DOCSLIB.ORG

Cardiac Muscle: Structure and Properties

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text
Cardiac Muscle: Structure and Properties CARDIOVASCULAR SYSTEM: CARDIAC MUSCLE: STRUCTURE AND PROPERTIES For: Semester II CC2TH/ GEN 2TH Prepared and Compiled By: OLIVIA CHOWDHURY DEPARTMENT OF PHYSIOLOGY SURENDRANATH COLLEGE April 29, 2020 OLIVIA CHOWDHURY •Anatomy of The Heart April 29, 2020 OLIVIA CHOWDHURY •The Layers Of The Heart Three layers: • Epicardium . Pericardium – a double serous membrane . Visceral pericardium (Next to heart) . Parietal pericardium (Outside layer) . Serous fluid fills the space between the layers of pericardium . Connective tissue layer • Myocardium . Middle layer . Mostly cardiac muscle • Endocardium . Inner layer . Endothelium April 29, 2020 OLIVIA CHOWDHURY • The Heart Valves Allows blood to flow in only one direction Four valves: Atrioventricular valves– between atria and ventricles Bicuspid/ Mitral valve between LA and LV Tricuspid valve between RA and RV Semilunar valves between ventricles and arteries Pulmonary semilunar valve Aortic semilunar valve April 29, 2020 OLIVIA CHOWDHURY •Direction Of Blood Flow In The Heart April 29, 2020 OLIVIA CHOWDHURY Right side of the heart: • receives venous blood from systemic circulation via superior and inferior vena cava into right atrium • pumps blood to pulmonary circulation from right ventricle Left side of the Heart: • receives oxygenated blood from pulmonary veins • pumps blood into systemic circulation April 29, 2020 OLIVIA CHOWDHURY •The Cardiac Muscle Myocardium has three types of muscle fibers: Muscle fibers which form contractile unit of heart Muscle fibers which form the pacemaker Muscle fibers which form conductive system April 29, 2020 OLIVIA CHOWDHURY •The Cardiac Muscle Striated and resemble the skeletal muscle fibre Sarcomere is the functional unit Sarcomere of the cardiac muscle has all the contractile proteins, namely actin, myosin, troponin tropomyosin. Cardiac muscle fibre is bound by sarcolemma. It has a centrally placed nucleus. Myofibrils are embedded in the sarcoplasm. Sarcoplasmic reticulum is less abundant than in skeletal muscle. Sarcolemma of cardiac muscle has specialized ion channels that skeletal muscle does not have: voltage-gated Ca2+ channels. April 29, 2020 OLIVIA CHOWDHURY • The Cardiac Muscle: Presence Of Intercalated Discs Fibers are branched Adjacent cardiac cells are joined end to end by specialized structures known as intercalated discs Heart functions as a syncytium (Atrial syncytium and ventricular syncytium) The discs contain several gap junctions providing cytoplasmic continuity. Rapid transmission of impulse. when one cardiac cell undergoes an action potential, the electrical impulse spreads to all other cells that are joined by gap junctions April 29, 2020 OLIVIA CHOWDHURY •Muscle Fibres which Form the Pacemaker Some of the muscle fibres of heart are modified into a specialized structure known as pacemaker. These muscle fibres forming the pacemaker have less striation. They are named pacemaker cells or P cells. Sino-atrial (SA) node forms the pacemaker in human heart. April 29, 2020 OLIVIA CHOWDHURY •Muscle Fibres Which Form Conductive System Conductive system of the heart is formed by modified cardiac muscle fibres Impulses from SA node are transmitted to the atria directly. However, the impulses are transmitted to ventricles through various components of conducting system April 29, 2020 OLIVIA CHOWDHURY •Conducting System Of The Heart April 29, 2020 OLIVIA CHOWDHURY • Properties of Cardiac Muscle Autorhythmicity Excitability (Bathmotropic action) Conductivity (Dromotropic action) Contractility (Inotropic action) April 29, 2020 OLIVIA CHOWDHURY • Autorhythmicity Definition: the ability of the heart to initiate its beat continuously and regularly without external stimulation myogenic (independent of nerve supply) due to the specialized excitatory & conductive system of the heart intrinsic ability of self-excitation (waves of depolarization) cardiac impulses April 29, 2020 OLIVIA CHOWDHURY •Locations Of Autorhythmic Cells Sinoatrial node (SA node) Specialized region in right atrial wall near opening of superior vena cava. Atrioventricular