The Effect of Osmotic Pressure Changes on the Isolated Muscle Spindle

Ottoson, D. The effect of osmotic pressure changes on the isolated muscle spindle. Acta physiol. scand. 1965. 64. 93 105.– The action of hypertonic and hypotonic solutions on the sensory endings of the muscle spindle has been studied in isolated preparations. It was found that changes of osmotic pressure by more than 25 per cent caused an augmentation of the activity of the resting spindle and modified its sensitivity to stretch. Increase of pressure produced a discharge the peak frequency of which increased linearly with osmotic strength. The maximum effect was usually obtained with concentrations of four to five times that of Ringer's solution. The responsiveness of the spindle to stretch decreased with increasing pressure. Decreasing the osmotic pressure produced a short‐lasting increase of the activity of the resting spindle followed by a decline and final cessation of the discharge. The responsiveness to stretch was increased during the period of repetitive firing and then decreased. Washing with Ringer's solution after immersion in hypotonic solutions regularly produced a prolonged discharge and a reduced sensitivity to stretch. It is concluded that the observed changes are mainly due to osmotic effects on the sensory endings of the spindle. The results suggest that the endings behave as simple osmotic sacs within a limited range of osmotic strengths and that the sensory membrane is equally sensitive to distention and folding.