Erhöhung der Beutefang-Effektivität durch Librium (original) (raw)
Journal of Comparative Physiology A, 1991
The tarsi of the modified front legs (whips) of the whip spider Heterophrynus elaphus contain two afferent giant fibers, GN 1 and GN2, with diameters at the tibia-tarsus joint of ca. 21 ~tm and 14 ~tm, respectively. The somata of these two neurons lie in the periphery, about 25 cm away from the CNS. These two neurons are interneurons which receive mechanoreceptive inputs from approximately 750 and 1500 bristles, respectively. The receptive fields of GN1 and GN2 overlap; they extend for 40 mm (GN1) and 90 mm (GN2) along the length of the tarsus. About 90 % of the synapses onto the giant fibers are axo-axonic. Mechanical stimulation of a single bristle is sufficient to elicit action potentials in one or both interneurons. The response of the interneurons adapts quickly. Average conduction time from the soma to the CNS is 45 ms for GN1 and 55 ms for GN2. Mean conduction velocities are 5.5 and 4.2 m/s, respectively. Activity in the giant fibers does not elicit a motor response; hence the giant fibers do not mediate an escape response. Possible functions of these giant fibers are discussed and compared to those of giant fiber systems in other arthropods.
Journal of Comparative Physiology A, 1991
The front legs of the whip spider H. elaphus are strongly modified to serve sensory functions. They contain several afferent nerve fibers which are so large that their action potentials can be recorded externally through the cuticle. In recordings from the tarsus 7 different types of afferent spikes were identified; 6 additional types of afferent spikes were discriminated in recordings from the tibia and femur. Most of the recorded potentials could be attributed to identifiable neurons serving different functions. These neurons include giant interneurons and giant fibers from diverse mechanoreceptors such as slit sense organs, trichobothria, and a joint receptor. In the present report these neurons are characterized using electrophysiological and histological methods. Their functions are discussed in the context of the animal's behavior.
Monosynaptic excitation of lateral giant fibres by proprioceptive afferents in the crayfish
Journal of Comparative Physiology A: Sensory, Neural, and Behavioral Physiology, 1997
Giant interneurones mediate a characteristic `tail ¯ip' escape response of the cray®sh, Procambarus clarkii, which move it rapidly away from the source of stimulation. We have analysed the synaptic connections of proprioceptive sensory neurones with one type of giant interneurone, the lateral giant. Spikes in sensory neurones innervating an exopodite-endopodite chordotonal organ in the tailfan, which monitors the position and movements of the exopodite, are followed at a short and constant latency by excitatory postsynaptic potentials in a lateral giant interneurone (LG) recorded in the terminal abdominal ganglion. These potentials are unaected by manipulation of the membrane potential of LG, by bath application of saline with a low calcium concentration, or by one containing the nicotinic antagonist, curare. The potentials evoked in LG by chordotonal organ stimulation are thus thought to be monosynaptic and electrically mediated. This is the ®rst demonstration that LG receives input from sensory receptors other than exteroceptors in the terminal abdominal ganglion.
The neural control of contraction in a fast insect muscle
Journal of Experimental Zoology, 1975
The wing muscles used in singing by the katydid, Neoconocephalus robustus, are extraordinarily fast. At 3 5 " C , the animal's thoracic temperature during singing, an isometric twitch lasts only five to eight msec (onset to 50% relaxation) and the fusion frequency of these muscles is greater than 400 Hz. Stimulating the motornerve to a singing muscle initiates a short (2.5 msec at 3 5 " C ) , sometimes overshooting depolarization of the muscle fibers. Despite their spike-like appearance, the electrical responses are largely synaptic potentials.
Physical Review X, 2014
The collisions of two simultaneously generated impulses in the medial giant axon of earthworms propagating in orthodromic and antidromic direction were investigated. The experiments have been performed in the extracted ventral cord of Lumbricus terrestris by using external stimulation and recording. The collision of two nerve impulses of orthodromic and antidromic propagation didn't result in the annihilation of the two signals contrary to the common notion that is based on the existence of a refractory period in the well-known Hodgkin-Huxley theory. However, the results are in agreement with the electromechanical soliton theory for nerve pulse propagation as suggested by Heimburg and Jackson [1].
