DOCSLIB.ORG

Muscle Spindle Modeling - a Tutorial

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text
Muscle Spindle Modeling - a Tutorial Faculty of Electrical Engineering Mechatronics Engineering Muscle Spindle Modeling - A Tutorial Professor: Dr. Mehdi Delrobaei Student Name: Sadaf Yari January-2019 Muscle Spindle Every day we move around endlessly, walking, exercising, etc. We perform these tasks without thinking about it. In fact, for the human body to make the simplest motion, such as lifting an arm, requires the human brain to perform a dozen calculations and control many complex procedures. Some muscles have to contract while others to expand. The final goal is reached through careful control of the muscles via feedback which provides the brain with information on the current situation of the different parts of the body. One such feedback mechanism is proprioception which contains information on the current location of body parts and the situation they are in. This is made possible by sensors, called proprioceptors, located in the muscles. Examples of proprioceptors include the muscle spindle and the Golgi tendon organ. The former provides length information of the muscle and the latter detects changes in the muscle stretch. Such information is useful for the brain when attempting to control the motion of the body parts. In this tutorial we will focus on the muscle spindle. First, a detailed anatomical and physiological description of the muscle spindle’s structure and function is given. In this part it is explained where exactly the muscle spindle is located and what it does. Then, a mathematical model, which is currently accepted generally, is discussed. What is muscle spindle? Muscles are the organs that cause movement in our body. Each motion in the body, wether volunatry or not, is caused by the contraction or release of a muscle. There are three types of muscles in the human body: 1. Skeletal muscles: Movements that are performed consiously, are carried out by these muscles. Most of them are attached to two bones across a joint, so the muscle serves to move parts of those bones close to each other. 2. Smooth muscles: the muscles found inside organs such as the intestines as well as blood vessels and contract to move substances through the organ. Movements casued by this type of muscle is involuntary. 3. Cardiac muscle: this muscle is found only in the heart and has characteristics of both skeletal and smooth muscles. Figure 1: Types of muscles Our focus here is on skeletal muscles that provide us the ability to move our body parts voluntarily. The structure of such a muscle can be seen in the figure 3. Figure 2: The connection of a muscle to bones causing them to move when it is contracted or released Figure 3: The structure of skeletal muscle The entire muscle, as well as the individual cells, is wrapped in collagen. Near the end the collagen merges to form the tendons, which attach the muscle to the bone. It is through this connective tissue that the force generated by the individual cells is transmitted to the bone. A group of muscle cells are bundled together by collagen to form a fascicle. Since muscle cells are elongated and cylindrical, each muscle cell is usually called a muscle fiber. In skeletal muscle, the muscle fibers are very large, multinucleated, and up to several millimeters in length. A skeletal muscle is attached to two bones connected by a joint. This system acts as a kinematic chain in which the links are moved through the contraction of the muscle. In order to control this system, the brain needs information on the current positions of the individual links and therefore the length information of the muscle fibers. This information is provided through several feedback sources. One of the available feedback mechanisms is proprioception. Literally, proprioception means “sense of self” and it is described as our sense of the relative positions of our body parts and the strength of effort being employed in movements. Proprioception is provided by proprioceptors, which are sensors nested in the skeletal muscles and the tendons. The muscle spindle is one type of proprioceptor that provides information about changes in muscle length. Muscle spindles are small sensory organs that are enclosed within a capsule. They are found throughout the body of a muscle, in parallel with extrafusal fibers. Within a muscle spindle, there are several small, specialized muscle fibers known as intrafusal fibers. Intrafusal fibers have contractile proteins (thick and thin filaments) at either end, with a central region that is devoid of contractile proteins. The central region is wrapped by the sensory dendrites of the muscle spindle afferent. When the muscle lengthens and the muscle spindle is stretched, this opens mechanically-gated ion channels in the sensory dendrites, leading to a receptor potential that triggers action potentials in the muscle spindle afferent. Figure 4: Muscle spindle Figure 5: Muscle spindle structure