Physical Agents: Muscle Tone and Electrical Currents

Comprehensive practice flashcards covering muscle tone neurophysiology, biomechanics, dyskinesias, physical agent interventions, and electrical stimulation principles (NMES, EMS, TENS, parameters, and electrode configurations).

How is muscle tone clinically defined, and what is its primary function?

Muscle tone is defined as the tension that remains in the muscles even at rest. It provides a background readiness for muscle contraction and maintains body posture before movement occurs.

In what portion of a muscle's available length should muscle tone be evaluated during assessment?

Muscle tone is measured in the midrange of the available length of the muscle being tested.

What are the two primary components that contribute to overall muscle tone?

1. Active resistance generated by neurally activated muscle fibres.
2. Passive biomechanical tension inherent in connective tissue and muscle at the length tested.

What are the three sequential steps involved in muscle activation?

1. Neural input
2. Release of calcium ions
3. Actin and myosin molecules forming cross-bridges

According to the length-tension curve shown, at what muscle length is maximal ($100\%$) active tension generated?

At the "functional length" or midrange (c), where optimal cross-bridge overlap between actin and myosin filaments occurs.

What sensory structure is illustrated here lying parallel to muscle fibers, innervated by Ia sensory afferent and gamma motor neurons?

Muscle spindle

What sensory organ is depicted in this diagram lying in series at the musculoskeletal junction, innervated by Ib sensory neurons?

Golgi Tendon Organ (GTO)

What is the clinical definition of spasticity?

Spasticity is a type of abnormal muscle tone and hypertonicity characterized by velocity-dependent resistance to passive muscle stretch.

What five clinical manifestations is spasticity explicitly stated NOT to be?

1. Abnormal posturing
2. A particular diagnosis or neural pathology
3. Hyperactive stretch reflex
4. Muscle spasm
5. Voluntary movement restricted to flexor or extensor synergies

How are flaccidity, hypotonicity, and clonus clinically differentiated?

• Flaccidity: Total lack of muscle tone.
• Hypotonicity: Decreased resistance to passive stretch.
• Clonus: Rhythmic, oscillating muscle contractions.

How are the dyskinesias choreiform movements, ballismus, tremors, athetoid movements, and dystonia distinguished?

• Choreiform movements (chorea): Dance-like, sharp, jerky movements.
• Ballismus: Large throwing movements.
• Tremors: Low amplitude, high frequency oscillating movements.
• Athetoid movements: Worm-like writhing motions.
• Dystonia: Involuntary muscle contraction.

Which cutaneous receptor techniques are used clinically to increase versus decrease muscle tone?

• To increase tone: Quick, light touch; manual contacts; brushing; quick icing.
• To decrease tone: Slow stroking; maintained holding; neutral warmth; prolonged icing.

What are the primary characteristics and common etiologies of alpha motor neuron damage?

• Characteristics: Flaccid paralysis, no motor units firing, absence of tone, and denervation.
• Common etiologies: Poliomyelitis, Guillain-Barre syndrome, crush or cutting injuries, and nerve compression.

What physical intervention techniques are indicated to reduce high muscle tone resulting from cerebral lesions?

Prolonged ice, prolonged stretch, positioning, inhibitory pressure, inhibitory casting, and re-education of voluntary movement patterns.

What are the clinical consequences of joint immobilization, such as with a cast, on muscle tone and function?

It provides a constant cutaneous stimulus from the cast with no other inputs, inhibits movement at one or more joints, alters muscle tone, and causes decreased strength and decreased ROM.

What is an electrical current, and what two prerequisites are needed for it to flow?

An electrical current is the flow of charged particles (electrons or ions) and energy between two points. It requires:

1. A driving force (voltage)
2. A material that will conduct electricity

What mathematical relationship is expressed by Ohm's Law?

$V = IR$, which states that Voltage ($V$) equals Current ($I$) multiplied by Resistance ($R$).

Based on this diagram of electrical current flow, what occurs under the anode versus the cathode?

• Under the anode ($+$): Positive ions are repelled into surrounding tissues, causing hyperpolarization and decreased nerve excitability.
• Under the cathode ($-$): Positive ions are attracted, causing depolarization of the nerve and generation of an action potential (increased excitability).

