MEDICAL LITERATURE has been deluged during the past few years with books and papers on penicillin; but a book which has been produced under the general editorship of Sir Alexander Fleming himself represents a complete and authoritative summary of penicillin therapy as it stands today.' The book contains a series of independent contributions by \"experienced and eminent men who have worked with penicillin in Great Britain\". Their opinions and practical methods differ slightly, and there is some overlapping; but these are not disadvantageous, comparison and contrast lending interest to the reading. In the first or general section of the book Fleming contributes two chapters, one on the history and development of penicillin, introducing some interesting sidelights in the romance of discovery, the other on the bacteriological control of penicillin therapy. In both chapters the information is set out in meticulous detail and with a clarity and simplicity which can be enjoyed by all readers. Fleming also gives the right perspective to the place of penicillin amongst the antibiotics and lays down the principles of treatment. Both chapters are well illustrated and are the most outstanding in the book. Included in this first section also are chapters on the chemistry and manufacture of penicillin and its pharmacy, pharmacology and methods of administration. The second section of the book is entirely clinical, giving each author's view on the use of penicillin therapy in a disease or an infection of some particular region of the body. The entire range of peniCillin-sensitive conditions is considered in twenty authoritative and clearly written chapters; these contain many references and illustrations. Dental and veterinary diseases are also given fairly full consideration. The final section is a condensed resume of much of the preceding chapters and is written for. the general practttioner. This chapter is superttuous: it does not contain enough detall to be of much practical value. The book as a Whole, however, will undoubtedly be considered a classical contribution to medical literature and is strongly recommended, not only because of the general interest of its topic, but as a reference book on penicillin therapy of hitherto unequalled excellence. The typography, although conforming to war economy standards, is clear and the paper is good. There is an excellent list of references and the index is satisfactory.

Gray's Anatomy

The facet joint is a crucial anatomic region of the spine owing to its biomechanical role in facilitating articulation of the vertebrae of the spinal column. It is a diarthrodial joint with opposing articular cartilage surfaces that provide a low friction environment and a ligamentous capsule that encloses the joint space. Together with the disc, the bilateral facet joints transfer loads and guide and constrain motions in the spine due to their geometry and mechanical function. Although a great deal of research has focused on defining the biomechanics of the spine and the form and function of the disc, the facet joint has only recently become the focus of experimental, computational and clinical studies. This mechanical behavior ensures the normal health and function of the spine during physiologic loading but can also lead to its dysfunction when the tissues of the facet joint are altered either by injury, degeneration or as a result of surgical modification of the spine. The anatomical, biomechanical and physiological characteristics of the facet joints in the cervical and lumbar spines have become the focus of increased attention recently with the advent of surgical procedures of the spine, such as disc repair and replacement, which may impact facet responses. Accordingly, this review summarizes the relevant anatomy and biomechanics of the facet joint and the individual tissues that comprise it. In order to better understand the physiological implications of tissue loading in all conditions, a review of mechanotransduction pathways in the cartilage, ligament and bone is also presented ranging from the tissue-level scale to cellular modifications. With this context, experimental studies are summarized as they relate to the most common modifications that alter the biomechanics and health of the spine-injury and degeneration. In addition, many computational and finite element models have been developed that enable more-detailed and specific investigations of the facet joint and its tissues than are provided by experimental approaches and also that expand their utility for the field of biomechanics. These are also reviewed to provide a more complete summary of the current knowledge of facet joint mechanics. Overall, the goal of this review is to present a comprehensive review of the breadth and depth of knowledge regarding the mechanical and adaptive responses of the facet joint and its tissues across a variety of relevant size scales.

