Muscular System Part 1 PDF

Human Physiology Muscular System Fundamentals Dr. Talton  After this section you will be able to: Describe the 4 functions and 4 characteristics of muscle Describe skeletal muscle structure Differentiate between the three kinds of muscle Describe origins, insertions, agonists,...

Human Physiology Muscular System Fundamentals Dr. Talton  After this section you will be able to: Describe the 4 functions and 4 characteristics of muscle Describe skeletal muscle structure Differentiate between the three kinds of muscle Describe origins, insertions, agonists, antagonists and synergists Describe the microscopic anatomy of a skeletal muscle fiber  Muscle Muscle is an organ: made of muscle tissue, blood vessels, nerves, fat, and other connective tissues Nearly 50% body’s mass is muscle Loading… Three types of muscle tissue Skeletal Myo: muscle Cardiac Sarco: flesh = muscle Smooth  Overview of Muscle Function Transforms chemical energy into mechanical energy  Muscle Functions Four main functions 1. Movement: responsible for all locomotion and manipulation Loading… Example: walking, digesting, pumping blood 2. Maintain posture and body position 3. Stabilize joints 4. Generate heat as they contract  Malignant hyperthermia is a severe reaction to certain drugs used for anesthesia. Without prompt treatment, the complications caused by malignant hyperthermia can be fatal.  What is a muscle fiber? Muscle fiber is the term given to skeletal and cardiac muscle cells Muscle cells fuse together to form cylindrical “fibers” Skeletal fibers are multinucleate Skeletal and cardiac fibers have multiple mitochondria https://doi.org/10.3389/fphys.2021.682091  Skeletal Muscle Almost all over the body Skeletal muscle fibers are the longest Have striations (stripes) Voluntary Consciously controlled Contract rapidly; fatigue easily  Cardiac Muscle Makes up bulk of heart walls Contain shorter muscle fibers Striated: less so than skeletal fibers Involuntary Cannot be controlled consciously Contraction regulated by pacemaker Responds to medulla oblongata to increase/decrease rate  Smooth muscle Primarily in walls of hollow organs Ex: stomach, urinary bladder, blood vessels, and airways Also in other areas: ocular, arrector pili, etc. Non-striated Involuntary: cannot be controlled consciously  Characteristics of Muscle Tissue All muscles share four main characteristics: 1. Excitability (responsiveness): ability to receive and respond to stimuli 2. Loading… Contractility: ability to shorten forcibly when stimulated 3. Extensibility: ability to be stretched/extend 4. Elasticity: ability to recoil to resting length  Gross anatomy of skeletal muscle: Hierarchy of organization Muscle organ level Fascicle tissue level Muscle fiber cellular level  Muscle Attachments Muscles span joints and attach to bones Muscles attachments are split into two classes: Insertion: attachment to movable bone/s Origin: attachment to stationary bone/s A B  Muscle Actions and Interactions What one muscle group “does,” another “undoes” 3 main functional groups: Prime mover (agonist) Produces specific movement Antagonist Opposes or reverses that movement Prime mover and antagonist are located on opposite sides of joint across which they act  Muscle Actions and Interactions Synergist helps prime movers Adds extra force to same movement Reduces “noise” – stops movements that are not needed Skeletal Muscles: Functional Groups Same muscle may act as a: Prime mover in one movement Antagonist for a different movement Synergist for a third movement  Microscopic Anatomy: Muscle fiber A skeletal muscle fiber is a long cylindrical fusion of cells: multinucleate Sarcolemma: muscle fiber plasma membrane Deep to endomysium Sarcoplasm: muscle fiber cytoplasm The muscle fiber contains modified organelles Myofibril Sarcolemma T-tubules are invaginations of plasma Sarcoplasmic reticulum (SR) network of smooth endoplasmic reticulum surrounding each myofibril Sarcoplasmic Reticulum and T Tubules Sarcoplasmic reticulum: network of smooth endoplasmic reticulum tubules surrounding each myofibril Stores and releases Ca2+ T tubules Invaginations of sarcolemma Increase sarcolemma’s surface area Allow electrical nerve transmissions to reach every myofibril  Myofibrils Myofibril: muscle organelle Repeating contractile units called sarcomeres (Zdisc Zdisc) Sarcomeres are made of actin and myosin filaments  Myofibrils Sarcomeres give muscles striations A band: actin and myosin