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PubMed1996

An immunocytochemical study of the distribution of AMPA selective glutamate receptor subunits in the normal human motor system.

Glutamate is the major mediator of fast excitatory neurotransmission in the mammalian central nervous system. Disturbances of this neurotransmitter system have been implicated in chronic degenerative neurological disease. Recently, major advances in our knowledge and understanding of the molecular biology of the glutamatergic receptor system have been made. It is now known that functional glutamate receptors consist of various combinations of some 20 identified subunits. A growing body of circumstantial evidence suggests that the non-N-methyl-D-aspartate subtype of glutamate receptors may mediate, at least in part, the selective motor neuron death seen in the human neurodegenerative disease amyotrophic lateral sclerosis. We have used subunit specific immunocytochemistry to study the distribution and potential subunit composition of the alpha-amino-3-hydroxy-5-methyl-4-isoxazole-propionic acid (AMPA) selective glutamate receptors, (a subgroup of non-N-methyl-D-aspartate selective glutamate receptors formed by combinations of GluR1-4 subunits), in the human motor system. Motor neurons in the spinal cord, brainstem, and motor cortex were relatively strongly immunoreactive with the GluR2/3 subunit antibody, moderately so with the GluR4 subunit antibody, and showed relatively low levels of immunoreactivity with the GluR1 subunit antibody. This is the first detailed study of AMPA receptor subunit expression in the human motor system. Motor neurons express a distinct subunit profile when compared with other groups of neurons in the human nervous system. There were no significant differences in the pattern of relative AMPA subunit expression (GluR2/3 > or = GluR4 > GluR1) between groups of motor neurons typically affected (in the spinal cord and hypoglossal nucleus), or spared (oculomotor and Onufs nucleus) by the amyotrophic lateral sclerosis disease process. However, oculomotor motor neurons had higher levels of expression of all AMPA subunit proteins which may indicate greater AMPA mediated glutamatergic input in the normal function of this neuronal population. This study does not support a role for differential subunit composition of AMPA receptors in determining the selective vulnerability of motor neurons in amyotrophic lateral sclerosis. However, the overall density of receptors may be of importance.

Aged↗
PubMed2001

The cortical motor system.

The cortical motor system of primates is formed by a mosaic of anatomically and functionally distinct areas. These areas are not only involved in motor functions, but also play a role in functions formerly attributed to higher order associative cortical areas. In the present review, we discuss three types of higher functions carried out by the motor cortical areas: sensory-motor transformations, action understanding, and decision processing regarding action execution. We submit that generating internal representations of actions is central to cortical motor function. External contingencies and motivational factors determine then whether these action representations are transformed into actual actions.

Animals↗
PubMed1992

Preparation and execution of movement: parallels between insect and mammalian motor systems.

1. The organization of the motor systems underlying locomotion in insects and mammals is surprisingly similar. There are also parallels between the insect motor system and the system underlying reaching and the occulomotor system in primates. 2. The movements generated by all these systems are planned or prepared before their execution and there is a partial separation of circuits for preparation and execution. 3. These circuits consist of multiple descending pathways interconnected to form overlapping loops which work co-operatively to determine the motor output. Thus, both insect and mammalian motor systems can be treated as parallel distributed (PDP) systems. 4. This enables a comparison of functional levels of processing in the different systems and also provides a basis for modelling motor systems with attractor neural networks.

Animals↗
PubMed1977

The study of recovery and modification of the evoked potentials and motor answers in the motor system.

After an electrical stimulus within the motor system there will follow a compulsion, a reflexlike process in functional dependency, naturally in illness (function disturbance) dependency as well. We can detect this process with the evoked potentials at the non-stimulated sites of the motor system and with the motor answers at the periphery. Because the motor system acts as a whole, it is certain that every process at a site has its correlates at the other sites, but the different part of the same process will be in a different grade pronounced (many times in opposite direction) at the different sites. If we want to know something from the basic process and to find the real correlates, we have to compare different evoked potentials within the motor system and motor responses at the periphery, or we have to enhance or depress the whole process or its parts. For the latter the double stimulation technique is suitable, but we have to take into consideration that during this investigation two alternating processes affect each other and therefore the result will not be direct.

