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The effects of age on the somatosensory nervous system have been observed at all of its morphological levels extending from the neuronal cytons of the dorsal root ganglia distally to specific sensory mechanoreceptors (Mathewson and Nava,’ 85; Spencer and Ochoa,’ 81; Kenshalo,’ 77, and Cauna,’ 65). Documentation of age-related regression of the peripheral nervous system has come from several sources: clinical, electrophysiological, neuropharmacological and histopathological (Ras and Nava,’ 86). One of the clinical manifestations of concern is the distal blunting of vibratory sensation. Sensitivity to vibratory stimuli in the absence of detectable neuropathy is significantly reduced with advanced age in humans (Era, et al.,’ 86). Thresholds for all frequencies are significantly higher in the elderly. This is especially true for the lower extremities after the sixth decade (Verrillo,’ 80). It has been suggested that these progressive losses of sensitivity to vibration stimuli may be the partial result of alterations in the morphology of the Pacinian corpuscle that occur with age (Cauna,’ 65). This rapidly adapting mechanoreceptor is capable of responding to sinusoidal vibratory stimuli in the range of 20–1500 Hz, with a maximum sensitivity of 200–400 Hz (Iggo,’ 85). These receptors are concentrated within the mesentery, subcutaneous tissues of the digits and footpads and the deep skeletal tissues (i.e., joints, ligaments, periosteum and interosseous membranes of mammals. |
