Muscle Anatomy and Functions Quiz
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Muscle Anatomy and Functions Quiz

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Questions and Answers

What is the smallest muscle in the human body?

  • Flexor digiti minimi
  • Temporalis
  • Stapedius (correct)
  • Sternocleidomastoid

    • Which of the following muscles is considered the biggest in the human body?

  • Gluteus Maximus (correct)
  • Latissimus Dorsi
  • Rectus Abdominis
  • Biceps Brachii

    • Skeletal muscle tissue can be characterized by which of the following features?

  • Involuntary control
  • Smooth shaped cells
  • Multinucleate and striated (correct)
  • Branching filaments

    • What function does cardiac muscle primarily serve?

    <p>Pumping blood throughout the body</p> Signup and view all the answers

    Which type of muscle tissue is controlled voluntarily?

    <p>Skeletal muscle</p> Signup and view all the answers

    How many muscles are typically found in the human face?

    <p>60</p> Signup and view all the answers

    What characteristic of muscle tissue allows it to respond to stimuli?

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

    Which of the following statements about muscle control is false?

    <p>Smooth muscle is voluntary.</p> Signup and view all the answers

    In which situation is temporal summation likely contributing to tetany?

    <p>Carrying a very heavy load</p> Signup and view all the answers

    What could be a characteristic of Olympic medalist Hidilyn Diaz regarding her muscle contractions?

    <p>She has a higher ratio of fast-twitch muscle fibers compared to most people</p> Signup and view all the answers

    Which statement about muscle hypertrophy in Olympic weightlifters is most likely accurate?

    <p>Her muscles have mostly experienced functional hypertrophy</p> Signup and view all the answers

    When would central fatigue likely be reduced in an athlete like Hidilyn Diaz?

    <p>If she utilizes proper technique during lifts</p> Signup and view all the answers

    What might differentiate Hidilyn Diaz's muscle attachments compared to an average individual?

    <p>Her muscles may have a greater cross-sectional area</p> Signup and view all the answers

    What is the primary role of the diaphragm during respiration?

    <p>Separates the thoracic cavity from the abdominal cavity.</p> Signup and view all the answers

    Which muscle group is primarily responsible for flexing the leg at the knee?

    <p>Hamstring group</p> Signup and view all the answers

    Which muscle allows for the rotation of the forearm laterally during supination?

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

    What is the characteristic shape of a unipennate muscle?

    <p>Feather-shaped</p> Signup and view all the answers

    Which muscle is involved in abducting the thigh and rotating it medially?

    <p>Gluteus medius</p> Signup and view all the answers

    What types of connective tissues attach muscles to bones?

    <p>Tendons and aponeuroses</p> Signup and view all the answers

    Which muscle group primarily extends the leg at the knee?

    <p>Quadriceps group</p> Signup and view all the answers

    Which skeletal muscle is responsible for closing the jaw?

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

    Which term refers to the fleshy part of the muscle between the origin and insertion?

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

    What does a pennate arrangement of muscle fibers allow for?

    <p>Enhanced strength</p> Signup and view all the answers

    Which type of muscle contraction is characterized by muscle length changing during contraction?

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

    What primarily contributes to cellular damage after exercise?

    <p>Eccentric contraction</p> Signup and view all the answers

    What causes central fatigue in muscle performance?

    <p>Decreased ability to activate motor neurons</p> Signup and view all the answers

    Which method of energy production for muscle contraction utilizes the body’s stored glucose?

    <p>Aerobic respiration</p> Signup and view all the answers

    What is the primary symptom associated with peripheral fatigue?

    <p>Muscle soreness</p> Signup and view all the answers

    Which process occurs during oxygen debt when skeletal muscles are used strenuously?

    <p>Conversion of pyruvic acid to glucose</p> Signup and view all the answers

    What are the conditions causing muscle fatigue?

    <p>Build-up of lactic acid and blood supply interruption</p> Signup and view all the answers

    What characterizes the process of muscle remodeling?

    <p>Continuous increase or decrease in mass</p> Signup and view all the answers

    What is the role of creatine phosphate in muscle energy production?

    <p>Facilitates rapid ATP regeneration</p> Signup and view all the answers

    Which of the following is NOT a type of muscle contraction?

    <p>Static contraction</p> Signup and view all the answers

    What is the primary function of DHPR in heart muscle contraction?

    <p>To cause an influx of Ca+2 into the muscle cell</p> Signup and view all the answers

    Which of the following proteins is involved in binding Ca+2 within the muscle cell?

    <p>Histidine-rich calcium-binding protein</p> Signup and view all the answers

    Which channel blocker specifically affects heart muscle contraction?

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

    What role does SERCA play during muscle relaxation?

    <p>It pumps Ca+2 back into the terminal cisternae</p> Signup and view all the answers

    How does RYR function in skeletal muscle compared to cardiac muscle?

    <p>RYR is mechanically linked to DHPR.</p> Signup and view all the answers

    Which statement accurately describes the sliding filament theory?

    <p>The power stroke involves myosin pulling actin filaments.</p> Signup and view all the answers

    What is observed in the latent period of a muscle twitch myogram?

    <p>Electrical activity begins without measurable tension.</p> Signup and view all the answers

    What is the role of calsequestrin in muscle cells?

    <p>It serves as a high-capacity Ca+2 binding protein.</p> Signup and view all the answers

    What initiates the release of Ca+2 from the sarcoplasmic reticulum in muscle contraction?

    <p>Mechanical linkage between DHPR and RYR</p> Signup and view all the answers

    Which process is affected by the decrease in Ca+2 levels in muscle cells?

    <p>The exposure of actin binding sites</p> Signup and view all the answers

    What does elasticity refer to in the context of muscle function?

    <p>The capability of a muscle to regain its original length after stretching</p> Signup and view all the answers

    Which of the following describes the action of a depressor muscle?

    <p>Lowers a part</p> Signup and view all the answers

    Which term best describes the action of an abductor muscle?

    <p>Moves a part away from the midline</p> Signup and view all the answers

    What is the naming basis for the muscle known as tibialis anterior?

    <p>Location of the muscle</p> Signup and view all the answers

    What action does a constrictor muscle perform?

    <p>Compresses a body part</p> Signup and view all the answers

    Which base pertains to the shape of the muscle known as serratus?

    <p>Saw-toothed</p> Signup and view all the answers

    What does the term 'flexor' refer to in muscle classification?

    <p>Muscle that bends a part near the joint</p> Signup and view all the answers

    Which orientation is indicated by the muscle name 'deltoid'?

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

    What type of muscle contraction occurs when the muscle length remains constant while tension is developed?

    <p>Isometric contraction</p> Signup and view all the answers

    How does fiber diameter influence muscle contraction?

    <p>Larger diameter fibers are less effective in fine movements.</p> Signup and view all the answers

    What is the relationship between the number of active motor units and force produced?

    <p>More active motor units yield a stronger force.</p> Signup and view all the answers

    Which type of contraction occurs when the muscle fibers shorten while generating external work?

    <p>Isotonic contraction</p> Signup and view all the answers

    What determines the amount of tension that a muscle fiber can develop?

    <p>The length of the muscle fiber and the number of active fibers.</p> Signup and view all the answers

    Which muscle primarily compresses the abdominal wall?

    <p>Transverse abdominis</p> Signup and view all the answers

    What is the primary action of the gluteus maximus muscle?

    <p>Extends the thigh</p> Signup and view all the answers

    Which muscle is involved in lateral rotation of the forearm?

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

    How does the diaphragm contribute to respiration?

    <p>Expands the thoracic cavity</p> Signup and view all the answers

    What is a characteristic of the circular muscle arrangement?

    <p>Sphincter-like</p> Signup and view all the answers

    Which muscle group flexes the arm at the elbow and simultaneously rotates the hand laterally?

    <p>Biceps brachii</p> Signup and view all the answers

    Which term describes the connective tissue that connects muscle to bone?

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

    Which muscle group is known for extending the leg at the knee?

    <p>Quadriceps group</p> Signup and view all the answers

    What type of arrangement do muscles like the deltoid exhibit?

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

    Which muscle allows the lips to pucker?

    <p>Orbicularis oris</p> Signup and view all the answers

    What role does acetylcholinesterase play in muscle contraction?

    <p>It degrades acetylcholine to prevent continuous stimulation.</p> Signup and view all the answers

    Which channel is primarily responsible for propagating the action potential in muscle fibers after acetylcholine binds to its receptors?

    <p>Voltage-gated Na+ channels</p> Signup and view all the answers

    How does Ca+2 contribute to muscle contraction during excitation-contraction coupling?

    <p>It facilitates the interaction between myosin and actin.</p> Signup and view all the answers

    What is the primary action that takes place at the neuromuscular junction to trigger muscle contraction?

    <p>Release of acetylcholine into the synaptic cleft.</p> Signup and view all the answers

    What occurs after the action potential travels along the sarcolemma and into the T-tubules?

    <p>Dihydropyridine receptors activate ryanodine receptors.</p> Signup and view all the answers

    Which of the following statements about Ca+2 during muscle relaxation is accurate?

    <p>Ca+2 is actively transported back into the sarcoplasmic reticulum.</p> Signup and view all the answers

    Which component primarily interacts with Ca+2 to facilitate muscle contraction?

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

    What initiates the release of Ca+2 from the sarcoplasmic reticulum?

    <p>Depolarization of the T-tubules by action potential.</p> Signup and view all the answers

    What is the role of the ryanodine receptor (RYR) in muscle contraction?

    <p>It facilitates the release of Ca+2 from the sarcoplasmic reticulum.</p> Signup and view all the answers

    What occurs during the period of relaxation in muscle contraction?

    <p>Calcium ions are pumped back into the sarcoplasmic reticulum.</p> Signup and view all the answers

    What characterizes complete (fused) tetanus?

    <p>Individual contractions are indistinguishable.</p> Signup and view all the answers

    What is the primary function of extrafusal fibers?

    <p>To provide the main force-generating structure of the muscle.</p> Signup and view all the answers

    Which type of motor neuron innervates intrafusal fibers?

    <p>Gamma motor neurons.</p> Signup and view all the answers

    How does incomplete (unfused) tetanus differ from complete (fused) tetanus?

    <p>Incomplete tetanus exhibits a noticeable oscillation of peak tension.</p> Signup and view all the answers

    What is the definition of a motor unit?

    <p>A motor neuron and the muscle fibers it innervates.</p> Signup and view all the answers

    What leads to smooth and continuous muscle movement?

