Muscle Physiology and Mechanism of Action
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Questions and Answers

What is the primary function of circular muscles in invertebrates?

  • To bring body parts closer together
  • To shorten and widen the body
  • To decrease the diameter of the body (correct)
  • To move limbs apart

    • How do longitudinal muscles interact with circular muscles in invertebrates?

  • They perform the same function as circular muscles
  • They assist in increasing body diameter
  • They are primarily used for flying
  • They work in opposition to circular muscles (correct)

    • Which function do adductor muscles serve in bivalve mollusks?

  • They aid in swimming
  • They control the movement of limbs
  • They bring the two shells together (correct)
  • They assist in burrowing into the ground

    • What kind of movement do many invertebrates use when crawling?

    <p>Waves of movement</p> Signup and view all the answers

    Which of the following groups of invertebrates is primarily associated with swimming?

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

    What characteristic distinguishes vertebrate muscular systems from invertebrate muscular systems?

    <p>Bundles of muscle fibers arranged in complex compartments</p> Signup and view all the answers

    Which type of muscle is primarily responsible for the movement of limbs and appendages in crustaceans?

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

    What type of movement mechanism is associated with earthworms burrowing into the ground?

    <p>Crawling with wave-like motions</p> Signup and view all the answers

    What protein filaments are found in myofibrils?

    <p>Thick (myosin) and thin (actin)</p> Signup and view all the answers

    What happens to the myosin head during the power stroke?

    <p>It pivots back to its low-energy configuration</p> Signup and view all the answers

    What is the role of dystrophin in muscular dystrophy?

    <p>It helps keep muscle cells intact</p> Signup and view all the answers

    What is one of the major functions of the vertebrate muscular system?

    <p>Production of body heat</p> Signup and view all the answers

    Which of the following statements is true about muscular dystrophy?

    <p>It is an inherited group of diseases</p> Signup and view all the answers

    Which type of muscle is responsible for involuntary movements such as heart contractions?

    <p>Cardiac muscles</p> Signup and view all the answers

    What is required for the myosin head to detach from the actin filament?

    <p>Binding of another ATP molecule</p> Signup and view all the answers

    In which type of muscular dystrophy is the disorder most common in boys?

    <p>Duchenne muscular dystrophy</p> Signup and view all the answers

    How do bones and joints contribute to movement in the vertebrate muscular system?

    <p>They act as levers for muscle force generation.</p> Signup and view all the answers

    What distinguishes parallel muscle fibers from pennate muscle fibers?

    <p>Parallel fibers are stronger, while pennate fibers are faster.</p> Signup and view all the answers

    What is the primary action of the myosin head during muscle contraction?

    <p>It forms cross-bridges with actin</p> Signup and view all the answers

    Which of the following is NOT a function of the vertebrate muscular system?

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

    Which statement best describes a sarcomere?

    <p>It is the contractile unit in muscle tissue</p> Signup and view all the answers

    What role does the nervous system play in the function of vertebrate muscles?

    <p>Sends signals coordinating contractions and relaxations</p> Signup and view all the answers

    What term is used for the specific points where muscles are attached to bones?

    <p>Origins and insertions</p> Signup and view all the answers

    Which characteristic of muscle fibers affects their function in movement?

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

    What is a key characteristic of skeletal muscles?

    <p>They are multinucleated.</p> Signup and view all the answers

    Which of the following correctly describes smooth muscles?

    <p>They have tapered ends and a single nucleus.</p> Signup and view all the answers

    Which muscle type is under involuntary control?

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

    What function is primarily associated with skeletal muscles?

    <p>Maintaining posture and producing heat.</p> Signup and view all the answers

    What distinguishes cardiac muscle from skeletal muscle?

    <p>Cardiac muscle fibers are branched.</p> Signup and view all the answers

    Where in the body would you typically find smooth muscle?

    <p>In the digestive tract and blood vessels.</p> Signup and view all the answers

    What role do intercalated discs play in cardiac muscle?

