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BPT 3rd Year - Electrotherapy I (LMF/Low & Medium Frequency)

Complete Analysis of Both PDFs (2011-2025)

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PART 1: REPEATED 5-MARK QUESTIONS WITH FREQUENCY COUNT

(Sorted by number of times asked - Most repeated first)

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PART 2: ALL 5-MARK QUESTIONS WITH COMPLETE ANSWERS

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1. DIADYNAMIC CURRENT (Asked 8 times)

MF (Monophase fixe) - Monophasic fixed
  ___   ___   ___
 |   | |   | |   |   50 pulses/sec
 
DF (Diphasic fixe) - Diphase fixed
 ___   ___   ___
|   |_|   |_|   |   100 pulses/sec (full-wave rectified)

CP (Courtes periodes) - Short periods
  MF (1 sec) → DF (1 sec) → MF → DF...

LP (Longues periodes) - Long periods
  DF gradually → MF over 6-10 seconds

RS (Rhythme syncopé) - Rhythmic syncopated
  Bursts of MF at 1-sec intervals with 1-sec pauses

• Stimulates sensory nerve fibers - causes hyperemia
• MF: analgesic effect, increases blood flow
• DF: stronger analgesia, reduces edema
• CP: reduces pain and muscle spasm
• LP: trophic effect, improves circulation
• RS: produces rhythmic muscle contractions

• Pain relief (analgesia)
• Reduction of muscle spasm
• Improvement of blood circulation
• Reduction of swelling / edema
• Trophic effects on tissues

• Painful conditions (LBA, cervical pain, arthritis)
• Muscle spasm
• Circulatory disorders
• Soft tissue injuries

• Electrodes: carbon rubber or metal electrodes with wet sponge
• Dose: 2-6 mA (sub-motor for analgesia)
• Duration: 10-15 minutes
• Frequency: daily or alternate days

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2. INTERFERENTIAL THERAPY (IFT) - Parameters & Effects (Asked 8 times)

Circuit 1: 4000 Hz ─────┐
                         ├──→ PATIENT → Beat frequency (1-150 Hz)
Circuit 2: 4001 Hz ─────┘    produced INSIDE the tissue

Beat Frequency = |f1 - f2|
Example: 4000 - 3900 = 100 Hz beat

• 1-10 Hz: Motor stimulation, muscle pumping
• 10-25 Hz: Strong rhythmic muscle contractions
• 25-50 Hz: Vascular effects, autonomic
• 80-100 Hz: Analgesia (endorphin gate control)
• 90-150 Hz: Acute pain, analgesia

1. Quadripolar - 4 electrodes; two circuits cross inside tissue
2. Bipolar - 2 electrodes; interference occurs in electrode/skin
3. Vacuum electrodes - suction cups (better contact, labile method)

• Analgesia (pain relief via gate control + endorphins)
• Muscle strengthening (rhythmic contractions)
• Improved blood circulation
• Reduced edema
• Stimulation of autonomic nerves

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3. GATE CONTROL THEORY OF PAIN (Asked 7 times)

• Large diameter fibers (Aβ): Carry non-pain (touch, pressure) impulses - they CLOSE the gate
• Small diameter fibers (Aδ, C): Carry pain impulses - they OPEN the gate
• Substantia Gelatinosa (SG): Gate mechanism in dorsal horn of spinal cord
• Transmission (T) cells: Project pain to brain

SPINAL CORD (Dorsal Horn)
                    Substantia
                    Gelatinosa (SG)
                         |
Aβ (large fiber) ────(+)─┤      T-cells → Brain (PAIN perceived)
                          │
Aδ/C (small fiber)──(-)──┘
    PAIN INPUT           GATE

GATE OPEN:  Small fibers active → SG inhibited → T-cells fire → PAIN
GATE CLOSED: Large fibers active → SG excited → T-cells inhibited → NO PAIN

• TENS works by stimulating large Aβ fibers → closes gate → reduces pain
• Conventional TENS: 80-150 Hz, low intensity → activates Aβ fibers → rapid pain relief
• Rubbing an injury activates Aβ fibers and reduces pain perception

