Muscle Contraction Overview
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Questions and Answers

What initiates the release of calcium ions from the sarcoplasmic reticulum?

  • Binding of ACh to receptors on the motor end plate
  • ATP binding to myosin cross bridges
  • Active transport of calcium ions into the muscle fibre
  • Action potential generated in the muscle cell (correct)

    • What role does troponin play in muscle contraction?

  • It transports calcium ions back into the SR
  • It uncovers binding sites on actin filaments (correct)
  • It binds to ATP and supplies energy
  • It forms cross bridges with myosin

    • What happens to ACh after it has triggered a muscle action potential?

  • It stimulates the release of calcium ions from the SR
  • It is actively transported into the muscle fibre
  • It is broken down by AChE at the neuromuscular junction (correct)
  • It remains bound to the receptors on the motor end plate

    • What is the first step in the contraction process of a skeletal muscle fibre?

    <p>An action potential is generated</p> Signup and view all the answers

    What is the purpose of the latent period in muscle contraction?

    <p>To prepare the muscle for peak tension</p> Signup and view all the answers

    What structural characteristic of muscle fibres aids in force development?

    <p>Parallel arrangement of muscle fibres</p> Signup and view all the answers

    Which of the following factors does NOT affect muscle strength?

    <p>Muscle fibre length</p> Signup and view all the answers

    What happens to calcium ions when there is no longer a local action potential?

    <p>They are actively taken up by the sarcoplasmic reticulum</p> Signup and view all the answers

    What primary role does aldosterone play in the body?

    <p>It promotes water retention in the kidneys.</p> Signup and view all the answers

    How does vasopressin contribute to urine production?

    <p>It helps retain water, concentrating the urine.</p> Signup and view all the answers

    What is the first step in the micturition reflex?

    <p>Stimulation of stretch receptors in the bladder wall.</p> Signup and view all the answers

    In the process of voluntary control of micturition, what happens before the relaxation of the external sphincter?

    <p>Bladder fullness is sensed.</p> Signup and view all the answers

    What occurs when the parasympathetic supply to the bladder is stimulated during micturition?

    <p>The bladder contracts and urine is expelled.</p> Signup and view all the answers

    What is the role of aldosterone in kidney function?

    <p>Increases sodium and water reabsorption into the bloodstream</p> Signup and view all the answers

    Which hormone is secreted by the posterior pituitary to help retain water?

    <p>Antidiuretic hormone (ADH)</p> Signup and view all the answers

    What is the main function of the proximal convoluted tubule in the nephron?

    <p>Reabsorbs ions, glucose, and water</p> Signup and view all the answers

    How do juxtamedullary nephrons differ from cortical nephrons?

    <p>Juxtamedullary nephrons are less abundant than cortical nephrons</p> Signup and view all the answers

    Which process involves the movement of non-filtered substances from peritubular capillaries into the tubular lumen?

    <p>Secretion</p> Signup and view all the answers

    What effect does caffeine have on ADH and water retention?

    <p>Inhibits ADH, leading to increased urine output</p> Signup and view all the answers

    What is the function of the glomerulus in the nephron?

    <p>Filters a protein-free plasma into the tubular component</p> Signup and view all the answers

    Which structure collects glomerular filtrate?

    <p>Bowman's capsule</p> Signup and view all the answers

    What is the role of cytokines in the communication between the immune system and the CNS?

    <p>Cytokines transport messages from the periphery into the brain.</p> Signup and view all the answers

    Which structure in the brain allows for the communication between the CNS and the peripheral immune system?

    <p>Circumventricular organs</p> Signup and view all the answers

    What impact does maternal immune activation have on brain development?

    <p>It can negatively alter brain development.</p> Signup and view all the answers

    What is the primary function of microglia in the brain?

    <p>They act as resident immune cells monitoring the environment.</p> Signup and view all the answers

    How is synaptic pruning during brain development linked to developmental disorders?

    <p>Inadequate pruning can lead to conditions like schizophrenia.</p> Signup and view all the answers

    What event during a maternal immune activation study is linked to increased risk of schizophrenia in offspring?

    <p>1957 Influenza epidemic</p> Signup and view all the answers

    Which of the following describes the neuroimmune system's role in injury and disease?

    <p>It provides protective immunity across the brain and spinal cord.</p> Signup and view all the answers

    What do microglia primarily monitor in their environment?

    <p>Synapses and neuronal activity</p> Signup and view all the answers

    Which response reflects the concept of the brain's immunological uniqueness?

    <p>The brain is a uniquely immunologically protected organ.</p> Signup and view all the answers

    What is the maternal immune activation model used to study?

    <p>The impact of maternal infections on offspring brain development.</p> Signup and view all the answers

    How does lower protein intake affect cardiovascular function in rats?

