Showing papers in "Progress in Brain Research in 1979"

Multisensory control of spinal reflex pathways.

Abstract: Publisher Summary This chapter reviews the convergence from different primary afferents on interneurones in reflex pathways. It summarizes results showing that interneurones of the reciprocal Ia inhibitory pathway receive a wide convergence resembling that found in agonist motoneurones. Interneurones in reflex pathways from Ib afferents are excited from cutaneous and joint afferents and also from Ia afferents. The chapter describes reflexes from the FRA (flexor reflex afferents)—that is, reflex actions from high threshold muscle afferents, joint afferents and cutaneous afferents that are mediated by common interneurones. A distinction is made between short-latency reflexes in the acute spinal and long-latency reflexes in acute spinal cats after DOPA i.v.; the half-centre organisation of the interneuronal network mediating the latter reflexes is recapitulated and discussed in relation to spinal generation of alternating activity in flexors and extensors. An important role of reflex pathways from the FRA in motor control is indicated by findings showing that their interneurones are excited from different higher motor centres and that many ascending pathways, spinocerebellar in particular, signal information regarding their interneuronal activity.

Fiber connections of the basal ganglia.

Abstract: Publisher Summary This chapter aims to incorporate the results of recent work on the anatomy into a general outline of the fiber connections of the basal ganglia. Progress of two types can be identified based on the anatomical studies of the basal ganglia: conformations and modifications of earlier findings, and major new conclusions as to the organization of the basal ganglia and their allied nuclei. Three major findings have singled out as representing not simply revisions but conclusions novel enough to reorient some lines of work on the basal ganglia. The first of these is the discovery of a high degree of compartmentalization within the striatum. The second major conclusion is that the nuclei allied to the corpus striatum proper provide not only important points of access into the circuitry of the basal ganglia but also outlets that extend the influence of the basal ganglia well beyond the confines of the traditional outflow channel from corpus striatum to thalamus to motor cortex. The third conclusion is that the two great subcortical divisions of the cerebral hemisphere—the corpus striatum and limbic system—are by no means insulated from one another but instead are tied together by pathways that over successive synaptic linkages lose their identities as skeletomotor or limbic.

The Role of Vision in the Control of Posture During Linear Motion

Abstract: Publisher Summary This chapter reviews some findings concerning the role of vision in the control of posture that have been obtained in recent years. It describes some results obtained in laboratories concerning the effect of vision on postural control during linear horizontal or vertical motion of either body or visual surround. Gains and phases obtained by measuring either linear vection or body pitch induced by sinusoidal motion of visual scenes are compared. These curves seem to confirm the general statement that vision contributes to postural stabilization in the low frequency range of body movements. However, new experimental findings are described in the chapter that shows successively: (1) Direction-specific influences of visual surround motion when visual and body motion are combined, demonstrating also the enhanced effect of vision when active postural tasks are used. (2) The action of vision on the early motor responses to postural perturbation. (3) A strong decrease of early motor responses during free fall in the monkey, which is shown to occur with visual stabilization within 50–100 msec from the onset of the fall. These results are interpreted as implying a role of vision in the general setting of the parameters of motor responses during posture and movement.

The accessory optic system and its relation to the vestibulocerebellum.

Abstract: Publisher Summary The accessory optic system (AOS) is a visual system organized in vestibular coordinates. Recordings from neurons in the three terminal nuclei of the AOS have revealed that this visual system processes information about the speed and direction of movement of large parts of the visual world. Best modulation of terminal nuclei neurons requires use of large textured stimuli and occurs at low speeds with peak sensitivity at 0.1–1 degree/sec. For medial terminal nucleus and lateral terminal nucleus, the preferred directions in space are vertical, but with a posterior component. For dorsal terminal nucleus, preference is for horizontal movement from posterior to anterior. Taken collectively, the preferred directions for terminal nuclei neurons define three directions in visual space: anterior, up with a posterior component, and down with a posterior component. The speed and direction selectivity of neurons of the accessory optic terminal nuclei are identical to those of the on-direction selective class of rabbit retinal ganglion cells and to those of visually driven climbing fibers in the cerebellar flocculus. It is most likely that the AOS serves to signal self-motion; the sensitivity of AOS neurons to slow speeds makes the AOS an ideal complement to the vestibular system.

