ISSN:0006-8977    

DOI:10.1159/000113902

出版商:S. Karger AG    

年代:1992

数据来源: Karger

ISSN:0006-8977    

DOI:10.1159/000113903

出版商:S. Karger AG    

年代:1992

数据来源: Karger

摘要:

Muscles effect locomotion, and their gross architecture still poses analytical problems. These problems involve the arrangement of myofibers and motor units within muscles and that of muscles around joints. The arrangement of fibers may involve a range of considerations from the equivalence or non-equivalence of sarcomeres to placement, attachment, and angulation of fascicles and entire muscles; consequently, these levels and their development and coordination overlap. Many problems at the macroscopic level require clarification of how an animal uses a compartment of suite of muscles and whether morphological differences reflect functional ones. The understanding of intermediate architecture, including issues of compartmentation, pinnation, and concatenation, remains more elusive, as some morphologically distinct muscles may be functionally equivalent. As yet we have inadequate appreciation of the opportunities or limitations provided to the control system by a particular arrangement of fibers, or vice versa. Exploration of the rules that govern these conditions provides abundant opportunities for cooperation among neurobiologists, developmental biologists, physiologists and morphologists.

ISSN:0006-8977    

DOI:10.1159/000113904

出版商:S. Karger AG    

年代:1992

数据来源: Karger

摘要:

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 (Dls) 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. Some of these changes include the breakup of the myomeres into a large number of discrete axial muscles, as well as the development of paired fins and limbs and the associated limb muscles. The primitive segregation of fiber types was lost in many of the muscles arising from the myomeres. Non-spiking slow fibers and spiking fast ones were retained in most vertebrates but were lost in most mammalian muscles. The motor column innervating axial muscles changed substantially with the development of a topographic map of the motor column onto the myotome in the embryo. The map probably arose at or before the evolution of amniotic vertebrates. The predominant mode of activation of axial muscles also changed within amniotes from the primitive 'swimming' motor pattern with alternation of activity on opposite sides and a rostrocaudal wave of muscle activity to a bilateral activation of muscles in mammals. However, even some amniotes, particularly reptiles, sometimes use motor patterns with primitive features. The change in motor pattern in mammals points to possible changes in the central circuits controlling the motoneurons. The major features of reticulospinal pathways are conservative among vertebrates. One of the most striking conservative pathways arises from the midbrain locomotor region that activates spinal networks for rhythmic movements in both fishes and mammals, even though there are substantial differences in the muscles, the movements and, possibly, the central pattern generators producing the movements in these animals.

ISSN:0006-8977    

DOI:10.1159/000113905

出版商:S. Karger AG    

年代:1992

数据来源: Karger

摘要:

A fundamental issue in the understanding of how the nervous system processes information is the way in which sensory information is used to initiate and guide movements. Recent progress has been made by taking an information processing approach in which information - for example, the spatial location of an object towards which an animal will orient - is tracked through the nervous system from sensory to motor levels. In this approach, neurally encoded information is characterized in terms of its representation within a neural or intrinsic coordinate system or set of neural coding parameters. For example, the retina codes spatial location in terms of the location of activity on the retinal surface, whereas motoneurons code spatial location in terms of the pulling directions of the muscles they activate. In between these two peripheral stages, the information passes through intermediate coordinate systems. These intermediate coordinate systems can be characterized by recording or altering the activity of small groups of neurons while an animal is performing a well-defined sensorimotor task. Spatial location information is used to guide orienting movements, those movements made by the eyes, ears, head, or body which function to center an object of interest in the animal's visual field. The optic tectum and forebrain, their connections to the medial mesencephalic and rhombencephalic brainstem tegmental cell groups, and subsequent connections to brainstem motor nuclei and spinal cord are employed to control fundamental aspects of this behavior. Studies reviewed herein indicate that following the retinotopic coding of spatial location in the retina and tectum, spatial location information appears to enter a different coordinate system at tegmental levels in which spatial aspects of orienting movement are coded in terms of their discrete horizontal and vertical components. This Cartesian coordinate system is an example of an abstract neural coordinate system, in that it is a simple, low-dimensional representation of spatial location which differs greatly from both sensory and motor representations. Also, this Cartesian representation may be common to many orienting movements, yet it appears to differ from the coordinate systems controlling other movement types such as stabilization or phasic movements. This suggests an hypothesis in which coordinate systems, especially at intermediate levels of processing, may be organized according to behavioral task as opposed to being determined by the particular sensory or motor system involved in the behavior. Understanding the evolutionary heritage and computational function of abstract neural coordinate systems, and the relation between different coordinate systems and behavioral tasks may be useful in understanding general aspects of sensory information processing and motor control.