node (AV node) Small bundle of specialized cardiac cells located at base of right atrium near septum Bundle of His (atrioventricular bundle) Cells originate at AV node and enters interventricular septum. Divides to form right and left bundle branches which travel down septum, curve around tip of ventricular chambers, travel back toward atria along outer walls Purkinje fibers Small, terminal fibers that extend from bundle of His and April 29, 2020 OLIVIA CHOWDHURY spread throughout ventricular myocardium Autorhythmic cells do not have stable resting membrane potential (RMP) Natural leakiness to Na & Ca spontaneous and gradual depolarization Unstable resting membrane potential = pacemaker potential/ prepotential) Gradual depolarization reaches threshold (-40 mv) spontaneous AP generation April 29, 2020 OLIVIA CHOWDHURY •Rate Of Generation Of AP At Different Sites Of TheHeart SA node acts as the pacemaker because it has the fastest rate ofgenerating action potential April 29, 2020 OLIVIA CHOWDHURY April 29, 2020 OLIVIA CHOWDHURY •Autorhymicity-Effect Of Stannius Ligature In Frog’s Heart • The properties of cardiac muscle are demonstrated using a quiescent heart. • A quiescent heart is a heart which has stopped beating but is still alive. • Such a preparation can be obtained by tying a Stannius Ligature in the frog’s heart. April 29, 2020 OLIVIA CHOWDHURY • Excitability Definition: The ability of cardiac muscle to respond to a stimulus of adequate strength & duration by generating an AP AP initiated by SA node travels along conductive pathway excites atrial & ventricular muscle fibres April 29, 2020 OLIVIA CHOWDHURY •Action Potential In Contractile Fibers April 29, 2020 OLIVIA CHOWDHURY •Refractory Period It is that period during which a second stimulus fails to evoke a response. Absolute Refractory Period : It is that period during which a second stimulus however strong , fails to evoke a response. Relative Refractory Period : It is that period during which a second stimulus evokes a response if it is sufficiently high. April 29, 2020 OLIVIA CHOWDHURY • Long refractory period (250msec) compared to skeletal muscle (3msec) • During this period membrane is refractory to further stimulation until contraction is over. • It lasts longer than muscle contraction, prevents tetanus • Gives time to heart to relax after each contraction, prevents fatigue • It allows time for the heart chambers to fill during diastole before next contraction April 29, 2020 OLIVIA CHOWDHURY •Contractility Definition: Ability of cardiac muscle to contract in response to stimulation. All Or None Law • The response to a threshold stimulus is maximal. If the stimulus is below threshold there is no response • The cardiac muscle follows the all or none law as a whole. • In the case of skeletal muscle, all-or-none law is applicable only to a single muscle fiber. April 29, 2020 OLIVIA CHOWDHURY Treppe or Staircase Phenomenon • When stimuli of same strength are applied at short intervals, a gradual increase in the height of contraction is observed for the first few contractions, after which there is no further increase. This gradual increase in the force of contraction is called staircase phenomenon. • This is due to the BENEFICIAL EFFECT- decrease in viscosity, mild increase in temperature and increase in the level of calcium ions. April 29, 2020 OLIVIA CHOWDHURY Summation of Subliminal Stimuli When a stimulus of subliminal strength is applied the cardiac muscle does not show any response. When a series of subliminal stimuli are applied in succession, the muscle responds with a contraction. It is due to the summation of all the subliminal stimuli that produce a threshold stimulus. April 29, 2020 OLIVIA CHOWDHURY •Conductivity Definition: property by which excitation is conducted through the cardiac tissue April 29, 2020 OLIVIA CHOWDHURY Tissue Conduction rate (m/s) Atrial muscle 0.3 Atrial pathways 1 AV node 0.05 Bundle of His 1 Purkinje system 4 Ventricular muscle 0.3-0.5 Thus, the velocity of impulses is maximum in Purkinje fibers and minimum in the AV node April 29, 2020 OLIVIA CHOWDHURY •Effects of Autonomic Nerve Activity on the Heart April 29, 2020 OLIVIA CHOWDHURY THANK YOU! April 29, 2020 OLIVIA CHOWDHURY.
