3. Introduction

• Definition of muscular tissue: Muscular tissue consists of specialized cells that contract to produce movement.

• Overview of how muscles enable movement through contraction.

  • Muscles work by contracting, which pulls on bones or other structures, creating movement.

• Muscle cells (fibers) convert chemical energy (from nutrients) into mechanical energy.

  • ATP is the main energy source used by muscle fibers during contraction.

• Three types of muscle tissue: skeletal, cardiac, and smooth.

  • Each type of muscle tissue has unique characteristics and functions.

4. Types of Muscle Tissue

• Skeletal Muscle Tissue:

  • Also called striated or voluntary muscle.

  • Makes up 40-50% of body weight; responsible for voluntary movements.

  • Structure: Crosswise striations visible under the microscope due to the arrangement of actin and myosin filaments.

  • Contractions are controlled consciously, allowing precise and powerful movements.

  • Functions: Movement of bones, maintenance of posture, and heat production.

• Cardiac Muscle Tissue:

  • Found only in the heart; responsible for heart contractions that pump blood throughout the body.

  • Cells have unique intercalated disks that facilitate synchronized contraction, ensuring efficient blood flow.

  • Involuntary control, allowing the heart to function as a single, coordinated unit.

  • Specialized pacemaker cells regulate the heartbeat.

• Smooth Muscle Tissue:

  • Also called nonstriated, involuntary, or visceral muscle.

  • Found in walls of internal organs like the digestive tract, blood vessels, and urinary bladder.

  • Involuntary control; helps with movements like peristalsis in the digestive tract, constriction of blood vessels, and emptying of the bladder.

  • Smooth muscle contractions are slower and more sustained compared to skeletal muscle.

5-7. Skeletal Muscle Tissue Overview

• Structure: Composed of skeletal muscle cells (fibers) and connective tissues.

  • Each muscle is made up of thousands of muscle fibers bundled together by connective tissue.

  • Attachments: Muscles extend from one bone across a joint to another bone, facilitating movement at the joint.

  • Tendons: Strong cords of fibrous connective tissue that attach muscles to bones.

    • Tendons transmit the force generated by muscle contractions to bones, resulting in movement.

  • Tendon Sheaths: Synovial-lined tubes that enclose some tendons, lubricated by synovial fluid to reduce friction.

  • Bursae: Small sacs filled with synovial fluid that reduce friction between tendons and bones, providing cushioning and smooth movement.

8-10. Microscopic Structure of Skeletal Muscle

• Muscle fibers contain myofilaments:

  • Thick Myofilaments: Made of the protein myosin, which has heads that form cross-bridges during contraction.

  • Thin Myofilaments: Made of the protein actin, along with regulatory proteins troponin and tropomyosin.

• Sarcomere: The basic functional unit of a muscle fiber, separated by Z lines.

  • A sarcomere is composed of overlapping thick and thin myofilaments, which slide past each other during contraction.

• Sliding Filament Model: Mechanism of muscle contraction where myofilaments slide past each other, shortening the muscle and generating force.

  • Myosin heads attach to binding sites on actin, forming cross-bridges, and pull the actin filaments inward.

• Contraction Requirements: Calcium ions and ATP are necessary for muscle contraction.

  • Calcium binds to troponin, causing a conformational change that moves tropomyosin, exposing binding sites on actin.

  • ATP provides the energy needed for myosin heads to detach, reset, and reattach to actin, continuing the contraction cycle.

11. Muscle Contraction Mechanism

• How muscle fibers shorten during contraction.

  • When stimulated, calcium ions are released from the sarcoplasmic reticulum into the muscle fiber.

  • Calcium binds to troponin, causing a shift in tropomyosin and exposing myosin-binding sites on actin.

  • Myosin heads bind to actin, forming cross-bridges, and pull the actin filaments toward the center of the sarcomere.

  • ATP binds to myosin, allowing it to release actin and re-cock for another power stroke.

• Role of Calcium and ATP: Essential for initiating and sustaining muscle contraction.

12. Functions of Skeletal Muscle

• Producing movement by pulling on bones, which act as levers.

• Origin and Insertion:

  • Origin: Attachment to the stationary bone; usually closer to the center of the body.

  • Insertion: Attachment to the bone that moves during contraction; usually further from the body's midline.

• Movement: Muscles contract, pulling the insertion bone closer to the origin bone, resulting in movement at the joint.

13-15. Muscle Movement Roles

• Prime Mover: The muscle mainly responsible for a particular movement.

  • Example: Biceps brachii during elbow flexion.

• Synergist: Muscles that assist the prime mover in performing a movement.

  • Example: Brachialis assists the biceps brachii during elbow flexion.

• Antagonist: Muscles that oppose the action of the prime mover.

  • Example: Triceps brachii opposes the biceps brachii during elbow flexion.

• Coordination of Movement: Proper movement requires a balance between prime movers, synergists, and antagonists to prevent injury and ensure smooth motion.

