Reflex Organization in the Swimmeret System of the Lobster

1. The intrasegmental feedback reflexes in the swimmeret system of the lobster Homarus americanus were activated while recording the responses from the swimmeret nerves and muscles. 2. Two main sources of sensory feedback were identified; proprioceptors in the coxal region of the swimmeret, and sensory setae on the edges of the two rami of each swimmeret. The reflexes activated by these inputs are described. 3. Reflexive feedback from the powerstroke movement to the powerstroke excita tory motor neurones is positive, further reinforcing the movement. Intrasegmental reflexes capable of independently initiating or terminating the powerstroke activity are absent, however. Therefore the powerstroke movement of each cycle can begin and end only in response to a purely central nervous motor command. It follows that the intrasegmental swimmeret reflexes are incapable of contributing to the periodicity seen in the motor output pattern which underlies swimmeret beating. 4. In addition to strengthening the powerstroke, the intrasegmental reflexes strengthen the linkage between the powerstroke and the returnstroke within each movement cycle. The reflexes may also reinforce the reciprocity between excitor and inhibitor axon activity to the main powerstroke and returnstroke muscles. 5. It is shown, however, that these three features of the motor output pattern are programmed into the CNS independently of the sensory feedback. The intrasegmental reflexes thus act as subservient amplifying devices for cyclic motor patterns which are produced independently by purely central nervous mechanisms.

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Reflex Organization in the Swimmeret System of the Lobster

Journal of Experimental Biology ◽

10.1242/jeb.51.3.565 ◽

1969 ◽

Vol 51 (3) ◽

pp. 565-573

Author(s):

W. J. DAVIS

Keyword(s):

Dynamic Properties ◽

Motor Command ◽

Homarus Americanus ◽

Reflex Response ◽

Limb Position ◽

Cycle Basis ◽

Sinusoidal Movement ◽

Wide Range ◽

Motor Neurones ◽

Maximum Amplification

1. The dynamic properties of the intrasegmental swimmeret reflexes of the lobster Homarus americanus were studied by recording the discharge of the motor neurones while the swimmeret was moved sinusoidally in its natural arc over a wide range of frequencies. 2. The reflex responses of the excitor neurones of both powerstroke (retractor) and returnstroke (protractor) muscles display hysteresis. In both cases the efferent response corresponding to a given limb position is usually greater during imposed retraction than during protraction. 3. The cyclic efferent reflex response follows the sinusoidal movement stimulus at movement frequencies up to and beyond those which occur naturally during swimmeret beating, with no change in the position of maximum reflex activity in the cycle. The reflexes are therefore capable of influencing the motor output on a cycle-by-cycle basis. 4. The strength of the reflex response is maximum between 1 and 3 Hz. of imposed movement, and declines to either side of this range. The dynamic properties of the reflexes are therefore adjusted so that the maximum amplification of the rhythmic central motor command occurs at the natural frequency of swimmeret beating.

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Impulse Patterns in the Flight Motor Neurones Of Bombus Californicus and Oncopeltus Fasciatus

Journal of Experimental Biology ◽

10.1242/jeb.52.1.59 ◽

1970 ◽

Vol 52 (1) ◽

pp. 59-77

Author(s):

BRIAN MULLONEY

Keyword(s):