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]
  • Ultrastructural Cardiac Muscle and Cardiac Microvasculature Changes in Experimental Murine Infections Acta Scientiae Veterinariae, Vol
    Acta Scientiae Veterinariae ISSN: 1678-0345 [email protected] Universidade Federal do Rio Grande do Sul Brasil Tejero, Felix; Arias-Mota, Lourdes Lorena; Roschman-González, Antonio; Aso, Pedro María; Finol, Héctor José Trypanosoma evansi: Ultrastructural Cardiac Muscle and Cardiac Microvasculature Changes in Experimental Murine Infections Acta Scientiae Veterinariae, vol. 38, núm. 3, 2010, pp. 279-285 Universidade Federal do Rio Grande do Sul Porto Alegre, Brasil Available in: http://www.redalyc.org/articulo.oa?id=289021902008 How to cite Complete issue Scientific Information System More information about this article Network of Scientific Journals from Latin America, the Caribbean, Spain and Portugal Journal's homepage in redalyc.org Non-profit academic project, developed under the open access initiative Acta Scientiae Veterinariae. 38(3): 279-285, 2010. ORIGINAL ARTICLE ISSN 1679-9216 (Online) Pub. 910 Trypanosoma evansi: Ultrastructural Cardiac Muscle and Cardiac Microvasculature Changes in Experimental Murine Infections* Felix Tejero1, Lourdes Lorena Arias-Mota1, Antonio Roschman-González2, Pedro María Aso3 & Héctor José Finol2 ABSTRACT Background: Trypanosoma evansi is the etiologic agent of the equine trypanosomosis, a disease related to the detriment of the extensive bovine farming in the Venezuelan grasslands. Even though macroscopic pathologies such as anemia, pale mucosa, icteric tissues, generalized edema, splenomegaly, liver and renal hypertrophy, abortion, anoestrus, emaciation, lymphadenopathies, striated muscle atrophy as well as epicardiac and endocardiac hemorrhages have been described for infections with the agent, no reports of any heart ultrastructural change in experimental or natural infections induced by Venezuelan T. evansi isolates are available. So, a transmission electron microscopic approach to the problem was needed. This work describes cell features of the cardiac myocyte and the cardiac microvasculature ultrastructure in mice experimentally infected with an equine local isolate of T.