Modelling In this section we give a, as much as possible, simple model of the spindle which consists of mathematical elements that are closely related to the anatomical parts of the spindle and show the same physiological properties. We begin by giving a general description of the spindle model. We then continue by examining the individual blocks. Next the model for an intrafusal fiber is considered and the underlying equations are explained in detail. For this purpose, first, the fusimotor activation is addressed. Secondly the mechanics of stretch within the intrafusal fiber is analyzed. Finally, sensory transduction from stretch to afferent endings is formulized. Ultimately, we describe the afferent firing model that deals with nonlinear summation between the intrafusal fibers’ transduction regions. The spindle model Three types of specialized fibers, known as intrafusal fibers, constitute the muscle spindle. These are the long nuclear bag 1 and bag 2 fibers and the shorter chain fibers which are in parallel with the extrafusal fibers (the fibers of the muscle itself). A typical spindle consists of one bag 1, one bag 2, and about 4 to 11 chain fibers. Using these fibers, the spindle provides feedback in the form of nerve impulses, a sequence of electrical potential spikes, to the central nervous system. Figure 3: Intrafusal and extarfusal muscles incorporation with motor neuron Figure 4: Three types of intrafusal fibers The dynamic range of the nerve impulses or action potentials fired from the nerve to activate the muscle is limited. Nevertheless, the spindle should be capable of sensing and accurately encoding the length and velocity over a wide range of kinematic conditions. In order to be able to accomplish this, the sensitivity to length or velocity has to be shifted by means of specialized fusimotor efferents (γ motorneurons). These efferents can be divided into dynamic fusimotor efferent and the static fusimotor efferent, which signal the transitions in phase and the intended movement of the motor unit to the CNS respectively. The bag 1 fiber is primarily sensitive to the velocity of the spindle, i.e. its rate of stretching; hence it has dynamic fusimotor efferent endings located on it. The bag 2 and chain fibers are modulated via static fusimotor efferents and contribute mainly to length sensitivity. The feedback to the CNS containing length and velocity information from the muscle is collected via the afferent endings which are nerve fibers wound around the intrafusal fibers. The primary afferent signal is provided through group Ia fibers which have their endings attached to the region in the middle of all three types of the intrafusal fibers. The secondary endings, located a little further from the middle of only the bag 2 and chain fibers, generate the secondary afferent signal which corresponds primarily to information on the length of the muscle. Now, we are going to construct a model of the spindle based on the anatomical and physiological descriptions explained above. The model is composed of three intrafusal fiber models corresponding to a bag 1, bag 2 and a chain fiber. At its input, the system receives the fascicle length (L) and two fusimotor inputs, the static and the dynamic fusimotor, in the form of potential spikes. From these inputs the model generates two output signals which are to be fed to the CNS via the primary and the secondary afferents. Figure5: schematics of the overall spindle model Figure6: spindle model consists of 3 intrafusal fiber models; it receives 3 inputs (fascicle length, in terms of optimal length L0, and static and dynamic fusimotor drives) to produce primary and secondary afferent firing The three intrafusal models are similar in the constituent blocks but have different coefficients to account for the differences in their physiological behaviors. Each intrafusal fiber model responds to two inputs: the fascicle length (L; in units of L0, which represents the optimal muscle fascicle length) and the relevant fusimotor drive (in the case of bag1 fiber it is dynamic fusimotor drive (γdynamic), whereas in the case of bag2 it is chain static fusimotor drive (γstatic)). The outputs of the intrafusal fiber models are combined to produce the final outputs of the model i.e. the primary (Ia) and secondary (II) afferent activity. In the coming sections we will first explain the intrafusal fiber model in more detail. We do so by first considering the fusimotor activation. Next the mechanics of stretch within the intrafusal fiber is analyzed. Finally it is clarified how stretch information is converted to signals for the afferent endings. In the second major section it is explained how the intrafusal fibers’ outputs are nonlinearly summed to yield the afferent firing model. The intrafusal fiber model As mentioned earlier, the intrafusal fiber models are the same in structure but to account for the fibers’ different physiologies the weights of the model parameters in the calculations varies (see Table 1).
