Muscle tone is the resistance felt when the resting limb is moved passively by the examiner.
Hypertonia – increased tone – two types – (1) Spasticity – upper motor neuron lesion – feel rapid build up of resistance during initial passive movement, then sudden lessening of resistance – ‘clasp knife’ phenomenon. (2) Rigidity – sustained resistance to passive movement – in basal ganglia diseases – ‘lead pipe’ phenomenon
Hypotonia – decreased tone – seen in lower motor neuron lesions, cerebellar lesions, muscle diseases
Clonus – involuntary contractions occurring when muscle is suddenly stretched