Action Potentials and Nerve Physiology

Vocabulary-style flashcards covering nerve physiology, muscle fiber types, electrical principles, and clinical electrotherapy parameters based on lecture notes.

Action Potential

Rapid depolarization and repolarization of a nerve membrane.

All-or-none Principle

A principle stating that an action potential occurs completely or not at all, with no partial potentials.

Absolute Refractory Period

A period where no new action potential can occur because $Na^+$ channels are inactivated.

Relative Refractory Period

A period where an action potential can occur but requires a stronger stimulus because some $Na^+$ channels have recovered.

Saltatory Conduction

The process in myelinated nerves where an action potential "jumps" from one Node of Ranvier to another, making conduction faster and more energy efficient.

Factors Increasing Conduction Velocity

Larger axon diameter, more myelination, and higher temperature.

Orthodromic Propagation

The normal direction of transmission, defined as CNS to Muscle for motor nerves and Periphery to CNS for sensory nerves.

Antidromic Propagation

Nerve transmission in the opposite of its normal direction (e.g., Distal to Proximal), commonly seen during electrical stimulation.

Rate Coding

Increasing force by increasing the number of action potentials and frequency of firing.

Henneman's Size Principle

The recruitment order in normal voluntary contraction where Type I fibers are recruited first, followed by Type IIa and then Type IIx.

NMES Recruitment Pattern

The activation of large diameter axons and Type II fibers first, leading to greater muscle fatigue.

Type I Muscle Fibers

Slow twitch, fatigue-resistant aerobic fibers used for endurance, characterized by smaller axons.

Type II Muscle Fibers

Fast twitch, power-oriented anaerobic fibers that fatigue quickly and have larger axons.

Power Formula

$$Power = Force \times Velocity$$

Cathode

The negative electrode ($-$) which is electron-rich and produces depolarization and excitation.

Anode

The positive electrode ($+$) which is electron-deficient and produces hyperpolarization.

Voltage

Also called electrical potential, it represents electrical pressure measured in Volts ($V$).

Current

The flow of electrons measured in Amperes ($A$), typically expressed in milliamperes ($mA$) or microamperes ($\mu A$).

Charge Formula

$Charge = Current \times Time$; measured in Coulombs ($C$).

Impedance

The opposition to current flow, which can be increased by air pockets, dry skin, or cracked electrodes.

Ohm's Law

$V = I \times R$, where $V$ is Voltage, $I$ is Current, and $R$ is Resistance.

Direct Current (DC)

Also called Galvanic current; a continuous flow in one direction with long pulse durations, used for iontophoresis and wound healing.

Alternating Current (AC)

A current that continuously changes direction, such as Russian stimulation or Interferential current.

Phase

One portion of a pulse; waveforms can be monophasic, biphasic, or triphasic.

Charge (Waveform Property)

Represented by the area under the curve; two different waveform shapes can have the same charge if their area is identical.

Accommodation

When a nerve becomes less responsive to continuous stimulation; prevented by modulation, ramping, or burst patterns.

Amplitude Depth Relationship

Higher intensity current activates deeper tissues, while lower intensity activates superficial tissues.

Rheobase

The minimum current intensity needed to stimulate tissue using a very long pulse duration.

Chronaxie

The pulse duration required to stimulate tissue using an intensity of $2 \times Rheobase$.

Tetanic Contraction

A sustained contraction due to rapid stimuli, typically occurring at $50-70\,pps$. (Pulses per second).

Current Density

Formula: $Current\,Density = \frac{Current}{Electrode\,Area}$. Higher density results from smaller electrodes.

Electrode Distance

Closer placement results in superficial current, while farther placement allows for deeper current penetration.

Duty Cycle

The ratio of ON time to OFF time (e.g., $10\,sec$ ON : $50\,sec$ OFF); lower duty cycles result in less fatigue.