In this type of hypertonicity the fusimotor is also excessively active giving an increase in sensitivity to the stretch receptors in muscle. The disturbance is thought to lie at a different level from that causing spasticity since there is a considerable difference in the type of change in response to stretch. It will be remembered that the subcortical nuclei comprising the basal ganglia are thought to help in the production of postural fixation by exerting their influence upon the stretch reflex mechanism via the reticular formation.
They help to maintain adequate postural fixation while allowing the necessary malleability for voluntary movement. If they become too effective as factors in postural fixation the stretch reflex mechanism may lose its malleability due to excessive fusimotor action. Damage in the area of limb between the cortex and basal ganglia may well lead to excessive…
