Physical Agents: Muscle Tone and Electrical Currents

Comprehensive vocabulary flashcards covering the neurophysiological and biomechanical principles of muscle tone, movement disorders, and the application and parameters of clinical electrical stimulation.

Muscle Tone

The tension that remains in the muscles even at rest, providing a background readiness to contract and holding a body position before movement occurs.

Active Resistance

The component of muscle tone generated by neurally activated muscle fibers.

Passive Biomechanical Tension

The component of muscle tone inherent in connective tissue and muscle at the specific length at which the muscle is tested.

Muscle Spindle

A sensory receptor oriented parallel to extrafusal muscle fibers, innervated by Ia sensory afferent neurons and gamma motor neurons, that responds to changes in muscle length.

Golgi Tendon Organ (GTO)

A sensory organ located in series with muscle fibers in connective tissue at the musculoskeletal junction, innervated by Ib sensory neurons to monitor muscle tension.

Flaccidity

A complete absence of muscle tone resulting in no resistance to passive elongation.

Hypotonicity

A state of decreased muscle tone characterized by reduced resistance to passive stretch.

Hypertonicity

A state of abnormally high muscle tone presenting increased resistance to passive elongation.

Spasticity

A velocity-dependent increase in resistance to passive muscle stretch and heightened resistance to quick stretch; one specific category of hypertonicity.

Clonus

Cyclical, rhythmic muscle oscillations and contractions that occur in response to a sudden passive stretch.

Choreiform Movements (Chorea)

Involuntary, jerky, sharp, and dance-like dyskinetic movements.

Ballismus

A form of dyskinesia characterized by high-amplitude, forceful, throwing-like involuntary movements of the limbs.

Tremors

Involuntary, rhythmic, low-amplitude, high-frequency oscillating movements.

Athetoid Movements

Slow, continuous, worm-like, writhing involuntary movements.

Dystonia

A movement disorder characterized by sustained or intermittent involuntary muscle contractions causing abnormal postures.

Neuromuscular Electrical Stimulation (NMES)

The application of electrical current to innervated muscle through intact peripheral nerves to restore function, build strength, promote muscle re-education, or reduce spasticity.

Electrical Muscle Stimulator (EMS)

The application of electrical stimulation directly to denervated muscles to maintain muscle viability, preserve blood flow, and retard denervation atrophy.

Electrical Current

The directed flow of charged particles (electrons or ions) and energy between two points, requiring a driving voltage and a conductive pathway.

Resting Potential

The baseline electrical balance across a cell membrane, characterized by positive charges outside and negative charges inside, that must be altered to initiate an action potential.

Ohm's Law

The physical law represented by the formula $V = IR$, which states that Voltage ($V$) equals Current ($I$) multiplied by Resistance ($R$).

Cathode

The negative electrode that attracts positive ions, creating local membrane depolarization and initiating an action potential.

Anode

The positive electrode that repels positive ions into adjacent tissues, creating local membrane hyperpolarization and reduced excitability.

Amplitude (Strength)

The maximum voltage or current delivered during a single pulse phase, which dictates the depth of tissue penetration and the magnitude of nerve fiber recruitment.

Pulse Duration

The elapsed time from the initiation to the completion of a single phase of an electrical pulse.

Frequency (Pulse Rate)

The rate at which pulses are administered, measured in pulses per second ($\text{pps}$) or Hertz ($\text{Hz}$), which dictates whether the motor response is a muscle twitch or a tetanic contraction.

Duty Cycle

The ratio of on-time to off-time during electrical stimulation, which directly impacts the rate of muscle fatigue.

Accommodation

The physiological elevation in excitation threshold exhibited by a nerve when an electrical stimulus has an excessively gradual rise time, requiring higher intensity to fire.

Modulation

The variation of one or more electrical stimulation parameters over time to prevent tissue adaptation to the current.

Sensory Level Stimulation

Electrical stimulation delivered at an amplitude and duration that depolarizes cutaneous A-beta nerve fibers, generating non-noxious paresthesias such as tingling or prickling without a motor twitch.

Motor Level Stimulation

Electrical stimulation delivered with sufficient amplitude and duration to depolarize large A-alpha motor axons, producing visible muscle contraction.

Noxious Level Stimulation

High-intensity electrical stimulation that depolarizes small, high-threshold A-delta and C-fibers, evoking a sharp, burning sensation along with strong muscle contractions.

Monopolar Configuration

An electrode arrangement featuring a smaller active electrode over the treatment target to increase current density, coupled with a larger dispersive electrode placed elsewhere to complete the circuit.

Bipolar Configuration

An electrode setup utilizing two electrodes of equal size placed within the target treatment area, creating uniform stimulation sensation under both.

Quadripolar Configuration

An electrode arrangement using four electrodes across at least two channels to treat large anatomical areas.