Photoperiod, pineal, melatonin and reproduction in hamsters.

Abstract: Publisher Summary This chapter discusses the experiments done on male hamsters. It should be noted, however, that corresponding results have been obtained in females in nearly all cases, regardless of whether photoperiodic effects, the results after pineal manipulations or after application of melatonin are considered. Many mammalian species show a marked annual cycle of gonadal and other functions. In a number of cases it has been shown that the photoperiod, that is, the length of the daily light cycle and its changes, are involved in the regulation of this cycle. The pineal has been shown to participate in the transduction of photoperiodic effects of short photoperiods leading to regression and also of long photoperiods stimulating recrudescence. The latter effect is not only a suppression of antigonadotrophic effects from the pineal, but a positive stimulation. The exact role of melatonin in the photoperiodic mechanism and its site of action are still unclear. Strong effects of melatonin application have been found in photoperiodic mammals. Recent experiments suggest that not only the amount of melatonin, but its pattern of synthesis and release may be important in the conveyance of photoperiodic effects. No support for the assumption that the site of action of melatonin is the pineal itself has been found in experiments with pinealectomized animals.

Calcium conductances in Purkinje cell dendrites: their role in development and integration.

Abstract: Publisher Summary This chapter reviews the role of calcium in both the integrative properties of neurons and in their role as modulators of other cell biological parameters. Voltage-dependent calcium conductance changes large enough to be self-regenerative have been observed in a multitude of neuronal elements, most of the work having been obtained in invertebrate neurons. In vertebrates, action potentials have been demonstrated in several types of central and peripheral neurons. In most cases, the inward calcium current has occurred at the somatic level, whereas the axon is for the most part devoid of such conductance. It is shown that spikes are preferentially recorded at dendritic level and play an important role in neuronal integration. Besides the all-or-none calcium dendritic action potentials, prolonged calcium-dependent local responses may also be seen in somas and dendrites. The ontogeny of this voltage-dependent membrane conductance indicates that the calcium component appears with the development of the dendritic trees. A general hypothesis is proposed for the role of calcium currents in neuronal function.

Adaptation of Optokinetic and Vestibulo-Ocular Reflexes to Modified Visual Input in the Rabbit

Abstract: Publisher Summary This chapter presents experiments that show that adaptive plasticity in the rabbit's compensatory eye movements is not limited to the vestibulo-ocular (VOR), but is also clearly present in the optokinetic (OKN). They also show that the VOR can be adapted, without being activated, by visual stimulation alone. It appears now that visual slip in the same direction as the eye movements in the head will increase the gain of both the VOR and the OKN, while slip in the direction opposite to that of the eye movements will also increase the gain of the OKN, but decrease that of the VOR. A further finding is the specificity of the adaptation as documented in the frequency response relations of OKN and VOR and the occasional manifestation of highly specific after-effect. It is hypothesized that during adaptation a copy of the slip pattern is accumulated in the nervous system and that this pattern is reproduced and interferes with OKN and VOR when a similar pattern of motion returns.

The Vestibulocortical Pathway: Neurophysiological and Anatomical Studies in the Monkey

Abstract: Publisher Summary All sensory systems have a cortical projection area. The evidence for a vestibular projection was mainly based on electrophysiological studies. With sensitive tracer techniques a direct vestibulothalamic pathway can now be demonstrated anatomically. Neurophysiological studies in the alert monkey show that a precise vestibular signal can be recorded in the thalamus as well as in the cortex. In neurophysiological studies neuronal activity was recorded in the ventroposterior lateralis pars oralis and ventroposterior inferioris, and area 2v, while the alert monkey was exposed to natural vestibular and optokinetic stimulation. In these structures neurons were found, which responded clearly to vestibular stimulation, with patterns similar to those found in the vestibular nuclei. In most cases, vestibular neurons in the thalamus and cortex could also be activated by optokinetic stimuli. It is suggested that the ascending vestibulocortical pathways contain information that is used for motor control and/or motion sensation.