    [Show full text]
  • 16 the Heart
    Physiology Unit 3 CARDIOVASCULAR PHYSIOLOGY: THE HEART Cardiac Muscle • Conducting system – Pacemaker cells – 1% of cells make up the conducting system – Specialized group of cells which initiate the electrical current which is then conducted throughout the heart • Myocardial cells (cardiomyocytes) • Autonomic Innervation – Heart Rate • Sympathetic and Parasympathetic regulation • �1 receptors (ADRB1), M-ACh receptors – Contractility • Sympathetic stimulus • Effects on stroke volume (SV) Electrical Synapse • Impulses travel from cell to cell • Gap junctions – Adjacent cells electrically coupled through a channel • Examples – Smooth and cardiac muscles, brain, and glial cells. Conducting System of the Heart • SA node is the pacemaker of the heart – Establishes heart rate – ANS regulation • Conduction Sequence: – SA node depolarizes – Atria depolarize – AV node depolarizes • Then a 0.1 sec delay – Bundle of His depolarizes – R/L bundle branches depolarize – Purkinje fibers depolarize Sinus Rhythm: – Ventricles depolarize Heartbeat Dance Conduction Sequence Electrical Events of the Heart • Electrocardiogram (ECG) – Measures the currents generated in the ECF by the changes in many cardiac cells • P wave – Atrial depolarization • QRS complex – Ventricular depolarization – Atrial repolarization • T wave – Ventricular repolarization • U Wave – Not always present – Repolarization of the Purkinje fibers AP in Myocardial Cells • Plateau Phase – Membrane remains depolarized – L-type Ca2+ channels – “Long opening” calcium channels – Voltage gated
    [Show full text]
  • (7E) Powerpoint Lecture Outline Chapter 8: Control of Movement
    Carlson (7e) PowerPoint Lecture Outline Chapter 8: Control of Movement This multimedia product and its contents are protected under copyright law. The following are prohibited by law: •any public performance or display, including transmission of any image over a network; •preparation of any derivative work, including extraction, in whole or in part, of any images; •any rental, lease, or lending of the program. Copyright 2001 by Allyn & Bacon Skeletal Muscle n Movements of our body are accomplished by contraction of the skeletal muscles l Flexion: contraction of a flexor muscle draws in a limb l Extension: contraction of extensor muscle n Skeletal muscle fibers have a striated appearance n Skeletal muscle is composed of two fiber types: l Extrafusal: innervated by alpha-motoneurons from the spinal cord: exert force l Intrafusal: sensory fibers that detect stretch of the muscle u Afferent fibers: report length of intrafusal: when stretched, the fibers stimulate the alpha-neuron that innervates the muscle fiber: maintains muscle tone u Efferent fibers: contraction adjusts sensitivity of afferent fibers. 8.2 Copyright 2001 by Allyn & Bacon Skeletal Muscle Anatomy n Each muscle fiber consists of a bundle of myofibrils l Each myofibril is made up of overlapping strands of actin and myosin l During a muscle twitch, the myosin filaments move relative to the actin filaments, thereby shortening the muscle fiber 8.3 Copyright 2001 by Allyn & Bacon Neuromuscular Junction n The neuromuscular junction is the synapse formed between an alpha motor neuron
    [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]
  • Skeletal and Cardiac Muscle Pericytes: Functions and Therapeutic Potential
    UCLA UCLA Previously Published Works Title Skeletal and cardiac muscle pericytes: Functions and therapeutic potential. Permalink https://escholarship.org/uc/item/99p1707r Authors Murray, Iain R Baily, James E Chen, William CW et al. Publication Date 2017-03-01 DOI 10.1016/j.pharmthera.2016.09.005 Peer reviewed eScholarship.org Powered by the California Digital Library University of California JPT-06957; No of Pages 10 Pharmacology & Therapeutics xxx (2016) xxx–xxx Contents lists available at ScienceDirect Pharmacology & Therapeutics journal homepage: www.elsevier.com/locate/pharmthera Associate editor: P. Madeddu Skeletal and cardiac muscle pericytes: Functions and therapeutic potential Iain R. Murray a,b, James E. Baily a, William C.W. Chen c,AyeletDard, Zaniah N. Gonzalez a, Andrew R. Jensen d, Frank A. Petrigliano d, Arjun Deb e,⁎, Neil C. Henderson f,⁎⁎ a BHF Center for Vascular Regeneration and MRC Center for Regenerative Medicine, University of Edinburgh, Edinburgh, UK b Department of Trauma and Orthopaedic Surgery, The University of Edinburgh, Edinburgh, UK c Reseach Laboratory of Electronics and Department of Biological Engineering, Massachusetts Institute of Technology, Boston, MA, USA d Orthopedic Hospital Research Center, University of California, Los Angeles, CA, USA e Division of Cardiology, Department of Medicine & Molecular Cell and Developmental Biology, and Eli and Edythe Broad Institute of Regenerative Medicine and Stem Cell Research, David Geffen School of Medicine and College of Letters and Sciences, University of California, Los Angeles, CA, USA f MRC Centre for Inflammation Research, University of Edinburgh, Edinburgh, UK article info abstract Keywords: Pericytes are periendothelial mesenchymal cells residing within the microvasculature. Skeletal muscle and car- Perivascular stem cell diac pericytes are now recognized to fulfill an increasing number of functions in normal tissue homeostasis, in- Mesenchymal stem cell cluding contributing to microvascular function by maintaining vessel stability and regulating capillary flow.