Low Frequency ◽

Motor Units ◽

Excitatory Input ◽

Oncopeltus Fasciatus ◽

Synaptic Coupling ◽

Motor Patterns ◽

Motor Neurones ◽

Pattern Characteristic ◽

Output Pattern ◽

Flight Muscles

1. Each of the motor neurones innervating the indirect flight muscles of Bombus and Oncopeltus fire regularly during flight, not in patterned bursts. The several motor neurones innervating one muscle fire at about the same rate and have a weak tendency to fire synchronously, but all possible relative timings occur in each flight. Neurones innervating different muscles have no preferred relative timing, and may have different frequencies. 2. The motor patterns of Bombus and Oncopeltus are very similar. These patterns could be generated by a model including common excitatory input to each of the neurones innervating one muscle and by weak electrotonic short-latency synaptic coupling between the motor neurones. Different sets of neurones would receive different excitatory input, and antagonistic sets seem to be coupled by a weak inhibitory mechanism. 3. Recruitment of motor units was observed in Bombus during low-frequency activity. 4. Synergistic units in Bombus fire in near-perfect synchrony during periods when the bee is warming up but not flying. When the bee begins to fly, there is a sudden shift to the output pattern characteristic of flight. 5. The patterns of impulses in these insects have characteristics shared by both dipteran patterns and by orthopteran and lepidopteran patterns. The flight systems of Orthoptera, Lepidoptera, Hemiptera, Hymenoptera and Diptera also have many anatomical similarities. The anatomical similarities and the several common characteristics of the motor output patterns in these orders support the hypothesis that there was one primordial flight mechanism common to the origin of these orders, from which the different mechanisms which exist today have evolved.

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Analysis of the Scaphognathite Ventilatory Pump in the Shore Crab Carcinus Maenas: III. NEUROMUSCULAR MECHANISMS

Journal of Experimental Biology ◽

10.1242/jeb.113.1.83 ◽

1984 ◽

Vol 113 (1) ◽

pp. 83-99 ◽

Cited By ~ 3

Author(s):

A. JOFFRE MERCIER ◽

JERREL L. WILKENS

Keyword(s):

Motor Pattern ◽

Carcinus Maenas ◽

Ventilation Rate ◽

Firing Frequency ◽

Motor Output ◽

Shore Crab ◽

Time Interval ◽

Motor Neurones ◽

Output Pattern ◽

Nerve Recordings

The motor output pattern to one of the ventilatory muscles of the scaphognathite (SC) in the shore crab, Carcinus maenas, was analysed from extracellular nerve recordings. During ‘forward mode’ bursting, an increase in the burst rate of L2b motor neurones is accompanied by an increase in the average intraburst firing frequency. The number of action potentials per burst, although variable, does not change consistently as a function of burst rate. The influence of individual aspects of the motor pattern on isotonic contractions of muscle L2b was examined. Increasing the intraburst frequency leads to greater contraction and work output, and allows the muscle to lift heavier loads. This effect is correlated with an increase in the level of postsynaptic depolarization, due, at least in part, to greater summation of EPSPs. Increasing the burst rate alone also enhances muscle contraction and work, and results in greater depolarization. This latter effect appears to involve an accumulation of short-term facilitation, which becomes more acute as the time interval between the bursts is progressively shortened. In addition, contraction and depolarization are augmented by increasing the number of impulses per burst or the number of axons recruited. These observations indicate some aspects of the motor output pattern which are appropriately modified to accommodate the changes in force and work demands which accompany a change in gill ventilation rate.

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Invariance of Oscillator Interneurone Activity During Variable Motor Output by Locusts

Journal of Experimental Biology ◽

10.1242/jeb.141.1.231 ◽

1989 ◽

Vol 141 (1) ◽

pp. 231-239

Author(s):

H. REICHERT ◽

C. H. F. ROWELL

Keyword(s):

Action Potentials ◽

Motor Output ◽

Motor Patterns ◽

Sensory Inputs ◽

Motor Neurones ◽

Depressor Muscle ◽

Premotor Interneurones ◽

Centre Of Rotation ◽

Flight Motor ◽

Oscillator Output

Simultaneous intracellular recordings were made in locusts from (a) flight motor neurones and (b) output interneurones of the flight oscillator. The insects were mounted with the head at the centre of rotation of an artificial horizon. During fictive flight, these animals responded to simulated deviations from course with the changes in motor output appropriate to course-correction manoeuvres, as previously described. In the motor neurone of depressor muscle MN98 (mesothoracic second basalar) these changes take the form of systematic variation in amplitude in the cyclical depolarization seen in the neurone in flight which, in turn, leads to variation in the number of action potentials per cycle (from 0–3) and in the latency of the first spike (up to 19 ms difference). These changes are closely related to the perceived movement of the horizon. The oscillator output, as recorded in metathoracic interneurone 511, shows, in contrast, very little change. The fraction of its variation which is correlated with horizon movement is vanishingly small (e.g. for number of action potentials per burst r2 = 0.008). The exteroceptive sensory inputs which modify motor output during steering do not, therefore, affect the oscillator appreciably. Thus, by exclusion, the motor patterns of compensatory steering are due exclusively to summation of the oscillator drive with the sensory inputs. This takes place in the motor neurones and especially in the premotor interneurones, as previously described.