    <p>They facilitate synchronized contraction.</p> Signup and view all the answers

    Which option describes the control mechanism for skeletal muscles?

    <p>Regulated under voluntary control.</p> Signup and view all the answers

    What is the primary function of smooth muscle in the digestive tract?

    <p>To propel food through the digestive tract</p> Signup and view all the answers

    Which physiological mechanism occurs after a blood vessel is severed?

    <p>Vasoconstriction to minimize bleeding</p> Signup and view all the answers

    How do smooth muscle fibers in the iris affect vision?

    <p>By regulating pupil size</p> Signup and view all the answers

    Which statement best describes the function of arterioles?

    <p>They regulate blood flow by constricting or dilating</p> Signup and view all the answers

    What stimulates the release of oxytocin during labor?

    <p>Stretching of the cervical area</p> Signup and view all the answers

    What role do smooth muscles in blood vessels play?

    <p>They regulate blood pressure and flow</p> Signup and view all the answers

    In the context of the muscular system, how does smooth muscle differ from skeletal muscle?

    <p>Smooth muscle facilitates the movement of substances in hollow organs</p> Signup and view all the answers

    What is the function of muscle contractions in the defecation reflex?

    <p>To facilitate the ejection of waste from the body</p> Signup and view all the answers

    Study Notes

    Myofibrils

    • Contain bundles of overlapping thick (myosin) and thin (actin) filaments.
    • Sarcomeres are repeating groups of thick and thin filaments.
    • Sarcomeres are contractile units, the fundamental unit of muscle action.

    Mechanism of Filament Sliding

    • Myosin head binds a molecule of ATP.
    • Myosin head is in its low-energy position.
    • Myosin hydrolyzes ATP to ADP and phosphate, releasing energy that extends the myosin head toward the thin filament.
    • Myosin head extends further, and its other binding site latches onto the binding site of an actin.
    • This results in a connection between the two filaments—a cross-bridge.
    • ADP and P are released, the myosin head pivots back to its low-energy configuration, pulling the thin filament toward the center of the sarcomere. This is called the power stroke.
    • The cross-bridge remains intact until another ATP molecule binds to the myosin head, the cycle repeats.

    Muscular Dystrophy

    • Inherited group of diseases that cause progressive weakness and loss of muscle mass.
    • Types include Duchenne MD and Becker MD.
    • More common in boys.

    Duchenne Muscular Dystrophy (DMD)

    • Genetic disorder characterized by progressive muscle degeneration and weakness.
    • Caused by alterations of the protein dystrophin.
    • Dystrophin helps keep muscle cells intact.
    • Affects voluntary movement of the body.

    Invertebrates Muscle System

    • Circular and longitudinal muscles are arranged in circular and longitudinal patterns around the body of invertebrates, such as worms.
    • Circular muscles wrap around the body in a ring-like manner and contract to narrow the body or segment.
    • Longitudinal muscles run lengthwise along the body segments and contract to shorten and widen the body.
    • Adductor muscles bring body parts closer together, while abductor muscles move them apart.

    Invertebrates Muscle System - Examples

    • Bivalve mollusks (oysters, clams) use adductor muscles to pull their shells together.
    • Crustaceans (crabs) use adductor muscles to control the closing of claws (chelae) and abductor muscles to control limbs and appendage movements.

    Invertebrate Movement Mechanisms

    • Crawling - Many use muscles to create waves of movement, such as worms and insects.
    • Swimming - Aquatic invertebrates, such as jellyfish and fish, use muscles to propel themselves through the water.
    • Flying - Insects and birds have developed wings and muscles for flight.
    • Burrowing - Invertebrates such as earthworms and moles use muscles to burrow into the ground.

    Vertebrates Muscle System

    • More complex than invertebrate muscle systems.
    • Muscles are organized into groups that work together in a coordinated manner.
    • These groups, muscle compartments, are often separated by connective tissue sheaths for organization and support.