• Does not explain phantom limb pain
• Does not fully account for central sensitization

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4. IONTOPHORESIS (Asked 7+ times)

• Like charges repel: Positive ions placed under anode (positive electrode) are driven into tissues
• Negative ions placed under cathode are driven into tissues
• Current creates an electrochemical gradient

        ANODE (+)          CATHODE (-)
           |                   |
    [Drug solution]       [Drug solution]
    Positive ions    →    Negative ions
    pushed inward    →    pushed inward
           ↓                   ↓
        SKIN SURFACE
           ↓
      Into the tissues

• Tap water iontophoresis
• Part immersed in tap water trays
• DC current 15-20 mA for 20-30 minutes
• 3x/week initially; maintenance once/week
• Mechanism: sweat gland duct plugging

1. Clean skin, check for cuts/abrasions
2. Prepare ion solution
3. Apply active electrode over treatment area
4. Indifferent electrode at distant site
5. Current: 1-4 mA/cm²; Duration: 15-20 min
6. Dosage: Current (mA) × Time (min) = mA-min (dose: 40-80 mA-min)

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5. STRENGTH DURATION (SD) CURVE (Asked 7 times)

• Rheobase: The minimum current required to produce a response using infinitely long pulse duration
• Chronaxie: The pulse duration required to produce a minimal contraction at twice the rheobase intensity
• Accommodation: Rise in threshold when a slowly rising current is used

Current
Intensity
(mA)
│  ●  ←── Rheobase (R)
│   \
│    ●
│     \
│      ●──●──●──●──●  ←── Excitability curve
│         ↑
│      2R ─
│         |
│         Chronaxie
│_______________________________________________
          Pulse Duration (ms)

Current
Intensity
│
│  ●  ← Denervated (high rheobase)
│  |  \
│  |   ● Denervated curve shifted RIGHT
│  ●    \  (needs longer pulses, more current)
│   \    ●──●──●
│    ●
│     ●──●──●──●  ← Normal innervated muscle
│_______________________________________________
                     Pulse Duration
        ↑               ↑
   Short            Long
   pulses           pulses needed
   stimulate        for denervated
   nerve            muscle

• Indicates partial denervation (mixed - some fibers innervated, some denervated)
• The kink represents the transition between healthy and denervated fibers

│  ●
│   ●
│    ●  ← KINK (partial denervation)
│     ●●
│        ●──●──●──●  ← Denervated portion
│___________________________________

• Normal nerve: Chronaxie < 1 ms; short pulse duration needed
• Denervated muscle: Chronaxie > 1 ms; long pulse duration needed
• Curve shifts right on denervation and left on reinnervation
• Used to monitor nerve regeneration progress

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6. BELL'S PALSY - Electrotherapy Management (Asked 7 times)

• Unilateral facial muscle weakness/paralysis
• Inability to close eye (lagophthalmos)
• Drooping of mouth corner
• Loss of nasolabial fold

• First assess with faradic and galvanic tests to determine if nerve is intact or denervated
• If faradic response present → neuropraxia → use faradic current
• If no faradic response → denervation → use galvanic (IDC) current

FACE - Motor Points Diagram:
         Frontalis      ●  Orbicularis oculi
           ●                       ●
      ●   Corrugator            ●
         ●  Zygomaticus major
              ●  Buccinator
                  ● Depressor angulioris
                      ● Mentalis

• Frequency: Daily
• Duration: Each muscle 3-5 minutes

• If there is pain (retroauricular), TENS at sensory level

• Protect eye (eye pad, tape)
• Avoid over-stimulation (faradism to normal muscles - contraction can worsen)

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7. FARADIC CURRENT - Physiological & Therapeutic Effects (Asked 6 times)

PRIMARY COIL        SECONDARY COIL
(AC supply)     →   (Patient circuit)
      ~~~                 ~~~
  Interrupted AC      Faradic current
                      (short pulses)

Waveform:
    /\    /\    /\
   /  \  /  \  /  \  ← Asymmetric biphasic
  /    \/    \/    \

