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Ch. 11 Introduction to the Nervous System and Nervous Tissue
Amerman- Human Anatomy & Physiology 3e
Amerman3rd EditionHuman Anatomy & PhysiologyISBN: 9780138247201, 9780138247928, 9780138201814Not the one you use?Change textbook
All textbooksAmerman 3rd EditionCh. 11 Introduction to the Nervous System and Nervous TissueProblem L3.4
Chapter 11, Problem L3.4

Albert, the patient in question 3, takes the drug lithium, which reduces the permeability of the neuronal axolemma to Na+ (that is, it allows fewer Na+ to enter the axon). Predict the effect this would normally have on his neuronal action potentials. Do you think this drug would be beneficial or harmful, considering his condition?

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Understand the role of Na+ in neuronal action potentials: Sodium ions (Na+) play a critical role in generating action potentials. During the depolarization phase, voltage-gated Na+ channels open, allowing Na+ to enter the neuron, which causes the membrane potential to become more positive.
Analyze the effect of reduced Na+ permeability: If the drug lithium reduces the permeability of the neuronal axolemma to Na+, fewer Na+ ions will enter the neuron during depolarization. This would likely slow down or reduce the magnitude of the depolarization phase of the action potential.
Consider the impact on action potential generation: With reduced Na+ entry, the threshold for generating an action potential may not be reached as easily, or the action potential may be weaker. This could lead to decreased neuronal excitability and slower signal transmission.
Evaluate the potential benefits or harms: Determine whether reduced neuronal excitability is beneficial or harmful based on the patient's condition. For example, if the patient has a condition like bipolar disorder, where excessive neuronal activity may contribute to symptoms, reducing excitability could be therapeutic. However, if the patient requires normal neuronal signaling for other functions, this could be harmful.
Conclude based on the patient's specific condition: Assess the overall effect of the drug by weighing its benefits (e.g., stabilizing mood in bipolar disorder) against potential side effects (e.g., impaired neuronal communication in other systems). This requires understanding the patient's medical history and condition in detail.

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Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Neuronal Action Potentials

Neuronal action potentials are rapid changes in the electrical membrane potential of a neuron that occur when it is stimulated. This process involves the influx of sodium ions (Na<sup>+</sup>) through voltage-gated channels, leading to depolarization. The action potential is crucial for the transmission of signals along the axon and communication between neurons.
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Action Potential

Sodium Ion Permeability

Sodium ion permeability refers to the ability of the neuronal membrane to allow Na<sup>+</sup> ions to pass through. When permeability is high, Na<sup>+</sup> enters the neuron rapidly, contributing to depolarization and the generation of action potentials. Conversely, reduced permeability, as seen with lithium, limits Na<sup>+</sup> entry, potentially impairing neuronal excitability and signaling.
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Ions - Sodium and Potassium Example 3

Lithium's Mechanism of Action

Lithium is a mood-stabilizing medication commonly used to treat bipolar disorder. It affects neuronal excitability by altering ion transport mechanisms, particularly reducing Na<sup>+</sup> permeability. While this can stabilize mood by dampening excessive neuronal firing, it may also hinder normal action potential generation, which could be detrimental depending on the patient's specific neurological condition.
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Related Practice
Textbook Question

Explain what would happen if depolarization of the trigger zone led to a negative feedback loop instead of a positive one.

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Textbook Question

During a surgical procedure, an anesthesiologist administers to the patient an inhaled anesthetic agent that opens Cl− channels in the postsynaptic membranes of neurons in the brain. Explain why this would put the patient 'to sleep' for the duration of the surgical procedure.

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Textbook Question

Predict the effect that tetrodotoxin would have on Albert's muscle fiber action potentials (see question 3). Would it affect end-plate potentials at the motor end plate? Why or why not?

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Textbook Question

The drug neostigmine blocks the actions of acetylcholinesterase in the synaptic cleft. What effect would this have on synaptic transmission? What effects might you expect to see as a result of this drug?

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Explain why cardiac muscle cells and some smooth muscle cells will continue to contract even when their nerve supply has been removed

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Textbook Question

A hypothetical poison blocks K+ leak channels. How would this affect the resting membrane potential of skeletal muscle fibers? Explain your reasoning.

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