    <p>Summation of individual twitches at high frequency.</p> Signup and view all the answers

    Which function is primarily associated with the lateral rectus muscle?

    <p>Abducting the eye.</p> Signup and view all the answers

    What happens to contractile force during the decline of active cross bridges?

    <p>Contractile force gradually declines.</p> Signup and view all the answers

    What type of muscle contraction occurs when a muscle lengthens while under tension?

    <p>Eccentric contraction</p> Signup and view all the answers

    Which of the following contributes most to cellular damage after exercise?

    <p>Eccentric contraction</p> Signup and view all the answers

    What is the primary cause of peripheral fatigue in muscle fibers?

    <p>Accumulation of metabolic waste</p> Signup and view all the answers

    What is the primary effect of oxygen debt in muscle metabolism?

    <p>Accumulation of lactic acid</p> Signup and view all the answers

    Which of the following is NOT a characteristic of muscle remodeling?

    <p>Fatigue resistance</p> Signup and view all the answers

    What is the primary function of skeletal muscle tissue?

    <p>Movement of bone</p> Signup and view all the answers

    Which type of muscle tissue is characterized by multinucleated fibers?

    <p>Skeletal muscle</p> Signup and view all the answers

    Which muscle is considered the longest muscle in the human body?

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

    What characteristic of muscle tissue allows it to be stretched beyond its normal length?

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

    Which of the following describes the control mechanism of smooth muscle?

    <p>Involuntary control</p> Signup and view all the answers

    Which muscle is known as Ms. Mhin's favorite muscle in the body?

    <p>Rectus Abdominis</p> Signup and view all the answers

    What is the primary role of cardiac muscle tissue?

    <p>Beating of the heart</p> Signup and view all the answers

    What is the biggest muscle in the human body?

    <p>Gluteus Maximus</p> Signup and view all the answers

    What is the primary function of the diaphragm during respiration?

    <p>Separates the thoracic cavity from the abdominal cavity</p> Signup and view all the answers

    Which muscle is responsible for flexing the arm at the elbow?

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

    What type of muscle arrangement is described as strap-like?

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

    Which of the following muscle groups is primarily responsible for extending the leg at the knee?

    <p>Quadriceps group</p> Signup and view all the answers

    Which muscle allows for the rotation of the forearm medially during pronation?

    <p>Pronator teres</p> Signup and view all the answers

    What do tendons connect?

    <p>Muscle to bone</p> Signup and view all the answers

    What is the primary role of the orbicularis oris muscle?

    <p>Puckering the lips</p> Signup and view all the answers

    Which muscle group assists in compressing the abdominal wall?

    <p>Rectus abdominis</p> Signup and view all the answers

    Which of the following muscles is part of the hamstring group?

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

    What is the action of the flexor digitorum profundus muscle?

    <p>Flexes the distal joints of the fingers</p> Signup and view all the answers

    What type of contraction involves muscle length being held constant while tension is generated?

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

    How does the diameter of a muscle fiber affect force production?

    <p>Larger diameter leads to more force</p> Signup and view all the answers

    What determines the type of movement produced by muscle fibers per motor unit?

    <p>Fewer fibers lead to finer movements</p> Signup and view all the answers

    What happens to muscle fibers during isometric contraction?

    <p>They remain the same length</p> Signup and view all the answers

    Which of the following factors contributes to the strength of contraction in muscles?

    <p>Fiber length and diameter combined</p> Signup and view all the answers

    What characterizes an isotonic contraction?

    <p>Change in muscle length with constant force</p> Signup and view all the answers

    The force generated by a muscle fiber is affected by what relationship between fiber length and tension?

    <p>Longer fibers generate more tension</p> Signup and view all the answers

    Which statement correctly describes the relationship between the number of active motor units and the force produced?

    <p>More units activated lead to greater force production</p> Signup and view all the answers

    Which factor does NOT affect the threshold of a muscle fiber?

    <p>Fiber length</p> Signup and view all the answers

    The active shortening of sarcomeres contributes to what type of muscle contraction?

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

    What initiates the release of Ca+2 from the sarcoplasmic reticulum?

    <p>Action potential traveling through T-tubules</p> Signup and view all the answers

    What is the role of acetylcholinesterase at the neuromuscular junction?

    <p>To degrade acetylcholine</p> Signup and view all the answers

    Which step follows the influx of Ca+2 into the muscle fiber?

    <p>Interaction of myosin and actin occurs</p> Signup and view all the answers

    What primarily causes muscle relaxation after contraction?

    <p>Ca+2 being pumped back into the sarcoplasmic reticulum</p> Signup and view all the answers

    What is the primary function of dihydropyridine receptors (DHPR) in muscle contraction?

    <p>Activating ryanodine receptors</p> Signup and view all the answers

    Which process follows the binding of acetylcholine to its receptor on the muscle membrane?

    <p>Opening of voltage-gated Na+ channels</p> Signup and view all the answers

    What structure facilitates the transmission of action potentials deep into muscle fibers?

    <p>T-tubules</p> Signup and view all the answers

    Which ions are primarily involved in the muscle contraction mechanism?

    <p>Ca+2 and Na+</p> Signup and view all the answers

    What occurs at the terminal cisternae during muscle contraction?

    <p>Release of Ca+2 into the myofibril</p> Signup and view all the answers

    What is the term used for the process by which muscle fiber depolarization initiates contraction?

    <p>Excitation-contraction coupling</p> Signup and view all the answers

    What does elasticity of a muscle refer to?

    <p>The ability of a muscle to recoil to its original length after being stretched</p> Signup and view all the answers

    Which term describes a muscle that raises a body part?

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

    How is the muscle 'Deltoid' classified based on its shape?

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

    Which of the following muscles moves a part towards the midline of the body?

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

    What is the primary action of a flexor muscle?

    <p>Bends a part near the joint</p> Signup and view all the answers

    Which muscle is located on top of the temporal bone?

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

    What type of muscle is described as 'constrictor'?

    <p>Closes or compresses openings</p> Signup and view all the answers

    How is the muscle named 'Tibialis anterior' classified?

    <p>By its location</p> Signup and view all the answers

    Which situation is most likely to contribute to temporal summation leading to tetany?

    <p>Carrying a very heavy load</p> Signup and view all the answers

    Which statement is likely true regarding Hidilyn Diaz's muscle activity while lifting?

    <p>The lifting involves primarily concentric contractions.</p> Signup and view all the answers

    Which of the following statements about Hidilyn Diaz's muscles might be true?

    <p>She experiences less central fatigue compared to most people.</p> Signup and view all the answers

    Which factor might influence the muscle contractions of an Olympic weightlifter?

    <p>The muscle insertion point relative to the fulcrum.</p> Signup and view all the answers

    Which factor is less likely to be true about the muscle contractions of elite athletes?

    <p>They typically exhibit lower levels of muscle endurance.</p> Signup and view all the answers

    What initiates the opening of RYR in heart muscle contraction?

    <p>Influx of Ca+2 from DHPR</p> Signup and view all the answers

    What role does SERCA play in muscle relaxation?

    <p>Pumps Ca+2 into the sarcoplasmic reticulum</p> Signup and view all the answers

    Which of the following proteins is responsible for binding Ca+2 in muscle cells?

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

    How does DHPR interact with RYR in skeletal muscle?

    <p>They are mechanically attached</p> Signup and view all the answers

    What is the significance of the latent period in a muscle twitch myogram?

    <p>Cross bridges begin to cycle without measurable tension</p> Signup and view all the answers

    What happens to tropomyosin when Ca+2 levels decrease in muscle cells?

    <p>It blocks the actin binding site again</p> Signup and view all the answers

    What is the primary action of calcium channel blocker drugs in heart muscle?

    <p>Prevent Ca+2 influx</p> Signup and view all the answers

    What is the primary function of DHP in muscle contraction?

    <p>Opening calcium channels</p> Signup and view all the answers

    What anchors calsequestrin near RYR in muscle cells?

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

    During muscle relaxation, how many Ca+2 ions does SERCA pump back into the terminal cisternae per ATP hydrolyzed?

    <p>2</p> Signup and view all the answers

    What is the primary role of the interaction between thick and thin filaments in a sarcomere?

    <p>Enabling muscle contraction</p> Signup and view all the answers

    Which protein is responsible for binding to actin and regulating myosin binding?

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

    What component of a sarcomere is responsible for holding thick filaments together?

    <p>M line</p> Signup and view all the answers

    What distinguishes the I band from the A band in a sarcomere?

    <p>The I band only contains thin filaments</p> Signup and view all the answers

    Which part of the sarcomere does the actin filament attach to?

    <p>Z disc</p> Signup and view all the answers

    What is the function of calcium ions in muscle contraction?

    <p>To initiate the binding of myosin to actin</p> Signup and view all the answers

    How many binding sites does a myosin head possess?

    <p>Two: one for actin and one for ATP</p> Signup and view all the answers

    Which component of muscle cells prevents myosin from binding to actin in the absence of calcium?

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

    What is the H zone in a sarcomere?

    <p>A lighter region surrounding the M line containing only thick filaments</p> Signup and view all the answers

    Which statement accurately describes myofibrils?

    <p>They are long, cylindrical organelles within muscle fibers</p> Signup and view all the answers

    What occurs during the period of relaxation in muscle contraction?

    <p>Pumping of Ca2+ back into the SR</p> Signup and view all the answers

    What characterizes incomplete (unfused) tetanus?

    <p>Distinct individual contractions are visible</p> Signup and view all the answers

    Which statement about motor units is true?

    <p>The smallest functional unit of muscle is a motor unit</p> Signup and view all the answers

    What happens to contractile force during the period of contraction?

    <p>It increases as the number of active cross bridges increases</p> Signup and view all the answers

    What type of muscle fiber is primarily responsible for generating the bulk of muscle force?

    <p>Extrafusal fibers</p> Signup and view all the answers

    What is the primary characteristic of complete (fused) tetanus?

    <p>Sustained higher force without relaxation</p> Signup and view all the answers

    Which factor does NOT contribute to the diversity in contraction speed among different muscles?

    <p>Location of muscle in the body</p> Signup and view all the answers

    What is the result of decreasing intervals between successive stimuli in muscle contraction?

    <p>Twitches are indistinguishable and fused</p> Signup and view all the answers

    Which type of motor neuron innervates intrafusal fibers?

    <p>Gamma motor neurons</p> Signup and view all the answers

    What allows for smooth and continuous movements in muscle function?

    <p>Summation of twitches at high-frequency stimulation</p> Signup and view all the answers

    Which situation is most likely to involve temporal summation leading to tetany?

