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Questions and Answers
What is necessary to evoke an action potential?
Myelinated fibers conduct impulses slower than unmyelinated fibers.
False
What is the role of the motor point in muscle innervation?
The motor point is the anatomic place where the nerve enters the muscle.
In Ohm's Law, current varies in proportion to voltage and inversely with __________.
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Match the type of tissue with its conductance:
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Which of the following describes a large motor unit?
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The speed of conduction decreases with prolonged ice treatment.
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Define current in the context of electricity.
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Study Notes
Action Potential
- A suprathreshold stimulation is needed for an action potential to occur, involving sufficient amplitude, duration, and rise time of the stimulus.
- The stimulus needs to overcome the membrane threshold to generate an action potential, which then propagates along the nerve fiber.
Nerve Conduction
- Conductors are materials allowing current flow (e.g., nerves, muscles, motor points, trigger points).
- Insulators impede current flow (e.g., adipose, scar tissue).
- Myelinated fibers conduct faster (sensory and motor nerves).
- Unmyelinated fibers conduct slower (C fibers for pain).
- Extreme or prolonged ice, pressure, and anoxia slow conduction.
Motor Point and Motor Unit
- The motor point is where the nerve enters the muscle.
- Charts are used for electrode placement for NMES.
- Motor units consist of a motor nerve and the muscle fibers it innervates.
- Small motor units have a low ratio (e.g., 1:5) for fine motor movements.
- Large motor units have a high ratio (e.g., 1:100 or more) for force production.
- Voluntary contractions recruit small motor units first, while E-Stim recruits large motor units first.
Principles of Electricity
- Current is the flow of charged particles and measured in amps, milliamps, or microamps.
- Current requires a source of electrons, a conductor, and a driving force (electromotive force).
- Voltage (measured in volts or millivolts) is the electromotive force.
- Resistance (measured in ohms) opposes the flow of ions.
- Ohm’s Law: Current (I) = Voltage (V) / Resistance (R).
Constant Current Devices
- Consistent physiological response.
- Current stays constant regardless of resistance changes.
- Disadvantage: Current concentrates in areas where electrodes lose contact.
Constant Voltage Devices
- Voltage remains constant, while current changes with resistance.
- Disadvantage: Response quality may vary due to resistance changes.
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Description
Explore the concepts of action potentials and nerve conduction in this quiz. Understand the factors that influence the generation of action potentials, the role of motor points, and the differences between myelinated and unmyelinated fibers. Test your knowledge on the essential aspects of nerve physiology.