ISSN:0006-8977    

DOI:10.1159/000113906

出版商:S. Karger AG    

年代:1992

数据来源: Karger

摘要:

The acceptance of the concept of central pattern generators (CPGs) led to the perception that descending inputs initiate stereotyped movements, such as locomotion, but play relatively minor roles after the movement begins. Sensory input could entrain the CPG, and the CPG was responsive to the proper inputs for switching, etc. Evidence is here presented that the influences of both descending and sensory inputs are two-way. Descending inputs are shown to be involved in an ongoing manner during locomotion, as it has been found that CPGs are phasically driving the same descending systems that themselves activate the CPGs. Similarly, sensory inputs are being actively processed by the CPG and, here again, produce a two-way interaction between sensory input and CPGs. Finally, mechanical factors are shown to be major contributors to the form of the movement. Thus, overall the CPG can only be considered as one of several contributors to any movement; all concurrently process the flow of information. Control is viewed as distributed, that is, as heterarchical as opposed to hierarchical. Because of the complexity of interaction between the levels of the system, it is argued that any change in the body will propagate through the system and effect the final output regardless of where the change originates. Thus, ontogenetic and phylogenetic changes must have influences felt throughout the entire system. Examples are presented to demonstrate that this is, indeed, the case. The effect of these changes will primarily be manifest in the interface between the layers, that is, in the interface between the descending and sensory inputs and the CPG, so that the changes can be adaptively accommodated on a moment by moment basis when necessary.

ISSN:0006-8977    

DOI:10.1159/000113907

出版商:S. Karger AG    

年代:1992

数据来源: Karger

摘要:

Our approach to understanding motor systems is a phylogenetic, 'outside-in' approach, the goal of which is to identify behavioral transitions during phylogenesis and elucidate their neurological basis. In this paper, we review the results of recent behavioral, biomechanical and neurological studies on frog feeding behavior. These studies show that highly protrusible tongues have evolved numerous times independently among frogs, and that the biomechanics and neuromuscular control of feeding behavior have been transformed repeatedly during frog evolution. Many of the independent lineages possess unique biomechanical mechanisms for protracting their tongues and unique neural mechanisms for coordinating feeding behavior. In frogs, there has been considerable evolution at the interface between reticular central pattern generators (CPGs) associated with feeding and sensory feedback circuits that modulate feeding motor output. In particular, the roles of hypoglossal and glossopharyngeal sensory feedback appear to have been relatively plastic in their evolution. Prey-type dependence of hypoglossal sensory feedback in Rana suggests that the interaction between descending visual control and sensory feedback also may be evolutionarily plastic. Comparative studies have found that motor systems sometimes evolve conservatively across morphological and behavioral transitions (i.e., the shoulder in birds) or, alternatively, they may be subject to considerably more evolutionary change than is reflected in morphological characteristics (i.e., feeding in cichlids). We hypothesize that the CPG circuits for feeding behavior in the reticular formation may evolve conservatively because they are highly integrated, multifunctional networks which cannot be optimized for one function without compromising others. In contrast, the interfaces between the CPG, sensory feedback and descending control should be less constrained. When changes in motor patterns occur during evolution, it is likely that sensory feedback or descending control may be involved.

ISSN:0006-8977    

DOI:10.1159/000113908

出版商:S. Karger AG    

年代:1992

数据来源: Karger

摘要:

The neural control of chromatophore display in cephalopod mollusks and teleost fishes is reviewed in the context of convergence of functional-anatomical pathways and mechanisms at several levels of organization. The effector elements or chromatophores are different in origin and design in the two groups of animals. Major functional differences appear to be in the speed of response (greatest in cephalopods) and the magnitude of non-neural control mechanisms (greatest in teleosts). Despite the differences, the elements demonstrate striking overall functional similarity. Elements of different types form highly organized array patterns of similar general complexity. Innervation patterns in cephalopods and teleosts seem comparable, with control being unidirectional (albeit in opposite directions); some elements demonstrate polyaxonal innervation. Motor units in both groups are generally composed of many chromatophores. Packard's concept of 'cronological units' of similar age-classes of chromatophores being innervated by similar age-classes of motor neurons greatly simplifies the understanding of relationships between the static arrays and the physiological units that utilize them to produce chromatic displays. The lower motor control areas for both groups have been grossly identified. Chromatomotor neurons in cephalopods are mostly located in the chromatophore lobes of the sub-esophageal brain while comparable systems in teleosts are situated in sympathetic chain ganglia (preganglionics) and the rostral spinal cord (postganglionics). Chromatic components are the simplest visually detectable units of color display, e.g. vertical bands and fin spots. They combine to form more complex chromatic patterns, which, in turn, are integrated with components of skin texture, posture and movement to produce display behaviors. Complexity of such systems seems to be of the same order of magnitude in both cephalopods and teleosts. Areas of the CNS related to each of the categorical levels have not been clearly defined. Crude patterning may take place in the basal and, perhaps, peduncle lobes in cephalopods and in the lower and intermediate medulla in teleosts. In both groups, higher level control relates to areas involved in sensorimotor integration and mediation of agonistic, sexual, and, perhaps, other types of behavior: the peduncle and optic lobes in cephalopods and the hypothalamus, tegmentum, otic tectum, torus semicircularis, thalamus and telencephalon in fishes. The systems appear to parallel each other in being organized hierarchically, with similar levels of complexity. Some of the regions may be especially important for regulating color patterns in response to visual input. Overall, chromatomotor control systems in cephalopods and teleosts demonstrate many apparent convergent features. Possible factors responsible for the similarities are discussed. The chromatic systems appear to be especially well-suited for the analysis of convergence in visually related neurobehavioral mechanisms.

ISSN:0006-8977    

DOI:10.1159/000113909

出版商:S. Karger AG    

年代:1992

数据来源: Karger

摘要:

The neural control of chromatophore display in cephalopod mollusks and teleost fishes is reviewed in the context of convergence of functional-anatomical pathways and mechanisms at several levels of organization. The effector elements or chromatophores are different in origin and design in the two groups of animals. Major functional differences appear to be in the speed of response (greatest in cephalopods) and the magnitude of non-neural control mechanisms (greatest in teleosts). Despite the differences, the elements demonstrate striking overall functional similarity. Elements of different types form highly organized array patterns of similar general complexity. Innervation patterns in cephalopods and teleosts seem comparable, with control being unidirectional (albeit in opposite directions); some elements demonstrate polyaxonal innervation. Motor units in both groups are generally composed of many chromatophores. Packard's concept of 'cronological units' of similar age-classes of chromatophores being innervated by similar age-classes of motor neurons greatly simplifies the understanding of relationships between the static arrays and the physiological units that utilize them to produce chromatic displays. The lower motor control areas for both groups have been grossly identified. Chromatomotor neurons in cephalopods are mostly located in the chromatophore lobes of the sub-esophageal brain while comparable systems in teleosts are situated in sympathetic chain ganglia (preganglionics) and the rostral spinal cord (postganglionics). Chromatic components are the simplest visually detectable units of color display, e.g. vertical bands and fin spots. They combine to form more complex chromatic patterns, which, in turn, are integrated with components of skin texture, posture and movement to produce display behaviors. Complexity of such systems seems to be of the same order of magnitude in both cephalopods and teleosts. Areas of the CNS related to each of the categorical levels have not been clearly defined. Crude patterning may take place in the basal and, perhaps, peduncle lobes in cephalopods and in the lower and intermediate medulla in teleosts. In both groups, higher level control relates to areas involved in sensorimotor integration and mediation of agonistic, sexual, and, perhaps, other types of behavior: the peduncle and optic lobes in cephalopods and the hypothalamus, tegmentum, otic tectum, torus semicircularis, thalamus and telencephalon in fishes. The systems appear to parallel each other in being organized hierarchically, with similar levels of complexity. Some of the regions may be especially important for regulating color patterns in response to visual input. Overall, chromatomotor control systems in cephalopods and teleosts demonstrate many apparent convergent features. Possible factors responsible for the similarities are discussed. The chromatic systems appear to be especially well-suited for the analysis of convergence in visually related neurobehavioral mechanisms.

ISSN:0006-8977    

DOI:10.1159/000316108

出版商:S. Karger AG    

年代:1992

数据来源: Karger