    <p>Lifting a very heavy object</p> Signup and view all the answers

    What is the primary contraction type employed by weightlifters during a clean and jerk maneuver?

    <p>Concentric contraction</p> Signup and view all the answers

    Which characteristic might differentiate an Olympic weightlifter's muscles from those of a typical individual?

    <p>Increased cross-sectional area of fibers</p> Signup and view all the answers

    What could explain a reduced level of central fatigue in elite athletes like Hidilyn Diaz?

    <p>Improved neuromuscular efficiency</p> Signup and view all the answers

    Which factor is most likely associated with the muscle adaptations of Olympic lifters compared to non-competitive individuals?

    <p>Changes in muscle fiber type distribution</p> Signup and view all the answers

    What does elasticity in muscle tissue specifically refer to?

    <p>The capability to recoil to original resting length after being stretched</p> Signup and view all the answers

    Which term describes a muscle that moves a body part away from the midline?

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

    Which of the following muscles is named for its location on the cranial bone?

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

    What does the term 'depressor' indicate about a muscle's action?

    <p>It lowers a body part</p> Signup and view all the answers

    Which of the following best describes the action of a flexor muscle?

    <p>It bends a part near the joint</p> Signup and view all the answers

    The muscle named 'Serratus' is best described by which characteristic?

    <p>It has a saw-toothed appearance</p> Signup and view all the answers

    Which classification of muscle action is associated with opening spaces or widening openings?

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

    How is the Deltoid muscle primarily classified?

    <p>By shape, resembling a triangle</p> Signup and view all the answers

    What type of injury is classified as a strain?

    <p>Over-stretched muscles or tendons</p> Signup and view all the answers

    Which condition is characterized by the production of more muscle fibers?

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

    What does RICE stand for in the treatment of muscle strains and sprains?

    <p>Rest, Ice, Compression, Elevation</p> Signup and view all the answers

    What is a common symptom of Myasthenia Gravis?

    <p>Muscle weakness</p> Signup and view all the answers

    Which of the following is NOT a recommended practice for preventing muscle strains?

    <p>Jumping right into intense activity</p> Signup and view all the answers

    What is characterized by progressive weakness of muscle due to a mutated dystrophin-glycoprotein complex?

    <p>Muscular Dystrophy</p> Signup and view all the answers

    What role do assistive devices serve for aging individuals?

    <p>Aid mobility</p> Signup and view all the answers

    Which condition is related to the painful inflammation of a tendon?

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

    Which of the following is a common treatment for malignant hyperthermia?

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

    Which of the following conditions is known for causing chronic pain primarily in joints, muscles, and tendons?

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

    What occurs during the period of contraction in muscle fibers?

    <p>Cross bridges are active</p> Signup and view all the answers

    What characterizes complete (fused) tetanus?

    <p>Sustained smooth force</p> Signup and view all the answers

    What type of muscle fiber is primarily responsible for generating force?

    <p>Extrafusal fibers</p> Signup and view all the answers

    Which statement best describes incomplete (unfused) tetanus?

    <p>Twitches gradually increase but oscillate</p> Signup and view all the answers

    How is a motor unit defined?

    <p>A motor neuron and the muscle fibers it innervates</p> Signup and view all the answers

    What happens to contractile force during the period of relaxation?

    <p>It begins to decline</p> Signup and view all the answers

    Which type of muscle fibers are innervated by gamma motor neurons?

    <p>Intrafusal fibers</p> Signup and view all the answers

    What leads to smooth, continuous movements in muscle contraction?

    <p>Summation of individual twitches</p> Signup and view all the answers

    What is the primary role of calcium ions during muscle contraction?

    <p>Facilitate the binding of myosin and actin</p> Signup and view all the answers

    What distinguishes different types of skeletal muscle fibers?

    <p>The speed of contraction and force generation</p> Signup and view all the answers

    What is the primary characteristic of isometric contraction?

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

    What primarily contributes to peripheral fatigue in muscles?

    <p>Accumulation of metabolic waste</p> Signup and view all the answers

    During oxygen debt, what happens to lactic acid produced in the muscles?

    <p>It is converted to glucose in the liver</p> Signup and view all the answers

    What is the primary cause of muscle fatigue during exercise?

    <p>Accumulation of lactic acid</p> Signup and view all the answers

    Which of the following describes the difference between hypertrophy and atrophy?

    <p>Hypertrophy refers to increased muscle mass; atrophy to decreased muscle mass</p> Signup and view all the answers

    Which process is primarily involved in rapid energy production for muscles?

    <p>Creatine phosphate breakdown</p> Signup and view all the answers

    What role does central fatigue play in muscle performance?

    <p>It results from decreased efficiency of motor neuron activation</p> Signup and view all the answers

    Which type of muscle contraction causes lengthening of the muscle under tension?

    <p>Eccentric contraction</p> Signup and view all the answers

    What is the immediate outcome when blood supply to a muscle is interrupted?

    <p>Rapid muscle fatigue</p> Signup and view all the answers

    How does the body manage recovery from intense exercise?

    <p>By promoting rest and hydration</p> Signup and view all the answers

    What type of contraction is characterized by muscle lengthening while contracting?

    <p>Eccentric contraction</p> Signup and view all the answers

    Which of the following is NOT a contributing factor to muscle fatigue?

    <p>Enhanced release of adrenaline</p> Signup and view all the answers

    Which method of energy production is characterized by rapid energy release during muscle contractions?

    <p>Creatine phosphate</p> Signup and view all the answers

    What condition is described as a muscle's inability to contract due to fatigue?

    <p>Muscle fatigue</p> Signup and view all the answers

    Which of the following is a common symptom of peripheral fatigue?

    <p>Muscle soreness</p> Signup and view all the answers

    What is the role of the diaphragm during respiration?

    <p>Separates the abdominal cavity from the thoracic cavity</p> Signup and view all the answers

    Which muscle group is responsible for flexing the arm at the elbow?

    <p>Biceps brachii</p> Signup and view all the answers

    What type of muscle arrangement is exemplified by the deltoid?

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

    Which of the following muscles assists in rotating the forearm medially?

    <p>Pronator teres</p> Signup and view all the answers

    What is the function of the orbitalis oris muscle?

    <p>Puckers the lips</p> Signup and view all the answers

    What does the term 'sartorius' refer to in the context of muscle arrangement?

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

    Which muscle is primarily responsible for extending the leg at the knee?

    <p>Rectus femoris</p> Signup and view all the answers

    What does the flexor carpi radialis muscle primarily do?

    <p>Flex and abduct the wrist</p> Signup and view all the answers

    What is primarily responsible for muscle contraction within the sarcomere?

    <p>Interaction between thick and thin filaments</p> Signup and view all the answers

    Which component of the sarcomere is responsible for anchoring thin filaments?

    <p>Z disc</p> Signup and view all the answers

    What is the role of tropomyosin in muscle contraction?

    <p>To prevent myosin from binding to actin</p> Signup and view all the answers

    What is found in the H zone of the sarcomere?

    <p>Only thick filaments</p> Signup and view all the answers

    Which of the following proteins directly binds to calcium ions during muscle contraction?

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

    How many binding sites does a myosin molecule have?

    <p>Two, one for actin and one for ATP</p> Signup and view all the answers

    Which zone represents the area where myosin filaments do not overlap with actin filaments?

    <p>I band</p> Signup and view all the answers

    What function does the sarcoplasmic reticulum serve in muscle fibers?

    <p>Stores calcium ions necessary for contraction</p> Signup and view all the answers

    What do striations in muscle fibers represent?

    <p>The arrangement of actin and myosin filaments</p> Signup and view all the answers

    Which part of the sarcomere serves as the connection point for thick filaments?

    <p>M line</p> Signup and view all the answers

    What triggers the release of Ca+2 from the sarcoplasmic reticulum during muscle contraction?

    <p>The activation of dihydropyridine receptors</p> Signup and view all the answers

    Which protein complex engages in the interaction that ultimately causes muscle contraction?

    <p>Myosin and actin</p> Signup and view all the answers

    What role does acetylcholinesterase play in muscle contraction?

    <p>It degrades acetylcholine after contraction.</p> Signup and view all the answers

    During what phase of muscle contraction is Ca+2 pumped back into the sarcoplasmic reticulum?

    <p>Muscle relaxation</p> Signup and view all the answers

    What initiates the action potential in a muscle fiber?

    <p>The binding of Ach to its receptor</p> Signup and view all the answers

    Which of the following correctly describes the role of T-tubules in muscle contraction?

    <p>They propagate action potentials into the muscle fiber.</p> Signup and view all the answers

    What is the primary effect of Ca+2 binding to troponin in muscle fibers?

    <p>It allows actin and myosin to form a cross-bridge.</p> Signup and view all the answers

    What is the role of dihydropyridine receptors in muscle contraction?

    <p>They facilitate the release of calcium from the sarcoplasmic reticulum.</p> Signup and view all the answers

    What results from the depolarization of the muscle fiber membrane?

    <p>Action potential generation in muscle fibers</p> Signup and view all the answers

    Which mechanism is responsible for muscle relaxation following contraction?

    <p>Active transport of Ca+2 back into the sarcoplasmic reticulum</p> Signup and view all the answers

    What type of muscle contraction involves a constant muscle length while generating tension?

    <p>Isometric contraction</p> Signup and view all the answers

    Which factor directly affects the amount of force produced by a muscle fiber?

    <p>Diameter of the fiber</p> Signup and view all the answers

    What happens to muscle tension when the number of active motor units increases?

    <p>Force produced increases</p> Signup and view all the answers

    In terms of muscle fiber length, what is the relationship between length and tension development?

    <p>Optimal length allows maximum tension</p> Signup and view all the answers

    Which contraction type primarily represents a situation where muscle fibers shorten and produce external work?

    <p>Isotonic contraction</p> Signup and view all the answers

    Which aspect is indirectly proportional to the threshold needed to activate muscle fibers?

    <p>Fiber diameter</p> Signup and view all the answers

    Which arrangement of fibers is typically associated with finer and more controlled movements?

    <p>Fewer fibers per motor unit</p> Signup and view all the answers

    What does not occur during isometric contractions?

    <p>Change in muscle length</p> Signup and view all the answers

    How does the tension relate to the contraction when the muscle fiber lengths are at an optimal state?

    <p>Maximum tension is observed</p> Signup and view all the answers

    What effect does the muscle fiber diameter have on generated force?