Localization of neurotransmitters, particularly glutamate, in hippocampus, septum, nucleus accumbens and superior colliculus.

Abstract: Publisher Summary This chapter presents a survey to identify the neurotransmitter in certain well-defined fibers in the hippocampal–septal system including the nucleus accumbens septi. The transmitters present in the neurons are identified by correlating the distribution of the transmitter marker to the distribution of axon terminals as defined by previous anatomical investigation; by studying the changes in the marker after interruption of specific afferent fibers and after destruction of intrinsic neurons by local injection of kainic acid; and also by studying the release of transmitter marker after stimulating specific nerve fiber bundles. The chapter discusses the structure as a ventral part of striatum, and its efferent projection as a ventral striato-pallidal pathway. Superior colliculus is, like the hippocampus, a laminar structure where many of the afferent fibers are well known. Hippocampus is a laminated structure where the pyramidal and granular cells are distributed in single layers that extend throughout the hippocampus proper and area dentata, respectively. The hippocampal neurons are excited by a series of known fibers such as commissural, perforant path, mossy fibers, and Schaffer collaterals, and inhibited by for example basket cells. The fibers are organized in a layered manner parallel to the cell bodies. In addition, all major neuronal excitatory members as well as the arteries to the hippocampal formation are arranged in lamellae parallel to each other in a plane nearly transverse to the longitudinal axis of the hippocampus.

Secretory processes in the mammalian pinealocyte under natural and experimental conditions.

Abstract: Publisher Summary In various recent reviews it has been concluded that the pineal body synthesizes a number of compounds and is an endocrine gland whose secretory products influence the development and function of the reproductive organs. It has been postulated that the pineal mediates certain environmental factors which regulate the function of the reproductive system. At present, no known pineal compound satisfies all of the classical criteria for a candidate hormone, that is, a substance produced exclusively in the pineal gland and having a specific functional influence on (a) distant target organ(s). In the light of the different concepts treated, the confused state of comprehension of pineal functions becomes more understandable. Only chemical identification of the different hormones synthesized in the pineal will permit the exact determination of pineal function. It is evident that one must think in terms of multiplicity of types of regulation in relation to the multiplicity of effects. Probably, the mammalian pineal gland is a synchronizer contributing to seasonal and probably also to circadian organization of functions. It is nonexclusively involved in different neuroendocrine mechanisms, which attunes the physiological adaptation of animals to their unique daily and annual patterns. When considering these points, most of the paradoxical and contradictory facts related to pineal function become less confusing.

Afferent and Efferent Organization of the Prepositus Hypoglossi Nucleus

Abstract: Publisher Summary This chapter provides general outline of findings regarding the afferent and efferent organization of the prepositus nucleus. From retrograde horseradish peroxidase (HRP) experiments, it appears that, qualitatively, the important inputs to this nucleus come from the vestibular nuclei, perihypoglossal nuclei, reticular formation, extraocular nuclei, accessory oculomotor nuclei and the cerebellum. The efferents of the prepositus hypoglossi were studied with autoradiographic, electrophysiologioal and both intraand extracellular HRP techniques. The prepositus appears to establish efferent connections bilaterally with the cerebellar cortex, the interposed and medial cerebellar nuclei, the vestibular nuclei, the perihypoglossal nuclei, the medial medullary and pontine reticular formation, the extraocular motor nuclei, the accessory occulomotor nuclei and the region around the parabigeminal nucleus. Intracellular injections of HRP reveal that a single prepositus neuron sends collaterals to several of the above brain stem areas. Evidence is also presented that indicates that there is a direct projection from prepositus to ocular motoneurons and that it is excitatory in effect. Such a wealth of anatomical connections suggests that the prepositus is much more than a simple site for either preoculomotor or precerebellar activity.