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Motor Patterns During Walking on a Slippery Walkway

Journal of Neurophysiology ◽

10.1152/jn.00499.2009 ◽

2010 ◽

Vol 103 (2) ◽

pp. 746-760 ◽

Cited By ~ 77

Author(s):

Germana Cappellini ◽

Yuri P. Ivanenko ◽

Nadia Dominici ◽

Richard E. Poppele ◽

Francesco Lacquaniti

Keyword(s):

Motor Output ◽

Emg Activity ◽

Head Orientation ◽

Cycle Duration ◽

Horizontal Shear ◽

Motor Patterns ◽

Spatiotemporal Organization ◽

Surface Conditions ◽

Gait Kinematics ◽

Slippery Surface

Friction and gravity represent two basic physical constraints of terrestrial locomotion that affect both motor patterns and the biomechanics of bipedal gait. To provide insights into the spatiotemporal organization of the motor output in connection with ground contact forces, we studied adaptation of human gait to steady low-friction conditions. Subjects walked along a slippery walkway (7 m long; friction coefficient ≃ 0.06) or a normal, nonslippery floor at a natural speed. We recorded gait kinematics, ground reaction forces, and bilateral electromyographic (EMG) activity of 16 leg and trunk muscles and we mapped the recorded EMG patterns onto the spinal cord in approximate rostrocaudal locations of the motoneuron (MN) pools to characterize the spatiotemporal organization of the motor output. The results revealed several idiosyncratic features of walking on the slippery surface. The step length, cycle duration, and horizontal shear forces were significantly smaller, the head orientation tended to be stabilized in space, whereas arm movements, trunk rotations, and lateral trunk inclinations considerably increased and foot motion and gait kinematics resembled those of a nonplantigrade gait. Furthermore, walking on the slippery surface required stabilization of the hip and of the center-of-body mass in the frontal plane, which significantly improved with practice. Motor patterns were characterized by an enhanced (roughly twofold) level of MN activity, substantial decoupling of anatomical synergists, and the absence of systematic displacements of the center of MN activity in the lumbosacral enlargement. Overall, the results show that when subjects are confronted with unsteady surface conditions, like the slippery floor, they adopt a gait mode that tends to keep the COM centered over the supporting limbs and to increase limb stiffness. We suggest that this behavior may represent a distinct gait mode that is particularly suited to uncertain surface conditions in general.

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Retracing your footsteps: developmental insights to spinal network plasticity following injury

Journal of Neurophysiology ◽

10.1152/jn.00575.2017 ◽

2018 ◽

Vol 119 (2) ◽

pp. 521-536 ◽

Cited By ~ 8

Author(s):

C. Jean-Xavier ◽

S. A. Sharples ◽

K. A. Mayr ◽

A. P. Lognon ◽

P. J. Whelan

Keyword(s):

Spinal Cord ◽

Neuronal Excitability ◽

Weight Bearing ◽

Rhythmic Activity ◽

Motor Output ◽

Parallel Mechanisms ◽

Sensory Afferents ◽

Motor Patterns ◽

Network Function ◽

Cord Injury

During development of the spinal cord, a precise interaction occurs between descending projections and sensory afferents, with spinal networks that lead to expression of coordinated motor output. In the rodent, during the last embryonic week, motor output first occurs as regular bursts of spontaneous activity, progressing to stochastic patterns of episodes that express bouts of coordinated rhythmic activity perinatally. Locomotor activity becomes functionally mature in the 2nd postnatal wk and is heralded by the onset of weight-bearing locomotion on the 8th and 9th postnatal day. Concomitantly, there is a maturation of intrinsic properties and key conductances mediating plateau potentials. In this review, we discuss spinal neuronal excitability, descending modulation, and afferent modulation in the developing rodent spinal cord. In the adult, plastic mechanisms are much more constrained but become more permissive following neurotrauma, such as spinal cord injury. We discuss parallel mechanisms that contribute to maturation of network function during development to mechanisms of pathological plasticity that contribute to aberrant motor patterns, such as spasticity and clonus, which emerge following central injury.