Differences in maximum velocity of shortening along single muscle fibres of the frog
The Journal of physiology, 1985
The velocity of 'unloaded' shortening (V0) and the force-velocity relation were studied during fused tetani (0.5-2.0 degrees C) in short successive segments along the entire length of single fibres isolated from the tibialis anterior muscle of Rana temporaria. The segments were defined by opaque markers of hair that were placed on the fibre surface, 0.5-0.8 mm apart, from one tendon insertion to the other. The change in distance between two adjacent markers (one segment) was monitored by means of a photoelectric recording system, while the fibre was released to shorten isotonically between 2.2 and 2.0 micron sarcomere lengths. The accuracy of the V0 measurement was better than 4% in all parts of the fibre. V0 varied along the length of the fibre, each fibre having a unique velocity pattern that remained constant throughout the experiment. The difference between the highest and lowest values of V0 within the fibre varied between 11 and 45% of the fibre mean in thirty-two prep...
Induction of the action potential mechanism in slow muscle fibres of the frog
The Journal of Physiology, 1971
The electrical and structural characteristics of 'slow' muscle fibres of the frog were studied in normal and denervated muscles, and in muscles undergoing re-innervation by a mixed nerve containing large and small motor axons. 2. In agreement with previous studies, slow fibres in normally innervated muscles were incapable of producing action potentials. 3. Approximately 2 weeks after the sciatic nerve was transacted or crushed, slow muscle fibres acquired the ability to generate action potentials. These fibres were positively identified as belonging to the slow type, because their passive-electrical and ultrastructural characteristics remained essentially unchanged after the operations. 4. The action potential mechanism induced in slow fibres is sodiumdependent, and is blocked by tetrodotoxin. 5. After long-term re-innervation by a mixed nerve, slow fibres lose their acquired ability to generate action potentials, presumably because small motor axons re-establish connexion with the fibres. 6. It is concluded that the action potential mechanism of slow muscle fibres is under neural control, and is normally suppressed by small motor axons.
Journal of Anatomy, 1998
In muscle spindles of the cat, independent control of dynamic and static components of the response of the primary sensory ending to stretch is provided by separate motor inputs to the various kinds of intrafusal muscle fibre : dynamic axons (γ or β) to the bag " fibres and static axons to the bag # (typically γ only) and chain (γ or β) fibres. Nonlinear summation of separately evoked effects during combined stimulation of dynamic and static motor axons appears to be due to mutual resetting by antidromic invasion of separate encoding sites, leading to partial occlusion of the momentarily lesser response by the greater. The encoding sites are thought to be located within the primary ending's preterminal branches which from first-order level are normally segregated to the bag " fibre and to the bag # and chain fibres. Here we describe the analysis of a special case that arose in a histophysiological study which had shown that the degree of occlusion was related to the minimum number of nodes between the putative encoding sites. Three-dimensional reconstruction of the primary ending revealed that the terminals of one chain fibre were derived entirely from the first-order branch that supplied the bag " fibre, including one terminal that was shared directly with the bag " (sensory cross-terminal). The other first-order branch supplied the bag # and remaining chain fibres as normal. The degree of occlusion seen during simultaneous stimulation of a dynamic β axon and a static γ axon indicated that the encoding sites were separated by both first-order branches. Schematic reconstruction of the motor innervation revealed that the static γ axon was most unlikely to have supplied the chain fibre which shared sensory terminals with the bag " , but that these fibres also shared a motor input with histological characteristics of β type. Ramp-frequency stimulation of the dynamic β axon at constant length evoked a driving effect which persisted after fatiguing the extrafusal component and was therefore explicable on the basis of the observed pattern of motor innervation, though the identity of the axon could not be conclusively proved. Individually, instances of shared sensory terminals and motor input of bag " and chain fibres are rare in the cat ; their combination in a single spindle with correlated physiology is described here for the first time. The observation is considered in relation to the importance of dynamic and static segregation in motor control, since it may imply that there is a lower limit to the degree of segregation that the developmental programme can provide.