Which biological tissues are classified as excitable versus non-excitable conductors in an electrical circuit?

• Excitable tissues: Muscles, nerves, blood, and cell membranes.
• Non-excitable tissues: Tendons, bones, cartilage, ligaments, and fascia.

What clinical conditions increase tissue impedance to electrical stimulation, and what conditions decrease it?

• Increases impedance: Edema, ischemia, atherosclerosis, scarring, and denervation.
• Decreases impedance: Open wounds and abrasions.

What are the three criteria necessary to achieve nerve membrane depolarization with electrical stimulation?

1. Amplitude (stimulus must be strong enough)
2. Rise time / decay time (stimulus must be fast enough to avoid accommodation)
3. Duration (stimulus must be long enough)

According to the strength-duration curve shown, what are the four clinical levels of stimulation and their corresponding nerve fibre activations?

1. Sub-sensory: No nerve activation or awareness.
2. Sensory: Non-noxious paresthesias (pins and needles); activates cutaneous A-beta fibres.
3. Motor: Muscle contraction; activates A-alpha fibres.
4. Noxious: Sharp/burning pain and strong contractions; activates A-delta and C fibres.

What are the target treatment responses for electrical frequencies of $100\,Hz$, $50\text{--}60\,Hz$, and $1\text{--}50\,Hz$?

• $100\,Hz$: Pain relief
• $50\text{--}60\,Hz$: Muscle contraction (tetanic)
• $1\text{--}50\,Hz$: Increased circulation (with contractions occurring around $30\,Hz$)

How do on:off duty cycle ratios of $1:1$, $1:3$, $1:5$, and $1:7$ impact muscle fatigue?

• $1:1$ ($10\,s$ on / $10\,s$ off): Fatigues muscle rapidly.
• $1:3$ ($10\,s$ on / $30\,s$ off): Common standard choice.
• $1:5$: Produces less fatigue.
• $1:7$: Produces no fatigue (used for passive muscle exercise).

How does motor unit recruitment via electrical stimulation differ from physiological recruitment by the central nervous system (CNS)?

• Recruitment order: CNS recruits small motor units first; E-stim recruits large, superficial Type II motor units first.
• Firing pattern: CNS fires asynchronously (energy-efficient, delays fatigue); E-stim recruits synchronously (very fatiguing).
• Propagation: CNS generates action potentials moving away from the cell body; E-stim generates action potentials traveling bidirectionally.

What are the defining purposes and patient populations for NMES, EMS, and TENS?

• NMES (Neuromuscular Electrical Stimulation): Stimulates intact peripheral nerves of innervated muscles for strengthening, re-education, ROM, spasm/spasticity reduction, and atrophy prevention.
• EMS (Electrical Muscle Stimulation): Directly stimulates denervated muscles to maintain viability, improve circulation, and retard fibrotic changes and atrophy.
• TENS (Transcutaneous Electrical Nerve Stimulation): Used for pain modulation.

What are the operational differences among the electrode setups (Monopolar, Bipolar, Quadripolar) illustrated in this reference?

• Monopolar: One small active electrode in the target area (concentrated current density) and a larger dispersive electrode placed away to complete the circuit.
• Bipolar: Two electrodes of equal size placed within the target treatment area (stimulation felt under both).
• Quadripolar: Four electrodes from at least two separate channels used to cover larger areas.

What are the absolute contraindications to the application of electrical currents?

• Cardiac demand pacemakers or arrhythmias
• Placement of electrodes over the carotid sinus
• Areas of venous or arterial thrombosis or thrombophlebitis
• Pregnancy (over and around the abdomen or low back; NMES in the 3rd trimester)

Why is ramp time clinically critical, and what physiological phenomenon occurs if the rise time is too slow?

A ramp time of approximately $2\,seconds$ provides comfort during muscle stimulation. If the rise time is too slow, the nerve will undergo accommodation (adaptation), requiring a stronger stimulus to elicit an action potential.

What electrical safety protocols must be observed when maintaining electrotherapy equipment?

All new equipment must be checked by the bioengineering department before initial use, undergo yearly maintenance checks, be plugged directly into three-pronged grounded receptacles without extension cords, have cords inspected for fraying, and have warning signs posted for individuals with pacemakers.