filaments cross over I band: only actin present  Myofibrils Striations on a skeletal muscle fiber are caused by repeated A-bands and I-bands  Myosin (thick) filament Myosin is a dimer 2 molecules wound at the tails Heads bind to ATP A myosin filament is formed when clusters of myosin proteins bind  Actin (Thin) Filament 2 actin chains twisted into a helix Contains two regulatory proteins Tropomyosin Long chain blocks myosin binding sites Troponin Bound to tropomyosin Has Ca2+ binding sites Actin and Myosin filaments overlap Myosin : thick filaments Actin : thin filaments Loading… Titin and nebulin Human Physiology Skeletal Muscle Contraction Dr. Talton  After this section you will be able to: Describe in detail the 4 steps of skeletal muscle contraction Discuss ATP production for muscle contraction Differentiate between the three types of muscle fiber Discuss how muscle responds to different types of exercise, and inactivity The sliding filament model Contraction takes place by the sliding of myosin (thick filaments) across actin (thin) filaments Loading… Relaxed Contracted Skeletal muscles are stimulated by motor neurons Decision to move is made in the brain, signal is transmitted down spinal cord to motor neurons which activate muscle fibers Loading…  Four steps for skeletal muscles to contract 1. Events at neuromuscular junction 2. Muscle fiber excitation 3. Excitation-contraction coupling 4. Cross bridge cycling  Neuromuscular Junction 1. Action potential arrives at axon terminal 2. Voltage-gated calcium channels open, calcium enters motor neuron 3. Calcium entry causes release of Acetylcholine (Ach) from synaptic vesicles into synaptic cleft  Excitation of the Muscle Fiber 4. ACh diffuses to nicotinic receptors (ligand-gated sodium channels) on sarcolemma 5. ACh binding opens channel, allowing Na+ to enter action potential in the muscle fiber. 6. Acetylcholinesterase degrades Ach vents at the Neuromuscular Junction lead to excitation of the muscle fiber  Excitation-Contraction (E-C) Coupling Physiological process that links the electrical excitation of a muscle cell to its contraction. Anatomy for E-C coupling Myofibril Sarcolemma T-tubules are invaginations of Loading… plasma Sarcoplasmic reticulum (SR) network of smooth endoplasmic reticulum surrounding each myofibril  E-C Coupling Action Potential travels along sarcolemma into T tubules. Voltage-sensitive dihydropyridine receptors (DHPRs) on T tubules open. This "pulls" on SR Ryanodine receptors (calcium channels), opening them and allowing the release of stored calcium ions (Ca²⁺) into the sarcoplasm. Excitation-Contraction (E-C) Coupling  1. Events at neuromuscular junction 2. Muscle fiber excitation 3. Excitation-contraction coupling 4. Cross bridge cycling How does Ca2+ release lead to contraction?  Actin is regulated by calcium-sensitive proteins Tropomyosin blocks myosin binding sites Troponin binds tropomyosin Has Ca2+ binding sites Calcium binds to troponin, causing a conformational change This shifts tropomyosin, exposing myosin binding sites on actin. Ca2+ binding to troponin enables actin-myosin binding At low intracellular Ca2+ concentration: Myosin cannot attach to actin Muscle fiber remains relaxed a2+ binding to troponin enables actin-myosin binding At higher intracellular Ca2+ concentrations Ca2+ binds to troponin Troponin moves tropomyosin, revealing myosin-binding sites Myosin binds to actin, forming a cross-bridge Cross bridge cycle 1. ADP-bound myosin head tightly binds to actin Cross bridge cycle 1. ADP-bound myosin head tightly binds to actin 2. Using energy stored from ATP hydrolysis, myosin head undergoes a “power stroke” releasing ADP Cross bridge cycle 1. ADP-bound myosin head tightly binds to actin 2. Using energy stored from ATP hydrolysis, myosin head undergoes a “power stroke” releasing ADP 3. ATP binds the myosin head, releasing it from actin Cross bridge cycle 1. ADP-bound myosin head tightly binds to actin 2. Using energy stored from ATP hydrolysis, myosin head undergoes a “power stroke” releasing ADP 3. ATP binds the myosin head, releasing it from actin 4. ATP is hydrolyzed and the myosin head stores the energy for the next power stroke ATP is needed to "reset" the muscle ATP releases the myosin head from actin ATP drives the Na/K pump ATP also drives the SERCA pump: Sarcoplasmic Reticulum Calcium ATPase o reuptake of Ca2+ by the S.R.  