Journal of Neurocytology, 1975
Spinal electromotor neurons in the gymnotid Sternarchus albifrons were studied by light and electron microscopy. In this species, the electric organ discharge, which is of high and relatively constant frequency, is generated by specialized axons which arise from the spinal electromotor neurons. The cell bodies are located in medial regions of the spinal cord. They are round to ellipsoid in outline and dendrites are not present. The initial myelin segment often extends partially over the cell body. Fine glial lamellae are interposed between closely adjacent cells, and somato-somatic gap junctions are not observed. The large majority of axosomatic synapses are characterized by gap junctions. Single axons are commonly found to establish gap junctions with two adjacent neurons. Only a few synapses have the characteristics associated with chemically mediated transmission. The morphological data provide evidence for electrotonic coupling between electromotor neurons by way of presynaptic fibres. The absence of dendrites in these neurons may provide a morphological correlate for their simple relay function.
Brazilian Journal of Medical and Biological Research, 1998
The main generator source of a longitudinal muscle contraction was identified as an M (mechanical-stimulus-sensitive) circuit composed of a presynaptic M-1 neuron and a postsynaptic M-2 neuron in the ventral nerve cord of the earthworm, Amynthas hawayanus, by simultaneous intracellular response recording and Lucifer Yellow-CH injection with two microelectrodes. Five-peaked responses were evoked in both neurons by a mechanical, but not by an electrical, stimulus to the mechanoreceptor in the shaft of a seta at the opposite side of an epidermis-muscle-nerve-cord preparation. This response was correlated to 84% of the amplitude, 73% of the rising rate and 81% of the duration of a longitudinal muscle contraction recorded by a mechanoelectrical transducer after eliminating the other possible generator sources by partitioning the epidermis-muscle piece of this preparation. The pre-and postsynaptic relationship between these two neurons was determined by alternately stimulating and recording with two microelectrodes. Images of the Lucifer Yellow-CH-filled M-1 and M-2 neurons showed that both of them are composed of bundles of longitudinal processes situated on the side of the nerve cord opposite to stimulation. The M-1 neuron has an afferent process (A1) in the first nerve at the stimulated side of this preparation and the M-2 neuron has two efferent processes (E1 and E3) in the first and third nerves at the recording side where their effector muscle cell was identified by a third microelectrode.
Fast and Slow Locomotor Burst Generation in the Hemispinal Cord of the Lamprey
Journal of Neurophysiology, 2003
A fundamental question in vertebrate locomotion is whether distinct spinal networks exist that are capable of generating rhythmic output for each group of muscle synergists. In many vertebrates including the lamprey, it has been claimed that burst activity depends on reciprocal inhibition between antagonists. This question was addressed in the isolated lamprey spinal cord in which the left and right sides of each myotome display rhythmic alternating activity. We sectioned the spinal cord along the midline and tested whether rhythmic motor activity could be induced in the hemicord with bath-applied d-glutamate or N-methyl-d-aspartate (NMDA) as in the intact spinal cord or by brief trains of electrical stimuli. Fast rhythmic bursting (2–12 Hz), coordinated across ventral roots, was observed with all three methods. Furthermore, to diminish gradually the crossed glycinergic inhibition, a progressive surgical lesioning of axons crossing the midline was implemented. This resulted in a gra...
Journal of Experimental Biology, 1976
1. Electrical activity accompanying motor activity can be recorded from the excised pharynx of Enchiridium punctatum. Multiple stimuli elicit behaviour which consists of an initial aperture closure followed by extension and then peristalsis. If the stimulus parameters are increased the preparation bends from side to side instead of proceeding through the behavioural sequence. Bending appears to inhibit other movements differentially. 2. The conduction involved with peristalsis is polarized and proceeds in a proximal direction. 3. With stimulus intensities greater than those needed to produce the behavioural response an initial muscle potential (IMP) is evoked. The IMP is frequency sensitive. Maximum facilitation occurs within 100 ms and drops to 50% of maximum within 250 ms. 4. Conduction velocities of the IMP range from 0–05 m s-1 to 1-9 m s-1. Conduction velocities appear to increase with facilitation.