    [Show full text]
  • Are Ryanodine Receptors Important for Diastolic Depolarization in Heart?
    ARE RYANODINE RECEPTORS IMPORTANT FOR DIASTOLIC DEPOLARIZATION IN HEART? A Dissertation submitted in partial fulfillment of the requirement for the Degree of Doctor of Medicine in Physiology (Branch – V) Of The Tamilnadu Dr. M.G.R Medical University, Chennai -600 032 Department of Physiology Christian Medical College, Vellore Tamilnadu April 2017 Ref: …………. Date: …………. CERTIFICATE This is to certify that the thesis entitled “Are ryanodine receptors important for diastolic depolarization in heart?” is a bonafide, original work carried out by Dr.Teena Maria Jose , in partial fulfillment of the rules and regulations for the M.D – Branch V Physiology examination of the Tamilnadu Dr. M.G.R. Medical University, Chennai to be held in April- 2017. Dr. Sathya Subramani, Professor and Head Department of Physiology, Christian Medical College, Vellore – 632 002 Ref: …………. Date: …………. CERTIFICATE This is to certify that the thesis entitled “Are ryanodine receptors important for diastolic depolarization in heart?” is a bonafide, original work carried out by Dr.Teena Maria Jose , in partial fulfillment of the rules and regulations for the M.D – Branch V Physiology examination of the Tamilnadu Dr. M.G.R. Medical University, Chennai to be held in April- 2017. Dr. Anna B Pulimood, Principal, Christian Medical College, Vellore – 632 002 DECLARATION I hereby declare that the investigations that form the subject matter for the thesis entitled “Are ryanodine receptors important for diastolic depolarization in heart?” were carried out by me during my term as a post graduate student in the Department of Physiology, Christian Medical College, Vellore. This thesis has not been submitted in part or full to any other university.
    [Show full text]
  • MUSCLE TISSUE Larry Johnson Texas A&M University
    MUSCLE TISSUE Larry Johnson Texas A&M University Objectives • Histologically identify and functionally characterize each of the 3 types of muscle tissues. • Describe the organization of the sarcomere as seen in light and electron microscopy. • Identify the endomysium, perimysium, and epimysium CT sleeves in muscle. • Relate the functional differences of the three muscle cell types. From: Douglas P. Dohrman and TAMHSC Faculty 2012 Structure and Function of Human Organ Systems, Histology Laboratory Manual MUSCLE FUNCTION: • GENERATION OF CONTRACTILE FORCE DISTINGUISHING FEATURES: • HIGH CONCENTRATION OF CONTRACTILE PROTEINS ACTIN AND MYOSIN ARRANGED EITHER DIFFUSELY IN THE CYTOPLASM (SMOOTH MUSCLE) OR IN REGULAR REPEATING UNITS CALLED SARCOMERES (STRIATED MUSCLES, e.g., CARDIAC AND SKELETAL MUSCLES) MUSCLE • DISTRIBUTION: SKELETAL – STRIATED MUSCLES MOSTLY ASSOCIATED WITH THE SKELETON MUSCLE • DISTRIBUTION: SKELETAL – STRIATED MUSCLES MOSTLY ASSOCIATED WITH THE SKELETON CARDIAC – STRIATED MUSCLES ASSOCIATEWD WITH THE HEART MUSCLE • DISTRIBUTION: SKELETAL – STRIATED MUSCLES MOSTLY ASSOCIATED WITH THE SKELETON CARDIAC – STRIATED MUSCLES ASSOCIATEWD WITH THE HEART SMOOTH – FUSIFORM CELLS ASSOCIATED WITH THE VISCERA, RESPIRATORY TRACT, BLOOD VESSELS, UTERUS, ETC. MUSCLE • HISTOLOGICAL INDENTIFICATION: SKELETAL MUSCLE – VERY LONG CYLINDRICAL STRIATED MUSCLE CELLS WITH MULTIPLE PERIPHERAL NUCLEI MUSCLE • HISTOLOGICAL INDENTIFICATION: SKELETAL MUSCLE – VERY LONG CYLINDRICAL STRIATED MUSCLE CELLS WITH MULTIPLE PERIPHERAL NUCLEI CARDIAC MUSCLE –
    [Show full text]
  • Stretch-Induced Contraction of Intrafusal Muscle in Cat Muscle Spindle1