1. Muscle contracts (twitch/tetanic depending on frequency)
2. Improves blood circulation (muscle pump)
3. Sensory nerve stimulation (comfortable tingling)
4. Stimulates intact motor nerve → muscle contraction

• Faradic current does NOT stimulate denervated muscle
• Only long-duration DC pulses (IDC) stimulate denervated muscle

• Re-educate paralyzed muscles (with intact nerve)
• Prevent disuse atrophy
• Strengthen weak muscles (quadriceps inhibition, deltoid inhibition)
• Maintain joint mobility
• Reduce edema (muscle pump action)
• Relieve muscle spasm
• Facilitate active voluntary movement

• Muscle weakness with intact innervation
• Quadriceps/deltoid inhibition
• Post-operative muscle wasting
• Flat feet, correction of posture

• Denervated muscle (use IDC instead)
• Skin infections, metal implants, cardiac pacemakers
• Thrombosis, malignancy, open wounds

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8. BIOFEEDBACK (Asked 6+ times)

PHYSIOLOGICAL          MONITORING           FEEDBACK
PROCESS               INSTRUMENT           SIGNAL
(EMG, skin temp,    →  (Sensors)    →   (Visual/Auditory)
BP, EEG)                                      ↓
                                         Patient learns
                                         to control process
                                              ↓
                                        Improved function

Surface electrodes on muscle
         ↓
    Amplifier
         ↓
  Signal processor
         ↓
   ┌─────────────┐
   │  Visual:    │ ← Bar graph rises when muscle contracts
   │  LED meter  │
   │  Auditory:  │ ← Beep or pitch changes with contraction
   │  Tone       │
   └─────────────┘
         ↓
   Patient sees/hears feedback
   and consciously controls muscle

• Sensitivity: Adjusts gain of amplifier
• Threshold: Level at which alarm sounds
• Smoothing: Averaging time for signal
• Feedback mode: Visual or auditory

• Muscle re-education after stroke, nerve injuries
• Quadriceps/deltoid inhibition treatment
• Urinary incontinence (pelvic floor training)
• Posture correction
• Relaxation training
• Facial palsy rehabilitation
• Stress management

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9. RADIAL NERVE PALSY (Asked 5 times)

                    Radial nerve (C5-C8)
                         |
         ┌───────────────┼──────────────────┐
         |               |                  |
   High lesion     Spiral groove        Below elbow
   (axilla)       (Saturday night palsy)
         |               |                  |
   All muscles      Wrist extensors    PIN syndrome
   affected         affected           (posterior
   + sensory        (wrist drop)       interosseous n.)

Normal Hand:                Wrist Drop (Radial n. palsy):
  ────────                       ┌────────
 /                              /
|  ← wrist extended            | ← wrist drops (flexed)
 \                              \
  ────────                       └────────

• Brachioradialis
• Extensor carpi radialis longus and brevis
• Extensor digitorum
• Extensor carpi ulnaris
• Extensor pollicis longus/brevis
• Abductor pollicis longus

1. Assessment: SD curve, nerve conduction test, Faradic-IDC test
2. If neuropraxia (nerve intact): Surged faradic current to prevent atrophy
3. If axonotmesis/neurotmesis: IDC to denervated extensors

• Pulse duration: 10-100 ms (depending on chronaxie)
• Frequency: 30-50 pulses/min
• Intensity: Minimal visible contraction
• Duration: 15-20 min (each muscle)

• Wrist cock-up splint (90° neutral position)
• Passive range of motion exercises
• FES for functional use
• Sensory re-education if sensory loss

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10. DELTOID INHIBITION (Asked 5 times)

PAIN at shoulder
       ↓
 Reflex arc activated
       ↓
 Inhibitory impulses to motor neurons of deltoid
       ↓
 Deltoid cannot contract voluntarily
       ↓
 Muscle wasting, subluxation risk

1. Faradic Stimulation:
   • Stimulate deltoid directly with surged faradic (innervated muscle)
   • Motor point of deltoid: tip of shoulder/middle of deltoid
   • Current: surged faradic, 1 ms pulse, 50 Hz
   • Intensity: visible muscle contraction
   • Duration: 20 minutes
2. EMG Biofeedback:
   • Surface electrodes over deltoid
   • Patient views EMG signal and attempts voluntary contraction
   • Helps overcome inhibition
3. Positioning: Arm supported to prevent subluxation during exercises
4. Progression: Assisted active → active → resisted exercises