Pineal sense organs--components of photoneuroendocrine systems.

Abstract: Publisher Summary Pineal sense organs of lower vertebrates are a major component of photoneuroendocrine systems They are equipped with indoleamine-containing sensory cells which may transducer photic information into a neuroendocrine response Pineal sense organs have a complex intrinsic circuitry consisting of a bineuronal chain and acetylcholinesterase-positive interneurons Local differences in the number and pattern of these interneurons appear to be essential for the generation of the achromatic or chromatic types of pineal response Nerve tracts of pineal sense organs project to optic and reticulomotor centers To date, the existence of nervous contacts with neuroendocrine effectors has not been proven On the other hand, efferents originating from different brain centers establish a feedback and control pathway to pineal sense organs Principally, pineal sense organs, due to the properties of their photoneuroendocrine cells, are capable of nervous and neuroendocrine messages directed toward target areas within the brain These mechanisms appear to be involved in color change, endocrine control, phototactic and locomotor reactions, detection of polarized light, and rhythmic phenomena This complex picture may depend on the fact that pineal sense organs represent only one component of photoneuroendocrine systems To date, their interplay with the retinohypothalamic apparatus and the deep encephalic photoreceptor(s) is only poorly understood The vertebrate diencephalon may possess primordial potencies for the formation of retinal, pineal and deep encephalic photoreceptors The photoneuroendocrine capacity of pineal sense organs is a crucial component of phylogenetic and cytobiological considerations concerning the evolution of the pineal gland

Vestibulospinal, reticulospinal and interstitiospinal pathways in the cat.

Abstract: Publisher Summary This chapter reviews the properties and motor actions of three descending systems: the vestibulospinal tracts, the reticulospinal tracts, and the interstitiospinal tract. The vestibulospinal tracts are the most direct pathways between the labyrinth and spinal motoneurons. The medial vestibulospinal tract (MVST) is the predominant direct pathway to axial motoneurons, the lateral vestibulospinal tract (LVST) the only direct pathway to limb motoneurons; not much is known about the recently discovered caudal vestibulospinal tract. The role of these direct pathways in functionally meaningful vestibulospinal reflexes remains to be determined. The reticulospinal tracts consist of three groups of descending fibers: one descending in the ventromedial funiculus (RST m ), one in the ipsilateral ventrolateral funiculus (RST i ), and one in the contralateral ventrolateral funiculus (RST c ). Excitatory RST m neurons scattered throughout nucleus reticularis (n.r.) pontis candalis and the dorsal part of n.r. gigantocellularis establish direct synaptic connections with motoneurons supplying a wide variety of muscles throughout the body. The reticulospinal systems receive major direct inputs from many different regions including vestibular nuclei, suggesting that they participate in vestibulospinal reflexes. The interstitiospinal tract, which has not been studied extensively, includes neurons that establish direct excitatory connections with neck motoneurons, but do not establish direct connections with limb and back motoneurons.

Cortical, Tectal and Medullary Descending Pathways to the Cervical Spinal Cord

Abstract: Publisher Summary Retrograde horseradish peroxidase (HRP) technique provides that care is taken to avoid damage to descending fibers of passage, small injections of HRP, confined to part of a single segment or to a few adjacent spinal segments, can be used to determine fairly precisely, the somatotopic organization of the cells of origin of descending spinal pathways. This chapter employs this approach, supplemented by anterograde autoradiographic tracing techniques and electrophysiological studies to determine the origins and terminations of descending pathways to the upper cervical spinal cord, their somatotopic pattern, and other features of their organization. It describes a corticospinal projection from a heretofore poorly understood region of the medial, parietal association cortex termed the supplementary sensory region. Among the subcortical systems the chapter describes the crossed descending spinal projection from the superior colliculus and the topographic organization of the cells of origin of this pathway in relation to the visual and somesthetic maps of the tectum. The somatotopic organization and spinal terminations of a previously unrecognized reticulospinal system originating in the caudal medulla are also described.