Brain↗
PubMedDate not supplied

[Use of the prompt identification principle in controlling complex motor systems (speed control)].

Some aspects of the adaptive control of animal motor system described in the form of differential equations system were discussed. It was considered that the system of motor control is a multilevel one in which each level has a definite range of correction capacity for movement deviations. Since the time of the sensory signal passing over the control nervous loop is comparable with the duration of the movement controlled, a mechanism of the fast adaptation to a nonstationary situation was suggested. This mechanism is based on the principle of urgent identification of the motor system state at the moment of movement initiation. Urgent identification occurs by means of estimating of the motor system reaction to a small precisely measured motor signal (test-impulse), which was generated simultaneously with the basic motor command outflow but reached the spinal motor structures more quickly. The mathematical description of the urgent identification principle performance in the motor control in the case of velocity estimating was suggested.

Animals↗
PubMed1999

Marine vessel control using the tiller-motor system.

Operator performance on the tiller-motor system was investigated in a field survey and in a tracking simulator. Boat operators in Study 1 reported both control difficulties and discomfort, when using their tiller-motor system. Participants in Study 2 operated a tiller-motor simulator of a boat navigating a river over a 20 min period. Directional and speed control performance was found to be poor, particularly on the first trials and under emergency conditions. These results support the suggestion that the incompatible nature of the control/response relationship in tiller-motor systems can cause operator difficulties. The dimensions of the simulator were systematically varied and found to influence operator shoulder extension, and ratings of exertion and discomfort. Recommendations for tiller-motor system design and installation are offered.

Adolescent↗
PubMed1992

The emotional motor system.

A large number of new descending motor pathways to caudal brainstem and spinal cord have been recognized recently. Nevertheless all the new pathways seem to belong to one of three motor systems in the central nervous system (CNS). This survey gives an overview of the pathways belonging to the so-called emotional motor system or the third motor system as defined by Holstege. The similarities and differences with the core, median and lateral paracore areas of the CNS as defined by Nieuwenhuys are discussed.

Animals↗
PubMed2006

Insights from models of rhythmic motor systems.

Computational models of rhythmic motor systems are valuable tools for the study of motor pattern generation and control. Recent modeling advances, together with experimental results, suggest that rhythmic behaviors, such as breathing or walking, are influenced by complex interactions among motor system components. Such interactions occur at all levels of organization, from the subcellular through to the cellular, synaptic, and network levels to the level of neuromuscular interactions and that of the whole organism. Simultaneously, safety mechanisms at all levels contribute to network stability and the generation of robust motor patterns.

Animals↗
PubMed2003

Development of motor system dysfunction following whiplash injury.

Dysfunction in the motor system is a feature of persistent whiplash associated disorders. Little is known about motor dysfunction in the early stages following injury and of its progress in those persons who recover and those who develop persistent symptoms. This study measured prospectively, motor system function (cervical range of movement (ROM), joint position error (JPE) and activity of the superficial neck flexors (EMG) during a test of cranio-cervical flexion) as well as a measure of fear of re-injury (TAMPA) in 66 whiplash subjects within 1 month of injury and then 2 and 3 months post injury. Subjects were classified at 3 months post injury using scores on the neck disability index: recovered (<8), mild pain and disability (10-28) or moderate/severe pain and disability (>30). Motor system function was also measured in 20 control subjects. All whiplash groups demonstrated decreased ROM and increased EMG (compared to controls) at 1 month post injury. This deficit persisted in the group with moderate/severe symptoms but returned to within normal limits in those who had recovered or reported persistent mild pain at 3 months. Increased EMG persisted for 3 months in all whiplash groups. Only the moderate/severe group showed greater JPE, within 1 month of injury, which remained unchanged at 3 months. TAMPA scores of the moderate/severe group were higher than those of the other two groups. The differences in TAMPA did not impact on ROM, EMG or JPE. This study identifies, for the first time, deficits in the motor system, as early as 1 month post whiplash injury, that persisted not only in those reporting moderate/severe symptoms at 3 months but also in subjects who recovered and those with persistent mild symptoms.