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11. FARADISM UNDER PRESSURE (Asked 5-6 times)

         Water trough (footbath)
         ┌──────────────────────┐
         │   WATER (electrode)  │
         │      ↑               │
         │  FOOT                │
         │  (sole in contact    │
         │   with water)        │
         └──────────────────────┘
           ↑                 ↑
     Indifferent          Active
     electrode            electrode
     (near ankle)         (in water)

         Physiotherapist's thumb
         applies pressure to arch

1. Patient sits with foot in faradic footbath
2. Water level should cover sole
3. Faradic current applied (surged mode)
4. Therapist places thumb under longitudinal arch and presses UP
5. This causes intrinsic muscles to contract against resistance
6. Teaches patient to feel contraction

• Flat foot (pes planus)
• Dropped arches
• Prevention of arch deformity

• Current: Surged faradic
• Duration: 15-20 minutes
• Dose: Daily x 10 sessions

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12. HIGH VOLTAGE PULSED GALVANIC CURRENT (HVPGC) (Asked 5 times)

Voltage
  ↑
  |  /\      /\      /\
  | /  \    /  \    /  \
  |/    \  /    \  /    \
  |      \/      \/      \
  |_________________________ Time (ms)
     ← Twin peaked pulse →
       (50-120 μs)

• Negative polarity: Bactericidal, increases tissue oxygen, promotes healing
• Positive polarity: Attracts neutrophils, promotes granulation tissue
• Both: Reduces edema by repelling negatively charged proteins

• Wound healing (chronic wounds, pressure sores)
• Edema reduction
• Tissue healing after injury
• Muscle stimulation (denervated muscle - long-duration pulses)
• Pain relief

• High voltage penetrates deeply with minimal skin discomfort
• Short pulse = minimal electrolytic effects
• Dual polarity for selective effects

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13. NERVE CONDUCTION TEST (Asked 5 times)

1. Motor Nerve Conduction Velocity (MNCV)
2. Sensory Nerve Conduction Velocity (SNCV)

Stimulating               Recording
Electrode                 Electrode
    ↓                         ↓
    S1──────nerve──────────── R
    |                         |
    S2                        |
    (proximal)                (muscle - CMAP)

MNCV = Distance (S1-S2) / [Latency S1 - Latency S2]
      = mm / ms = m/s

• Reduced NCV: Demyelination (e.g., GBS, CTS)
• Reduced amplitude: Axonal loss (e.g., peripheral neuropathy)
• Prolonged distal latency: Entrapment neuropathy

• Electrophysiological equivalent of tendon jerk
• Tests S1 nerve root integrity
• Stimulate tibial nerve → H wave appears in soleus after 30 ms

• Tests proximal segment of motor nerve
• Stimulate distally → impulse travels antidromically → re-fires motor neuron → small late response (F-wave)

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14. TENS - TYPES AND PARAMETERS (Asked 5+ times)

┌─────────────────────────────────────────────────────────────┐
│ TYPE      │ Freq   │ Pulse  │ Intensity │ Mode of Action   │
├─────────────────────────────────────────────────────────────┤
│Conventional│80-150Hz│50-80μs│ Sensory   │ Gate Control     │
│(High freq) │        │       │(tingling) │ (Aβ fibers)      │
├─────────────────────────────────────────────────────────────┤
│Acupuncture │1-4 Hz  │200μs  │ Motor     │ Endorphin release│
│(Low freq)  │        │       │(twitching)│                  │
├─────────────────────────────────────────────────────────────┤
│Burst mode  │1-4 Hz  │High   │ Motor     │ Endorphin release│
│            │bursts  │freq   │           │+ Gate control    │
│            │        │within │           │                  │
├─────────────────────────────────────────────────────────────┤
│Brief       │150 Hz  │<1 ms  │ High      │ Gate control     │
│Intense     │        │       │(strong)   │ (C-fiber block)  │
└─────────────────────────────────────────────────────────────┘

