Because gait and balance disturbances are common manifestations of functional disturbances of many parts of the nervous system, alterations in gait are important physical signs in diagnosing dysfunction of these structures. Diseases affecting the proprioceptive, vestibular, or visual sensory systems commonly produce an unsteady or ataxic gait. Weakness produced by muscle and motor nerve diseases alter locomotion in characteristic patterns. Upper motor neuron disorders cause weakness and spasticity, which typically become evident during locomotion. Basal ganglia disorders produce distinctive hypokinetic and hyperkinetic gaits. Cerebellar dysfunction causes ataxia. However, many gait and balance disorders seen in the clinic are not readily explained by disturbances of a single neural structure.
As described earlier in the section on anatomy, some of the basic circuitry governing locomotion and balance is known. However, many clinical abnormalities of gait and posture are not due to disturbances of this basic circuitry but to the individual's adaptation (or failure of adaptation) of normal or slightly abnormal balance and gait synergies to day-to-day living. The neuroanatomical basis of this higher level of control and adaptation of balance and gait is less well understood. For this reason, gait and balance syndromes are arranged by systems rather than anatomically; they include disorders of (1) locomotor and balance synergies, (2) primary sensory function, (3) perception/ orientation, (4) force production, (5) force scaling, and (6) adaptation/cognition/attention.
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