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Analysis and modeling of the multisegmental coordination of shortening behavior in the medicinal leech. I. Motor output pattern

Journal of Neurophysiology ◽

10.1152/jn.1992.68.5.1683 ◽

1992 ◽

Vol 68 (5) ◽

pp. 1683-1692 ◽

Cited By ~ 21

Author(s):

G. Wittenberg ◽

W. B. Kristan

Keyword(s):

Motor Neurons ◽

Longitudinal Muscle ◽

Motor Pattern ◽

Mechanical Stimulus ◽

Medicinal Leech ◽

Motor Output ◽

Simultaneous Excitation ◽

Ventral Longitudinal Muscle ◽

Output Pattern ◽

Simple Behavior

1. To understand how a multisegmental animal coordinates motor activity over more than one segment, we studied shortening behavior in the medicinal leech, in which several segments contract longitudinally in response to a moderately strong mechanical stimulus. 2. We first demonstrated that the neuronal activity responsible for shortening behavior occurred in semi-intact and isolated nerve cord preparations, and then characterized the responses of motor neurons in isolated preparations. The motor output during shortening was simultaneous excitation of motor neurons innervating dorsal longitudinal muscle and of motor neurons innervating ventral longitudinal muscle. 3. The stronger the stimulus, the more segments produced the shortening motor output, with the segments nearest the stimulus recruited first. 4. Although the shortening response was produced in several segments near the site of stimulation, it was never produced in the stimulated segment, where the local bending motor output pattern was produced. The motor pattern suggests that shortening, initially considered a very simple behavior, requires the involvement of at least few segmentally iterated interneurons.

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Plastic Changes in Hand Proprioception Following Force-Field Motor Learning

Journal of Neurophysiology ◽

10.1152/jn.00543.2010 ◽

2010 ◽

Vol 104 (3) ◽

pp. 1213-1215 ◽

Cited By ~ 9

Author(s):

Daniel J. Goble ◽

Joaquin A. Anguera

Keyword(s):

Motor Learning ◽

Force Field ◽

Recent Work ◽

Modulation of motor patterns by sensory feedback during earthworm locomotion

Neuroscience Research ◽

10.1016/j.neures.2004.01.002 ◽

2004 ◽

Vol 48 (4) ◽

pp. 457-462 ◽

Cited By ~ 7

Author(s):

Kenji Mizutani ◽

Toshinobu Shimoi ◽

Hiroto Ogawa ◽

Yoshiichiro Kitamura ◽

Kotaro Oka

Keyword(s):

Sensory Feedback ◽

Motor Patterns

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The Central Nervous Control of Complex Movements in the Uropods of Crayfish

Journal of Experimental Biology ◽

10.1242/jeb.51.1.135 ◽

1969 ◽

Vol 51 (1) ◽

pp. 135-150

Author(s):

J. L. LARIMER ◽

D. KENNEDY

Keyword(s):

Central Element ◽

Simultaneous Recording ◽

Motor Output ◽

Afferent Feedback ◽

Rhythmic Pattern ◽

Nervous Control ◽

Motor Pathways ◽

Combined Movements ◽

Motor Neurones ◽

Two Sides

1. The control of postural uropod muscles in the crayfish has been investigated by stimulating ‘command’ interneurones isolated from central connectives. Reciprocity is preserved between exciters and inhibitors innervating the same muscle, and between motor axons serving antagonists. 2. The control of combined movements, involving groups of muscles that are neither synergists nor antagonists, was analysed by simultaneous recording. Most command fibres affected several different motor pathways, and different command fibres produced different combinations of output. It is concluded that quite complex movements may be encoded in the connexions of a single central element. 3. In several instances it was shown unequivocally that single central neurones were responsible for releasing the motor output. One identified command neurone produces a stereotyped, rhythmic pattern of activity in several motor pathways. This effect did not depend upon afferent feedback for its form or frequency. 4. Command interneurones often produce asymmetrical responses in the appendages of the two sides. Some of these make connexions only to the ipsilateral motor neurones, others only to contralateral ones, and most make differential connexions on the two sides.

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