Load more

Recommended publications
  • VIEW Open Access Muscle Spindle Function in Healthy and Diseased Muscle Stephan Kröger* and Bridgette Watkins
    Kröger and Watkins Skeletal Muscle (2021) 11:3 https://doi.org/10.1186/s13395-020-00258-x REVIEW Open Access Muscle spindle function in healthy and diseased muscle Stephan Kröger* and Bridgette Watkins Abstract Almost every muscle contains muscle spindles. These delicate sensory receptors inform the central nervous system (CNS) about changes in the length of individual muscles and the speed of stretching. With this information, the CNS computes the position and movement of our extremities in space, which is a requirement for motor control, for maintaining posture and for a stable gait. Many neuromuscular diseases affect muscle spindle function contributing, among others, to an unstable gait, frequent falls and ataxic behavior in the affected patients. Nevertheless, muscle spindles are usually ignored during examination and analysis of muscle function and when designing therapeutic strategies for neuromuscular diseases. This review summarizes the development and function of muscle spindles and the changes observed under pathological conditions, in particular in the various forms of muscular dystrophies. Keywords: Mechanotransduction, Sensory physiology, Proprioception, Neuromuscular diseases, Intrafusal fibers, Muscular dystrophy In its original sense, the term proprioception refers to development of head control and walking, an early im- sensory information arising in our own musculoskeletal pairment of fine motor skills, sensory ataxia with un- system itself [1–4]. Proprioceptive information informs steady gait, increased stride-to-stride variability in force us about the contractile state and movement of muscles, and step length, an inability to maintain balance with about muscle force, heaviness, stiffness, viscosity and ef- eyes closed (Romberg’s sign), a severely reduced ability fort and, thus, is required for any coordinated move- to identify the direction of joint movements, and an ab- ment, normal gait and for the maintenance of a stable sence of tendon reflexes [6–12].
    [Show full text]
  • Muscle Tissue
    10 Muscle Tissue PowerPoint® Lecture Presentations prepared by Jason LaPres Lone Star College—North Harris © 2012 Pearson Education, Inc. 10-1 An Introduction to Muscle Tissue • Learning Outcomes • 10-1 Specify the functions of skeletal muscle tissue. • 10-2 Describe the organization of muscle at the tissue level. • 10-3 Explain the characteristics of skeletal muscle fibers, and identify the structural components of a sarcomere. • 10-4 Identify the components of the neuromuscular junction, and summarize the events involved in the neural control of skeletal muscle contraction and relaxation. © 2012 Pearson Education, Inc. 10-1 An Introduction to Muscle Tissue • Learning Outcomes • 10-5 Describe the mechanism responsible for tension production in a muscle fiber, and compare the different types of muscle contraction. • 10-6 Describe the mechanisms by which muscle fibers obtain the energy to power contractions. • 10-7 Relate the types of muscle fibers to muscle performance, and distinguish between aerobic and anaerobic endurance. © 2012 Pearson Education, Inc. 10-1 An Introduction to Muscle Tissue • Learning Outcomes • 10-8 Identify the structural and functional differences between skeletal muscle fibers and cardiac muscle cells. • 10-9 Identify the structural and functional differences between skeletal muscle fibers and smooth muscle cells, and discuss the roles of smooth muscle tissue in systems throughout the body. © 2012 Pearson Education, Inc. An Introduction to Muscle Tissue • Muscle Tissue • A primary tissue type, divided into: • Skeletal muscle tissue • Cardiac muscle tissue • Smooth muscle tissue © 2012 Pearson Education, Inc. 10-1 Functions of Skeletal Muscle Tissue • Skeletal Muscles • Are attached to the skeletal system • Allow us to move • The muscular system • Includes only skeletal muscles © 2012 Pearson Education, Inc.