Sources of ATP Muscle fibers store oxygen (myoglobin) and glucose (glycogen) Glycolysis Quick No oxygen required Small amount of ATP produced Glucose → 2Pyruvate + 2ATP + 2NADH 2 Pyruvate + 2NADH → 2Lactic Acid + 2NAD+  Sources of ATP Muscle fibers store oxygen (myoglobin) and glucose (glycogen) Aerobic respiration (citric acid cycle and electron transport chain) Slow Oxygen required Large amount of ATP produced. C6H12O6 + 6O2 → 6CO2 + 6H2O + 36- 38ATP  Sources of ATP Phosphocreatine breakdown produces a short burst of energy Helps regenerate ATP during high- intensity, short-duration exercises Skeletal Muscle is classified by speed and fatigue resistance Slow twitch and fast twitch fibers differ in their structure, function, and how they generate energy. Each muscle contains both types of fibers proportion varies depending on the muscle's function and the individual's training. Slow twitch (Type I) fibers Structure: Small diameter Function: Endurance activities Energy Source: Aerobic respiration Contraction Speed: Slow to contract, and slow to fatigue. Color: Lots of myoglobin, mitochondria and blood supply give a red appearance. How Muscles Respond to Exercise Aerobic (endurance) exercise, such as jogging, swimming, biking leads to increased: Muscle capillaries Loading… Number of mitochondria Results in resistance to fatigue  Fast-twitch fibers (Type IIA) - Intermediate Structure: Larger diameter Function: Power and speed. Energy Source: Aerobic respiration + Glycolysis (generates energy quickly) Contraction Speed: Contract rapidly, but fatigue quickly. Color: Appear pink Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved  Fast-twitch fibers (Type IIB/X) Structure: Large diameter Function: Short bursts of power and speed Energy Source: Primarily glycolysis Contraction Speed: Contract rapidly; fatigue quickly. Color: Pale Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved  How Muscles Respond to Exercise Resistance exercise, such as weight-lifting or isometric exercises, leads to Increased mitochondria, glycogen stores Increased muscle size (hypertrophy) and strength Can gain 50% more muscle within a year Fast-twitch and slow-twitch muscles  Muscle Fiber Recruitment During High- Intensity Exercise Dynamic Recruitment: Starts with Type I (slow-twitch): Energy-efficient, recruited first. Adds Type IIa (fast oxidative): For moderate power demands. Engages Type IIx (fast-twitch): High force output for intense efforts. Body continuously adjusts fiber recruitment based Hu et al, 2021 Homeostasis & Homeostatic Imbalance Muscles can adapt to work as a homeostatic norm They “plateau” They must be overloaded to produce further gains. Inactivity doesn’t cause plateau, instead it weakens and diminishes muscle strength and size. Muscle strength can decline 5% per day  Homeostatic Imbalance Paralyzed muscles may atrophy (shrink) to one-fourth initial size If fibrous connective tissue replaces lost muscle tissue rehabilitation is impossible Human Physiology Heart Anatomy & Blood Flow Dr. Talton  After this section you will be able to: Describe the gross anatomy of the heart Describe the role of heart valves in unidirectional blood flow Illustrate and describe the pulmonary and systemic circuits  Loading… Approximately the size of a fist, less than 1 lb Gross Anatomy of the Heart Gross Anatomy of the Heart: Walls Composed of three layers Endocardium Lines inner heart; branches into vessels Myocardium Loading… Cardiac muscle; contracts to pump blood Epicardium Extension of the serosa  Gross Anatomy of the Heart: Membranes Serous membrane of the heart is called pericardium Thin, double-layered membranes Separated by a serous cavity filled with serous fluid Fluid secreted by both layers of membrane Parietal pericardium is external lining Visceral pericardium covers the heart (epicardium)  Gross Anatomy of the Heart: Chambers Atria are the superior chambers of the heart Intertrial septum separates the left and right atrium Ventricles are the inferior chambers of the heart Larger; thicker myocardium Interventricular septum separates the left and right ventricles In the 17th Century William Harvey discovered the path of blow flow Galen believed there were two types of blood flowing to the body blood made in the lungs flowed in arteries blood made in the liver flowed in veins Harvey discovered unidirectional flow  Harvey’s experiment Taken with an infra-red camera to make blood more visible. Credit: Dave Ansell Blood flows unidirectionally Heart valves ensure unidirectional flow Atrioventricular valves located between atria and ventricles Tricuspid (right) and mitral (right) valves Semilunar valves located between ventricles and major arteries Loading… Pulmonary (right) and aortic (left) valves Valves open in response to pressure Gross Anatomy of the Heart Physiology of blood flow: AV Valves Physiology of blood flow: AV Valves Physiology of blood flow: Semilunar Valves Physiology of blood flow: Semilunar Valves  Basic overview of circulation: double circuit 1. Deoxygenated blood from body enters right side of the heart. 