16-17. Posture and Tonic Contractions

• Tonic Contractions: Involve a small number of muscle fibers contracting to maintain posture without producing movement.

  • These contractions are important for maintaining muscle tone and readiness for action.

• Good Posture: Maintains optimal body alignment, reducing strain on muscles and ligaments.

  • Poor posture can lead to muscle fatigue, pain, and decreased efficiency of body movement.

• Role of Skeletal Muscles: Counteract the pull of gravity to maintain body position, ensuring stability and balance.

18-19. Heat Production

• Muscles produce heat through contractions, which helps maintain body temperature.

  • During ATP breakdown, energy is released, and a portion of it is converted to heat.

• Fever: Elevated body temperature due to illness; muscles may produce more heat to fight infections.

• Hypothermia: Body temperature below normal; shivering is a mechanism to generate heat through rapid muscle contractions.

  • Shivering helps maintain core body temperature during exposure to cold.

20-21. Muscle Fatigue

• Causes of Fatigue: Repeated stimulation without adequate rest depletes ATP and oxygen, leading to the accumulation of lactic acid.

  • Lactic acid buildup lowers pH, affecting enzyme activity and reducing contraction efficiency.

• Oxygen Debt: The body needs extra oxygen post-exercise to metabolize lactic acid and restore ATP levels.

  • Heavy breathing after exercise helps repay the oxygen debt.

• Labored Breathing: Required to repay oxygen debt after intense activity and restore homeostasis.

22-23. Integration with Other Systems

• Muscular system works closely with other systems to facilitate movement and maintain homeostasis.

• Respiratory System: Supplies oxygen for ATP production, essential for muscle contraction.

• Circulatory System: Delivers nutrients and oxygen, removes carbon dioxide and waste products from muscles.

• Nervous System: Controls muscle contractions through motor neurons.

  • Examples of conditions affecting movement: Multiple sclerosis (damage to nerves), brain hemorrhage (interruption of motor signals), spinal cord injury (loss of motor control).

24. Learning Objectives (Lesson 9.2)

• Understand muscle stimulation, types of muscle contractions, effects of exercise, and common muscular disorders.

• Learn about the major muscles of the body and their functions.

• Recognize how exercise and lifestyle choices affect muscle health.

25-26. Motor Unit and Muscle Stimulation

• Motor Unit: Consists of a motor neuron and all the muscle fibers it controls.

  • A single motor neuron may control hundreds of muscle fibers, allowing for coordinated contractions.

• Neuromuscular Junction (NMJ): Point where a motor neuron meets a muscle fiber.

  • The NMJ is where the nerve impulse triggers the release of acetylcholine (ACh), leading to muscle contraction.

• Threshold Stimulus: Minimum level of stimulus required to trigger a contraction.

• All-or-None Response: Muscle fibers contract fully when stimulated above the threshold; there is no partial contraction of individual fibers.

27. Types of Muscle Contraction (1/3)

• Twitch Contractions: Quick, jerky responses to a single stimulus.

  • Not useful for most types of movement but can be observed in laboratory settings.

• Tetanic Contractions: Sustained contractions caused by rapid, repeated stimuli.

  • These contractions are smooth and are used for normal movements and maintaining posture.

28-29. Isotonic and Isometric Contractions

• Isotonic Contractions: Muscle changes length, producing movement (e.g., lifting weights).

  • Concentric: Muscle shortens as it contracts (e.g., lifting a dumbbell).

  • Eccentric: Muscle lengthens while maintaining tension (e.g., lowering a dumbbell slowly).

• Isometric Contractions: Muscle tension increases without a change in length (e.g., holding a plank position).

  • Important for maintaining stability and posture.

30-31. Effects of Exercise on Skeletal Muscles (1/3)

• Strength Training: Increases muscle size (hypertrophy) by increasing myofilament density, leading to greater force production.

  • Examples include weightlifting and resistance band exercises.

• Endurance Training: Improves the efficiency of oxygen delivery without significantly increasing muscle size.

  • Examples include running, cycling, and swimming.

  • Enhances cardiovascular health and increases the number of mitochondria in muscle cells.

32-33. Types of Movements by Skeletal Muscle (1/3)

• Flexion: Decreases the angle between two bones (e.g., bending the elbow).

• Extension: Increases the angle between two bones (e.g., straightening the knee).

• Abduction: Movement away from the midline (e.g., raising the arm sideways).

• Adduction: Movement toward the midline (e.g., bringing the arm back to the body).

34. Types of Movements (2/3)

• Rotation: Movement around a longitudinal axis (e.g., turning the head from side to side).

• Supination and Pronation: Hand positions resulting from forearm rotation.

  • Supination: Palm facing upward (as if holding a bowl of soup).

  • Pronation: Palm facing downward.

35. Types of Movements (3/3)

• Dorsiflexion and Plantar Flexion: Movements of the foot.

  • Dorsiflexion: Lifting the top of the foot toward the shin (e.g., standing on your heels).

  • Plantar Flexion: Pointing the foot downward (e.g., standing on tiptoes).