    <p>Directly proportional</p> Signup and view all the answers

    Study Notes

    Trivia About Muscles

    • There are about 60 muscles in the face.
    • It takes 20 muscles to smile and over 40 to frown.
    • The Stapedius is the smallest muscle in the body.
    • The Gluteus Maximus is the biggest muscle in the body.
    • The longest muscle in the body is the Sartorius.

    Types of Muscle Tissue

    • Skeletal muscle: attached to the skeleton, filamentous shape, voluntary control, striated, multinucleated, responsible for movement of the bone
    • Smooth muscle: found in the walls of hollow organs, spindle shaped, involuntary control, not striated, mononucleated, responsible for movement of internal organs
    • Cardiac muscle: located in the heart, branching filamentous shape, involuntary control, striated, mononucleated, responsible for beating of the heart

    Skeletal Muscle Tissue

    • Excitability: ability to respond to a stimulus.
    • Contractility: ability to shorten and generate a pulling force.
    • Extensibility: ability to be stretched.

    Movement of Muscles

    • Origin: the attachment of a muscle to the bone that remains stationary.
    • Insertion: the attachment of the muscle to the bone that moves.
    • Belly: the fleshy part of the muscle between the origin and the insertion.

    Movement of Skeletal Muscle

    • Muscles work in pairs.
    • Contraction: shortening.
    • Extension: Lengthening.

    Major Skeletal Muscles: The Head

    • Sternocleidomastoid: pulls the head to one side, pulls the head to the chest.
    • Splenius Capitis: rotates the head, allows the head to bend to the side.
    • Frontalis: raises the eyebrows.
    • Orbicularis Oris: allows the lips to pucker.
    • Orbicularis Oculi: allows the eyes to close.
    • Platysma: pulls the corners of the mouth down.
    • Zygomaticus: pulls the corners of the mouth up.
    • Masseter and Temporalis: close the jaw.

    Major Skeletal Muscles: Upper Arm

    • Pectoralis Major: pulls the arm across the chest, rotates and adducts the arms.
    • Latissimus Dorsi: extends and adducts the arm, rotates the arm inwards.

    Major Skeletal Muscles: Forearm

    • Biceps Brachii: flexes the arm at the elbow, rotates the hand laterally.
    • Brachialis: flexes the arm at the elbow.
    • Brachioradialis: flexes the forearm at the elbow.
    • Triceps Brachii: extends the arm at the elbow.
    • Supinator: rotates the forearm laterally (supination).
    • Pronator Teres: rotates the forearm medially (pronation).

    Major Skeletal Muscles: Wrist, Hand, and Fingers

    • Flexor Carpi Radialis and Flexor Carpi Ulnaris: flex and abduct the wrist.
    • Extensor Carpi Radialis Longus and Brevis: extend the wrist and abduct the hand.
    • Palmaris Longus: flexes the wrist.
    • Flexor Digitorum Profundus: flexes the distal joints of the fingers, but not the thumb.
    • Extensor Carpi Ulnaris: extends the wrist.
    • Extensor Digitorum: extends the fingers, but not the thumb.

    Major Skeletal Muscles: Respiratory

    • Diaphragm: separates the thoracic cavity from the abdominal cavity, contraction causes inspiration.
    • External and Internal Intercostals: expand and lower the ribs during breathing.

    Major Skeletal Muscles: Abdominal

    • External and Internal Obliques: compress the abdominal wall
    • Transverse Abdominis: compresses the abdominal wall.
    • Rectus Abdominis: flexes the vertebral column, compresses the abdominal wall.

    Major Skeletal Muscles: Pectoral Girdle

    • Trapezius: raises the arms, pulls the shoulders downwards.
    • Pectoralis Minor: pulls the scapula downwards.

    Major Skeletal Muscles: Leg

    • Psoas Major and Iliacus: flexes the thigh.
    • Gluteus Maximus: extends the thigh.
    • Gluteus Medius and Minimus: abduct the thighs, rotates them medially.
    • Adductor Longus and Magnus: adduct the thighs, rotate them laterally.
    • Biceps Femoris, Semitendinosus, and Semimembranosus: known as the hamstring group, flex the leg at the knee.

    Major Skeletal Muscles: Leg

    • Rectus Femoris, Vastus Lateralis, Vastus Medialis, and Vastus Intermedius: extend the leg at the knee.
    • Sartorius: flexes the leg at the knee and thigh, abducts the thigh, rotates the thigh laterally but rotates the lower leg medially.

    Major Skeletal Muscles: Ankle, Foot, and Toes

    • Tibialis Anterior: inverts the foot, points the foot up (dorsiflexion).
    • Soleus: flexes the foot.
    • Flexor Digitorum Longus: flexes the foot and toes.
    • Extensor Digitorum Longus: extends the toes and point the foot up.
    • Gastrocnemius: flexes the foot and flexes the leg at the knee.

    Muscle Naming Conventions

    • Size: Maximus (largest), Minimus (smallest), Longus (longest), Brevis (short), Major (large).
    • Direction of fibers: Rectus (straight), Transverse (perpendicular to long axis), Oblique (diagonal).
    • Number of Origins: Biceps (2), Triceps (3), Quadriceps (4).
    • Origin and Insertion: Sternocleidomastoid (originates from sternum and clavicle, inserts on mastoid process of temporal bone), Flexor Carpi Radialis (flexes wrist), Abductor Pollicis Brevis (flexes thumb), Abductor Magnus (abducts thigh), Extensor Digitorum (extends fingers).

    Arrangement of Fascicles

    • Parallel: strap-like (example: Sartorius).
    • Fusiform: spindle-shaped (example: Biceps Femoris).
    • Pennate: feather shaped.
    • Unipennate: example: Extensor Digitorum Longus.
    • Bipennate: example: Rectus Femoris.
    • Multipennate: example: Deltoid.
    • Convergent: example: Pectoralis Major.
    • Circular: sphincters (example: Orbicularis Oris).

    Organization Level of Muscles

    • Skeletal muscles are made of muscle fibers, nerves, blood vessels, and connective tissues.
    • Each muscle is served by one nerve, one artery, and one or more veins.

    Attachments of Muscles

    • Tendons: narrow bands of connective tissue that connect muscles to bone.
    • Ligaments: bands of connective tissue that join bone to bone.
    • Aponeuroses: bands of connective tissue that attach flat muscle to another muscle or to several bones.

    Structure of Skeletal Muscle

    • Composed of striated muscle cells and connective tissue.

    Muscle Contraction

    • Terminal Cisternae: several Ca+2 binding proteins.
    • Calsequestrin: a Ca+2 binding protein.
    • Histidine-rich calcium-binding protein (HRC): a Ca+2 binding protein.
    • Sarcalumenin: a Ca+2 binding protein.
    • Triadin: anchors calsequestrin near RYR.
    • SERCA (Sarcoplasmic or ER calcium ATPase): pumps Ca+2 into SR.
    • DHPR and RYR Interaction: In heart muscle, DHPR opens, causing Ca+2 influx, then Ca+2 influx causes RYR to open. In skeletal muscle, DHPR is mechanically attached to RYR. When DHPR changes shape, RYR opens.
    • Calcium Channel Blocker Drugs: work on heart muscles, not on skeletal muscles.

    Sliding Filament Theory

    • The myosin head binds to actin, forming a cross bridge, pulling the actin towards the center of the sarcomere, shortening the sarcomere.
    • The myosin head detaches from the actin, binds to another actin, and pulls again.

    Muscle Relaxation

    • SERCA pumps 2 Ca+2 back into the terminal cisternae per ATP hydrolyzed.
    • Lowered Ca+2 allows tropomyosin to block actin binding sites again, decreasing the actin-myosin interaction.

    The Muscle Twitch

    • Myogram: a recording of electrical activity during muscle contraction.
    • Latent Period: Cross bridges begin to cycle, but muscle tension is not yet measurable.

    Types of Muscle Contraction

    • Isotonic Contraction: length changes while contracting.
    • Concentric: shortening (muscle contracts).
    • Eccentric: lengthening (muscle is being stretched).
    • Isometric Contraction: muscle contracts but does not change in length (load is too heavy or immovable).

    Types of Fatigue

    • Peripheral Fatigue: occurs in muscle fibers.
    • Causes: accumulation of metabolic waste (lactate, hydrogen ions).
    • Symptoms: muscle soreness, weakness, cramping.
    • Recovery: rest, hydration, nutrition.
    • Central Fatigue: occurs in the central nervous system (brain and spinal cord).
    • Causes: decreased ability of the central nervous system to activate motor neurons.
    • Symptoms: feeling tired, difficulty concentrating, reduced motivation.
    • Recovery: rest, sleep, stress management.

    Production of Energy for Muscle

    • ATP (adenosine triphosphate): A type of chemical energy needed for sustained or repeated muscle contractions.
    • Creatine phosphate: rapid production of energy.
    • Aerobic respiration: uses the body’s store of glucose.
    • Lactic Acid Production: a byproduct of anaerobic respiration.

    Production of Energy: Oxygen Debt

    • Occurs when skeletal muscles are used strenuously for several minutes, and cells are low in oxygen.
    • Pyruvic Acid: converts to lactic acid which builds up.
    • Lactic Acid: taken to the liver for conversion to glucose, requiring more energy.

    Production of Energy: Muscle Fatigue

    • Muscle has lost its ability to contract.
    • Causes: accumulation of lactic acid, interruption of blood supply to the muscle, a motor neuron loses its ability to release acetylcholine onto muscle fiber.

    Muscle Remodeling

    • Hypertrophy: increase in mass.
    • Atrophy: decrease in mass.

    Questions

    • Temporal summation leading to tetany might be occurring when standing at attention or carrying a very heavy load (E).
    • Olympic medalist Hidilyn Diaz might experience less central fatigue compared to most people because she has trained extensively and her body is accustomed to strenuous exercise (C).

    Elasticity

    • Muscles have the ability to recoil to their original resting length after being stretched.

    Naming Skeletal Muscles

    • Location: Muscles are named based on their proximity to bones and body parts.
    • Shape: The shape of the muscle can also be used for naming (e.g., deltoid - triangle shaped).
    • Size: Size descriptors like "maximus" (largest), "minimus" (smallest), "longus" (longest), and "brevis" (short) are used.
    • Direction: Muscle fiber orientation influences names - "rectus" (straight), "transverse", and "oblique".
    • Number of Origins: The number of points of attachment, like biceps (2), triceps (3), and quadriceps (4).
    • Attachments: Names can reflect the origin and insertion points (e.g., sternocleidomastoid - originates from sternum and clavicle, inserts on mastoid process).
    • Action: Describes the function, like flexor, extensor, abductor, adductor, etc.