    <p>Increases MAP and HR</p> Signup and view all the answers

    What is the primary role of arterioles in the circulatory system?

    <p>Adjust resistance to regulate blood flow to organs</p> Signup and view all the answers

    Which component of blood is primarily responsible for oxygen transport?

    <p>Erythrocytes</p> Signup and view all the answers

    What process occurs when the kidneys detect reduced oxygen carrying capacity in the blood?

    <p>Secretion of erythropoietin</p> Signup and view all the answers

    What role does the medullary cardiovascular control center play?

    <p>Influences heart rate and blood vessel resistance</p> Signup and view all the answers

    Which type of blood vessels are responsible for the exchange of materials between blood and surrounding tissues?

    <p>Capillaries</p> Signup and view all the answers

    What is the effect of vasoconstriction on blood flow and resistance?

    <p>Decreases blood flow and increases resistance</p> Signup and view all the answers

    What is the main component of plasma?

    <p>Water</p> Signup and view all the answers

    What is the role of precapillary sphincters?

    <p>Control blood flow into capillaries</p> Signup and view all the answers

    Which factor is NOT involved in adjusting arteriolar resistance?

    <p>Blood pH</p> Signup and view all the answers

    What is the key function of platelets in the circulatory system?

    <p>Help form blood clots</p> Signup and view all the answers

    What type of antibodies appear in human plasma after six months of age?

    <p>Both A and B antibodies</p> Signup and view all the answers

    What do the terms 'vasoconstriction' and 'vasodilation' refer to?

    <p>Alterations in the circumference and radius of blood vessels</p> Signup and view all the answers

    What triggers the release of nitric oxide as a local vasoactive mediator?

    <p>Chemical changes in the environment</p> Signup and view all the answers

    Study Notes

    Muscle Contraction

    • Acetylcholine (ACh) released by motor neuron axon binds to receptors on motor end plate, triggering action potential
    • Action potential propagates across muscle cell membrane and down T-tubules
    • T-tubule action potential triggers Ca2+ release from sarcoplasmic reticulum (SR)
    • Calcium ions bind to troponin on actin filaments, shifting tropomyosin to expose cross-bridge binding sites on actin
    • Myosin cross-bridges attach to actin and bend, pulling actin filaments towards the center of the sarcomere, powered by ATP
    • Ca2+ is actively reuptaken by the SR when the local action potential ceases, leading to relaxation

    Sarcoplasmic Reticulum

    • Modified endoplasmic reticulum forming a network surrounding each myofibril
    • Not continuous but encircles myofibrils throughout their length
    • Segments wrap around each A band and I band

    Relaxation

    • Dependent on calcium reuptake into the SR
    • Acetylcholinesterase (AChE) breaks down ACh at the neuromuscular junction, stopping muscle fiber action potential
    • When the local action potential is absent, calcium moves back into the SR

    Contractile Activity

    • Latent period: delay between stimulation and contraction onset
    • Contraction time: period from contraction onset to peak tension development, varies depending on muscle fiber type

    Factors Affecting Muscle Strength

    • Sex: males have higher muscle mass due to testosterone
    • Body weight
    • Age
    • Fitness
    • Muscle type
    • Muscle cross-sectional area

    Vascular Physiology

    • Circulatory system components: heart, blood vessels, blood
    • Blood is constantly reconditioned to maintain constant composition.
    • Reconditioning organs receive more blood than needed for metabolic processes:
      • Lungs: O2 and CO2 exchange
      • Kidneys: blood volume and electrolyte regulation
      • Skin: temperature regulation
    • Blood flow to other organs can be adjusted based on metabolic needs.
    • Brain and heart are most sensitive to disrupted blood supply.

    Distribution of Cardiac Output at Rest

    • Right side of the heart pumps 100% of blood to lungs
    • Left side of the heart:
      • 21% digestive system
      • 6% liver (hepatic portal system between digestive system and liver)
      • 20% kidneys
      • 9% skin
      • 13% brain
      • 3% heart muscle
      • 15% skeletal muscle
      • 5% bone
      • 8% other

    The Vascular Tree

    • Arteries carry blood from heart to tissues.
    • Arterioles are smaller branches of arteries.
    • Capillaries are the smallest vessels where exchange with surrounding cells occurs.
    • Venules are formed when capillaries rejoin.
    • Veins are formed when venules merge, returning blood to the heart.

    Blood Vessels

    • Vessel walls composed of alternating layers of connective tissue, smooth muscle, and epithelial cells.