Adult↗
PubMed2001

The motor system: the whole and its parts.

Our knowledge of components of the human motor system has been growing steadily, but our understanding of its integration into a system is lagging behind. It is suggested that a combination of measurements of forces and movements of the motor system in a functionally meaningful environment in conjunction with computer simulations of the motor system may help us in understanding motor system properties. Neurotrauma can be seen as a natural deviation, with recovery as a slow path to yet another deviant state of the motor system. In that form they may be useful in explaining the close interaction between form and function of the human motor system.

Computer Simulation↗
PubMed1992

The spinal motor system in early vertebrates and some of its evolutionary changes.

Recent studies of the spinal motor systems of vertebrates allow us to begin to infer the organization of the motor apparatus of primitive vertebrates. This paper attempts to define some of the features of the motor system of early vertebrates based on studies of the motor systems in anamniotes and in Branchiostoma. It also deals with some changes in the primitive motor system during evolution. The primitive motor system consisted of myomeric axial muscles, with a functional subdivision of the musculature into non-spiking slow muscle fibers segregated in the myomeres from spiking fast ones. These fibers were innervated by two major classes of motoneurons in the cord-large motoneurons innervating faster fibers and small motoneurons innervating slow fibers. There was not a simple isomorphic mapping of the position of motoneurons in the motor column onto the location of the muscle fibers they innervated in the myomeres. Early vertebrates used these axial muscles to bend the body, and the different types of muscle fibers and motoneurons reflect the ability to produce slow swimming movements as well as very rapid bending associated with fast swimming or escapes. The premotor network producing bending was most likely a circuit composed of a class of descending interneurons (DIs) that provided excitation of ipsilateral motoneurons and other interneurons, and inhibitory commissural interneurons (CIs) that blocked contralateral activity and played an important role in generating the rhythmic alternating bending during swimming. This DI/CI network was retained in living anamniotes. At least two major descending systems linked the sensory systems in the head to these premotor networks in the spinal cord. The ability to turn on swimming by activation of DI/CI premotor networks in the cord resided at least in part in a midbrain locomotor region (MLR) that influenced spinal networks via projections to the reticular formation. Reticulospinal neurons were important not only for initiation of rhythmic swimming but also in the production of turning movements. The reticulospinal cells involved in turns produced their effects in part via monosynaptic connections with motor neurons and premotor interneurons, including some involved in rhythmic swimming. A prominent and powerful Mauthner cell was most likely present and important for rapid escape or startle movements. Some features of this primitive motor apparatus were conserved during the evolution of vertebrate motor systems, and others changed substantially. Many features of the early motor system were retained in living anamniotes; major changes occur among amniotes.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1989

Sound-generating (sonic) motor system in a teleost fish (Porichthys notatus): sexual polymorphisms and general synaptology of sonic motor nucleus.

The sonic motor nucleus of the plainfin midshipman, Porichthys notatus, is a midline nucleus located at the junction of the caudal medulla and rostral spinal cord. Its motoneurons innervate sonic "drumming" muscles that are attached to the lateral walls of the swimbladder. There are two classes of sexually mature males referred to as Type I and Type II. The Type I males are larger and generate sounds during the breeding season. The Type II males are smaller and, like adult females, have not yet been shown to generate sounds. This study examined possible sex differences in the size of sonic motoneurons, and the type and distribution of their afferent terminal boutons. The average soma diameter of motoneurons of Type I males is about 50% larger than that of Type II males and females. There is also a small but significant difference in soma diameter between Type II males and females; they are smaller in the former class. There were no sex differences in the presence or distribution of different classes of axosomatic and axodendritic terminal boutons, which included: (1) active zones with either clear, round, or pleomorphic vesicles, (2) active zones with both clear, round vesicles, and larger dense core vesicles, (3) "mixed synapses" with gap junctions and active zones usually associated with pleomorphic vesicles. The results are discussed within the context of sexual differentiation of vertebrate motor systems and the functional organization of the sonic motor system in fishes. Sex differences in soma diameter correlate with a number of sex differences in the gross and ultrastructural features that distinguish the sonic muscles of Type I males from those of Type II males and females, which are similar to each other. The absence of qualitative sex differences in synaptic morphology suggest that the central neuronal circuitry of the sonic motor system is similar among all three adult morphs.

