action potential.

In summary, the action potential threshold is a crucial value in neurophysiology, set at -55 mV, enabling neurons to communicate effectively without requiring excessive changes in membrane potential.

Problem

_ are all identical, whereas can be larger or smaller depending on the level of stimulation.

Action potentials; graded potentials.

Graded potentials; action potentials.

Depolarizations; hyperpolarizations.

Repolarizations; depolarizations.

Problem

Which of the following statements about graded potentials is FALSE?

Graded potentials act as short distance signals.

The magnitude of a graded potential is proportional to the magnitude of the stimulus.

Graded potentials occur mainly in axons.

Graded potentials can be depolarizing or hyperpolarizing.

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Here’s what students ask on this topic:

What are the main differences between graded potentials and action potentials?

Graded potentials are variable strength signals that occur when ion channels open or close in response to stimuli, typically on dendrites and the cell body. They can be depolarizing or hyperpolarizing and vary in strength based on the stimulus. In contrast, action potentials are brief, identical depolarization events that propagate along axons. They are initiated only when the membrane reaches a threshold of approximately -55 mV and are always depolarizing. Action potentials follow the all-or-none principle, meaning they either occur fully or not at all, regardless of the stimulus strength once the threshold is reached.

How do graded potentials and action potentials differ in terms of signal strength and distance traveled?

Graded potentials vary in strength depending on the magnitude of the stimulus and are designed for short-distance travel, typically occurring on dendrites and the cell body. In contrast, action potentials are all identical in strength and are designed for long-distance travel along axons. The strength of an action potential does not vary with the stimulus once the threshold is reached, adhering to the all-or-none principle.

What is the threshold value for an action potential, and why is it important?

The threshold value for an action potential is approximately -55 mV. This value is crucial because it determines whether an action potential will be initiated. If the membrane potential at the initial segment of the axon reaches this threshold due to depolarization from graded potentials, an action potential will fire. This all-or-none phenomenon ensures that action potentials are consistent and reliable signals for neuronal communication.

Can graded potentials be both depolarizing and hyperpolarizing? Explain.

Yes, graded potentials can be both depolarizing and hyperpolarizing. Depolarizing graded potentials make the membrane potential more positive, moving it closer to the threshold for an action potential. Hyperpolarizing graded potentials make the membrane potential more negative, moving it further from the threshold. The type of graded potential depends on the nature of the stimulus and the specific ion channels that open or close in response.

Why are action potentials described as an all-or-none phenomenon?

Action potentials are described as an all-or-none phenomenon because they either occur fully or not at all. Once the membrane potential at the initial segment of the axon reaches the threshold of approximately -55 mV, an action potential will always fire with the same magnitude. This ensures that the signal is consistent and reliable, regardless of the strength of the initial stimulus, as long as the threshold is reached.