    Arterioles

    • Major resistance vessels; radius can be adjusted independently to:
      • Distribute cardiac output among organs based on need
      • Regulate arterial blood pressure

    Capillaries

    • Thin-walled, small radius, extensively branched for efficient exchange
    • Sites of exchange between blood and tissues (diffusion and bulk flow)

    Slow Velocity of Flow Through Capillaries

    • Slow flow provides adequate exchange time.
    • Types of passive exchanges: diffusion and bulk flow

    Capillaries Under Resting Conditions

    • Many capillaries are closed.
    • Precapillary sphincters control blood flow into capillaries.
    • Metarteriole connects arteriole and venule.

    Independent Exchange of Solutes Across the Capillary Wall

    • Solutes cross primarily by diffusion down their concentration gradients.

    Lymphatic System

    • One-way vessel network returning interstitial fluid to blood.
    • Initial lymphatics permeate most tissues, collecting interstitial fluid (lymph).

    Blood Flow and the Pressure Gradient

    • Blood flow rate depends on pressure gradient and vessel resistance.
    • Pressure gradient is the difference between beginning and end of a vessel.
    • Resistance influenced by blood viscosity, vessel length, and vessel radius.

    Vasoconstriction and Vasodilation

    • Mechanisms adjusting arteriolar resistance.
    • Vasoconstriction: narrowing of vessel, increased resistance
    • Vasodilation: enlargement of vessel, decreased resistance, increased flow.

    Local Vasoactive Mediators

    • Endothelial cells release chemical mediators regulating arteriolar caliber.
    • Nitric oxide (NO) is a well-studied vasoactive mediator.

    The Medullary Cardiovascular Control Centre

    • Located in the medulla of the brainstem.
    • Influenced by epinephrine and norepinephrine from sympathetic stimulation of the adrenal medulla.
    • Influenced by vasopressin and angiotensin II, which play a role in fluid balance and are potent vasoconstrictors.

    The Baroreceptor Reflex

    • Short-term control adjustments occur within seconds, involving changes in cardiac output and peripheral resistance.
    • Long-term control adjustments take minutes to days, adjusting total blood volume through urine output and thirst regulation.
    • Arterial baroreceptors located in carotid arteries and the aortic arch.

    Components of the Blood

    • Plasma: 90% water, containing albumins, globulins, and fibrinogen.
    • Erythrocytes (red blood cells): important for O2 transport.
    • Leukocytes (white blood cells): immune system's mobile defense units.
    • Platelets (thrombocytes): cell fragments involved in hemostasis.

    Erythrocytes (Red Blood Cells)

    • Lack nucleus, organelles, and ribosomes.
    • Biconcave disc shape provides larger surface area for O2 diffusion and thinness allows for rapid diffusion.
    • Flexible membrane allows erythrocytes to travel through narrow capillaries.

    Haemoglobin

    • Found only in red blood cells, contains iron.
    • Reddish when oxygenated, bluish when deoxygenated.
    • Two parts: globin portion (four polypeptide chains) and heme groups bound to each polypeptide.

    Erythrocytes' Short Life Span

    • RBCs survive for about 120 days.
    • Spleen removes old erythrocytes from circulation.
    • Erythropoiesis (RBC production) occurs in red bone marrow.
    • Erythropoietin, secreted by the kidneys, stimulates RBC production.

    ABO Blood Types

    • Blood types determined by surface antigens on erythrocytes.
    • Type A blood contains A antigens.
    • Type B blood contains B antigens.
    • Type AB blood contains both A and B antigens.
    • Type O blood contains neither A nor B antigens.
    • Antibodies against foreign RBC antigens develop in plasma after six months of age.

    Rh Blood Types

    • Rh-positive blood contains the Rh factor.
    • Rh-negative blood lacks the Rh factor.
    • Anti-Rh antibodies are produced only by Rh-negative individuals after exposure to Rh-positive blood.

    Leukocytes (White Blood Cells)

    • Immune cells: neutrophils, eosinophils, basophils, monocytes, lymphocytes.

    Platelets (Thrombocytes)

    • Cell fragments from megakaryocytes, lack nuclei.
    • High concentrations of actin and myosin.
    • Functional for about 10 days, removed by tissue macrophages.
    • Thrombopoietin, produced by the liver, stimulates megakaryocyte production and platelet production.

    Haemostasis

    • Prevents blood loss from damaged vessels.
    • Three steps: vascular spasm, platelet plug formation, blood coagulation.

    Psychoneuroimmunology

    • Field studying interactions between the nervous, immune (and endocrine) systems.
    • Brain was previously considered "immunoprivileged" due to the blood-brain barrier and lack of lymphatic system.
    • Brain is now regarded as "immunologically unique".

    Communication Between CNS and Immune System

    • Immune system messengers (cytokines) transported from periphery to brain.
    • Cytokines activate afferent nerves (like the vagus nerve).
    • Circumventricular organs are brain regions lacking the blood-brain barrier, facilitating communication.
    • Shared language: receptors and ligands (peptides, steroids, cytokines).