    [Show full text]
  • Interpretation of Sensory Information from Skeletal Muscle Receptors for External Control Milan Djilas
    Interpretation of Sensory Information From Skeletal Muscle Receptors For External Control Milan Djilas To cite this version: Milan Djilas. Interpretation of Sensory Information From Skeletal Muscle Receptors For External Control. Automatic. Université Montpellier II - Sciences et Techniques du Languedoc, 2008. English. tel-00333530 HAL Id: tel-00333530 https://tel.archives-ouvertes.fr/tel-00333530 Submitted on 23 Oct 2008 HAL is a multi-disciplinary open access L’archive ouverte pluridisciplinaire HAL, est archive for the deposit and dissemination of sci- destinée au dépôt et à la diffusion de documents entific research documents, whether they are pub- scientifiques de niveau recherche, publiés ou non, lished or not. The documents may come from émanant des établissements d’enseignement et de teaching and research institutions in France or recherche français ou étrangers, des laboratoires abroad, or from public or private research centers. publics ou privés. UNIVERSITE MONTPELLIER II SCIENCES ET TECHNIQUES DU LANGUEDOC T H E S E pour obtenir le grade de DOCTEUR DE L'UNIVERSITE MONTPELLIER II Formation doctorale: SYSTEMES AUTOMATIQUES ET MICROELECTRONIQUES Ecole Doctorale: INFORMATION, STRUCTURES ET SYSTEMES présentée et soutenue publiquement par Milan DJILAS le 13 octobre 2008 Titre: INTERPRETATION DES INFORMATIONS SENSORIELLES DES RECEPTEURS DU MUSCLE SQUELETTIQUE POUR LE CONTROLE EXTERNE INTERPRETATION OF SENSORY INFORMATION FROM SKELETAL MUSCLE RECEPTORS FOR EXTERNAL CONTROL JURY Jacques LEVY VEHEL Directeur de Recherches, INRIA Rapporteur
    [Show full text]
  • THE MUSCLE SPINDLE Anatomical Structures of the Spindle Apparatus
    56 Chapter Three Figure 3-2. Organization of muscle from macro- scopic to microscopic levels. Reprinted with permis- sion from Oatis CA. Kinesiology: The Mechanics and Pathomechanics of Human Movement. Philadelphia, Pa: Lippincott Williams & Wilkins; 2004:46. which contains only actin (thin) filaments. The darker area is the A-band, which contains alternating actin and myosin (thick) filaments. The Z-line consists of a connective tissue network that bisects the I-band, anchors the thin filaments, and provides structural integrity to the sarcomere. The H- Figure 3-1. Successive connective tissue sheaths with- zone, located in the middle of the A-band, is the region of in muscle. Reprinted with permission from Oatis thick filaments not overlapped by thin filaments. The M- CA. Kinesiology: The Mechanics and Pathomechanics band bisects the H-zone and represents the middle of the of Human Movement. Philadelphia, Pa: Lippincott sarcomere. The M-band consists of protein structures that Williams & Wilkins; 2004:47. support the arrangement of the myosin filaments. During muscle contraction, the sarcomere I-band and H-zone decrease in length while the length of the A-band remains constant.2,3 THE MUSCLE SPINDLE The muscle spindle is a long, thin structure located adjacent and parallel to muscle fibers and is composed of multiple components that have both afferent and efferent innervation (Figures 3-4a and 3-4b). The muscle spindle functions as a stretch receptor and responds to static and dynamic length changes of skeletal muscle.4-6 This complex receptor is found in all muscles, primarily in extremity, inter- costal, and cervical muscles.
    [Show full text]
  • Single-Cell Analysis Uncovers Fibroblast Heterogeneity
    ARTICLE https://doi.org/10.1038/s41467-020-17740-1 OPEN Single-cell analysis uncovers fibroblast heterogeneity and criteria for fibroblast and mural cell identification and discrimination ✉ Lars Muhl 1,2 , Guillem Genové 1,2, Stefanos Leptidis 1,2, Jianping Liu 1,2, Liqun He3,4, Giuseppe Mocci1,2, Ying Sun4, Sonja Gustafsson1,2, Byambajav Buyandelger1,2, Indira V. Chivukula1,2, Åsa Segerstolpe1,2,5, Elisabeth Raschperger1,2, Emil M. Hansson1,2, Johan L. M. Björkegren 1,2,6, Xiao-Rong Peng7, ✉ Michael Vanlandewijck1,2,4, Urban Lendahl1,8 & Christer Betsholtz 1,2,4 1234567890():,; Many important cell types in adult vertebrates have a mesenchymal origin, including fibro- blasts and vascular mural cells. Although their biological importance is undisputed, the level of mesenchymal cell heterogeneity within and between organs, while appreciated, has not been analyzed in detail. Here, we compare single-cell transcriptional profiles of fibroblasts and vascular mural cells across four murine muscular organs: heart, skeletal muscle, intestine and bladder. We reveal gene expression signatures that demarcate fibroblasts from mural cells and provide molecular signatures for cell subtype identification. We observe striking inter- and intra-organ heterogeneity amongst the fibroblasts, primarily reflecting differences in the expression of extracellular matrix components. Fibroblast subtypes localize to discrete anatomical positions offering novel predictions about physiological function(s) and regulatory signaling circuits. Our data shed new light on the diversity of poorly defined classes of cells and provide a foundation for improved understanding of their roles in physiological and pathological processes. 1 Karolinska Institutet/AstraZeneca Integrated Cardio Metabolic Centre, Blickagången 6, SE-14157 Huddinge, Sweden.