/pdf/spinal-facet-joint-biomechanics-and-mechanotransduction-in-192d0mti4j.pdf

Spinal facet joint biomechanics and mechanotransduction in normal, injury and degenerative conditions

We reviewed neural control and biomechanical description of gait in both non-disabled and post-stroke subjects. In addition, we reviewed most of the gait rehabilitation strategies currently in use or in development and observed their principles in relation to recent pathophysiology of post-stroke gait. In both non-disabled and post-stroke subjects, motor control is organized on a task-oriented basis using a common set of a few muscle modules to simultaneously achieve body support, balance control, and forward progression during gait. Hemiparesis following stroke is due to disruption of descending neural pathways, usually with no direct lesion of the brainstem and cerebellar structures involved in motor automatic processes. Post-stroke, improvements of motor activities including standing and locomotion are variable but are typically characterized by a common postural behaviour which involves the unaffected side more for body support and balance control, likely in response to initial muscle weakness of the affected side. Various rehabilitation strategies are regularly used or in development, targeting muscle activity, postural and gait tasks, using more or less high-technology equipment. Reduced walking speed often improves with time and with various rehabilitation strategies, but asymmetric postural behaviour during standing and walking is often reinforced, maintained, or only transitorily decreased. This asymmetric compensatory postural behaviour appears to be robust, driven by support and balance tasks maintaining the predominant use of the unaffected side over the initially impaired affected side. Based on these elements, stroke rehabilitation including affected muscle strengthening and often stretching would first need to correct the postural asymmetric pattern by exploiting postural automatic processes in various particular motor tasks secondarily beneficial to gait.

Gait post-stroke: Pathophysiology and rehabilitation strategies.

https://amcor.asahikawa-med.ac.jp/modules/xoonips/download.php?id=26746115

Human upright posture control models based on multisensory inputs; in fast and slow dynamics.

The idea that predictions shape how we perceive and comprehend the world has become increasingly influential in the field of systems neuroscience. It also forms an important framework for understanding neuropsychiatric disorders, which are proposed to be the result of disturbances in the mechanisms through which prior information influences perception and belief, leading to the production of suboptimal models of the world. There is a widespread tendency to conceptualize the influence of predictions exclusively in terms of ‘top-down’ processes, whereby predictions generated in higher-level areas exert their influence on lower-level areas within an information processing hierarchy. However, this excludes from consideration the predictive information embedded in the ‘bottom-up’ stream of information processing. We describe evidence for the importance of this distinction and argue that it is critical for the development of the predictive processing framework and, ultimately, for an understanding of the perturbations that drive the emergence of neuropsychiatric symptoms and experiences.

/pdf/forms-of-prediction-in-the-nervous-system-3z1c498izz.pdf

Forms of prediction in the nervous system

The vestibular system is crucial for postural control; however there are considerable differences in the task dependence and frequency response of vestibular reflexes in appendicular and axial muscles. For example, vestibular reflexes are only evoked in appendicular muscles when vestibular information is relevant to postural control, while in neck muscles they are maintained regardless of the requirement to maintain head on trunk balance. Recent investigations have also shown that the bandwidth of vestibular input on neck muscles is much broader than appendicular muscles (up to a factor of 3). This result challenges the notion that vestibular reflexes only contribute to postural control across the behavioral and physiological frequency range of the vestibular organ (i.e., 0–20 Hz). In this review, we explore and integrate these task-, muscle- and frequency-related differences in the vestibular system’s contribution to posture, and propose that the human nervous system has adapted vestibular signals to match the mechanical properties of the system that each group of muscles controls.

/pdf/task-muscle-and-frequency-dependent-vestibular-control-of-3v7k8e4q1c.pdf

Task, muscle and frequency dependent vestibular control of posture

Increasingly complex models of the neck neuromusculature need detailed muscle and kinematic data for proper validation. The goal of this study was to measure the electromyographic activity of superficial and deep neck muscles during tasks involving isometric, voluntary, and reflexively evoked contractions of the neck muscles. Three male subjects (28-41 years) had electromyographic (EMG) fine wires inserted into the left sternocleidomastoid, levator scapulae, trapezius, splenius capitis, semispinalis capitis, semispinalis cervicis, and multifidus muscles. Surface electrodes were placed over the left sternohyoid muscle. Subjects then performed: (i) maximal voluntary contractions (MVCs) in the eight directions (45 deg intervals) from the neutral posture; (ii) 50 N isometric contractions with a slow sweep of the force direction through 720 deg; (iii) voluntary oscillatory head movements in flexion and extension; and (iv) initially relaxed reflex muscle activations to a forward acceleration while seated on a sled. Isometric contractions were performed against an overhead load cell and movement dynamics were measured using six-axis accelerometry on the head and torso. In all three subjects, the two anterior neck muscles had similar preferred activation directions and acted synergistically in both dynamic tasks. With the exception of splenius capitis, the posterior and posterolateral neck muscles also showed consistent activation directions and acted synergistically during the voluntary motions, but not during the sled perturbations. These findings suggest that the common numerical-modeling assumption that all anterior muscles act synergistically as flexors is reasonable, but that the related assumption that all posterior muscles act synergistically as extensors is not. Despite the small number of subjects, the data presented here can be used to inform and validate a neck model at three levels of increasing neuromuscular-kinematic complexity: muscles generating forces with no movement, muscles generating forces and causing movement, and muscles generating forces in response to induced movement. These increasingly complex data sets will allow researchers to incrementally tune their neck models' muscle geometry, physiology, and feedforward/feedback neuromechanics.