    0270~6474/81/0110-1069$02.00/O The Journal of Neuroscience Copyright 0 Society for Neuroscience Vol. 1, No. 10, pp. 1069-1074 Printed in U.S.A. October 1981 STRETCH-INDUCED CONTRACTION OF INTRAFUSAL MUSCLE IN CAT MUSCLE SPINDLE1 R. E. POPPELE*x ’ AND D. C. QUICK+ *Laboratory of Neurophysiology and *Departments of Neurology and Anatomy, University of Minnesota, Minneapolis, Minnesota 55455 Abstract Measurements of tension, stiffness, and sarcomere length of intrafusal muscle during ramp stretch of isolated muscle spindles have revealed a stretch-induced contraction of the bag1 fiber. This behavior can account for the very high sensitivity of primary endings to stretch as well as the enhanced sensitivity evoked by dynamic fusimotor stimulation. An intriguing aspect of mammalian muscle spindle Materials and Methods behavior is the very high sensitivity of the primary ending Spindle afferent discharge was recorded from dorsal compared to that of the secondary ending in the same root filaments of anesthetized cats (pentobarbital so- receptor. There are at least two morphological differ- dium, Nembutal, Abbott Laboratories, 35 mg/kg). The ences between primary and secondary endings that might hindlimb was denervated except for the medial gas- account for this difference. The primary ending is formed trocnemius, and ventral roots’L5 through Sl were cut. on the intrafusal bundle in a region called the equator Activity of single muscle spindle receptors was identified where there are very few myofilaments. The secondary in the usual manner (e.g., Poppele, 1981). Mechanical endings are formed in the juxtaequatorial region where measurements were made on isolated spindles obtained there are abundant myofilaments.
    [Show full text]
  • Research Article Histological, Histochemical
    Egypt. J. Exp. Biol. (Zool.), 8(2): 273 – 285 (2012) © The Egyptian Society of Experimental Biology RESEARCH ARTICLE Nabila I. El-Desouki* Amal I. El-Refaiy** Dalia F. A. Abou-Zaid* Amira A. Abdel - Kader* HISTOLOGICAL, HISTOCHEMICAL, AND IMMUNOHISTOCHEMICAL STUDIES OF THE CARDIAC MUSCLE OF THE ALBINO RAT UNDER IMMOBILIZATION STRESS AND THE CURATIVE ROLE OF DIAZEPAM ABSTRACT: The present study is planned to study the effect CORRESPONDENCE: of immobilization stress on the cardiac muscle Nabila Ibrahim El-Desouki of adult male albino rats and the curative role of Department of Zoology, Faculty of Science, diazepam. The study was carried out on 80 Tanta University, Egypt. albino rats; the animals were divided into eight groups: group 1 served as control rats; group 2 E-mail: [email protected] unstressed rats injected intraperitoneally daily with 0.1 mg/kg b.w. diazepam for 30 days; groups 3, 4, and 5 served as immobilized Amal I. El-Refaiy** stressed-rats for 30 days (by restricting Dalia F. A. Abou-Zaid* movement for 2 hr daily at different durations Amira A. Abdel - Kader* 5, 15, and 30 days, respectively); groups 6, 7, and 8 stressed rats treated daily with 0.1 mg/kg *Dept. of Zoology, Faculty of Science, Tanta b.w. diazepam for 30 days. The histological University study of the cardiac myofibres of the stressed- **Dept. of Biological & Environmental rats revealed disorganization of the muscle Science, Faculty of Home Economic, Al-Azhar fibres, vacuolation of the sarcoplasm, pyknosis Univ. of the nuclei, congestion and dilatation of blood vessels in endomysium. The thickness of collagen fibres gradually increased and became ARTICLE CODE: 35.01.12 compact dense in the stressed rats till 30 days, and they were more obvious around the blood vessels.
