scholarly journals Same Spinal Interneurons Mediate Reflex Actions of Group Ib and Group II Afferents and Crossed Reticulospinal Actions

2006 ◽  
Vol 95 (6) ◽  
pp. 3911-3922 ◽  
Author(s):  
A. Cabaj ◽  
K. Stecina ◽  
E. Jankowska
Keyword(s):  
Muscle Afferents ◽  
Spinal Motoneurons ◽  
Reticulospinal Neurons ◽  
Spinal Interneurons ◽  
Reticulospinal Tract ◽  
Group Ii Muscle Afferents ◽  
Peripheral Afferents ◽  
Group Ii ◽  
Group Ii Afferents ◽  
Selection Of

The aim of the study was to analyze interactions between neuronal networks mediating centrally initiated movements and reflex reactions evoked by peripheral afferents; specifically whether interneurons in pathways from group Ib afferents and from group II muscle afferents mediate actions of reticulospinal neurons on spinal motoneurons by contralaterally located commissural interneurons. To this end reticulospinal tract fibers were stimulated in the contralateral medial longitudinal fascicle (MLF) in chloralose-anesthetized cats in which the ipsilateral half of the spinal cord was transected rostral to the lumbosacral enlargement. In the majority of interneurons mediating reflex actions of group Ib and group II afferents, MLF stimuli evoked either excitatory or inhibitory postsynaptic potentials (EPSPs and IPSPs, respectively) or both EPSPs and IPSPs attributable to disynaptic actions by commissural interneurons. In addition, in some interneurons EPSPs were evoked at latencies compatible with monosynaptic actions of crossed axon collaterals of MLF fibers. Intracellular records from motoneurons demonstrated that both excitation and inhibition from group Ib and group II afferents are modulated by contralaterally descending reticulospinal neurons. The results lead to the conclusion that commissural interneurons activated by reticulospinal neurons affect motoneurons not only directly, but also by enhancing or weakening activation of premotor interneurons in pathways from group Ib and group II afferents. The results also show that both excitatory and inhibitory premotor interneurons are affected in this way and that commissural interneurons may assist in the selection of reflex actions of group Ib and group II afferents during centrally initiated movements.

Responses of cortical neurons (areas 3a and 4) to ramp stretch of hindlimb muscles in the baboon

1976 ◽  
Vol 39 (3) ◽  
pp. 484-500 ◽  
Author(s):  
J. Hore ◽  
J. B. Preston ◽  
P. D. Cheney
Keyword(s):  
Cortical Neurons ◽  
Muscle Length ◽  
Muscle Afferents ◽  
Muscle Stretch ◽  
Hindlimb Muscles ◽  
Group I ◽  
Hindlimb Muscle ◽  
Area 3A ◽  
Group Ii Muscle Afferents ◽  
Group Ii

1. A study was made of the response of single cortical units in areas 3a and 4 to electrical stimulation of hindlimb muscle nerves and to ramp stretch of hindlimb muscles in baboons anesthetized with chloralose.2. Stimulation of hindlimb muscle nerves revealed a group I projection primarily to area 3a but with some input into adjacent area. 4. A major group II projection was found in area 4 adjacent to area 3a. A small number of area 3a neurons receive convergence from both group I and group II muscle afferents.3a. On the basis of their response pattern to ramp stretch, units were classified into one of six categories and their cytoarchitectonic location was determined. Units in area 3a had hynamic sensitivities equivalent to that of the primary spindle afferents. Although the discharge of some area 3a neurons also reflected differences in muscle length, most area 3a neurons had low position sensitivities. One unit type in area 3a did not respond to maintained muscle stretch and signaled only velocity of stretch.4. Units in area 4 had position sensitivities equivalent to that of primary and secondary spindle afferents. Although the discharge of some area 4 units reflected different velocities of muscle stretch, these units had dynamic sensitivities similar to those of secondary spindle afferents rather than those of primary afferents. One type of unit in area 4 had no dynamic component to muscle stretch and signaled only muscle length.5. The results demonstrate that there is a transfer of dynamic and position sensitivity from spindle afferents to cortical neurons. Furthermore, data processing has occurred because some units respond only to the steady-state length of muscle, while other units encode only the dynamic phase of stretch. This behavior is different from the responses to ramp stretch of either group I or group II muscle afferents in the baboon.6. The results demonstrate that single units in cerebral cortex can encode the information transmitted to the central nervous system by muscle spindle afferents. The purpose for which this information is used remains undetermined.

Reflex pathways from group II muscle afferents

1987 ◽  
Vol 65 (2) ◽  
pp. 282-293 ◽  
Author(s):  
A. Lundberg ◽  
K. Malmgren ◽  
E. D. Schomburg
Keyword(s):  
Muscle Afferents ◽  
Reflex Pathways ◽  
Group Ii Muscle Afferents ◽  
Group Ii
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