    [Show full text]
  • Emphasizing Task-Specific Hypertrophy to Enhance Sequential Strength and Power Performance
    Journal of Functional Morphology and Kinesiology Review Emphasizing Task-Specific Hypertrophy to Enhance Sequential Strength and Power Performance S. Kyle Travis 1,* , Ai Ishida 1 , Christopher B. Taber 2 , Andrew C. Fry 3 and Michael H. Stone 1 1 Center of Excellence for Sport Science and Coach Education, Department of Sport, Exercise, Recreation, and Kinesiology, East Tennessee State University, Johnson City, TN 37604, USA; [email protected] (A.I.); [email protected] (M.H.S.) 2 Department of Physical Therapy and Human Movement Science, Sacred Heart University, Fairfield, CT 06825, USA; [email protected] 3 Jayhawk Athletic Performance Laboratory, Department of Health, Sport, and Exercise Sciences, University of Kansas, Lawrence, KS 66046, USA; [email protected] * Correspondence: [email protected] Received: 20 August 2020; Accepted: 21 October 2020; Published: 27 October 2020 Abstract: While strength is indeed a skill, most discussions have primarily considered structural adaptations rather than ultrastructural augmentation to improve performance. Altering the structural component of the muscle is often the aim of hypertrophic training, yet not all hypertrophy is equal; such alterations are dependent upon how the muscle adapts to the training stimuli and overall training stress. When comparing bodybuilders to strength and power athletes such as powerlifters, weightlifters, and throwers, while muscle size may be similar, the ability to produce force and power is often inequivalent. Thus, performance differences go beyond structural changes and may be due to the muscle’s ultrastructural constituents and training induced adaptations. Relative to potentiating strength and power performances, eliciting specific ultrastructural changes should be a variable of interest during hypertrophic training phases.
    [Show full text]
  • Cortex Brainstem Spinal Cord Thalamus Cerebellum Basal Ganglia
    Harvard-MIT Division of Health Sciences and Technology HST.131: Introduction to Neuroscience Course Director: Dr. David Corey Motor Systems I 1 Emad Eskandar, MD Motor Systems I - Muscles & Spinal Cord Introduction Normal motor function requires the coordination of multiple inter-elated areas of the CNS. Understanding the contributions of these areas to generating movements and the disturbances that arise from their pathology are important challenges for the clinician and the scientist. Despite the importance of diseases that cause disorders of movement, the precise function of many of these areas is not completely clear. The main constituents of the motor system are the cortex, basal ganglia, cerebellum, brainstem, and spinal cord. Cortex Basal Ganglia Cerebellum Thalamus Brainstem Spinal Cord In very broad terms, cortical motor areas initiate voluntary movements. The cortex projects to the spinal cord directly, through the corticospinal tract - also known as the pyramidal tract, or indirectly through relay areas in the brain stem. The cortical output is modified by two parallel but separate re­ entrant side loops. One loop involves the basal ganglia while the other loop involves the cerebellum. The final outputs for the entire system are the alpha motor neurons of the spinal cord, also called the Lower Motor Neurons. Cortex: Planning and initiation of voluntary movements and integration of inputs from other brain areas. Basal Ganglia: Enforcement of desired movements and suppression of undesired movements. Cerebellum: Timing and precision of fine movements, adjusting ongoing movements, motor learning of skilled tasks Brain Stem: Control of balance and posture, coordination of head, neck and eye movements, motor outflow of cranial nerves Spinal Cord: Spontaneous reflexes, rhythmic movements, motor outflow to body.
