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Activity 6.5 — Reflex Arc (Knee Jerk)
NCERT Activity 6.5: Tap below the kneecap with a reflex hammer and trace the neural pathway — the reflex arc that bypasses the brain for a rapid response.
How To Perform
1
Observe the Setup
See the seated person with the leg hanging freely and the doctor's hammer ready.
2
Tap the Patellar Tendon
The doctor taps just below the kneecap to stimulate the receptors.
3
Trace the Reflex Arc
Follow the electrical signal: Sensory neuron → Spinal cord → Motor neuron.
4
Watch the Leg Kick
The quadriceps contracts and the leg kicks forward — a rapid reflex!
5
Classify the Response
Understand why reflexes are faster than voluntary movements.
⚠️ Safety Notes
- •The knee-jerk test is a standard medical examination — it is safe and painless.
- •Only a light tap on the patellar tendon is needed — do not strike hard.
- •The person should be relaxed with legs dangling freely for an accurate reflex.