Poliomyelitis: Symptoms, Transmission, and Treatment

• The muscular system, integumentary system, and skeletal system are required topics for the Anatomy event for the 2020 competition.

Muscular System Knowledge Areas:

• Anatomy of skeletal, cardiac, and smooth muscle
• Roles of skeletal, cardiac, and smooth muscle in the body
• Skeletal muscle fibers, their types, and functions
• Skeletal muscular contraction
• Neuromuscular junction, nervous system role in muscle function, and muscle sensory systems
• Musculoskeletal interactions
• Identification of major skeletal muscles, including their origins, insertions, and functions
• Effects of exercise and aging on the muscular system
• Homeostatic imbalances affecting the muscular system

Health Concepts:

• Interaction of skeletal and muscular systems for movement
• Cellular and gross anatomy of skeletal, cardiac, and smooth muscle
• Physiology of skeletal muscle contraction and the neuromuscular junction
• Skeletal muscle movement of bones, maintenance of posture, and heat production
• Skeletal muscle actions, including origin, insertion, and interactions of muscles
• Location, identification, origin, insertion, and function of major muscles on the 2020 Science Olympiad Major Skeletal Muscle List
• Exercise and aging effects on cellular and gross anatomical structures of the muscular system
• Muscle and tendon injuries and prevention, like strains and sprains
• Diseases from the cellular level to the whole person, specifically Poliomyelitis, Muscular Dystrophies, Myasthenia gravis, tetanus, myositis

National Topics:

• Kinds of muscle contraction
• Classes of muscle fibers and their functions
• Cardiac and smooth muscle roles in the body
• Role of the nervous system in muscle function
• Muscle sensory systems like spindles and Golgi tendon organs
• Additional diseases: Carpal Tunnel Syndrome, Botulism, Fibromyalgia, and Chronic fatigue syndrome
• Treatments and/or prevention for all conditions (drugs, surgery, etc.)

Muscles and Muscle Tissue:

• Types of muscle tissue: skeletal, cardiac, and smooth muscle
• Skeletal and smooth muscle cells are elongated and called muscle fibers

Skeletal Muscles:

• Attach to skeleton and cover it
• Longest muscle fibers and are striated
• Voluntary muscles, subject to conscious control
• Primarily to give the body its mobility

Cardiac Muscles:

• Found only in the heart, constitutes the walls of the heart
• Cells are striated but not elongated
• Can contract without stimulation, but involuntary; no conscious control over the heart
• The nervous system controls changes in the heartbeat

Smooth Muscles:

• Found in walls of hollow visceral organs like the stomach, bladder, and respiratory passages
• Functions to force substances, especially fluids
• Fibers are elongated but not striated
• Involuntary; no conscious control over actions

Muscle Tissue Characteristics:

• Excitability/Responsiveness: Ability to receive stimuli and respond by generating electrical impulses that cause cells to contract
• Contractility: Ability of a cell to shorten in response to stimuli, unique to muscle tissues
• Extensibility: Ability to extend or stretch; can stretch beyond resting length when muscles are relaxed
• Elasticity: Ability to recoil and resume resting length after stretching

Muscle Functions:

• Producing movements via skeletal muscles (locomotion and manipulation), cardiac muscles (blood pumping), and smooth muscles (squeezing substances)
• Maintaining posture by constant tiny movements to counteract forces like gravity
• Stabilizing joints by assisting bones, ligaments, and tendons.
• Generating heat; skeletal muscles account for at least 40% of body mass and help maintain normal body temperature
• Providing protection by enclosing internal organs

Skeletal Muscle Anatomy

• Made of muscle fibers, blood vessels, nerve fibers, and connective tissue
• Innervated by a nerve and supplied by blood vessels

Blood Supply:

• Vital because muscles use huge amounts of energy
• Constant delivery of oxygen and nutrients via arteries
• Metabolic wastes removed via veins
• Tiny capillaries accommodate changes in muscle length during contraction

Connective Tissue Sheaths:

• Support cells and hold muscle together as a whole

• Epimysium: Dense irregular connective tissue surrounding the muscle

• Fascicles: Bundles of muscle fibers inside each muscle

• Perimysium: Fibrous connective tissue surrounding each fascicle

• Endomysium: Sheath of fine areolar connective tissue surrounding each individual muscle fiber

• Skeletal muscles produce movement by working with bones, ligaments, and tendons

• Most muscles attach to bones in two places: the origin and the insertion

• During muscle contraction, the insertion moves toward the origin

• Muscles may attach directly or indirectly

Microscopic Anatomy of Skeletal Muscle Fiber:

• Long, cylindrical cell
• Sarcolemma: Plasma membrane with multiple oval-shaped nuclei underneath
• Large diameter, ranging from ten to a hundred micrometers in diameter
• Length is up to thirty centimeters long due to the fusing of hundreds of embryonic cells
• Sarcoplasm: Similar to cytoplasm, contains glycosomes and myoglobin; also contains organelles, myofibrils, a sarcoplasmic reticulum, and T-tubules

Myofibrils:

• Hundreds to thousands in a single muscle fiber
• Run in the same direction as muscle fibers, tightly packed, taking up 80% of cell volume
• Sarcomeres: Responsible for contraction; contain three types of myofilaments

Three Types of Myofilaments:

• Thick filaments: Primarily in the center, contain myosin

• Thin filaments: Primarily towards the sides, contain actin

  • Tropomyosin: Blocks myosin-binding sites on actin
  • Troponin: Binds to actin, tropomyosin, and calcium ions

• Elastic filaments: Composed of titin, which holds the thick filaments in place

• Cross bridge cycle: Myosin, actin, tropomyosin, troponin, and titin all play a role in generating movement by proteins sliding past each other

  • Also dystrophin, nebulin, myomesin, and C proteins

• Sarcoplasmic reticulum is a smooth endoplasmic reticulum

• Tubules surround myofibrils; some run perpendicular and occur in pairs called terminal cisterns

• Regulates calcium ion levels in the cell

• Stores calcium ions (Ca2+) and releases them when the muscle fiber is stimulated

T-tubules:

• Elongated tubes that run between paired terminal cisterns, forming triads
• Continuations of the sarcolemma that conduct electrical impulses to every sarcomere, releasing calcium ions

Sliding Filament Model:

• Myosin heads latch onto myosin-binding sites on actin, forming cross bridges
• Cross bridges form and break several times during a single muscle contraction, generating tension and sliding thin filaments toward the center of the sarcomere
• Occurs in sarcomeres throughout the cell, shortening the cell. Z discs are pulled toward the M line, I bands shorten, Z discs become closer, H zone disappears, and A bands move closer together

Physiology of Skeletal Muscle Fibers:

• Activated by somatic motor neurons whose axons extend to muscle cells
• Each axon ending forms several short, curling branches that form a neuromuscular junction with a single muscle fiber
• Axon terminal is separated from the muscle fiber by the synaptic cleft: space filled with a gel-like substance
• Synaptic vesicles: small membranous sacs located within the axon terminal, contain acetylcholine (a neurotransmitter)
• Junctional folds: folds in sarcolemma that form the neuromuscular joint that provide a surface area for acetylcholine receptors.

Events at the Neuromuscular Junction:

• Action potential reaches an axon terminal, releasing acetylcholine into the synaptic cleft
• Acetylcholine diffuses across the cleft, attaching to acetylcholine receptors on the sarcolemma
• Acetylcholinesterase: Enzyme that terminates the effects of acetylcholine by breaking it down to acetic acid and choline
• Acetylcholine binding to receptors opens ligand-gated ion channels, increasing sodium and decreasing potassium diffusion, thus, causing the membrane potential to change
• Depolarization: change in membrane potential
• Endplate potential: Localized depolarization spreads to adjacent membranes and opens voltage-gated sodium channels, allowing sodium ions to enter. Once the threshold potential is reached, an action potential is generated
• Action potential moves along with the sarcolemma, opening more voltage-gated sodium channels
• Repolarization wave causes voltage-gated sodium channels to close and voltage-gated potassium channels to open, causing another change in membrane potential
• Refractory period will occur: Muscle fibers cannot be stimulated, and repolarization is complete