Clinical importance of melatonin.

Abstract: Publisher Summary Melatonin can be used as a diagnostic tool, possibly in identifying risk groups, for example, for cancer, as a marker for biological rhythms, as a marker of receptor function in the nervous system, and possibly also as a therapeutic tool in different disorders. Melatonin was discovered in 1958 by Lerner and others. The chemical structure of melatonin is known. The substance can be measured in body fluids by bioassays and recently by immunoassays (RIA) due to the work by two eminent scientists, Rosalyn Yalow and Josephine Arendt and others.. Six RIA assays have been compared and can now be validated accurately by a new technique using negative ionization gas chromatographic mass spectrometric assay. This chapter highlights the clinical importance of melatonin.

Comparative morphology of the vertebrate pineal complex.

Abstract: Publisher Summary This chapter explores whether there is evidence for the assumption that the mammalian pineal organ is a complex rather than a single organ with a uniform function. It is pointed out that the pineal organ is structurally very complex, especially in rodents. The uneven development of the pineal organ in rodents and the topographical relationships of the pineal organs in other mammalian orders have prompted a classification which is based on the shape, the size, and localization of the pineal organ. A tentative classification of the pineal organs of thoroughly studied species shows that closely related species have similar types of pineals. Based on the different localizations of the pineal organs in relation to the third ventricle, the problem of a release of pineal hormones into the CSF is discussed. It is concluded that comparative morphological studies do not support the notion that secretion directly into the CSF is an important principle. The separation of pineal tissue into superficial and deep pineals in some rodents poses the question as to whether the two parts are structurally and functionally identical. The available data suggest that they are dissimilar. The chapter also discusses the possible subdivision of pineal tissue into cortical and medullary regions. Recent results obtained in rats illustrate the importance of carefully analyzing the pineal parenchyma in order not to miss a perhaps meaningful mosaic-like architecture of the organ. It is concluded that in some species the use of the term pineal complex is justified from a purely morphological point of view.

Information Carried by the Spinocerebellar Paths

Abstract: Publisher Summary Information from the spinal cord reaches the anterior lobe of the cerebellum through about twenty paths that terminate as mossy fibers or climbing fibers. Among these paths a minority carry information primarily about peripheral events. The best known and only quite convincing examples are the dorsal spinocerebellar tract (DSCT) and its forelimb equivalent, the cuneocerebellar tract (CCT). These two tracts contain components activated monosynaptically from afferents of muscle spindles, tendon organs, joint receptors and different types of cutaneous receptors. The modality and space specific information carried by these tracts is well suited for signalling peripheral events. The majority of the other paths provide the cerebellum with information about the activity in groups of segmental or suprasegmental neurones presumably representing lower motor centres. The ascending paths are either activated or inhibited from the neurones forming these centres or formed by ascending axon collaterals of these neurones. The connections to the ascending paths are complex and different for each path indicating that they carry information from different motor centres. The spino-olivocerebellar paths are particularly interesting since they project to narrow sagittal zones in the cerebellar cortex.

Organization and Programming of Motor Activity during Posture Control

Abstract: Publisher Summary This chapter aims to synthesize a hierarchical model of posture control from experimental observations of stance posture control of normal human subjects. A conceptual synthesis of human experimental observations enhances knowledge about sensorimotor controls derived from the study of animal preparations in several important ways. Studies of chronic and acute cat preparations have revealed much detail about the neural mechanisms within the spinal cord that generate the basic locomotor movement patterns. However, the interruption of many central nervous system functions in these preparations has thus far prevented any study of the adaptive and postural balance controls, which under normal conditions are integrated into the ongoing movement behaviors. The postural adjustments are functionally useful responses elicited by the unexpected movements of a platform upon which a subject stood. Results show that these adjustments are too complexly interwoven into an organizational structure involving many leg muscles to be characterized simply as the response of each individual muscle to its own stretch input. In place of the concept of stretch responses, the hierarchical model suggests that the response activity of each muscle is stereotypically organized into a structure controlled by the pattern of movement inputs from the entire leg.