Electromyography of superficial and deep neck muscles during isometric, voluntary and reflex contractions

Background and Aim: Primary (Ia) afferents have been shown to influence both homonymous (parent muscle) and heteronymous (muscles other than the parent muscle) motoneurons. Specifically, the Ia muscle spindle afferents of Soleus have been shown to influence motoneurons of muscles acting at the knee and hip joints through both monosynaptic and polysynaptic pathways in humans [1,2]. The purpose of this study was to investigate the heteronymous (thigh and back muscle) responses to noisy Achilles tendon vibration during quiet standing. 
Methods: Noisy vibration (10-115 Hz) was applied to right Achilles tendon to investigate the frequency characteristics of the heteronymous responses in bilateral Semitendinosus, Vastus Lateralis, and Erector Spinae muscles. Participants (n=12; 5 Male) maintained standing balance for a series of two minute trials. Coherence was estimated between the tendon probe acceleration (input signal) and the rectified EMG (output signal) of each muscle.
Results: We found significant coherence between the tendon probe acceleration and the EMG of ipsilateral Soleus (across a 10-70 Hz bandwidth), Semitendinosus (10-60 Hz), and Vastus Lateralis (10-60 Hz). Responses were observed bilaterally in Erector Spinae (10-50 Hz), with both ipsilateral and contralateral muscles showing similar coherence.
Conclusions: Results from this study provide evidence that muscle spindle feedback from the triceps surae influences the activity of proximal muscles that are important for the control of standing balance. 

[1] Pierrot-Deseilligny et al., Exp. Brain Res. 42, 337-350, 1981; 
[2] Meunier et al., Exp. Brain Res. 96, 534-544, 1993;Acknowledgments: Funded by NSERC

Heteronymous muscle responses to noisy achilles tendon vibration during standing

The vestibular system undergoes anatomical and physiological declines with adult aging (Sloane et al. 1989) that may contribute to postural impairments, but a link to a vestibular mechanism is unclear.  The purpose of our study was to determine whether the vestibular control of standing balance is changed with age.  Eight young (~26 y) and 8 old (~75 y) men stood freely on a force plate while subjected to stochastic vestibular stimuli (0-25Hz, 1.5mA) with their head turned to the right and arms positioned at their sides.  Surface electromyography was recorded from the left soleus and medial gastrocnemius.  Muscle and whole-body balance responses were quantified using time domain correlations (cumulant density) between muscle activity and horizontal forces with the vestibular stimuli.  The peak amplitude of the short latency responses were ~45% and ~25% lower for the soleus and medial gastrocnemius, respectively, in the older than young men. No difference was detected for the peak amplitude of the medium latency response in the soleus, but the older men had a 45% larger response in the medial gastrocnemius than young.  The peak amplitude of the short latency balance response was ~10% less whereas the medium latency response was ~65% larger in the old compared with young.  Thus, healthy adult aging affects the myogenic responses to an isolated vestibular error signal that lead to alterations in the whole-body response to such stimuli.  The findings imply that aging is likely linked to increased central processing of the vestibular signals to maintain upright balance.Acknowledgments: Supported by NSERC, CIHR, MSFHR

Jean-SÃ©bastien Blouin

Papers

Task, muscle and frequency dependent vestibular control of posture

Electromyography of superficial and deep neck muscles during isometric, voluntary and reflex contractions

Heteronymous muscle responses to noisy achilles tendon vibration during standing

The effect of adult aging on standing balance responses to stochastic vestibular stimulation