Characteristics of adaptation of muscle stretch receptors of dynamic type.

Experiments on cats with a de-efferented triceps surae muscle showed that some stretch receptors of dynamic type adapt quickly within the first few seconds after stretching of the muscle and its keeping at the new length, whereas other receptors reveal two components of adaptation-fast and slow. Units with different types of adaptation are found in the same muscle; their afferents belong mainly to group I, although there is a zone of overlapping with group II afferents. These differences are manifested at high values of initial stretching of the muscle. It is suggested that the slow component of adaptation is based on a mechanical factor depending on the visco-elastic properties of the tissues in the region of the sensory nerve endings.