1. Over or near the painful area
2. Along the nerve supply to the area
3. Over trigger points or acupuncture points
4. Contralateral placement (mirror image)
5. Dermatome placement

For Low Back Pain:
  ●──────●
  |  L4  |   ← Two electrodes straddling
  |  L5  |     the painful area
  ●──────●
     BACK

• Acute pain: Conventional TENS (high freq, sensory level) or Brief Intense
• Chronic pain: Acupuncture TENS (low freq, motor level) - longer lasting effect

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15. FARADIC-IDC TEST (Electrical Diagnostic Test) (Asked 3 times)

TEST 1: FARADIC TEST
- Apply surged faradic current to motor point
- Normal response: Vigorous tetanic contraction
- No response: Possible denervation

TEST 2: IDC (GALVANIC) TEST  
- Apply DC interrupted current with long pulse (300 ms)
- Normal: Brisk contraction (CCC = Cathodal Closing Contraction)
- Denervated: Slow, vermicular (worm-like) contraction

• Complete RD: No faradic response, sluggish IDC response
• Partial RD: Reduced faradic response, some IDC

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16. PAIN PATHWAY (Asked 4-5 times)

PAIN STIMULUS
     ↓
Free nerve endings (nociceptors)
     ↓
  Aδ fibers (sharp, fast pain)
  C fibers (dull, slow pain, burning)
     ↓
Dorsal Horn of Spinal Cord
(Substantia Gelatinosa - Lamina I, II, V)
     ↓
Neurotransmitters: Substance P, Glutamate
     ↓
Spinothalamic Tract (STT)
     ↓
Thalamus (VPL nucleus)
     ↓
Somatosensory Cortex (parietal lobe)
(Conscious perception of pain)

DESCENDING MODULATION:
Cortex → PAG (periaqueductal grey) → Raphe nuclei
→ Dorsal horn → Release enkephalins → Pain inhibited

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17. SATURDAY NIGHT PALSY (Radial Nerve at Spiral Groove) (Asked 4 times)

• Wrist drop (loss of wrist/finger extension)
• Sensory loss over dorsum of hand (1st web space)
• Triceps and elbow extension SPARED (lesion is below triceps branch)

High Lesion (Axilla):          Spiral Groove:
- Triceps paralyzed            - Triceps INTACT
- All extensors lost           - Wrist drop
- Elbow extension lost         - Sensory loss dorsum hand

• SD curve at the wrist extensors
• If neuropraxia: Faradic (normal response)
• If axonotmesis: IDC to extensors, wrist splint, FES

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18. TRANSFORMER - Types and Uses (Asked 4-5 times)

         Primary Coil      Secondary Coil
         (N1 turns)        (N2 turns)
         ─────────────────────────────
         |    |||||||||     |||||||  |
AC input → |    |||||||||  →  |||||||  → Output
         |    |||||||||     |||||||  |
         ─────────────────────────────
                Iron Core

Formula: V1/V2 = N1/N2 = I2/I1

1. Step-Up Transformer: N2 > N1 → V2 > V1 (increases voltage)
2. Step-Down Transformer: N2 < N1 → V2 < V1 (decreases voltage) - used in therapy apparatus
3. Isolating/Safety Transformer: N1 = N2 → V1 = V2 (isolates patient from mains)
4. Auto Transformer (Variable): Single winding with sliding tap (Variac)

• Step down mains voltage (240V → 6V) for patient safety
• Isolating transformer prevents earth shock
• Variable transformer (potentiometer) allows intensity control
• Power supplies for TENS, IFT, stimulators

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19. FUNCTIONAL ELECTRICAL STIMULATION (FES) (Asked 6 times)

Microprocessor Controller
        ↓
   Stimulator
        ↓
 Surface Electrodes
  (or implanted)
        ↓
 Peripheral Nerve / Muscle
        ↓
  FUNCTIONAL MOVEMENT
  (walking, grasping, etc.)