Skeletal Muscle Fiber Classification:

• Classified as slow or fast fibers based on contraction velocity
• Classified as oxidative or glycolytic fibers based on the pathways they use for forming ATP

Fiber Types:

• Slow oxidative (SO) fibers:

  • Contract slowly because their myosin ATPases are slow
  • Dependent on oxygen delivery and aerobic pathways
  • High levels of myoglobin (red), low glycogen stores, small fiber diameters, many mitochondria, and many capillaries
  • Suited for endurance activities

• Fast oxidative (FO) fibers:

  • Contract quickly because their myosin ATPases are fast
  • Dependent on aerobic pathways but also use glycolytic reserves
  • High myoglobin levels (red to pink), moderate glycogen stores, moderate fiber diameters, many mitochondria, and many capillaries
  • Suited for activities like sprinting and walking

• Fast glycolytic (FG) fibers:

  • Contract rapidly because their myosin ATPases are fast Independent of oxygen and use glycolytic reserves for fuel
  • Low myoglobin levels (white), low glycogen stores, large fiber diameters, few mitochondria, and few capillaries
  • Suited for short, rapid, intense movements

• Muscle tension: Force exerted by a muscle on an object

• Load: Force exerted on the muscle by the weight of the object

Contractions:

• Isometric: Force exerted by the muscle, but the load doesn't move, and muscle fibers don't change lengths

• Isotonic: Force overcomes the load, and muscle fibers change lengths

  • Concentric: Isotonic contractions in which the force overcomes the load and the muscle fiber shortens
  • Eccentric: Isotonic contractions in which the force overcomes the load and the muscle fiber lengthens

• Muscle tone: All muscles, even when relaxed, are almost always slightly contracted

• It keeps the muscles firm, healthy, and ready to respond to stimuli. It also assists in joint stabilization and posture maintenance

• ATP: Muscle contraction requires energy, which is supplied by ATP

• Muscles store about four to six seconds' worth of ATP

• ATP must be regenerated as quickly as it is broken down because it is the only energy source directly used

• ATP hydrolyzes to ADP and inorganic phosphate, so there are three pathways that may regenerate it

ATP Regeneration:

• Direct Phosphorylation:
  • Creatine phosphate (CP) is used to regenerate ATP
  • CP couples with ADP and adds a phosphate group (plus energy) to form ATP almost instantly.
  • Creatine kinase catalyzes this reaction
  • Muscle cells store two to three times more CP than ATP
  • Accounts for about 15 seconds of power for rigorous activity
  • CP is replenished during rest or inactivity
• Anaerobic Glycolysis:
  • Used when stored ATP and CP are exhausted.
  • ATP generated by catabolizing glucose or glycogen
  • It does not require oxygen
  • Glucose breaks down into two pyruvic acid molecules during glycolysis
  • Pyruvic acid undergoes aerobic respiration as well
  • It harvests five percent as much ATP as aerobic respiration but produces it two and a half times faster
  • Lasts for 30-40 seconds of strenuous activity
• Aerobic Respiration:
  • Produces ninety-five percent of the ATP used during rest, light exercise, and moderate exercise
  • Requires oxygen, which combines with glucose, producing carbon dioxide, water, and ATP
  • Glycogen is the main source of energy at first, then pyruvic acid, and then fatty acids
  • Produces a large quantity of ATP but is very slow

Smooth Muscle Microscopic Anatomy:

• Occupies the walls of the body's hollow organs, but not the heart
• Muscle fibers are spindle-shaped cells with varying sizes, each havingonecentralized nucleus
• Only a tenth the width of skeletal muscle fibers and are thousands of times shorter
• Smooth muscles lack coarse connective tissue sheaths but have fine connective tissue between cells
• Typically organized into two sheets

The Longitudinal Layer:

• Outer layer that contains muscle fibers that ru

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