Journal of Neurophysiology, Vol 41, Issue 6 1546-1556, Copyright © 1978 by APS
Receptor potential and spike initiation in two varieties of snake muscle spindles
Y. Fukami
1. Receptor potentials, in response to ramp-and-hold stretch, have been
recorded from two varieties of snake muscle spindles. 2. The two types of
spindles have a similar sensitivity of impulse discharge to amplitude of
receptor potential during the static phase of stretch. 3. Receptor
potentials from short-capsule spindles show a high dynamic sensitivity to
velocity of stretch. Amplitude of dynamic receptor potentials is well
related to frequency of dynamic discharge except beyond a certain velocity
of stretch where the frequency deviates progressively more than expected
from linearity. 4. Receptor potentials from long-capsule spindles show a
low dynamic sensitivity to velocity of stretch and amplitude of dynamic
receptor potentials is well correlated with dynamic firing frequency. 5.
The threshold level of receptor potential for initiating spike discharge
varies with the velocity of stretch, the relation being similar for the two
types of spindles. 6. It is concluded that the basis for functional
differentiation of snake spindles may lie in the mechanism by which
deformation of sensory endings is transformed into receptor potential. 7.
Late adaptation of impulse discharge, a characteristic feature of the
response of the short-capsule spindle to maintained stretch, has been
related to length changes of the sensory region measured directly with
Nomarski optics. The linear relation found between the slow adaptive fall
of impulse discharge and the simultaneous shortening of the sensory region
strongly suggests a mechanical basis for the late adaptation.