    [Show full text]
  • Lab 2 Intrinsic Cardiac Conduction System Spring 2016 V10.Pdf
    Lab 2 The Intrinsic Cardiac Conduction System 1/23/2016 MDufilho 1 Figure 18.13 Intrinsic cardiac conduction system and action potential succession during one heartbeat. Superior vena cava Right atrium 1 The sinoatrial (SA) node (pacemaker) generates impulses. Pacemaker potential Internodal pathway 2 The impulses Left atrium SA node pause (0.1 s) at the atrioventricular (AV) node. Atrial muscle 3 The Subendocardial atrioventricular conducting (AV) bundle network connects the atria (Purkinje fibers) AV node to the ventricles. 4 The bundle branches Pacemaker Ventricular conduct the impulses Inter- potential muscle through the ventricular interventricular septum. septum Plateau 5 The subendocardial conducting network depolarizes the contractile 0 100 200 300 400 cells of both ventricles. Milliseconds Anatomy of the intrinsic conduction system showing the sequence of Comparison of action potential shape at electrical excitation various locations 1/23/2016 MDufilho 2 Video • Conducting System Of The Heart 1/23/2016 MDufilho 3 Figure 18.12 Pacemaker and action potentials of pacemaker cells in the heart. 1 Pacemaker potential This slow depolarization is due to both opening of Na+ channels and closing of K+ channels. Notice that the membrane potential is Action Threshold never a flat line. +10 potential 0 2 Depolarization The action –10 potential begins when the 2 2 pacemaker potential reaches –20 threshold. Depolarization is due –30 3 3 to Ca2+ influx through Ca2+ –40 channels. –50 3 Repolarization is due to 1 1 2+ –60 Pacemaker Ca channels inactivating and potential K+ channels opening. This allows –70 + Membrane potential(mV) K efflux, which brings the membrane potential back to its most negative voltage.
    [Show full text]
  • Cardiovascular Physiology
    Introductory Human Physiology © Copyright Emma Jakoi CV 1. HEART ELECTRICAL ACTIVTY Emma Jakoi, Ph.D. LEARNING OBJECTIVES 1. Describe the conduction system of the heart 2. Explain spontaneous electrical activity (pacemaker) in cardiac muscle. 3. Explain action potentials of ventricular cardiac muscle. 4. Explain the cardiac conduction system, pacemakers, and regulation of heart rate by the autonomic nervous system. 5. Explain the ECG and its correspondence to the cardiac action potential (AP). EXCITATION IN CARDIAC MUSCLE The cardiovascular system transports blood containing oxygen, carbon dioxide, nutrients and wastes, between the environment and the cells of the body. It consists of a heart (pump) and blood vessels which deliver nutrients to the tissues (arteries) and ferry waste products away from the tissues (veins). The heart is a muscular organ (Fig 1) which can contract in a rhythmic manner without direct stimulus from the nervous system. Each heart beat begins with the flow of ions across the plasma membrane of the cardiac muscle cell. This current is generated in specialized cells called pacemaker cells. The impulse from the pacemaker cells flows in a unidirectional manner through out the heart via specialized conducting tissue (Fig 1) and into the heart muscle. The electrical impulse results in mechanical contraction of the cardiac muscle through a series of intracellular events involving calcium. Figure 1. Electrical conduction within the heart starts at the sinoatrial (SA) node and passes sequentially to the atriaventricular (AV) node, Bundle of His, left and right bundle branches, and the Purkinje fibers. So the electrical activity moves from the base (A-V junction) to the apex (tip of ventricle) distant from the atria and then sweeps up the sides of the ventricles towards the base.
    [Show full text]