    Classification of Muscles by Action

    • Flexor: Bends a body part closer to the joint.
    • Extensor: Straightens a body part away from the joint.
    • Abductor: Moves a body part away from the midline of the body.
    • Adductor: Moves a body part toward the midline of the body.
    • Dilator: Opens spaces or widens openings.
    • Constrictor: Closes or compresses openings.
    • Levator: Raises a body part.
    • Depressor: Lowers a body part.

    Muscle Named by Location

    • Tibialis Anterior: Located in front of the tibia.
    • Frontalis: Found on top of the frontal bone.
    • Temporalis: Situated on top of the temporal bone.
    • Epicranius: Located around the cranium.

    Movement of Muscles

    • Origin: The fixed attachment of the muscle to the bone that remains stationary.
    • Insertion: The attachment of the muscle to the bone that moves.
    • Belly: The fleshy part of the muscle between the origin and insertion points.

    Movement of Skeletal Muscle

    • Skeletal muscles contract upon receiving signals from the brain.
    • Muscles operate in pairs to produce coordinated movements.
    • Two primary movements of skeletal muscles:
      • Contraction: Shortening of muscle fibers.
      • Extension: Lengthening of muscle fibers

    Major Skeletal Muscles: The Head

    • Sternocleidomastoid: Pulls the head to one side, pulls the head to the chest.
    • Splenius Capitis: Rotates the head, bends it to the side.
    • Orbicularis Oris: Allows the lips to pucker.
    • Frontalis: Raises the eyebrows.
    • Orbicularis Oculi: Allows the eyes to close.
    • Platysma: Pulls down the corners of the mouth.
    • Zygomaticus: Pulls the corners of the mouth upwards.
    • Masseter and Temporalis: Close the jaw.

    Major Skeletal Muscles: Upper Arm

    • Pectoralis Major: Pulls the arm across the chest, rotates and adducts the arm.
    • Latissimus Dorsi: Extends and adducts the arm, rotates it inwards.

    Major Skeletal Muscles: Forearm

    • Biceps Brachii: Flexes the arm at the elbow, rotates the hand laterally.
    • Brachialis: Flexes the arm at the elbow.
    • Brachioradialis: Flexes the forearm at the elbow.
    • Triceps Brachii: Extends the arm at the elbow.
    • Supinator: Rotates the forearm laterally (supination).
    • Pronator Teres: Rotates the forearm medially (pronation).

    Major Skeletal Muscles: Wrist, Hand, and Fingers

    • Flexor Carpi Radialis and Flexor Carpi Ulnaris: Flex and abduct the wrist.
    • Extensor Carpi Radialis Longus and Brevis: Extend the wrist and abduct the hand.
    • Palmaris Longus: Flexes the wrist.
    • Flexor Digitorum Profundus: Flexes the distal joints of the fingers, but not the thumb.
    • Extensor Carpi Ulnaris: Extends the wrist.
    • Extensor Digitorum: Extends the fingers, but not the thumb.

    Major Skeletal Muscles: Respiratory

    • Diaphragm: Separates the thoracic cavity from the abdominal cavity, contraction causes inspiration.
    • External and Internal Intercostals: Expand and lower the ribs during breathing.

    Major Skeletal Muscles: Abdominal

    • External and Internal Obliques: Compress the abdominal wall.
    • Transverse Abdominis: Also compresses the abdominal wall.
    • Rectus Abdominis: Flexes the vertebral column, compresses the abdominal wall.

    Major Skeletal Muscles: Pectoral Girdle

    • Trapezius: Raises the arms, pulls the shoulders downward.
    • Pectoralis Minor: Pulls the scapula downward.

    Major Skeletal Muscles: Leg

    • Psoas Major and Iliacus: Flexes the thigh.
    • Gluteus Maximus: Extends the thigh.
    • Gluteus Medius and Minimus: Abduct the thighs, rotate them medially.
    • Adductor Longus and Magnus: Adduct the thighs, rotate them laterally.
    • Biceps Femoris, Semitendinosus, and Semimembranosus: Known as the hamstring group, flex the leg at the knee.
    • Rectus Femoris, Vastus Lateralis, Vastus Medialis, and Vastus Intermedius: Extend the leg at the knee.
    • Sartorius: Flexes the leg at the knee and thigh, abducts the thigh, rotates the thigh laterally, and rotates the lower leg medially.

    Major Skeletal Muscles: Ankle, Foot, and Toes

    • Tibialis Anterior: Inverts the foot and points it upwards (dorsiflexion).
    • Soleus: Flexes the foot.
    • Extensor Digitorum Longus: Extends the toes and points the foot upwards.
    • Flexor Digitorum Longus: Flexes the foot and toes.
    • Gastrocnemius: Flexes the foot and flexes the leg at the knee.

    Muscle Named By Size

    • Maximus: Largest.
    • Minimus: Smallest.
    • Longus: Longest.
    • Brevis: Shortest.
    • Major: Large.

    Muscle Named By Direction of Fibers

    • Rectus: Straight, parallel to the long axis.
    • Transverse: Perpendicular to the long axis.
    • Oblique: Diagonal to the long axis.

    Muscle Named For: Number of Origins, Origin and Insertion, Action

    • Biceps (2), Triceps (3), Quadriceps (4): Refer to the number origins.
    • Sternocleidomastoid: Originates from the sternum and clavicle, inserts on the mastoid process of the temporal bone.
    • Flexor Carpi Radialis, Extensor Carpi Radialis: Flexors and extensors of the wrist, respectively.
    • Abductor Pollicis Brevis, Adductor Pollicis: Abduct and adduct the thumb, respectively.
    • Abductor Magnus: Abducts the thigh.
    • Extensor Digitorum: Extends the fingers.

    Arrangement of Fascicles

    • Parallel: Strap-like (e.g., Sartorius).
    • Fusiform: Spindle shaped (e.g., Biceps femoris).
    • Pennate: Feather shaped, classified as:
      • Unipennate: (e.g., Extensor digitorum longus).
      • Bipennate: (e.g., Rectus femoris).
      • Multipennate: (e.g., Deltoid).
    • Convergent: (e.g., Pectoralis major).
    • Circular: Sphincters, encircle openings (e.g., Orbicularis oris).

    Organization Levels of Muscles

    • Skeletal muscles are composed of muscle fibers, nerves, blood vessels, and connective tissues.
    • Each muscle is served by one nerve, one artery, and one or more veins.
    • Skeletal muscle fibers can only contract under nerve stimulation, unlike cardiac and smooth muscle.

    Attachments of Muscles

    • Tendons: Narrow connective tissue bands that connect muscles to bone.
    • Ligaments: Connective tissue bands joining bones to bones.
    • Aponeuroses: Flat connective tissue bands attaching flat muscles to other muscles or bones.

    Structure of Skeletal Muscle

    • Skeletal muscles are composed of striated muscle cells and connective tissue.

    Neuromuscular Junction

    • The junction where a motor neuron communicates with a muscle fiber.
    • This is the site where nerve impulses are transmitted to muscle fibers, triggering contraction.

    Muscle Contraction

    • Excitation-Contraction Coupling
      1. Action potential arrives at the neuromuscular junction, reaching the muscle fiber.
      2. Action potential travels along the sarcolemma, triggering release of calcium ions (Ca+2) from the sarcoplasmic reticulum (SR).
      3. Ca+2 initiates the interaction of myosin and actin, leading to muscle contraction.
      4. Ca+2 is pumped back into the SR, causing muscle relaxation.

    Step 1: Neuromuscular Junction

    • Action potential reaches the end of the motor neuron, increasing calcium influx and releasing acetylcholine (Ach).
    • Ach binds to receptors on the muscle membrane, allowing sodium (Na+) influx which generates a local potential.
    • This activates voltage-gated sodium channels, triggering an action potential.
    • Acetylcholinesterase degrades Ach.

    Step 2: Sarcolemma and SR

    • Action potential travels through T-tubules, activating dihydropyridine receptors (DHPR).
    • DHPR activates ryanodine receptors (RYR) in the terminal cisternae of the SR.
    • This triggers the release of Ca+2 into the myofibril.

    Types of Skeletal Muscle Fibers

    • Different skeletal muscles contract at varying speeds due to different types of muscle fibers.

    Tetanus

    • Fusion of muscle twitches that occurs with high-frequency stimulations, resulting in smooth, continuous movements.
    • Incomplete (Unfused) Tetanus: Individual contractions are observed, brief relaxation periods between contractions, peak tension increases but oscillates.
    • Complete (Fused) Tetanus: Individual contractions are indistinguishable, sustained, smooth, high force generated.

    Motor Unit

    • The smallest functional unit of a muscle, consisting of a motor neuron and the muscle fibers it innervates.
    • The basic unit of movement.
    • Extrafusal fibers: Primary muscle fibers that contract, innervated by alpha motor neurons.
    • Intrafusal fibers: Sensory fibers embedded within the muscle, detect stretch, innervated by gamma motor neurons.

    Fiber Length (Length-Tension Relation)

    • Tension generated during contraction is affected by muscle fiber length.
    • Isometric contraction: Muscle length remains constant while tension increases.
    • Isotonic contraction: Force is constant, but muscle length changes.

    Factors Determining Muscle Tension

    • Fiber Diameter:
      • Larger diameter fibers generate greater force and have higher thresholds.
      • Smaller diameter fibers generate lower force and have lower thresholds.
    • Number of Active Fibers:
      • Number of fibers per motor unit: Fewer fibers = finer movements, more fibers = gross movements.
      • Number of active motor units: More activated units = stronger force produced.

    Types of Muscle Contraction

    • Isometric Contraction: Muscle length remains constant, tension increases, no external work done.
    • Isotonic Contraction: Muscle length changes, tension is constant, external work is done.

    Trivia about muscles

    • There are approximately 60 muscles in the human face.
    • Smiling requires 20 muscles, while frowning requires over 40.
    • The longest muscle in the body is the Sartorius.
    • The smallest muscle in the body is the Stapedius.
    • The largest muscle in the body is the Gluteus Maximus.

    Types of Muscle Tissue

    • There are three types of muscle tissue: skeletal, smooth, and cardiac.
    • Skeletal muscle is attached to the skeleton and is responsible for movement.
    • Smooth muscle is found in the walls of hollow organs and is responsible for involuntary movement.
    • Cardiac muscle is found in the heart and is responsible for the beating of the heart.