Interaction between central and peripheral mechanisms in the control of locomotion.

Abstract: Publisher Summary This chapter discusses two conceptually different types of reflex control during walking: (i) the peripheral control of the central pattern generators (CPGs) and (ii) the control of certain reflex pathways by the CPGs These two different types of peripheral control signals will act to adapt the stepcycle to the external environment If the limb extends slower than normally, it would be mechanically ineffective to terminate the support phase early Correspondingly, if the limb extends faster than “expected” the support phase would be shortened These reflex mechanisms will thus assure that flexion is induced at an appropriate time and may be particularly important when the animal changes speed It is shown that afferent signals induced by dynamic hip movements and static hip position in cat and by analogous effects in fish can powerfully drive the central spinal locomotor networks in both cat and fish The locomotor generator in both cat and fish can in turn exert phasic gain control of short latency reflexes, which act directly on the α-motoneurones

Recent Advances in Pineal Cytochemistry. Evidence of the Production of Indoleamines and Proteinaceous Substances by Rudimentary Photoreceptor Cells and Pinealocytes of Amniota

Abstract: Publisher Summary Pineal cells produce rhythmic signals and appear very responsive. In the pineal organ of Amniota, several types of messages may be elaborated: (1) in some reptiles, lacertilians and probably chelonians, the input of photic information may be converted into electrical signals, which are conducted to other parts of the brain; (2) in all groups of Amniota (reptiles, birds and mammals) chemical (neurohormonal) signals seem to be produced. Mainly from biochemical and physiological data it is concluded that two different categories of active pineal constituents (chemical signals) responsible for endocrine capabilities are elaborated; indoleamines now discovered in all Amniota and also low molecular weight compounds (possibly peptidic or polypeptidic), are found only in mammals. Other groups have not been investigated in this respect. However, at present, no pineal compound fully satisfies the classical criteria for a candidate hormone. This chapter highlights recent advances in pineal cytochemistry and also provides evidence of the production of indoleamines and proteinaceous substances by rudimentary photoreceptor cells and pinealocytes of amniota.

Innervation of the vertebrate pineal.

Abstract: Publisher Summary This chapter discusses the literature published since 1965, the main problems of the innervation of the vertebrate pineal organ, and the nomenclature of the nervous connections of the epiphysis cerebri and of the accessory pineal organs with the epithalamus in submammalian vertebrates. The chapter presents the current state of knowledge about the innervation, with emphasis on the studies of the 13 years. In lower vertebrates, pineal nerve cells are distributed all over the pineal parenchyma sending their axons toward the brain. In adult mammals, these pineal nerve cells and, consequently, their central projections are absent; an efferent innervation is well developed. The difference in the nervous organization of the pineal in lower vertebrates and mammals raised different questions; therefore this chapter separately describes the results on the innervation of the pineal organ obtained in mammals and lower vertebrates.

Vestibulo-ocular reflex pathways of rabbits and their representation in the cerebellar flocculus.

Abstract: Publisher Summary This chapter introduces recent data concerning construction of the flocculo-vestibulo-ocular system obtained in the albino rabbits. Presence of a clear differential localization is demonstrated in both the flocculus and the inferior olive, in connection with certain components of the vestibulo-ocular reflex (VOR). Narrow strips thus defined in the flocculus may form functional units of the cerebellar cortex, corresponding to microzones in the vermal cortex. It is impressive that these strips are related directly to single extraocular muscles. Apparently, the VOR-flocculus system represents a prototype of the functional localization in the cerebellum. Detailed structural knowledge of the VOR-flocculus system is useful as a basis for the experimental approach to neuronal mechanisms of cerebellar functions. It is necessary to further extend dissection of functional units in the flocculus in connection with not only the excitatory but also inhibitory components of the VOR. It is also desirable to study organization of various inputs to the flocculus, from labyrinths, eyes, neck, etc., in close relationship with the functional localization within the flocculus and the inferior olive.