36-38. Skeletal Muscle Groups - Head and Neck

• Facial Muscles: Responsible for facial expressions.

  • Orbicularis oculi: Closes the eyelids.

  • Orbicularis oris: Puckers the lips.

  • Zygomaticus: Raises the corners of the mouth (smiling).

• Muscles of Mastication: Involved in chewing.

  • Masseter: Elevates the mandible (closes the jaw).

  • Temporalis: Assists in closing the jaw.

• Neck Muscles: Important for head movement and support.

  • Sternocleidomastoid: Flexes and rotates the head.

  • Trapezius: Elevates the shoulders and extends the head.

39-40. Muscles of Upper Extremities

• Pectoralis Major: Flexes, adducts, and rotates the upper arm medially (e.g., pushing movements).

• Latissimus Dorsi: Extends, adducts, and medially rotates the upper arm (e.g., pulling movements).

• Biceps Brachii: Flexes the forearm at the elbow and supinates the forearm.

• Triceps Brachii: Extends the forearm at the elbow, important for pushing movements.

41-42. Muscles of the Trunk

• Abdominal Muscles: Support the trunk, allow movement, and hold organs in place.

  • Rectus Abdominis: Flexes the vertebral column (e.g., sit-ups).

  • External Oblique: Helps rotate the trunk and compress abdominal contents.

  • Internal Oblique: Works with external oblique for trunk rotation and compression.

  • Transversus Abdominis: Compresses abdominal contents, providing core stability.

• Respiratory Muscles:

  • Intercostal Muscles: Assist in expanding and compressing the rib cage during breathing.

  • Diaphragm: Primary muscle for breathing; contracts to increase the volume of the thoracic cavity during inhalation.

43-44. Muscles of Lower Extremities (1/2)

• Iliopsoas: Flexes the thigh at the hip joint, important for walking and running.

• Gluteus Maximus: Extends and laterally rotates the thigh, crucial for climbing and standing up.

• Hamstring Group: Flexes the leg at the knee and extends the thigh at the hip.

  • Semimembranosus, Semitendinosus, Biceps Femoris: Work together to perform knee flexion and hip extension.

45-46. Muscles of Lower Extremities (2/2)

• Quadriceps Femoris Group: Extends the leg at the knee joint, important for walking, running, and jumping.

  • Rectus Femoris, Vastus Lateralis, Vastus Medialis, Vastus Intermedius.

• Gastrocnemius: Plantar flexes the foot at the ankle, important for pushing off while walking or running.

• Tibialis Anterior: Dorsiflexes the foot, important for controlling foot placement during walking.

47. Major Muscular Disorders (1/2)

• Myopathies: General term for muscle disorders, ranging from mild to severe.

  • Symptoms may include muscle weakness, cramps, stiffness, and spasms.

• Muscle Strain: Overstretching or tearing of muscle fibers, often causing pain and inflammation.

  • Common in athletes due to overuse or improper warm-up.

• Sprain: Involves ligament damage near a joint, often due to sudden twisting or impact.

  • Can result in swelling, bruising, and reduced joint mobility.

48. Major Muscular Disorders (2/2)

• Cramps: Involuntary, painful muscle spasms that can be caused by dehydration, electrolyte imbalance, or overuse.

• Crush Injuries: Severe trauma that can cause kidney failure due to the release of myoglobin from damaged muscle cells.

  • Requires immediate medical attention to prevent complications.

• Stress-Induced Muscle Tension: Can lead to headaches, neck pain, and back pain.

  • Often related to psychological stress or poor posture.

49-50. Muscle Infections

• Poliomyelitis: Viral infection affecting motor nerves, leading to paralysis and muscle atrophy.

  • Preventable through vaccination.

• Overview of bacterial and parasitic infections affecting muscles.

  • Tetanus: Caused by Clostridium tetani bacteria, leading to severe muscle spasms.

  • Trichinosis: Parasitic infection from undercooked meat, causing muscle pain and inflammation.

51. Muscular Dystrophy

• Group of genetic disorders causing muscle degeneration and weakness.

  • Duchenne Muscular Dystrophy (DMD): Most common type, affecting mainly boys; characterized by rapid progression of muscle weakness, usually beginning in early childhood.

  • Becker Muscular Dystrophy: Similar to DMD but with a slower progression.

52. Myasthenia Gravis

• Autoimmune disorder causing chronic muscle weakness and fatigue.

  • The immune system attacks acetylcholine receptors at the neuromuscular junction, impairing communication between nerves and muscles.

  • Symptoms include drooping eyelids, difficulty swallowing, and generalized muscle weakness.

53-55. Summary of Major Muscle Groups

• Review of Muscle Groups: Head, neck, upper extremities, trunk, and lower extremities.

• Identification: Key muscles, their locations, and functions in movement.

• Function Recap: Role of each muscle group in daily activities and movement.

  • Emphasize how different muscle groups work together for coordinated movements.

  • Highlight common exercises that target each muscle group.