    Characteristics of Muscle Tissue

    • Muscle tissue is excitable, meaning it can respond to a stimulus.
    • Muscle tissue is contractile, meaning it can shorten and generate a pulling force.
    • Muscle tissue is extensible, meaning it can be stretched to its normal resting length and beyond.

    Movement of Muscles

    • Origin: The point of attachment of a muscle to a bone that remains stationary during contraction.
    • Insertion: The point of attachment of a muscle to a bone that moves during contraction.
    • Belly: The fleshy portion of a muscle between the origin and insertion.
    • Muscles work in pairs to produce movement: Contraction (shortening) and Extension (lengthening).

    Major Skeletal Muscles of the Head

    • Sternocleidomastoid: Pulls the head to one side, pulls the head toward the chest.
    • Splenius Capitis: Rotates the head and allows it to bend to the side.
    • Frontalis: Raises the eyebrows.
    • Orbicularis Oris: Allows the lips to pucker.
    • Orbicularis Oculi: Allows the eyes to close.
    • Platysma: Pulls the corners of the mouth down.
    • Zygomaticus: Pulls the corners of the mouth up.
    • Masseter and Temporalis: Muscles responsible for closing the jaw.

    Major Skeletal Muscles of the Upper Arm

    • Pectoralis major: Pulls the arm across the chest, rotates and adducts the arms.
    • Latissimus Dorsi: Extends and adducts the arm, rotates the arm inwardly.

    Major Skeletal Muscles of the Forearm

    • Biceps Brachii: Flexes the arm at the elbow, rotates the hand laterally.
    • Brachialis: Flexes the arm at the elbow.
    • Brachioradialis: Flexes the forearm at the elbow.
    • Triceps Brachii: Extends the arm at the elbow.
    • Supinator: Rotates the forearm laterally (supination).
    • Pronator Teres: Rotates the forearm medially (pronation).

    Major Skeletal Muscles of the Wrist, Hand, and Fingers

    • Flexor Carpi Radialis and Flexor Carpi Ulnaris: Flex and abduct the wrist.
    • Palmaris Longus: Flexes the wrist.
    • Flexor Digitorum Profundus: Flexes the distal joints of the fingers (not the thumb).
    • Extensor Carpi Radialis Longus and Brevis: Extends the wrist and abducts the hand.
    • Extensor Carpi Ulnaris: Extends the wrist.
    • Extensor Digitorum: Extends the fingers (not the thumb).

    Major Skeletal Muscles of Respiration

    • Diaphragm: Separates the thoracic cavity from the abdominal cavity. Contraction aids in inspiration (breathing in).
    • External and Internal Intercostals: Expand and lower the ribs during breathing.

    Major Skeletal Muscles of the Abdomen

    • External and Internal Obliques: Compress the abdominal wall.
    • Transverse Abdominis: Compresses the abdominal wall.
    • Rectus Abdominis: Flexes the vertebral column, compresses the abdominal wall.

    Major Skeletal Muscles of the Pectoral Girdle

    • Trapezius: Raises the arms, pulls the shoulders downward.
    • Pectoralis Minor: Pulls the scapula downward.

    Major Skeletal Muscles of the Leg

    • Psoas Major and Iliacus: Flexes the thigh.
    • Gluteus Maximus: Extends the thigh.
    • Gluteus Medius and Minimus: Abducts the thighs, rotates them medially.
    • Adductor Longus and Magnus: Adducts the thighs, rotates them laterally.
    • Biceps Femoris, Semitendinosus, and Semimembranosus (Hamstring Group): Flexes the leg at the knee.
    • Rectus Femoris, Vastus Lateralis, Vastus Medialis, and Vastus Intermedius (Quadriceps): Extend the leg at the knee.
    • Sartorius: Flexes the leg at the knee and thigh, abducts the thigh, rotates thigh laterally, rotates lower leg medially.

    Major Skeletal Muscles of the Ankle, Foot, and Toes

    • Tibialis Anterior: Inverts the foot and points the foot up (dorsiflexion).
    • Extensor Digitorum Longus: Extends the toes and points the foot up.
    • Soleus: Flexes the foot.
    • Flexor Digitorum Longus: Flexes the foot and toes.
    • Gastrocnemius: Flexes the foot and flexes the leg at the knee.

    Muscle Naming Conventions

    • Size: Maximus (largest), Minimus (smallest), Longus (longest), Brevis (shortest), Major (large).
    • Direction of Fibers: Rectus (straight, parallel to the long axis), Transverse (perpendicular to the long axis), Oblique (diagonal to the long axis).
    • Number of Origins: Biceps (two), Triceps (three), Quadriceps (four).
    • Origin and Insertion: Sternocleidomastoid (originates from sternum and clavicle, inserts on mastoid process of temporal bone).
    • Action: Flexor Carpi Radialis (flexes the wrist), Abductor Pollicis Brevis (abducts the thumb), Abductor Magnus (abducts the thigh), Extensor Digitorum (extends the fingers).

    Arrangement of Fascicles

    • Parallel: Strap-like (Sartorius).
    • Fusiform: Spindle-shaped (Biceps Femoris).
    • Pennate: Feather-shaped.
      • Unipennate: Extensor Digitorum Longus.
      • Bipennate: Rectus Femoris.
      • Multipennate: Deltoid.
    • Convergent: Pectoralis Major.
    • Circular: Sphincters (Orbicularis Oris).

    Organization Level of Muscles

    • Skeletal muscles are composed of muscle fibers, nerves, blood vessels, and connective tissues.
    • Each muscle is served by one nerve, one artery, and one or more veins.

    Attachments of Muscles

    • Tendons: Narrow bands of connective tissue that attach muscles to bones.
    • Ligaments: Bands of connective tissue that join bone to bone.
    • Aponeuroses: Bands of connective tissue that attach flat muscles to other muscles or to several bones.

    Structure of Skeletal Muscle

    • Composed of striated muscle cells and connective tissue.

    Neuromuscular Junction

    • The site where a motor neuron communicates with a muscle fiber.

    Muscle Contraction (Excitation-Contraction Coupling)

    • The process by which depolarization of a muscle fiber initiates contraction.
    • Steps:
      • Action potential travels to the neuromuscular junction and reaches the muscle fiber.
      • Action potential travels along the sarcolemma (muscle fiber membrane), causing the release of calcium ions (Ca+2) from the sarcoplasmic reticulum.
      • Ca+2 initiates the interaction of myosin and actin, causing muscle contraction.
      • Ca+2 is pumped back into the sarcoplasmic reticulum, causing muscle relaxation.

    Muscle Contraction: Step 1 (Neuromuscular Junction)

    • Action potential reaches the end of the motor neuron, increasing calcium influx.
    • This triggers the release of acetylcholine (Ach).
    • Ach binds to Ach receptors on the muscle membrane, causing sodium (Na+) influx.
    • This generates a local potential which opens voltage-gated Na+ channels and initiates an action potential.
    • Ach is then degraded by acetylcholinesterase.

    Muscle Contraction: Step 2 (Sarcolemma and SR)

    • The action potential travels through T-tubules and activates dihydropyridine receptors (DHPR).
    • Activated DHPRs activate ryanodine receptors (RYR) in the terminal cisternae, leading to the release of Ca+2 into the myofibril.

    Factors Determining Muscle Tension

    • Fiber Length (Length-Tension Relation): The effect of muscle fiber length on the amount of tension it can develop.
      • Tension is generated when a muscle contracts and decreases its length.
      • Types of Contraction:
        • Isometric: Muscle length is held constant while tension is generated.
        • Isotonic: Force or tone is held constant, but there is a change in muscle length.
    • Fiber Diameter:
      • Larger diameter = Greater force produced.
      • Smaller diameter = Lower threshold.
    • Number of Active Fibers:
      • Motor Unit: A motor neuron and all the muscle fibers it innervates.
        • Fewer fibers per motor unit = Finer movement.
        • More fibers per motor unit = Grosser movement.
      • Number of Active Motor Units:
        • More motor units activated = Stronger force produced.

    Types of Muscle Contraction

    • Isotonic:
      • Muscle length changes during contraction.
      • Concentric: Muscle shortens.
      • Eccentric: Muscle lengthens (contributes most to cellular damage after exercise).
    • Isometric:
      • Muscle contracts but does not change in length.
      • Load is too heavy or immovable.

    Types of Fatigue

    • Peripheral Fatigue:
      • Location: Muscle fibers.
      • Cause: Accumulation of metabolic waste (lactate, hydrogen ions).
      • Symptoms: Muscle soreness, weakness, cramping.
      • Recovery: Rest, hydration, nutrition.
    • Central Fatigue:
      • Location: Central nervous system (brain and spinal cord).
      • Cause: Decreased ability of the central nervous system to activate motor neurons.
      • Symptoms: Feeling tired, difficulty concentrating, reduced motivation.
      • Recovery: Rest, sleep, stress management.

    Production of Energy for Muscle Contraction

    • ATP (adenosine triphosphate): A type of chemical energy needed for sustained or repeated muscle contractions.
    • Muscles have three ways to store or make ATP:
      • Creatine Phosphate: Rapid production of energy.
      • Aerobic Respiration: Uses the body’s store of glucose.
      • Lactic Acid Production:

    Production of Energy: Oxygen Debt

    • Occurs when skeletal muscles are used strenuously for several minutes and cells are low in oxygen.
    • Lactic acid builds up, leading to muscle fatigue.

    Production of Energy: Muscle Fatigue

    • A condition in which a muscle has lost its ability to contract.
    • Causes:
      • Accumulation of lactic acid.
      • Interruption of blood supply to a muscle.
      • A motor neuron loses its ability to release acetylcholine onto muscle fibers.

    Muscle Remodeling

    • Muscles undergo continuous remodeling.
    • Hypertrophy: Increase in muscle mass.
    • Atrophy: Decrease in muscle mass.
    • Remodeling involves adjustments in the number of contractile proteins, energy-supplying enzymes, and other factors within the muscle.

    Elasticity

    • The ability of a muscle to recoil to original resting length after being stretched.

    Naming Skeletal Muscles

    • Location: The location of the muscle is often used to name it (e.g., Tibialis anterior - muscle in front of the tibia).
    • Shape: The shape of the muscle can also be a part of its name (e.g., Deltoid - triangular shaped, Serratus - saw-toothed).
    • Relative Size: Relating the size of the muscle to surrounding structures or other muscles (e.g., Pectoralis major - larger than Pectoralis minor).
    • Direction/Orientation of Fibers: The direction in which the fibers run can influence its name (e.g., Rectus - straight, Oblique - diagonal).
    • Number of Origins: The number of origins (where a muscle attaches to a bone) can be included in the name (e.g., Biceps, Triceps).
    • Location of Attachments: Where the muscle attaches to bones, both origin and insertion (e.g., Sternocleidomastoid - attaches to the sternum, clavicle, and mastoid process).
    • Action: The primary function of the muscle is often part of its name (e.g., Flexor, Extensor, Abductor, Adductor, Dilator, Constrictor, Levator, Depressor).