During walking (swing phase):
  Heel switch (in shoe) detects toe-off
           ↓
  Triggers stimulator
           ↓
  Electrodes over peroneal nerve
           ↓
  Tibialis anterior contracts → Dorsiflexion
           ↓
  Patient clears the floor during walking

• Restores functional movement
• Prevents muscle atrophy
• Improves circulation
• May retrain neuroplasticity

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20. ELECTROMYOGRAPHY (EMG) (Asked 4+ times)

1. Surface Electrodes: Placed on skin over muscle (non-invasive)
2. Needle Electrodes: Inserted into muscle belly (more precise)
   • Concentric needle
   • Monopolar needle
   • Bipolar needle

Normal MUAP:         Fibrillation (denervated):
    /\                     /\  small
   /  \                   /  \  regular
__/    \___            __/    \___/\___ 
  Biphasic             Spontaneous at rest
  3-15 ms

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21. H-REFLEX (Asked 5 times)

Stimulate tibial nerve (low intensity)
         ↓
    Ia afferent fibers activated
    (sensory to spinal cord)
         ↓
    Synapses with motor neurons
    in spinal cord (S1)
         ↓
    Motor response back to muscle
         ↓
    H-wave recorded in soleus
    (latency ~30 ms)

Stimulus → ───────────────────────────────────── Nerve
            ↑ stimulus site (popliteal fossa)
                     
Recording at soleus:
Time: 0ms        30ms (H-wave)      60ms (M-wave)
       |           |                   |
  Direct M-wave   H-wave            (if high stim)
  (3-5 ms)        (30 ms)

• S1 radiculopathy assessment
• Peripheral neuropathy
• Upper motor neuron lesions (exaggerated H-reflex amplitude)

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22. SINUSOIDAL CURRENT (Asked 3+ times)

Current (+)
  │    ╭──╮           ╭──╮
  │   /    \         /    \
  │  /      \       /      \
──┼─/────────\─────/────────\──→ Time
  │            \   /          \   /
  │             ╰─╯            ╰─╯
Current (-)
     ← 1 cycle (20 ms at 50 Hz) →

• Frequency: 50 Hz (mains frequency)
• Symmetrical biphasic (no electrolytic effect)
• Smooth, comfortable stimulation

• Stimulates sensory and motor fibers
• Produces muscle contraction (innervated muscle only)
• Improves circulation
• Analgesic at sensory level

• Muscle strengthening (innervated)
• Circulatory improvement
• Relaxation
• Sometimes used as carrier frequency for IFT

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23. DIADYNAMIC CURRENT (Detailed - same as #1 above but with extra notes)

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24. FOOT DROP / WRIST DROP (Asked 4 times)

• Caused by: Common peroneal nerve palsy (lateral compression at fibular head)
• Muscles affected: Tibialis anterior, extensor digitorum, peroneus longus/brevis
• Deformity: Cannot dorsiflex the foot; steppage gait

1. SD curve to map denervation
2. IDC to tibialis anterior (if denervated)
3. FES (peroneal nerve stimulator) for functional walking
4. Peroneal nerve stimulator: Heel switch triggers stimulation during swing phase

• Radial nerve palsy - spiral groove level
• Electrotherapy: See Radial Nerve Palsy answer above

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25. RUSSIAN CURRENT (Asked 3 times)

Bursts at 50 Hz:
│  ████  ████  ████  ████
│  ████  ████  ████  ████
│────────────────────────→ Time
  10 ms ON  10 ms OFF
  (50 Hz burst rate)

Inside each burst:
  2500 Hz sine waves
  \/\/\/\/\/\/\/\/\/

• Carrier: 2500 Hz (comfortable through skin impedance)
• Burst frequency: 50 Hz
• On time: 10 ms; Off time: 10 ms (50% duty cycle)
• Intensity: Motor level (strong muscle contraction)

• Muscle strengthening in athletes
• Post-surgical muscle wasting
• Tetanic contractions for strength gain

• 2500 Hz carrier reduces skin impedance → more current into tissue
• Tolerated better than low-frequency DC at same motor level

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26. RECORDING ELECTRODES FOR EMG (Asked 3 times)