    Major Functions of Vertebrate Muscle System

    • Body movement and maintenance of posture.
    • Respiration.
    • Production of body heat.
    • Communication.
    • Constriction of organs and vessels.
    • Heart beat.

    Types of Vertebrate Muscles

    • Skeletal Muscles
    • Cardiac Muscles
    • Smooth Muscles

    Skeletal Muscles

    • Striated or voluntary - under the control of the will.
    • Forms the large proportion of body musculature.
    • Cells are multinucleated.
    • Shape depends on location and function.

    Skeletal Muscles

    • Structure: Composed of elongated, multinucleated striations, connected to bones via tendons.
    • Control: Voluntary.
    • Function: Body movements, maintaining posture, and producing heat during contraction.
    • Examples: Biceps brachii, quadriceps, and pectoralis major.

    Smooth Muscles

    • Smooth or Nonstriated or Involuntary - movement is not under the control of the will, but under the control of the sympathetic nervous system.
    • May also be called involuntary muscle or visceral muscle.
    • Cells are tapered ends, single nucleus, and no striations.
    • Nerve impulses bring about contractions, but cannot be controlled.
    • Visceral refers to internal organs, many of which contain smooth muscle.

    Smooth Muscles

    • Structure: Spindle-shaped cells, single nucleus, no striations.
    • Control: Involuntary.
    • Function: Contraction, peristalsis, blood vessel constriction, pupil dilation, urinary bladder emptying.
    • Examples: Digestive tract, blood vessels, Respiratory system, urinary system, reproductive system, eye, etc.

    Cardiac Muscle

    • Cardiac or Striated Involuntary Muscle.
    • Found only in the heart.
    • Striated but involuntary.

    Cardiac Muscle

    • Structure: Cardiac muscle fibers are striated, branched, and interconnected by intercalated discs which facilitate synchronized contraction. Usually mononucleated.
    • Control: Involuntary control, regulated by the autonomic nervous system and hormones.
    • Function: Pumps blood throughout the body by contracting the heart.
    • Location: Found exclusively in the walls of the heart.

    Smooth Muscle Functions

    • Contractions facilitate functions of the organs in which it is found.
    • In the stomach and intestines, smooth muscle contracts in waves called peristalsis to propel food through the digestive tract.
    • In the walls of arteries and veins, smooth muscle constricts or dilates to maintain normal blood pressure.
    • Arterioles are small arteries, smooth muscle in their walls permits them to constrict (close) or dilate (open).

    Vascular Spasm

    • Smooth muscle contracts (myogenic response) after a blood vessel is severed.
    • Platelets release serotonin, causing vasoconstriction to minimize bleeding.

    Labor Contractions

    • Cervical stretching during labor sends signals to the hypothalamus, triggering oxytocin release, which stimulates strong uterine contractions for delivery.

    Pupil Regulation

    • Smooth muscle fibers in the iris control pupil size, regulating light entry into the eye.

    Defecation Reflex

    • Rectal stretching triggers sensory impulses to the spinal cord, leading to smooth muscle contraction, relaxation of the internal anal sphincter, and defecation.

    Correlation of Muscular System Structures

    • Protection - Skeletal muscles surround vital organs to shield them from injury. Smooth muscles in blood vessels regulate blood pressure and flow, protecting against damage. Muscular diaphragm separates chest and abdominal cavities, protecting organs.
    • Support - Skeletal muscles maintain posture and stabilize joints. Smooth muscles in blood vessels support blood pressure and circulation. Muscular walls of hollow organs provide structural integrity.
    • Movement - Skeletal muscles contract to move bones and joints. Smooth muscles facilitate movement of substances through hollow organs (e.g., peristalsis). Cardiac muscle pumps blood throughout the body.

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    Muscular System Overview PDF

    Description

    This quiz explores the structure and function of myofibrils, focusing on the sliding filament mechanism of muscle contraction, and the implications of muscular dystrophy. Test your understanding of the contractile units and the biochemical processes involved in muscle action.

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