Broad tuning of turtle spinal interneurons:
Individual interneurons (i.e., neurons intermediate between sensory neurons and motor neurons)
in the
turtle spinal cord often are most strongly activated (i.e., generate action potentials at an
increased
rate) by tactile stimulation of one location on the body surface and
are
progressively less activated as one moves away from this location,
either
anteriorly or posteriorly. Such a neuron is "tuned" to the
location at which tactile stimulation activates it most, but is only
"broadly tuned" (rather
than "sharply tuned") if it is activated to some degree by
stimulation over a wide area of the body surface. Many turtle
spinal
interneurons are broadly tuned to either a rostral scratch, a pocket
scratch,
or a caudal scratch region , but are activated to some extent by
stimulation
that would elicit 2 or more of the 3 forms of scratching (see examples
to the
left). These findings suggest the hypothesis that a large number
of
broadly tuned interneurons act together to mediate the precise
selection of one
form of scratching that the turtle spinal cord displays.
To the left are 9 examples of broadly
tuned
spinal interneurons; all were recorded from the same turtle.
(from
Berkowitz , J. Neurophysiol.
86:1017-1025, 2001.)
Strong interactions between scratch and swim spinal cord networks |
Hyperpolarization of scratch-specialized neurons during swim |
T neurons, a new
morphological & physiological class of spinal interneurons
|
Rhythmic activity of interneurons during two types of scratching |
Rhythmic activity of interneurons during left and right motor rhythms |