    Muscle Classification by Action

    • Flexor: Bends a part near the joint.
    • Extensor: Straightens a part near the joint.
    • Abductor: Moves a part away from the midline of the body.
    • Adductor: Moves a part towards the midline of the body.
    • Dilator: Opens spaces or widens openings.
    • Constrictor: Closes or compresses openings.
    • Levator: Raises a body part.
    • Depressor: Lowers a body part.

    Sarcomere

    • The smallest functional unit of a muscle fiber.
    • Made up of repeating units within myofibrils.
    • Interaction between thick (myosin) and thin (actin) filaments within the sarcomere are responsible for muscle contraction.

    Parts of a Sarcomere

    • A band: The area where myosin (thick) filaments are present, including regions with overlapping actin filaments.
    • I band: The area between thick filaments where only thin filaments are present.
    • Z disc: Protein to which actin (thin) filaments are connected.
    • M line: Protein to which myosin (thick) filaments are connected.
    • H zone: The area surrounding the M line where only myosin filaments are present (actin filaments don't reach this area).

    Myofilaments

    • Thick filaments: Composed of the protein myosin.
    • Thin filaments: Composed of the protein actin.

    Molecular Composition of Myofilaments

    • Actin: Protein of the thin filament. Has binding sites for myosin.
    • Myosin Head: Myosin molecule consists of 2 myosin heads facing outwards. Binds to active sites on actin to form cross bridges. Has motor functions and binding sites for actin and ATP.
    • Tropomyosin: A protein that wraps around actin and prevents myosin from grabbing it. Involved in skeletal muscle contraction.
    • Troponin: A protein complex with three subunits:
      • Troponin I: Binds to actin and helps inhibit myosin binding.
      • Troponin T: Binds to tropomyosin.
      • Troponin C: Has binding sites for calcium ions.

    Sarcoplasmic Reticulum

    • A network of endoplasmic reticulum that stores calcium ions, essential for muscle contraction.

    Muscle Contraction

    • DHPR (Dihydropyridine Receptor): Acts as a voltage sensor in the T-tubules.
    • RYR (Ryanodine Receptor): A calcium release channel located on the sarcoplasmic reticulum.
    • Calcium Channel Blockers: These drugs (e.g. amlodipine, nifedipine) work on heart muscles, not skeletal muscles.
    • Terminal Cisternae: Areas of the SR that store large amounts of calcium.
    • Calcium Binding Proteins: Several proteins help bind calcium in the SR:
      • Calsequestrin:
      • Histidine-rich Calcium-binding Protein (HRC):
      • Sarcalumenin:
    • Triadin: Anchors calsequestrin near RYR.
    • SERCA (Sarcoplasmic or ER calcium ATPase): Pumps calcium back into the SR.

    Sliding Filament Theory

    • This theory explains how muscle contraction occurs:
      1. Calcium Release: Calcium ions are released from the SR.
      2. Binding to Troponin: Calcium binds to Troponin C, causing a conformational change.
      3. Tropomyosin Movement: The conformational change in troponin moves tropomyosin away from the myosin binding sites on actin.
      4. Cross-Bridge Formation: Myosin heads bind to actin, forming cross-bridges.
      5. Power Stroke: Myosin heads pivot, pulling the actin filaments towards the center of the sarcomere.
      6. Detachment and Reattachment: Myosin detaches from actin and reattaches to a new binding site. This cycle repeats, pulling the actin filaments further.
      7. Sarcomere Shortening: The sarcomere shortens as the actin filaments slide past the myosin filaments, resulting in muscle contraction.

    Muscle Relaxation

    • Calcium Removal: SERCA pumps calcium back into the SR, decreasing calcium levels in the cytosol.
    • Tropmyosin Block: Tropomyosin returns to its blocking position over the myosin binding sites on actin.
    • Muscle Lengthening: The sarcomere lengthens, returning to its resting length, and muscle relaxation occurs.

    The Muscle Twitch

    • Myogram: A recording of electrical activity during muscle contraction.
    • Latent Period: Cross-bridges begin to cycle, but muscle tension is not measurable yet.
    • Period of Contraction: Cross-bridges are active leading to an increase in tension.
    • Period of Relaxation: Calcium is pumped back into the SR, and tension decreases.

    Types of Skeletal Muscle Fibers

    • Different muscles contract at different speeds, due to the presence of different types of muscle fibers.

    Tetanus

    • Summation of twitches that occur at high frequency stimulations.
    • Incomplete (Unfused) Tetanus: Individual contractions are observed, brief relaxation between contractions, and peak tension increases, but oscillates.
    • Complete (Fused) Tetanus: Individual contractions are indistinguishable, resulting in a sustained, smooth contraction with higher force.

    Motor Unit

    • The smallest functional unit of a muscle; the basic unit of movement.
    • Consists of a motor neuron and the muscle fibers it innervates.

    Muscle Fiber Types

    • Extrafusal Fibers: Innervated by alpha motor neurons, comprise the bulk of the muscle and are responsible for force generation.
    • Intrafusal Fibers: Innervated by gamma motor neurons, involved in proprioception (sensing the position and movement of the body).

    Questions and Answers

    • Question: In which of the following situations may temporal summation leading to tetany be occurring?

    • Answer: E. B and D only. Temporal summation leading to tetany is more likely to occur in situations where there is a sustained muscle contraction, like standing at attention or carrying a heavy load.

    • Question: Which of the following might be true of Olympic medalist Hidilyn Diaz?

    • Answer: E. B and C are true. A weightlifter like Hidilyn Diaz likely has muscles that insert closer to the fulcrum (the joint), providing a mechanical advantage for lifting heavy weights. She also likely experiences less central fatigue, which refers to the brain's ability to sustain effort and coordination over extended periods.

    Muscle Properties

    • Elasticity is a muscle's ability to return to its original resting length after being stretched

    Naming Skeletal Muscles

    • Location: Muscles are named based on their location in relation to specific bones.
    • Shape: Muscles are often named after their shape (e.g., Deltoid, trapezius).
    • Relative Size: Size relative to other muscles (e.g., Teres minor, Teres major).
    • Direction of Muscle Fibers: The orientation of muscle fibers (e.g., Rectus abdominis, Oblique).
    • Number of Origins: The number of attachment points.
    • Location of Attachments: The origins and insertions of muscles.
    • Action: The movement the muscle causes (e.g., Flexor, Extensor).

    Muscle Actions

    • Flexor: Bends a part near a joint.
    • Extensor: Straightens a part near a joint.
    • Abductor: Moves a part away from the midline of the body.
    • Adductor: Moves a part towards the midline of the body.
    • Dilator: Opens spaces or widens openings
    • Constrictor: Closes or compresses openings.
    • Levator: Raises a body part.
    • Depressor: Lowers a body part.

    Muscle Named by Location

    • Tibialis Anterior: Located in front of the tibia.
    • Frontalis: Muscle on top of the frontal bone.
    • Temporalis: Muscle on top of the temporal bone.
    • Epicranius: Located around the cranium.

    Muscle Contraction

    • Period of contraction: Cross bridges are active, generating tension.
    • Period of relaxation: Calcium is pumped back into the sarcoplasmic reticulum (SR), reducing cross-bridge formation and muscle tension.

    Muscle Fiber Types

    • Skeletal muscle fibers differ in their speed of contraction due to the different types of fibers present.
    • Fast-twitch fibers: Contract rapidly and generate high force, but fatigue quickly.
    • Slow-twitch fibers: Contract slowly and generate less force, but are fatigue-resistant.

    Tetanus

    • Summation of twitches: Repeated stimulation of a muscle fiber at high frequency leads to a sustained contraction called tetanus.
    • Incomplete (Unfused Tetanus): Muscle fibers relax briefly between stimulations; peak tension increases but oscillates.
    • Complete (Fused Tetanus): Muscle fiber contractions fuse together, resulting in a smooth, sustained contraction at high force.

    Motor Unit

    • The smallest functional unit of a muscle: Consists of a motor neuron and all the muscle fibers it innervates.
    • Smallest amount of muscle that can be activated voluntarily.
    • Extrafusal fibers: The bulk of muscle fibers, generating force; innervated by alpha motor neurons
    • Intrafusal fibers: Specialized sensory fibers within muscle spindles; innervated by gamma motor neurons.

    Types of Muscle Contraction

    • Isotonic Contraction: Muscle changes length while contracting.
      • Concentric: Muscle shortens.
      • Eccentric: Muscle lengthens, often resulting in muscle damage after exercise.
    • Isometric Contraction Muscle contracts but does not change length; load is too heavy or immovable.

    Muscle Fatigue

    • Central Fatigue: Results from the central nervous system (brain and spinal cord) being unable to effectively activate motor neurons.
    • Peripheral Fatigue: Occurs in muscle fibers, due to the accumulation of metabolic waste, such as lactate and hydrogen ions.

    Production of Energy for Muscle Contraction

    • ATP (adenosine triphosphate): The primary energy source for muscle contraction.
    • Creatine Phosphate: Provides a rapid source of energy for muscle contraction.
    • Aerobic Respiration: Uses glucose and oxygen to produce ATP, providing a sustained energy source for muscle activity.
    • Lactic Acid Production: A byproduct of anaerobic respiration, which can lead to muscle fatigue.

    Oxygen Debt

    • Muscle cells require oxygen to perform aerobic respiration.
    • During intense exercise, oxygen demand exceeds supply.
    • Oxygen debt: The amount of oxygen needed to restore muscle cells to their resting state after exercise.
    • Lactic acid buildup: Can contribute to muscle fatigue during intense exercise.

    Muscle Fatigue

    • A condition where a muscle loses its ability to contract.
    • Causes:
      • Lactic acid buildup
      • Interruption of blood supply to the muscle
      • Motor neurons losing the ability to release acetylcholine (neurotransmitter crucial for muscle contraction).

    Muscle Remodeling

    • Muscles undergo continuous remodeling in response to activity and inactivity.
    • Hypertrophy: Increase in muscle mass due to increased contractile proteins, energy-supplying enzymes, and sarcomere number.
    • Atrophy: Decrease in muscle mass due to inactivity or nerve damage.
    • Hyperplasia: Increase in muscle fiber number; rare phenomenon, usually occurring under extreme conditions.