    [Show full text]
  • Nomina Histologica Veterinaria, First Edition
    NOMINA HISTOLOGICA VETERINARIA Submitted by the International Committee on Veterinary Histological Nomenclature (ICVHN) to the World Association of Veterinary Anatomists Published on the website of the World Association of Veterinary Anatomists www.wava-amav.org 2017 CONTENTS Introduction i Principles of term construction in N.H.V. iii Cytologia – Cytology 1 Textus epithelialis – Epithelial tissue 10 Textus connectivus – Connective tissue 13 Sanguis et Lympha – Blood and Lymph 17 Textus muscularis – Muscle tissue 19 Textus nervosus – Nerve tissue 20 Splanchnologia – Viscera 23 Systema digestorium – Digestive system 24 Systema respiratorium – Respiratory system 32 Systema urinarium – Urinary system 35 Organa genitalia masculina – Male genital system 38 Organa genitalia feminina – Female genital system 42 Systema endocrinum – Endocrine system 45 Systema cardiovasculare et lymphaticum [Angiologia] – Cardiovascular and lymphatic system 47 Systema nervosum – Nervous system 52 Receptores sensorii et Organa sensuum – Sensory receptors and Sense organs 58 Integumentum – Integument 64 INTRODUCTION The preparations leading to the publication of the present first edition of the Nomina Histologica Veterinaria has a long history spanning more than 50 years. Under the auspices of the World Association of Veterinary Anatomists (W.A.V.A.), the International Committee on Veterinary Anatomical Nomenclature (I.C.V.A.N.) appointed in Giessen, 1965, a Subcommittee on Histology and Embryology which started a working relation with the Subcommittee on Histology of the former International Anatomical Nomenclature Committee. In Mexico City, 1971, this Subcommittee presented a document entitled Nomina Histologica Veterinaria: A Working Draft as a basis for the continued work of the newly-appointed Subcommittee on Histological Nomenclature. This resulted in the editing of the Nomina Histologica Veterinaria: A Working Draft II (Toulouse, 1974), followed by preparations for publication of a Nomina Histologica Veterinaria.
    [Show full text]
  • Effect of Lntrafusal Muscle Mechanics on Mammalian Muscle Spindle Sensitivity’
    0270.6474/85/0507-1881$02.00/O The Journal of Neurowence CopyrIght 0 Society for Neuroscience Vol. 5, No. 7, pp. 1881-1885 Printed in U.S.A. July 1985 Effect of lntrafusal Muscle Mechanics on Mammalian Muscle Spindle Sensitivity’ R. E. POPPELE*V2 AND D. c. QUICK* * Laboratory of Neurophysiology and $ Department of Anatomy, University of Minnesota, Minneapolis, Minnesota 55455 Abstract Materials and Methods Spindles were dissected free from tenuissimus muscles taken from anes- Sensitivity differences between primary and secondary thetized cats (pentobarbttal sodium, Nembutal, Abbott Laboratories, 35 mg/ endings of mammalian muscle spindles under various con- kg, or ketamine hydrochloride, Parke, Davis, 20 mg/kg). The isolated recep- ditions of stretch and fusimotor activation may be due to tor, together with about 1 cm of nerve, was mounted in a small chamber by differences in their respective mechanoelectric transducers tying each pole (near the capsule sleeve) to a small tungsten wire shaft or to mechanical properties of the intrafusal muscle support- connected to a servo-controlled Ling vibrator (model 108). The chamber was ing those endings. This study of isolated cat muscle spindles continuously perfused with oxygenated, modified Krebs’ solution (Poppele et al., 1979). The nerve was drawn onto a pair of electrodes in an adjacent examines the strain in individual intrafusal muscle fibers chamber containtng a high density fluorocarbon compound (FC-80, 3M Co.). resulting from stretch and fusimotor stimulation. The degree The entire assembly was mounted on a Zeiss photomicroscope equipped of local stretch occurring at the sensory endings under these with tine camera and Nomarski optics (see Poppele et al., 1979, and Poppele conditions was measured.
    [Show full text]
  • Spinal Reflexes
    Spinal Reflexes Lu Chen, Ph.D. MCB, UC Berkeley 1 Simple reflexes such as stretch reflex require coordinated contraction and relaxation of different muscle groups Categories of Muscle Based on Direction of Motion Flexors Æ reduce the angle of joints Extensors Æ increase the angle of joints Categories of Muscle Based on Movement Agonist Æmuscle that serves to move the joint in the same direction as the studied muscle Antagonist Æ muscle that moves the joint in the opposite direction 2 1 Muscle Spindles •Small encapsulated sensory receptors that have a Intrafusal muscle spindle-like shape and are located within the fibers fleshy part of the muscle •In parallel with the muscle fibers capsule •Does not contribute to the overall contractile Sensory force endings •Mechanoreceptors are activated by stretch of the central region Afferent axons •Due to stretch of the whole muscle Efferent axons (including intrafusal f.) •Due to contraction of the polar regions of Gamma motor the intrafusal fibers endings 3 Muscle Spindles Organization 2 kinds of intrafusal muscle fibers •Nuclear bag fibers (2-3) •Dynamic •Static •Nuclear chain fibers (~5) •Static 2 types of sensory fibers •Ia (primary) - central region of all intrafusal fibers •II (secondary) - adjacent to the central region of static nuclear bag fibers and nuclear chain fibers Intrafusal fibers stretched Sensory ending stretched, (loading the spindle) increase firing Muscle fibers lengthens Sensory ending stretched, (stretched) increase firing Spindle unloaded, Muscle fiber shortens decrease firing 4 2 Muscle Spindles Organization Gamma motor neurons innervate the intrafusal muscle fibers. Activation of Shortening of the polar regions gamma neurons of the intrafusal fibers Stretches the noncontractile Increase firing of the center regions sensory endings Therefore, the gamma motor neurons provide a mechanism for adjusting the sensitivity of the muscle spindles.