The mechanism of action of vasotocin in the mammalian brain.

Abstract: Publisher Summary This chapter focuses on the mechanism of action of vasotocin in the mammalian brain. Presence of the nonapeptide hormone arginine-vasotocin (AVT) in the pineal gland of all mammals so far investigated, including man as well as the presence of the nonapeptide hormone lysine-vasotocin in the pineal gland of the pig have been demonstrated by differential bioassay, chromatographic and enzymatic studies. This work was confirmed by chemical analysis, radioimmunoassay as well as by immunocytochemistry. AVT is synthesized both in the fetal and adult pineal gland most likely by ependymal cells showing the same secretory characteristics as subcommissural (SCO) cells. In the adult pineal gland AVT appears to be synthesized by ependymal cells of the pineal recess and stored in so far undefined cells of the pineal gland proper. The identical structure and secretory activity of the ependymal cells from the pineal recess and the SCO and the ability of the SCO to synthesize AVT, suggest that the SCO and the pineal gland (at least in its interaction with AVT) represents a functional ependymosecretory complex AVT displays a diurnal rhythm in the pineal and cerebrospinal fluid (CSF) suggesting its release into the CSF during the night in the dark.

What Are the Proprioceptors of the Neck

Abstract: Publisher Summary The receptors that play an important role in neck reflexes and other postural processes have never been identified. Certain attractive candidates are the large numbers of muscle spindles first described by Voss and Cooper and Daniel in dorsal neck muscles of man and the cat. Neck muscle spindles resemble those described in the hindlimb, with the exception that many neck muscle spindles have a reduced intrafusal fibre complement of only a single nuclear bag fibre and a few nuclear chain fibers. In most neck muscles, the majority of spindles do not occur as single receptors but are arranged in complexes of up to 10 spindles in tandem, paired and parallel linkages. Most muscle spindle endings from large dorsal neck muscles had physiological properties similar to primary or secondary endings of hindlimb muscle spindles. About 20% of neck spindle endings had a mixture of response properties so that they could not be defined as primary or secondary endings by physiological criteria. Afferents from neck muscles conducted at relatively low velocities ranging from a low of 13 m/sec to a high of 90 m/sec. These conducting velocities are consistent with anatomical observations that neck muscle afferent fibers from neck muscles seldom exceed a diameter of 16 μm.

Coupled Stretch Reflexes in Ankle Muscles: An Evaluation of the Contributions of Active Muscle Mechanisms to Human Posture Stability

Abstract: Publisher Summary This chapter examines the stabilizing role of stretch reflexes acting on the ankle flexors and extensors. For this purpose, the reaction forces and the EMG activity of the ankle musculature were recorded while a platform on which the subjects stood was quickly rotated about the ankles. The force responses correcting the postural disturbances were divided into three components: (1) Forces generated by short (40 msec) and medium (90 or 130 msec) latency muscle activity; (2) Visco-elastic forces of the activated muscles; (3) Inertial reaction forces. The analysis of the time course and amplitude of each of these components suggests that short-latency segmental reflexes have a minor role in correcting postural disturbances. Any improvements in the stiffness of the stretch reflex are predominantly provided by medium-latency responses. Because medium-latency responses in ankle flexors and extensors are organized as a time-locked coupled response, their net action stabilizes the standing posture. The force provided by medium latency reflex muscle activity approximately equaled that provided by the inherent visco-elasticity of activated muscles.

Synaptic and functional organization of vestibulo-ocular reflex pathways.