    Muscle Strains and Sprains

    • Strains: Injuries caused by overstretched muscles or tendons.
    • Sprains: More serious injuries involving tears to tendons, ligaments, and cartilage of joints.
    • RICE treatment: Rest, Ice, Compression, Elevation.

    Muscle Strain and Sprain Prevention

    • Warm-up: Prepares muscles for activity, increasing temperature and flexibility.
    • Stretching: Improves muscle performance; perform after warming up or exercising.
    • Cool-down: Slowing down gradually helps to remove lactic acid and prevent blood pooling.

    Aging and Muscles

    • Decreased strength and speed of contraction: Muscle fibers become slower and weaker with age.
    • Reduced dexterity and gripping ability:
    • Potential decrease in mobility:
    • Exercise and assistive devices: Regular exercise, like swimming, and assistive devices can help maintain muscle health in older adults.

    Diseases and Disorders of the Muscular System

    • Botulism: A bacterial infection that affects nerve function, leading to muscle weakness.
    • Fibromyalgia: Chronic pain condition affecting joints, muscles, and tendons.
    • Muscular Dystrophy: Inherited disorder characterized by progressive muscle weakness and loss of muscle tissue.
    • Myasthenia Gravis: Autoimmune disorder that causes muscle weakness.
    • Rhabdomyolysis: Damage to kidney function due to severe muscle injury and release of muscle proteins into the bloodstream.
    • Tendonitis: Painful inflammation of a tendon and its attachment to bone.
    • Torticollis (Wryneck): A condition where the head is tilted to one side due to a spasm or shortening of the sternocleidomastoid muscle.

    Clinical Applications

    • Muscular Dystrophy: Caused by mutations in the dystrophin-glycoprotein complex, leading to progressive muscle weakness.
    • Malignant Hyperthermia: A rare condition where certain anesthetics trigger a release of calcium in susceptible individuals.
    • Dantrolene: Used to treat malignant hyperthermia.

    Types of Muscles

    • Rhomboideus major: A muscle that pulls the shoulder blade toward the spine.
    • Trapezius: A large muscle in the back that helps move the shoulder blade and extends the neck.
    • Orbicularis A muscle that closes the mouth or eyes.

    Muscle Movements

    • Origin: The attachment of a muscle to a bone that stays stationary.
    • Insertion: The attachment of a muscle to a bone that moves.
    • Belly: The fleshy part of the muscle between the tendons of origin and insertion.
    • Contraction: Shortening the length of a muscle fiber.
    • Extension: Lengthening the length of a muscle fiber.

    Major Head Muscles

    • Sternocleidomastoid: A muscle in the neck extends the neck forward.
    • Splenius capitis: A neck muscle that rotates the head.
    • Orbicularis Oris: A muscle surrounding the mouth that controls puckering and closing of the mouth.
    • Frontalis: A muscle that raises the eyebrows.
    • Orbicularis Oculi: A muscle that closes the eyes.
    • Platysma: A muscle that moves the corners of the mouth downward.
    • Zygomaticus: A muscle that pulls the corners of the mouth upward.
    • Masseter and Temporalis: A set of jaw muscles that closes the jaw.

    Major Arm Muscles

    • Pectoralis major: A muscle that pulls the arm across the chest, rotates and adducts the arms.
    • Latissimus dorsi: A muscle that extends and adducts the arm, rotates the arm inwardly.
    • Biceps brachii: A muscle that flexes the arm at the elbow and rotates the hand.
    • Brachialis: A muscle that flexes the arm at the elbow.
    • Brachioradialis: A muscle that flexes the forearm at the elbow.
    • Triceps brachii: A muscle that extends the arm at the elbow.
    • Supinator: A muscle that rotates the forearm laterally.
    • Pronator teres: A muscle that rotates the forearm medially.

    Major Wrist, Hand, and Finger Muscles

    • Flexor carpi radialis and flexor carpi ulnaris: Muscles that flex and abduct the wrist.
    • Palmaris longus: This muscle flexes the wrist.
    • Flexor digitorum profundus: This muscle flexes the distal joints of the fingers, but not the thumb.
    • Extensor carpi radialis longus and brevis: Muscles that extend the wrist and abduct the hand.
    • Extensor carpi ulnaris: A muscle that extends the wrist.
    • Extensor digitorum: A muscle that extends the fingers, but not the thumb.

    Major Respiratory Muscles

    • Diaphragm: A dome-shaped muscle that separates the thoracic and abdominal cavities and contracts to inspire (breathe in).
    • External and internal intercostals: These muscles expand and lower the ribs during breathing.

    Major Abdominal Muscles

    • External and internal obliques: These muscles compress the abdominal wall.
    • Transverse abdominis: This muscle compresses the abdominal wall.
    • Rectus abdominis: A muscle that flexes the vertebral column and compresses the abdominal wall.

    Major Pectoral Girdle Muscles

    • Trapezius: A muscle that raises the arms and pulls the shoulders downward.
    • Pectoralis minor: This muscle pulls the scapula downward.

    Major Leg Muscles

    • Psoas major and iliacus: Muscles that flex the thigh.
    • Gluteus maximus: A muscle that extends the thigh.
    • Gluteus medius and minimus: Muscles that abduct and rotate the thighs medially.
    • Adductor longus and magnus: Muscles that adduct and rotate the thighs laterally.
    • Biceps femoris, semitendinosus, and semimembranosus: These muscles make up the hamstring group, which flexes the leg at the knee.
    • Rectus femoris, vastus lateralis, vastus medialis, and vastus intermedius: These muscles are part of the quadriceps muscle group and extend the leg at the knee.
    • Sartorius A muscle that flexes the leg at the knee and thigh. It abducts the thigh, rotating it laterally, but rotates the lower leg medially.

    Major Ankle, Foot, and Toe Muscles

    • Tibialis anterior: This muscle inverts the foot and points the foot up.
    • Extensor digitorum longus: A muscle that extends the toes and points the foot up.
    • Soleus: A muscle that flexes the foot.
    • Flexor digitorum longus: A muscle that flexes the foot and toes.
    • Gastrocnemius: A muscle that flexes the foot and flexes the leg at the knee.

    Naming Muscles

    • Maximus, minimis, longus, brevis, major: refer to the size of the muscle.
    • Rectus, transverse, oblique: refer to the direction of muscle fibers.
    • Biceps, triceps, quadriceps: refer to the number of origins.
    • Origin and Insertion: Muscles can be named for their points of attachment.
    • Action: Some muscles are named for their actions.

    Arrangement of Fascicles

    • Parallel: A muscle that is strap-like. Example: Sartorius.
    • Fusiform: A muscle that is spindle shaped. Example: Biceps femoris.
    • Pennate: A muscle that is feather shaped:
      • Unipennate: Example: Extensor digitorum longus.
      • Bipennate: Example: Rectus femoris.
      • Multipennate: Example: Deltoid.
    • Convergent: A muscle with fibers that converge at a single point. Example: Pectoralis major.
    • Circular: A muscle that encircles an opening. Example: Orbicularis oris.

    Muscle Structure

    • Muscle fibers: Individual muscle cells.
    • Myofibrils: Within a muscle fiber are a bundle of long protein filaments called myofibrils. They are the contractile elements of muscle cells.
    • Sarcomere: The basic functional unit of a myofibril. Contains protein filaments called myosin and actin.
    • Sarcoplasmic reticulum: A network of membranes that stores calcium ions, essential for muscle contraction.

    Composition of Myofilaments

    • Myosin: Thick filaments composed of the protein myosin.
    • Actin: Thin filaments composed of the protein actin.
    • Tropomyosin: A protein associated with actin, preventing myosin from interacting with actin.
    • Troponin: A protein complex attached to tropomyosin, It can bind calcium ions and regulate muscle contraction.

    Neuromuscular Junction

    • The point where a motor neuron communicates with a muscle fiber.
    • Acetylcholine (Ach) is released from the motor neuron, triggering the muscle to contract.

    Muscle Contraction

    • Excitation-contraction coupling: The process by which a nerve impulse triggers a muscle contraction.
    • Steps of Muscle Contraction:
      • Action Potential: A nerve impulse travels down a motor neuron, triggering the release of acetylcholine at the neuromuscular junction.
      • Sarcolemma and SR: The action potential spreads across the muscle fiber membrane and travels into the muscle fiber via T-tubules, stimulating the release of calcium ions from the sarcoplasmic reticulum.
      • Myosin and Actin: The presence of calcium ions allows myosin to bind to actin and initiate the sliding filament mechanism of muscle contraction.

    Muscle Tension

    • Length-Tension Relation: The amount of tension a muscle can generate is influenced by its length.
    • Isometric Contraction: Muscle contracts, but its length remains the same.
    • Isotonic Contraction: Muscle contracts, and there is a change in its length.
      • Concentric: Muscle shortens.
      • Eccentric: Muscle lengthens.

    Muscle Tension: Factors

    • Fiber diameter: Larger fibers produce more force.
    • Number of active fibers: More fibers produce more force.
    • Number of active motor units: More motor units activated produce more force.

    Muscle Fatigue

    • Peripheral fatigue: Fatigue resulting from the build-up of metabolites in the muscle fibers.
    • Central fatigue: Fatigue resulting from changes in the central nervous system.

    Muscle Remodeling

    • Hypertrophy: Muscle growth in size, due to an increase in the number of contractile proteins and other components in muscle cells.
    • Atrophy: Muscle shrinkage, caused by a decrease in the number of contractile proteins.

    Production of Energy

    • ATP: The primary source of energy for muscle contraction.
    • Creatine Phosphate: A molecule in muscles that quickly provides energy for short bursts of activity.
    • Aerobic Respiration: The long-term process of using glucose and oxygen to make ATP.
    • Lactic Acid Production: Anaerobic process that occurs when oxygen is limited, producing lactic acid.

    Oxygen Debt

    • The accumulation of lactic acid during intense exercise. Requires additional oxygen to convert the lactic acid back to glucose in the liver.

    Muscle Fatigue

    • The inability of a muscle to contract.
    • Causes:
      • Accumulation of lactic acid:
      • Interruption of blood supply:
      • Motor neuron failure:

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    Test your knowledge on muscle anatomy, types, and functions with this engaging quiz. Discover interesting facts about skeletal, smooth, and cardiac muscle tissues, as well as their unique characteristics and roles in the body. Perfect for biology enthusiasts and students alike!

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