    Neuroimmunology: Areas of Study

    • Brain: immune interactions with the CNS.
    • Brain: microglia and neuron maintenance.
    • Lymphatic vessels: immune-CNS interactions.
    • Brain and spinal cord: protective immunity.
    • Cervical lymph nodes and spleen: nervous system interactions.
    • Gut: immune system-CNS interactions involving the microbiota.

    Neuroimmune System: Microglia

    • Permanent resident immune cells of the CNS, located throughout the brain.
    • "Police officers" of the brain, respond to injury, trauma, and diseases.
    • Constantly sampling their environment, monitoring synapses.

    Role of Neuroimmune System in Brain Development

    • Microglia prune excess synapses during brain development.
    • Aberrant synaptic pruning associated with developmental disorders (schizophrenia, ASD).
    • Neuroimmune system essential for neurogenesis, neuronal migration, synaptogenesis, angiogenesis, myelination, and apoptosis.

    Impacts of Early Immune Activation

    • Disturbances to the neuroimmune system impact brain development.
    • Maternal immune activation can affect brain development (unknown mechanism).
    • Examples: 1957 Influenza epidemic (increased risk of schizophrenia), 1964 rubella pandemic (increased risk of autism and schizophrenia).
    • Maternal Immune Activation (MIA) model:
      • Poly(I:C) mimics viral infection
      • Lipopolysaccharide (LPS) mimics bacterial infection
      • Effects: behavioral and brain
    • MIA may prime individuals for disease.

    Primary and Secondary Lines of Defence

    • Primary lines of defense are barriers preventing entry of foreign material.

    Aldosterone and ADH

    • Aldosterone (secreted by adrenals) increases salt and water reabsorption in the bloodstream to increase blood volume and restore blood pressure levels.
    • ADH (vasopressin, secreted by the posterior pituitary) promotes water retention (collecting duct) and concentrates urine.
    • Caffeine and alcohol inhibit ADH, leading to dehydration.

    Functional Anatomy of Urine Production and Excretion

    • Kidneys are the main urine production organ.
    • Bladder, urethra, and ureter are involved in urine excretion.

    Regions of the Nephron

    • Nephrons originate in the cortex.
    • Glomerulus filters protein-free plasma into the tubular component.
    • Peritubular capillaries supply renal tissue and exchange fluid with the tubular lumen.
    • Bowman's capsule collects glomerular filtrate.
    • Proximal convoluted tubule reabsorbs ions, glucose, and water.
    • Loop of Henle creates a concentration gradient to pump water back into the blood.
    • Distal convoluted tubule recycles urea and further concentrates urine.

    Cortical and Juxtamedullary Nephrons

    • Cortical nephrons (more abundant) have glomeruli in the outer cortex.
    • Juxtamedullary nephrons have glomeruli in the inner cortex and a longer Loop of Henle, performing more urine concentration.

    Filtration, Reabsorption, Secretion, and Excretion

    • Glomerular filtration is non-discriminant, filtering protein-free plasma into Bowman's capsule.
    • Reabsorption selectively moves filtered substances into the peritubular capillaries.
    • Secretion moves non-filtered substances from peritubular capillaries into the tubular lumen.
    • Excretion is the removal of waste products in urine.

    Vasopressin and Aldosterone Effects

    • Vasopressin, also known as antidiuretic hormone (ADH), helps the body retain water, contributing to hydration.
    • Aldosterone causes the kidneys to increase salt and water reabsorption into the bloodstream, increasing blood volume.
    • This increase in blood volume helps restore normal levels of salt and water.
    • Vasopressin's primary action is to increase water uptake in the collecting duct of the kidney, concentrating the urine.

    Micturition Reflex and Voluntary Control

    • Micturition, the process of urination, is regulated by both reflex and voluntary control.
    • The micturition reflex is triggered when stretch receptors in the bladder wall are stimulated by increased distention.
    • Afferent fibers transmit impulses to the spinal cord, activating the parasympathetic nervous system to the bladder.
    • This stimulation inhibits the motor neuron supply to the external sphincter, causing bladder contraction and relaxation of the external sphincter.
    • The process allows urine expulsion and represents the primary control mechanism in infants.
    • In voluntary control, the same process occurs with the key difference being that bladder fullness is felt before the external sphincter relaxes.
    • This voluntary control is learned and developed through potty training in children.
    • The external sphincter can be deliberately relaxed, along with the pelvic diaphragm, to initiate urination.

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    Description

    Explore the key processes involved in muscle contraction, including the roles of acetylcholine, calcium ions, and the sarcoplasmic reticulum. This quiz highlights the steps from action potential to muscle relaxation, providing a comprehensive understanding of muscle physiology.

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