Abstract: Publisher Summary This chapter explains the central connections of the individual semicircular canals subserving the vestibulo-ocular reflex (VOR) The three pathways relaying the reflex are the median longitudinal fasciculus (MLF), the brachium conjunctivum (BC), and the ascending tract of Deiters' (ATD) The VOR reflex originates in the anterior and posterior semicircular canals The MLF contains the axons of the relay neurons for the inhibitory pathways from the anterior and posterior canals and the excitatory pathways from the posterior canals to the ocular motoneurons The BC contains the axons of the relay neurons for the excitatory pathway from the anterior canal to the IIIrd nucleus The important limb of the vestibulo-ocular reflex traveling through the BC should not be ignored simply because the vertical vestibulo-ocular reflex is abolished by MLF lesions The horizontal VOR originates in the bilateral horizontal semicircular canals The disynaptic excitatory pathway, from the ipsilateral horizontal canal to the medial rectus motoneurons is relayed via the ATD The chapter reviews the disynaptic excitatory and inhibitory input to abducens motoneurons and internuclear neurons

The Histology and Pathology of the Human Pineal Gland

Abstract: Publisher Summary The overall architecture of the pineal gland is extremely variable. Some glands have a well defined, lobular structure, strands of connective tissue separating the groups of parenchymal cells. In others the connective tissue is more extensive and the bands are wider. In some of these glands only small islands of parenchymal cells surrounded by connective tissue are seen. On the other hand, the connective tissue may be extremely sparse so that in these glands there are sheets of parenchymal cells with only the occasional fine connective tissue septa containing blood vessels. It is important to note that there may be a good deal of variation in the amount of the connective tissue in different parts of the gland. The amount of connective tissue in the pineal gland that should be regarded as normal is a matter for debate, but although some workers have found that there is some increase in the amount of fibrous tissue in the gland with age this is minimal and it should be noted that even in old age the majority of the glands still contain large numbers of parenchymal cells. That it is possible to measure melatonin in the blood as well as many of the hypothalamic and pituitary hormones, it is likely that the mechanisms whereby pineal tumors produce their endocrine effects may be eventually resolved. In fact there is no reason to doubt that both, effects from the secretion of endocrinologically active substances by pineal tumors and interference with the hypothalamic centers and tracts, may well be significant in individual cases.

Colliculoreticular Organization in the Oculomotor System

Abstract: Publisher Summary This chapter summarizes saccadic eye movement-related discharge in superior colliculus (SC) neurons and in median pontomedullary reticular formation (RF) neurons and reviews the organization of colliculoreticular pathways, particularly with a view towards clarifying the mechanisms involved in controlling saccadic eye movements in primates. New data on the functional type of SC input to the RF are presented. A new interpretation is placed on the possible role played in saccadic generation by a class of neurons called quasi-visual cells. Saccade-related discharge of brain stem reticular formation neurons is discussed and comparisons are made between presaccadic activity in neurons in SC and RF. Studies showing the existence and nature of synaptic input from the SC to specific functional types of RF cells are reviewed and new preliminary results indicating the functionally identified type of SC neuron supplying at least a portion of these connections are shown. The possible role played by the neurons and synaptic connections described in these two anatomic structures is hypothesized in the form of saccadic control model.

Short history of pineal discovery and research.

Abstract: Publisher Summary The history of pineal research can be divided into three periods. The first starts at about 300 B.C. with the discovery of the organ and ends at about the middle of the 19th century. Most of it is characterized by much speculation due to the strong influence of prevailing philosophical systems and traditional, insufficient knowledge the development of which was hampered by lack of personal experience and very restricted means of investigation. Especially in ancient times, the science of man can only be understood in relation with the history of philosophy. This first period ends with the rejection, by most authors, of all theories about pineal function, so far advanced, and a more or less general lack of interest in the organ. During the second period lasting till about the middle of the present century, interest in the pineal organ was very much revived, first in connection with the development of comparative anatomy and then by the discovery of the endocrine organs. This period is strongly linked with the first technical revolution in the 19th century, which provided investigators with much more refined methods of research. A sharp boundary between the second and the third period of pineal research cannot easily be drawn. Most of the characteristics of this third period is the rapid development of pineal biochemistry and pharmacology.