An upright bipedal gait depends on the successful integration of postural control and locomotion.
These functions are widely distributed in the central nervous system.
Command and control centers in the brainstem, cerebellum, and forebrain modify the action of spinal pattern generators to promote stepping.
Step generation is dependent on locomotor centers in the pontine tegmentum, midbrain, and subthalamic region.
Locomotor synergies are executed through the reticular formation and descending pathways in the ventromedial spinal cord.
Cerebral control provides a goal and purpose for walking and is involved in avoidance of obstacles and adaptation of locomotor programs to context and terrain.
Standing balance depends on good-quality sensory information about the position of the body center with respect to the environment, support surface, and gravitational forces.
Sensory information for postural control is primarily generated by the visual system, the vestibular system, and proprioceptive receptors in the muscle spindles and joints.
A healthy redundancy of sensory afferent information is generally available, but loss of two of the three pathways is sufficient to compromise standing balance.
Balance disorders in older individuals sometimes result from multiple insults in the peripheral sensory systems (e.g., visual loss, vestibular deficit, peripheral neuropathy) that critically degrade the quality of afferent information needed for balance stability.