All of the following signs a can be seen in corticospinal tract injury except:

Ans. d. Clasp-knife spasticity (Ref: Bradley's Neurology in Clinical Practice 5/e p2185, 2190)Clasp-Knife Effect:When the muscles are hypertonic, as in a UMN lesion, the sequence of moderate stretch - muscle contraction, strong stretch - muscle relaxation is seen.Passive flexion of the elbow meets immediate resistance as a result of the stretch reflex in the triceps muscle.Further stretch activates the inverse stretch reflex. The resistance to flexion suddenly collapses, and the arm flexes.Continued passive flexion stretches the muscle again, and the sequence is repeated.This sequence of resistance followed by a 'give' when a limb is moved passively is known as the clasp-knife effect because of its resemblance to the closing of a pocket knife.It is also known as lengthening reaction because it is the response of a spastic muscle to lengthening. Upper Motor Neuron LesionsLower Neuron LesionsPowerDecreasedQ Weakness (Muscle groups or Limbs being affected and not individual musclesQ)Very much decreased Weakness (severe) due to paralysis of individual musclesQ.ToneHypertonia (Clasp knife spasticityQ)Flaccidity (HypotoniaQ)Wasting/AtrophyMinimalQ, if present and due to disuse atrophy.Marked (cardinal featureQ)Reflexes * Superficial reflexesLostQLostQ* Deep reflexesBrisk/ExaggeratedQExaggeratedQ* ClonusMay be + ntQAbsentQ* PlantarExtensorQFlexor or no responseQFasciculationsAbsentQPresentQReaction of degeneration in musclesAbsentQPresentQ