2. Deoxygenated blood is pumped into the lungs 3. Oxygenated blood from lungs enters left side of the heart 4. Oxygenated blood is pumped into the whole body  Circulation: Pulmonary Circulation Superior vena cava and Inferior vena cava Bring deoxygenated blood from the body to the right atrium Circulation: Pulmonary Circulation Deoxygenated blood in right atrium puts pressure on AV valve Tricuspid valve opens and blood rushes into the right ventricle https://www.quora.com/What-are-the-differences-between-the-ventricle-and-atrium-of-a-heart  Circulation: Pulmonary Circulation Right ventricle pumps deoxygenated blood into the pulmonary trunk through the pulmonary valve Left and right pulmonary arteries take deoxygenated blood to the lungs  Circulation: Pulmonary Circulation Left and right pulmonary veins (4) bring oxygenated blood to the left atrium Blood drains into the left ventricle through the mitral (bicuspid) valve Pulmonary circulation sets the stage for systemic circulation The heart pumps oxygenated blood around the body (including to itself and to the lungs!)  Circulation: Systemic Circulation Left ventricle pumps oxygenated blood to the aorta through aortic semilunar valve Aorta branches into various arteries to take blood around the body: systemic circulation  Study Tip: sketch the pathway of blood Right side of the heart Left side of the heart 1. Superior and inferior vena cava → F F F F 2. Right atrium → F 6. F 7. F 3. Tricuspid valve → 8. F 9. Four pulmonary veins 4. Right ventricle → → 5. Pulmonary semilunar valve → 6. Pulmonary trunk → 10. Left atrium → 7. Pulmonary arteries → 11. Mitral valve → 8. Lungs 12. Left ventricle → 13. Aortic semilunar valve → 14. Aorta → 15. Systemic circulation!!!  Study Tip: sketch the pathway of blood Right side of the heart Left side of the heart 1. Superior and inferior vena cava → F F F F 2. Right atrium → F 6. F 7. F 3. Tricuspid valve → 8. F 9. Four pulmonary veins 4. Right ventricle → → 5. Pulmonary semilunar valve → 6. Pulmonary trunk → 10. Left atrium → 7. Pulmonary arteries → 11. Mitral valve → 8. Lungs 12. Left ventricle → 13. Aortic semilunar valve → 14. Aorta → 15. Systemic circulation!!! Terminology: Match the letter to the definitions. If a term is undefined; define it at the end. 1. _i__ Thin filament. 2. _j__ Store neurotransmitters, and following a Ca2+ driven signal, release neurotransmitters. 3. _d__ The space/cleft in between the axon terminal and the muscle fiber. 4. _n__ The functional unit of the muscle fiber. 5. __a_ The ion responsible for depolarizing the muscle membrane by traveling through the ligand-gated channel down its electrochemical gradient. 6. __p_ Located on the sarcoplasmic reticulum and once opened, allows Ca2+ to flow from the sarcoplasmic reticulum into the sarcoplasm. Should read “mechanically-gated channels” 7. __g_ Thick filament 8. __k_ A neurotransmitter responsible for binding the ligand-gated channel at the neuromuscular junction. 9. _o__ This organelle is a rod of repeating sarcomeres 10. _f__ These invaginations allow depolarization of the muscle membrane to quickly penetrate from the sarcolemma to the myofibril. 11. _m__ The plasma membrane of a muscle fiber. 12. _e__ The enzyme responsible for stopping the depolarization of the muscle membrane at the neuromuscular junction. 