Animals↗
PubMed2001

[Transcranial magnetic stimulation in child and adolescent psychiatry: excitability of the motor system in tic disorders and/or attention deficit hyperactivity disorders].

Motor system excitability can be investigated in vivo by means of single and paired pulse transcranial magnetic stimulation (TMS). Whereas the cortical silent period reflects the general degree of inhibitory mechanisms mainly within the sensorimotor loop, intracortical excitability measures the focused degree of inhibitory and facilitatory mechanisms within the motor cortex. In child and adolescent psychiatric disorders with uncontrollable motor behavior such as tics in tic disorder or motoric hyperactivity in attention deficit hyperactivity disorder (ADHD), different dysfunctional patterns of motor system excitability could be demonstrated compared to age-matched healthy controls: (1) In tic disorder, a shortened cortical silent period was observed, providing evidence of deficient inhibitory mechanisms within the sensorimotor loop, probably primarily at the level of the basal ganglia. (2) In ADHD, a decreased intracortical inhibition was found, probably reflecting deficient inhibitory mechanisms within the motor cortex (but enhancement of intracortical inhibition after oral intake of 10 mg methylphenidate). In order to investigate neurophysiological aspects of comorbidity, (3) motor system excitability was also measured in children with combined ADHD and tic disorder. The findings of a reduced intracortical inhibition as well as a shortened cortical silent period in these comorbid children provide evidence of additive effects at the level of motor system excitability. These decreased inhibitory mechanisms within the entire sensorimotor loop and especially the motor cortex could be essential neurobiological substrates of the deficient inhibitory motor control and regulation, respectively, in tic disorder and ADHD.

Adolescent↗
PubMed1992

Electromyographic evidence of a multiple motor system: implications for apraxia.

Geschwind (1975) postulated that a multiple motor system accounts for a discrepancy in apraxias in response to commands for truncal and limb movements. Kuypers (1968) provided experimental evidence of a multiple motor system in primates. We present evidence of this multiple motor system in the form of Fourier-transformed electromyographic data in humans of the predominantly short duration motor units for discrete control in hand musculature and the predominantly longer duration motor units in the truncal musculature. Furthermore, the right and left erector spinae muscles had different Fourier-transformed electromyographic data which, in our opinion, represent the medial motor system used by apraxias.

Adult↗
PubMedDate not supplied

[The physiology of the lid motor system].

OBJECTIVE: The physiology and anatomy of the lid motor system have been widely studied from experimental and clinical points of view during last years. These studies, mainly carried out in animals, have helped to understand its functioning in normal and pathologic situations. Despite the apparent simplicity of this motor system, lids are able of doing many types of movements, depending on each particular situation. Besides participating in reflex and spontaneous blinks, lids take part actively in motor responses of major complexity and that requires a better precision, for instance, during emotional responses as laughing or crying in human beings. Lid movements also accompanies the eyes in such a manner not to cover the pupil while they maintain a fixed position in the orbit or during reflex and voluntary saccades. DEVELOPMENT: This paper deals with the neural circuits underlying lid motor system and how the activity in them translates, through the corresponding muscles, in a coherent response despite the different situations imposed by the different stimuli. In this way, it is described each element and how they contribute in the whole we observe as lid movements, in its repertoire. CONCLUSION: The facial motor system has been quite preserved through phylogeny, so it can be said that human beings possess a mechanism for lubricating and protecting the eye that, except for certain differences, share with the rest of the terrestrial living beings.

