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Questions and Answers
What is the unit of measurement for resistance?
The vertical axis of the Strength Duration Curve represents pulse duration.
False
What does Ohm’s Law state regarding current, voltage, and resistance?
Current varies in proportion to voltage and inversely with resistance.
An electromotive force of 1 volt is required to drive one amp of current across _____ ohm.
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Match the following electrotherapeutic device types with their characteristics:
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What is the expected initial response of sensory nerves during electrical stimulation?
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Pulses with longer durations need a higher amplitude to reach the threshold of the same nerve.
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What property describes a material's ability to oppose the flow of ions?
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Current is measured in _____, while voltage is measured in volts.
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Which electrical stimulation type may result in less effective responses due to resistance changes?
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What describes the relationship between current, voltage, and resistance according to Ohm’s Law?
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Constant Voltage devices produce current that does not vary regardless of resistance changes.
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What is the relationship between strength (amplitude) and pulse duration in electrical stimulation?
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The charge delivered by pulses can be calculated by the formula _____.
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Match the following types of electrical stimulation to their primary characteristics:
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What is one advantage of using Constant Current devices?
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The muscle membrane has a lower threshold compared to nerve membranes.
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What happens to sensory nerves under electrical stimulation when the amplitude is increased?
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An ampere is equal to _____ electrons per second.
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Which of the following types of electrical stimulation is capable of delivering enough charge to reach the threshold of the muscle membrane?
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Study Notes
Current
- The flow of electrically charged particles.
- Measured in amps, milliamps, and microamps.
- Requires a source of electrons, a conductor, and a driving force (electromotive force).
- One amp equals 6.25 x 10^18 electrons/second.
Voltage
- A measure of electromotive force.
- Measured in volts and millivolts.
Resistance
- The ability of a material to oppose the flow of ions.
- Measured in ohms.
Ohm's Law
- States that current in a conductor is proportional to voltage and inversely proportional to resistance.
- Formula: I = V/R
Constant Current Devices
- Deliver a consistent current regardless of resistance changes.
- Advantages:
- Consistent physiological response.
- Like cruise control in a car.
- Disadvantages:
- Current concentrates in areas of good contact if electrode contact is lost.
Constant Voltage Devices
- Deliver a constant voltage, but current changes with resistance.
- Disadvantages:
- Response quality changes with resistance variations.
- May be less effective or comfortable.
Strength Duration Curve
- Correlates pulse amplitude and duration.
- Area of a pulse (S x D) = charge.
- Vertical axis: Strength (amplitude of pulse).
- Horizontal axis: Pulse duration.
- HVPC has the shortest pulse duration.
- DC has the longest pulse duration.
- Inverse relationship between strength and duration.
- Short durations require higher amplitude.
- Long durations need less amplitude.
- Charge is equal in both cases.
Sequence of Nerve Activation
- Sensory nerves are activated first, followed by motor nerves, and then pain nerves.
- Sensory nerve threshold is lower than pain nerve threshold.
Expected Response with Increasing Amplitude
- Sensory: Buzzing, tingling.
- Motor: Weak contraction that strengthens with increased motor unit recruitment.
- Pain.
Muscle Membrane Threshold
- Muscle membrane has a higher threshold than nerve membranes.
- Only DC can reach the threshold of the muscle membrane due to its long duration.
Electricity Fundamentals
- Current is the flow of charged particles.
- Amperes (A), milliamperes (mA), and microamperes (µA) are used to measure current.
- Voltage is the electromotive force that drives current.
- Volts (V) and millivolts (mV) measure voltage.
- Resistance opposes the flow of current.
- Ohms (Ω) measure resistance.
- Ohm's Law states that current (I) is directly proportional to voltage (V) and inversely proportional to resistance (R): I = V/R.
Constant Current & Constant Voltage Devices
- Constant Current devices maintain a consistent current flow regardless of resistance changes.
- Advantages: Consistent physiological response.
- Disadvantages: Current concentration can occur if electrode contact is lost, which can cause discomfort or harm.
- Constant Voltage devices maintain a constant voltage.
- Advantages: More adaptable to changing resistance.
- Disadvantages: Current variation can lead to inconsistent or uncomfortable responses.
Strength-Duration Curve (S-D Curve)
- Strength-Duration Curve illustrates the relationship between pulse amplitude (strength) and pulse duration.
- Charge (S x D) is the area under the S-D curve.
- Vertical axis: Strength (pulse amplitude).
- Horizontal axis: Pulse duration (time).
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Types:
- HVPC (High-Voltage Pulsed Current): Shortest pulse duration.
- DC (Direct Current): Longest pulse duration.
- Inverse Relationship: Shorter pulses require higher amplitude to reach threshold, while longer pulses require lower amplitude.
Nerve Activation with Electrical Stimulation
- The sequence nerves are activated with electrical stimulation is: Sensory, Motor, Pain.
- Sensory nerves have the lowest threshold.
- Pain nerves have the highest threshold.
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Increasing amplitude while keeping duration constant leads to:
- Sensory: Buzzing, tingling sensations.
- Motor: Weak contractions becoming stronger.
- Pain: Painful sensations.
Muscle Membrane Stimulation
- Muscle membranes require significantly higher stimulation than nerve membranes.
- Direct Current (DC) has a long enough duration to reach the muscle membrane threshold.
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Description
Test your knowledge on the fundamentals of electrophysiology, including concepts like current, voltage, and resistance. Explore Ohm's Law and the distinctions between constant current and constant voltage devices. Challenge yourself to understand how these principles apply in practical scenarios.
