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Questions and Answers
What is the result of applying a subthreshold stimulus?
What is the result of applying a subthreshold stimulus?
What characterizes catelectrotonus in terms of membrane potential?
What characterizes catelectrotonus in terms of membrane potential?
Which of the following statements about anelectrotonus is correct?
Which of the following statements about anelectrotonus is correct?
How does chronaxie change during catelectrotonus?
How does chronaxie change during catelectrotonus?
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What happens to excitability at the anode during strong currents?
What happens to excitability at the anode during strong currents?
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What type of degeneration occurs in the distal fragments of a nerve after it is cut?
What type of degeneration occurs in the distal fragments of a nerve after it is cut?
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How long does it typically take for regeneration of a nerve to start after a cut?
How long does it typically take for regeneration of a nerve to start after a cut?
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Which of the following types of currents represents a low intensity and longer duration electric stimulus?
Which of the following types of currents represents a low intensity and longer duration electric stimulus?
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What type of stimulus will produce an action potential in a nerve fiber?
What type of stimulus will produce an action potential in a nerve fiber?
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Which characteristic best describes retrograde degeneration?
Which characteristic best describes retrograde degeneration?
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What is the effect of increasing the intensity of a stimulus on utilization time?
What is the effect of increasing the intensity of a stimulus on utilization time?
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What is the role of macrophages following Wallerian degeneration?
What is the role of macrophages following Wallerian degeneration?
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Chronaxie is defined as what in relation to electric stimuli?
Chronaxie is defined as what in relation to electric stimuli?
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What does the rheobase represent in the context of excitability?
What does the rheobase represent in the context of excitability?
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How does an increase in chronaxie affect excitability?
How does an increase in chronaxie affect excitability?
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Which statement best describes what occurs when the rate of application of a stimulus rises rapidly?
Which statement best describes what occurs when the rate of application of a stimulus rises rapidly?
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Which of the following is an example of a non-excitable tissue?
Which of the following is an example of a non-excitable tissue?
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What characterizes leak channels in cellular membranes?
What characterizes leak channels in cellular membranes?
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What type of ionic channels responds to changes in membrane potential?
What type of ionic channels responds to changes in membrane potential?
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How does a constant current affect nerve stimulation?
How does a constant current affect nerve stimulation?
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What resting membrane potential is typically associated with excitable tissues like nerve and muscle?
What resting membrane potential is typically associated with excitable tissues like nerve and muscle?
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Study Notes
Medical Physiology - The Nerve (Part II)
- Course offered by: Prof. Dr. Magdi Ali El-Damarawi
- Course: Medical Physiology
- Faculty: Faculty of Medicine
- University: Gala University
Intended Learning Outcomes
- Students will be able to list different types of nerve degeneration
- Students will be able to recognize the time of nerve regeneration
- Students will be able to mention the types and characteristics of electric stimuli
- Students will be able to list factors determining stimulus effectiveness
- Students will be able to understand strength-duration curves
- Students will be able to define chronaxie, rheobase, and minimal time
- Students will be able to list types of cell membrane ionic channels
- Students will be able to understand the effect of subthreshold stimulus on the nerve cell membrane
Degeneration Reaction
- Degeneration reaction (RD) occurs due to nerve cutting
- Three types of degeneration:
- Wallerian Degeneration: Distal part, starts 3-4 days post-injury, axon and myelin sheath degenerate, debris removed by macrophages
- Retrograde Degeneration: Proximal part, extends to first node of Ranvier proximal to injury, affects cell body
- Transneural Degeneration: Rare, involves the entire nerve pathway
Nerve Regeneration
- Starts 20 days after injury and completes within 80 days
Types of Electric Stimuli
- Galvanic current:
- Low intensity
- Long duration
- From batteries
- Faradic current:
- High intensity
- Shorter duration
- Alternative current
Factors Determining Stimulus Effectiveness
-
Intensity:
- Subthreshold: No response
- Threshold: Action potential occurs
- Suprathreshold: Same response in single nerve fiber, greater response in mixed nerve
-
Duration:
- Utilization time/maximal time: Time needed for a stimulus to trigger a response
- Strength-duration curve: Relationship between stimulus intensity and duration
Additional Facts Regarding the Stimulus
- Stimuli of short duration won't excite, regardless of intensity.
- Very weak stimuli won't excite, regardless of duration.
- Rheobase: Minimum stimulus intensity for excitation
- Chronaxie: Time needed at double the rheobase intensity to achieve excitation; indicates excitability
- Minimal time (T): Time below which no stimulation occurs, regardless of intensity
Rate of Stimulus Application
- Rapid application causes a response
- Slow application results in no response due to the accommodation of the nerve
- Mechanism: Inactivation gates of sodium channels open and close simultaneously, stimulating to constant current only during circuit make and break
Excitable vs. Non-excitable Tissues
-
Excitable: Nerve, skeletal, cardiac, and smooth muscles
- Have a resting membrane potential (RMP) of -70 to -90 mV
- Develop action potentials (AP) on stimulation
-
Non-excitable: Liver, pancreas, red blood cells (RBCs), etc.
- Have a RMP of -10 to -30 mV
- Do not develop APs on stimulation
Types of Ionic Channels
- 2 types:
- Leak (passive) channels: Always open, specific to ions based on diameter and shape
- Examples: Sodium leak, potassium leak
- Gated (active) channels: Voltage-gated and ligand-gated channels
- Leak (passive) channels: Always open, specific to ions based on diameter and shape
Effect of Subthreshold Stimulus
- Subthreshold stimulus does not produce propagated action potential
- Instead, it generates non-propagated potentials like electrotonic potentials (electrotons) and local response
Electrotonic Potentials (Electrotonus)
- Results from subthreshold galvanic current (less than 7 mV)
- Consists of two types:
- Catelectrotonus: Increased excitability, depolarization
- Anelectrotonus: Decreased excitability, hyperpolarization
Propagation of Action Potential
- Direction of propagation in unmyelinated nerves
Action Potential Propagation in Myelinated Nerves
- Mechanism of nerve impulse propagation in myelinated nerves:
- Role of Nodes of Ranvier in saltatory conduction
Assignment 4
- Summary needed about the mechanism of action potential conduction in myelinated nerves
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Description
This quiz covers key concepts of nerve physiology, focusing on nerve degeneration and regeneration. Students will explore various types of nerve degeneration, electric stimuli characteristics, and factors affecting stimulus effectiveness. Prepare to enhance your understanding of crucial physiological phenomena.