Blinking↗
PubMed2003

Relative contributions of eyelid and eye-retraction motor systems to reflex and classically conditioned blink responses in the rabbit.

Early compensatory mechanisms between eyelid and eye-retraction motor systems following selective nerve and/or muscle lesions were studied in behaving rabbits. Reflex and conditioned eyelid responses were recorded in 1). controls and following 2). facial nerve section, 3). retractor bulbi muscle removal, and 4). facial nerve section and retractor bulbi muscle removal. Animals were classically conditioned with a delay paradigm by using a tone (350 ms, 600 Hz, 90 dB) as conditioned stimulus, followed 250 ms later by an air puff (100 ms, 3 kg/cm(2)) as unconditioned stimulus. Conditioned eyelid responses generated in the absence of the facial motor system (i.e., by the almost sole action of the retractor bulbi motor system) presented a wavy profile, due to the succession of eye-retraction movements. Learned eyelid responses generated in the absence of the eye-retraction motor system (i.e., by the almost exclusive action of the facial motor system) were similar to those of controls, but were reduced in amplitude and peak velocity. Finally, the isolated action of the extraocular recti muscle produced very small eyelid movements during both reflex and learned eyelid responses. Although each of these motor systems could act independently of the others, the motor result of their joint action did not coincide with the simple addition of their separate actions. Both facial and eye-retraction motor systems appear to be necessary for normal eyelid closure during blinking in rabbits. Central reorganization to compensate for loss of either of these systems may explain why the response of each system in isolation cannot be added linearly to obtain normal blink response magnitudes and profiles.

Animals↗
PubMed1996

Skilled forelimb movements in prey catching and in reaching by rats (Rattus norvegicus) and opossums (Monodelphis domestica): relations to anatomical differences in motor systems.

Traditional anatomical/behavioral classifications suggest that rats and opossums have simple motor systems and are impoverished with respect to their ability to make prehensile movements. Nevertheless, the motor system in rats and opossums represent extremes in relative size and complexity suggesting that a behavioral analysis of the movement competencies of these species will provide insights into the significance of such anatomical differences. This paper examines the movements that the two species use in catching crickets and in reaching for food items. Both species could use a single limb to reach out and grasp prey during prey catching and both could use a single limb to take food from a shelf. Both species could transport the food to the mouth by using a single paw. The food handling behavior of the rats was more complex than that of the opossums, however. They used a variety of prey catching movements and extensively manipulated the prey to remove the legs and wings before eating only the head and body. Additionally the rats made rotatory limb movements of aiming, pronation, and supination, when reaching. For both cricket catching and reaching, they used their digits more than did the opossums. The suggestion also emerged from the results that the movements of the opossums were more fixed and species-typical whereas those of the rats were more plastic and individualistic. Thus, the skilled movements of both species are more complex than is generally recognized and the greater complexity of the rat movements parallels their more complex motor system. These results are discussed in relation to anatomical differences in the motor system and, specifically, to differences in the terminal fields of the pyramidal tract. It is concluded that the motor abilities of nonprimate mammals have been vastly underrated.

Animals↗
PubMed2002

Functional magnetic resonance imaging for the evaluation of the motor system: primary and secondary brain areas in different motor tasks.

Functional magnetic resonance imaging was used to characterize the primary and secondary motor system in subjects performing different motor tasks. Nine right-handed subjects performed simple motor tasks using hand, foot, knee, tongue, lips, eyes and the diaphragm-pelvis. All tasks revealed significant activation in primary and secondary motor areas. In the average across subjects, only the activity in the precentral gyrus was statistically distinctive for each motor task and followed the distribution of the motor homunculus. We consider these results as a possible basis of presurgical planning, extending the currently used procedures over a broader spectrum of motor tasks and brain structures leading to a more precise evaluation of functional areas for intracerebral interventions.

Adult↗