         ●  Active electrode
         |    (over muscle belly - motor point)
      ────── Muscle
         |
         ●  Reference electrode  
         |    (over tendon or adjacent area)

         ●  Ground electrode
             (neutral site, reduces noise)

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27. ELECTRIC SHOCK / EARTH SHOCK (Asked 5 times)

• Current (not voltage) is the dangerous factor
• Resistance of body (skin resistance reduces if wet)
• Path of current through body (across heart = most dangerous)
• Duration of contact
• Frequency (50 Hz AC is more dangerous than DC)

• Occurs when patient is connected to earth (ground) AND touches a live conductor
• Current path: Live wire → patient → earth → complete circuit
• Prevention: Isolation transformer, residual current device (RCD), dry conditions

1. Isolation transformer (no earth reference)
2. Proper earthing of apparatus
3. Regular maintenance
4. Do not use near water
5. Fuses in circuits
6. RCD (ELCB) - residual current circuit breaker

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28. PROPAGATION OF ACTION POTENTIAL (Asked 4+ times)

• At rest: Inside of neuron is -70 mV (negative)
• Maintained by Na⁺/K⁺ ATPase pump
• K⁺ leaks out; Na⁺ channels closed at rest

Voltage
(mV)
+40 ─────────╮
             │╰─ Repolarization
  0 ─────────╯                 ╭─────────
             Depolarization    │ After-hyperpolarization
-55 ─ Threshold ─────────────────────────────
-70 ─ Resting ─────────────────────────────→ Time (ms)
             ↑                          ↑
         Stimulus              Return to resting potential
         applied

1. Stimulus reaches threshold (-55 mV)
2. Voltage-gated Na⁺ channels OPEN → Na⁺ rushes IN → Depolarization (+40 mV)
3. Na⁺ channels inactivate; K⁺ channels OPEN → K⁺ rushes OUT → Repolarization
4. After-hyperpolarization (slightly below -70 mV)
5. Na⁺/K⁺ pump restores ionic balance

Direction of propagation →
────────────────────────────────
  Depolarized    ←●→ Excited    Resting
  (refractory)   segment       segment
────────────────────────────────
  Local currents flow forward → depolarize next segment
  (cannot go backward - refractory period prevents it)

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29. FARADIC FOOT BATH (Asked 6 times)

     FOOT BATH TANK
  ┌────────────────────┐
  │  WATER             │
  │     FOOT           │
  │   (immersed)       │
  │ Active electrode   │
  │ (metal plate in    │
  │  water)            │
  └────────────────────┘
       │
       │ Indifferent electrode
       │ (wet sponge at calf)
       │
  [Faradic current machine]
  Surged mode

• Lumbricals
• Interossei
• Flexor digitorum brevis
• Abductor hallucis
• Flexor hallucis brevis

• Flat foot / Pes planus
• Dropped arches
• Weak intrinsic muscles
• Part of rehabilitation for foot conditions

• Mode: Surged faradic (rhythmic contractions)
• Intensity: Visible toe/arch movement
• Duration: 15-20 minutes
• Temperature: Tepid water (37-38°C for comfort)

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30. BELL'S PALSY vs FACIAL PALSY (Asked 4 times)

UMN Lesion (stroke):          LMN Lesion (Bell's palsy):
  Forehead: NORMAL               Forehead: PARALYZED
  (UMN has bilateral             (All ipsilateral muscles
  cortical representation         affected)
  for forehead)
  
  Lower face: Weak               All face: Weak
  (contralateral control)

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SUMMARY: TOP MOST REPEATED QUESTIONS (Must Prepare!)

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Note: Both PDFs are the same subject - Electrotherapy I (Low & Medium Frequency), BPT 3rd Year, Tamil Nadu Dr. M.G.R. Medical University - Sub. Code 6259 (older regulations 2004-2011) and Sub. Code 6281 (2017-2018 regulations onwards). All answers above cover all 5-mark questions from both papers. Focus especially on the ⭐⭐⭐ topics as they appear almost every year.Your credits are exhausted. You can purchase a top-up or subscribe to a plan to continue using Orris. If you're already subscribed, your daily credits will reset tomorrow.