    [Show full text]
  • Periostin Is Required for the Maintenance of Muscle Fibers During Muscle Regeneration
    International Journal of Molecular Sciences Article Periostin Is Required for the Maintenance of Muscle Fibers during Muscle Regeneration Naoki Ito 1,2,3 , Yuko Miyagoe-Suzuki 2 , Shin’ichi Takeda 2,* and Akira Kudo 3,* 1 Laboratory of Molecular Life Science, Institute of Biomedical Research and Innovation (IBRI), Foundation for Biomedical Research and Innovation at Kobe (FBRI), Kobe 650-0047, Japan; [email protected] 2 National Center of Neurology and Psychiatry, Department of Molecular Therapy, National Institute of Neuroscience, Tokyo 187-8502, Japan; [email protected] 3 Department of Biological Information, Tokyo Institute of Technology, Yokohama 226-8501, Japan * Correspondence: [email protected] (S.T.); [email protected] (A.K.) Abstract: Skeletal muscle regeneration is a well-organized process that requires remodeling of the extracellular matrix (ECM). In this study, we revealed the protective role of periostin, a matricellular protein that binds to several ECM proteins during muscle regeneration. In intact muscle, periostin was localized at the neuromuscular junction, muscle spindle, and myotendinous junction, which are connection sites between muscle fibers and nerves or tendons. During muscle regeneration, periostin exhibited robustly increased expression and localization at the interstitial space. Periostin-null mice showed decreased muscle weight due to the loss of muscle fibers during repeated muscle regeneration. Cultured muscle progenitor cells from periostin-null mice showed no deficiencies in their proliferation, differentiation, and the expression of Pax7, MyoD, and myogenin, suggesting that the loss of muscle Citation: Ito, N.; Miyagoe-Suzuki, Y.; fibers in periostin-null mice was not due to the impaired function of muscle stem/progenitor cells.
    [Show full text]
  • A Smooth Sustained Muscle Cell Contraction
    A Smooth Sustained Muscle Cell Contraction ConsecratedhitchilyIf lapidific and or libellously, planar and numeric Chanderjit how Stephen historic usually isbureaucratizing Jon?nidificating Solute his or some brimful,spectrometry samfoos Walter disembowelledso never vendibly! demobilized retiredly any orsonatina! keel The strongest muscle contractions are normally achieved by A increasing stimulus above. Smooth skeletal cardiac both cardiac and skeletal both cardiac and smooth. Asm cells are made is that it a cell? Skeletal muscles only pull in waste direction For customer reason is always note in pairs When one muscle in each pair contracts to stay a joint for other its breach then contracts and pulls in the opposite quarter to straighten the locker out again. Chapter 14 Muscle Contraction Michael D Mann PhD. The initial transient phase is followed by a sustained contraction. A sarcomere is Athe wavy lines on core cell trail seen get a microscope. Which type of muscle works automatically? When a muscle is to illicit a three load isotonic conditions after stimulation starts. Smooth Muscle storage is accomplished by sustained contractions of ring-like bands of increase muscle called sphincters. When shivering produces random skeletal muscle contractions to generate heat. Smooth muscle than is associated with numerous organs and tissue. The smooth muscles are one as linings of the gastrointestinal tract that. Smooth muscle cells can remain pregnant a rash of contraction for long periods. Within myocytes caused by the organization of myofibrils to become constant tension. Tetanus continued sustained smooth contraction due its rapid stimulation wave summation. Layers of more muscle may act together miss one unit to guide simultaneous.
    [Show full text]