Unit 2_ Muscular System Pt 1 PDF

Unit 2: Muscular System Pt 1 Objectives Explain sliding filament theory Describe interaction of nervous and muscular system Compare and contrast different types of muscles Describe different types of contractions Overview Overview The muscular system also moves things ins...

Unit 2: Muscular System Pt 1 Objectives Explain sliding filament theory Describe interaction of nervous and muscular system Compare and contrast different types of muscles Describe different types of contractions Overview Overview The muscular system also moves things inside the body. Includes the movement of the digestive system, the cardiovascular system, and the respiratory system. Skeletal: Under voluntary control Striated fibers Cardiac Involuntary Striated Smooth No Striations Involuntary Overview Muscle is a general term for all contractile tissue. The contractile property of muscle tissue allows it to become short and thick as a result of a nerve impulse and then to relax once that impulse is removed. This alternative contraction and relaxation causes movement. Overview The cells of muscle tissue are called muscle fibers. Muscle tissue is constructed of bundles of these fibers, each approximately the diameter of human hair. The body has three major types of muscles: skeletal, smooth, cardiac. Function and Movement Skeletal muscle is divided into layers of cylinders packed inside each other. Epimysium surrounds the outer muscle. Perimysium surround the fascicle (bundles of muscle fibers/cells, inside the muscle. i. Each muscle fiber is encased in endomysium (connective tissue sheath) and filled with myofibrils (cylinders). ii. Myofibrils form a muscle segment when put together. Movement Sarcomeres are sub-units of myofibrils. Each fiber has ability to contract due to two types of thick and thin threadlike structures (myofilaments). Thick myofilaments contain myosin. Think myofilaments contain actin. Z-lines: bands separating thick and thin units Functional Unit Other modifications needed for contraction Sarcolemma: specialized cell membrane Sarcoplasmic reticulum (SR): modified endoplasmic reticulum that stores calcium T-tubules: help spread excitation into the inside of cell Proteins: tropomyosin and troponin Contraction Overview Muscle contraction causes the two types of myofilaments to slide toward each other. This shortens each sarcomere, and therefore the entire muscle. Requires formation of temporary connections (cross-bridges) between myosin and actin fibers to pull the sarcomere together Contraction A chemical signal (neurotransmitter) from acetylcholine begins process. Excited muscle releases calcium from the (SR), which flows to muscle fiber. Body uses ATP to help formation of myosin heads, breaking the cross- bridges. New ATP binds; myosin head returns to pre-contraction state Contraction Skeletal muscle contraction requires coordination of muscular and nervous systems. Contraction initiation requires impulse from a motor neuron (at neuromuscular junction) to cause release of a acetylcholine. Opens sodium channels Sets process in motion https://app.jove.com/embed/player?id=10871&t=1&s=1&fpv=1 Contraction Acetylcholine is released from a neuron. Acetylcholine binds to muscle and causes sodium channels to open. Sodium flows into the muscle fiber, and the fiber becomes excited. This excitement causes the release of calcium into the cytoplasm from the S R. https://app.jove.com/embed/player?id=12183&t=1&s=1&fpv=1 Contraction The calcium allows formation of cross-bridges between myosin heads and actin myofilaments. ATP is used up, allowing cross-bridges to break and reform, pulling the actin myofilaments closer together as they slide along the myosin myofilaments. The sarcomere shortens. Many shortened sarcomeres result in shortening of many muscle fibers. This is muscle contraction. Acetylcholinesterase degrades acetylcholine so the muscle can relax. https://app.jove.com/embed/player?id=11803&t=1&s=1&fpv=1 Relaxation Acetylcholinesterase degrades acetylcholine so the muscle can relax. Increased Details: Muscle Contraction Muscle is a specialized contractile tissue, essential for movement in animals. Muscle contraction allows for diverse movements like the tentacles of an octopus and the precision of a ballerina. Contraction is driven by molecular interactions, conserved across many animal species. Increased Details: Sacromeres Sarcomeres are the basic structural units of muscle fibers. Muscle appears striped (striated) under a microscope due to the arrangement of sarcomeres. Thousands of sarcomeres can exist within a single muscle cell, working together to contract the muscle. Sarcomeres are made up of actin (thin) filaments and myosin (thick) filaments. Figure 1: A gastrocnemius muscle (calf) with striped pattern of sarcomeres Increased Details: Sliding Filament Theory Proposed by Huxley and Hanson in 1954. Actin filaments slide past myosin filaments, shortening the sarcomere. Myosin remains central in the sarcomere, while actin filaments slide past it. Myosin pulls on actin via cross-bridges, using ATP for energy (Figure: relaxed vs. contracted sarcomere). As actin slides, Z-discs at the ends of sarcomeres are pulled closer together, shortening the sarcomere and contracting