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Glite Dictionary
knee-jerk reflex

knee-jerk reflex

1 3.9
A sudden automatic kick of the lower leg when the tendon below the kneecap is tapped
  • noun
  • /niː dʒɜrk ˈriːflɛks/
  • Specialized
translation icon : reflejo patelar
  • The doctor tested my knee-jerk reflex by tapping just below my kneecap.

Examples

  • The doctor tested my knee-jerk reflex with a small hammer.

  • A strong knee-jerk reflex can indicate a healthy nervous system.

  • Children often find it amusing to watch their knee-jerk reflex in action during checkups.

  • Loss of the knee-jerk reflex can be a sign of nerve damage.

  • The doctor demonstrated the knee-jerk reflex by striking the patient's knee with a small hammer.

  • When the doctor tapped his knee, the knee-jerk reflex caused his leg to kick out automatically.

  • She was surprised by her strong knee-jerk reflex when the doctor tested her response during the check-up.

Synonyms

knee jerk
vsknee-jerk reflex
3 4.3

Lower leg suddenly kicks out when the area below the kneecap is tapped

is the hyphenated formal term used for the same reflex
patellar reflex
vsknee-jerk reflex
  • Specialized
1 6.0

A quick kick of the lower leg after a tap below the kneecap

is the medical name often used in examinations for the same response
myotactic reflex
vsknee-jerk reflex
  • Specialized
8.8

A muscle tightens when its tendon is stretched to help keep the body upright

is the specific lower leg extension from tapping that tendon rather than any muscle
stretch reflex
vsknee-jerk reflex
  • Specialized
6.5

An automatic muscle tightening that happens when a muscle is pulled

is confined to sudden leg extension after a tendon tap rather than general stretch

Surface Forms

knee-jerk reflex singular
knee-jerk reflexes plural

Morphology

knee-jerk + reflex

The phrase is compositionally built: 'knee-jerk' describes a jerk of the knee and 'reflex' denotes an automatic bodily response, so the meaning of an automatic extension of the lower leg is directly derivable from the parts. While 'knee-jerk' can be used metaphorically in other contexts, in this physiological sense the structure is literal and cross-linguistically transparent, so a B1 learner who knows 'knee', 'jerk' and 'reflex' would readily understand it.

Etymology

Knee-jerk reflex comes from a simple test where a doctor taps just below the kneecap and the lower leg quickly jerks out. Because this knee-jerk action happens without thinking, the phrase describes a fast, 'automatic' reaction.