15. __l_ An electrical change which makes the inside of the cell more positive 16. __h_ Modified endoplasmic reticulum in the muscle fiber that stores and releases calcium. A Label A, C, D and E on the muscle fiber shown below: A: MYOFIBRILS B: MITOCHONDRIA C: T- TUBULE D: SARCOLEMMA E: SARCOPLASMIC RETICULUM SARCOMERE Z DISC Label the (i) sarcomere, A BAND I BAND I BAND (ii) A band, (iii) I bands, and (iv) Z discs in both the electron microscope image and cartoon representation below Human Physiology Cardiovascular physiology Dr. Talton  After this section you will be able to: Describe the structure of cardiac muscle Describe the generation of action potentials in the heart Recognize key features of an electrocardiogram and the cardiac cycle Comparing the 3 types of muscle Loading… Silverthorn, Pearson  Cardiac muscle fundamentals Cardiac muscle fibers have one nucleus Branched Linked via intercalated disks (part of the sarcolemma) Intercalated discs: desmosomes and gap junctions Desmosomes connect the cells Gap junctions electrically link them: allow ion flow Loading… Cardiac muscle action potentials Cardiac muscle action potentials: ion channels 1. Voltage-Gated Sodium Channels: Opening Voltage: Around -70 mV (threshold) Closing Voltage: Around +20 mV (inactivation follows) 2. Fast Potassium Channels : Opening Voltage: Around +20 mV (after depolarization) Closing Voltage: Around 0 mV, after the brief repolarization phase. 3. Calcium Channels: Opening Voltage: Around -40 mV (begin to open during early depolarization) Closing Voltage: +10 mV to 0 mV (close toward the end of the plateau phase) 4. Slow Potassium Channels : Opening Voltage: Begin to open at around 0 mV (as the plateau phase ends) Closing Voltage: Fully close as the membrane returns to resting potential (-90 mV) Plateau phase prevents sustained contractions Allows relaxation in between each heartbeat Heart fills back up with blood Where does a heartbeat come from? Cardiac muscle is controlled by: Pacemaker cells (1% of cardiomyocytes that spontaneously depolarize) The autonomic nervous system Epinephrine (stress hormone) Pacemaker cells Cardiac muscle cells typically depolarize and contract without nervous system stimulation Pacemaker cells spontaneously depolarize and send impulses to the rest of the cardiac muscle cells through gap junctions Pacemaker cells The sinoatrial node (SA) depolarizes the atria Atria contract The impulse travels to the ventricles through the Loading… atrioventricular (AV) node and the AV bundle Ventricles contract https://www.youtube.com/watch?v=C1AoNYyeA50&feature=emb_title Electrocardiography Electrocardiography An electrocardiogram (ECG) records electrical signals in the heart P wave: depolarization wave from the SA node through the atria. QRS complex results from ventricular depolarization T wave caused by ventricular repolarization  The cardiac cycle Cardiac cycle: blood flow through heart during one heartbeat Systole: period of heart contraction Ventricles contract Eject blood to pulmonary trunk and aorta Diastole: period of heart relaxation Ventricles relax Ends with contraction of atria releasing blood into ventricles The cardiac cycle Phas of th card cycl  Human Physiology Blood Vessels & Blood Pressure Dr. Talton After this section you will be able to: Describe the structure and function of blood vessels Interpret blood pressure values Explain how blood pressure is distributed in blood vessels Describe the baroreceptor reflex Blood Vessel Structure and Function Blood vessels: circulatory system Arteries: carry blood away from heart; oxygenated except pulmonary circulation and umbilical vessels Loading… Veins: carry blood toward heart; deoxygenated except for pulmonary circulation and umbilical vessels Capillaries: tiny vessels between A & V; contact with tissue cells Blood circulates in blood vessels Arteries branch into smaller arterioles Veins converge from smaller venules Capillaries are the site of transfer of nutrients, gas, etc  Blood vessel walls Walls of blood vessels differ Endothelium (inner layer; the same in all) Elastic connective tissue Smooth muscle Fibrous connective tissue Loading… Endothelium Secretes chemical signals that regulate blood pressure, blood vessel growth, and absorption  Blood Pressure Blood pressure (BP): force of blood exerted on wall of blood vessel Expressed in mm Hg Measured in arteries near the heart when your heart contracts when your heart is at rest and pumps blood out between beats systolic/diastolic (e.g., 120/80 mmHg)  Pressure readings: how much higher the pressure is compared to atmospheric pressure. Systolic pressure of 120 mmHg means 120 mmHg above the atmospheric pressure.  Veins Low blood pressure; adaptations ensure return of blood to heart Muscular pump: contraction of skeletal muscles “milks” blood back toward heart Venous valves: prevent backflow of blood  What does blood pressure tell us? Efficiency of cardiac muscle Can the heart supply the body without straining? Flexibility/elasticity of arteries Narrow, stiff, or blocked arteries increase resistance to blood flow  Blood pressure ranges Healthy BP (