the muscle. Increased Detail: Cross Bridge Cycling Cross bridges form when myosin heads bind to actin filaments. Myosin undergoes a power stroke, pulling actin filaments toward the center of the sarcomere. This process is ATP-dependent, where ATP provides the energy for: Myosin to detach from actin Resetting the myosin head for the next contraction Increased Detail: Power Stroke Myosin binds to actin, forming a cross-bridge. ATP hydrolysis (breaking down of ATP) powers the myosin head to pull actin (called the power stroke). The cycle repeats as myosin releases, rebinds, and pulls actin in a continuous process, leading to muscle contraction. Increased Details: Role of Calcium Calcium binds to troponin, causing tropomyosin to expose binding sites on actin. This process enables the cross-bridge cycle, where myosin pulls actin, shortening the muscle. In resting muscles, tropomyosin blocks myosin binding sites on actin. When calcium binds to troponin, tropomyosin shifts, exposing myosin-binding sites on actin, allowing contraction to occur. ATP and Calcium ATP provides energy for the power stroke and the release of myosin from actin. Calcium is required to initiate contraction by unlocking the binding sites on actin. Without ATP or calcium, muscles cannot contract effectively: Lack of ATP causes rigor mortis (myosin stays attached to actin). Motor Unit A motor unit consists of one α- motor neuron and all the muscle fibers it innervates. When activated, all fibers in the unit contract together. Motor units vary in size; smaller units control fine movements, while larger ones handle powerful movements. This is related to the muscle's function. There are three types of motor units: slow fatigue-resistant (Type I), fast fatigable (Type IIb), and fast fatigue-resistant (Type IIa), each suited to different tasks. Muscular Fuel (1 of 3) Muscles need fuel in the form of food and oxygen to survive and function. The body stores glycogen in the muscle, where it waits to be converted to a useable energy source. ○ When needed, glycogen is converted to glucose which releases energy. Muscular Fuel (2 of 3) Muscles with very high demands also store fat and use it as energy. Energy release causes heat production. That is why an exercising athlete gets overheated. Muscular Fuel (3 of 3) Higher demand muscles also have a greater blood supply to carry much-needed oxygen. The greater blood supply gives them a darker color. ○ An example of this is a chicken which has white and dark meat. Contraction Types Reflexive ○ Not under voluntary control ○ Respiration and DTRs Tonic ○ Describes resting state (tone) ○ Gives a firmness to joints Phasic: ○ Isotonic Produces ○ Isometric No movement Isotonic Subsets Concentric: ○ Muscle shortening Eccentric: ○ Muscle lengthening Function of Muscle Prime Mover (agonist): ○ Contracts concentrically Antagonist ○ Eccentric contraction Fixator ○ Isometric contraction Synergist ○ Assists prime mover Contraction and Relaxation (1 of 4) Movement of the body is the result of contraction (shortening) of certain muscles while there is relaxation of others. The primary mover (or agonist) is the chief muscle causing movement. As the muscle contracts it pulls the bone, causing movement. Contraction and Relaxation (2 of 4) Point of origin ○ The end of the muscle that is attached to the stationary bone Point of insertion ○ Muscle end attached to the moving bone Contraction and Relaxation (3 of 4) Synergistic muscles assist the primary mover. Antagonist muscles cause movement in the opposite direction of the agonist. All movement is a result of contraction of primary movers and relaxation of opposing muscles. Figure 7–3 Cardiac Muscle Forms wall of heart (myocardium) Intrinsic regulation with ANS influence Blood supply to cardiac muscle is double that of skeletal muscle Cardiac Intercalated discs connect cardiac muscle fibers Cause one fiber to contract, then pulls next fiber into a contraction creating a domino effect Wave of motion squeezes blood out very efficiently Cardiac muscle does not repair itself. Damage always leaves a scar. Scar tissue doesn’t contract like normal tissue because it is rigid; decreases cardiac output. Smooth Muscle Involuntary with direct ANS innervation Responds slower than striated muscle Responsible for peristalsis and sphincters Visceral or Smooth Muscle (1 of 4) Located in ○ All organs, except the heart ○ Blood vessels ○ Bronchial airways Visceral or Smooth Muscle (2 of 4) The ability of smooth muscle to contract and relax is essential to the internal body processes, like digestion and regulation of blood pressure. Involuntary muscles; contract less rapidly than skeletal muscles ○ Skeletal muscles contract 50x faster Receives smaller blood supply, resulting in poor repair of injured tissue Visceral or Smooth Muscle (3 of 4) Vasodilation: enlarging the diameter of a blood vessel ○ Can lead to decreased blood pressure due to smooth muscle relaxation Vasoconstriction: decreasing the diameter of a blood vessel ○ Can lead to increased blood pressure Visceral or Smooth Muscle (4 of 4) Sphincters: special type of smooth muscle found throughout digestive system ○ Donut-shaped ○ Act as doorways to let material in and out ○ Contraction closes the door; relaxation opens it