Biology - Support and Movement in Animals | Biology

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Study GuideBiology–Support and Movement in Animals1. Human MuscleMuscles allow the body tomove, maintain posture, and produce force. Each muscle is made up ofthousands of muscle fibers, and each fiber is actually asingle muscle cell.These cells arespecially designed to shorten and relax, which is what creates movement.Let’s explore how muscles are built, how they contract, where their energy comes from, and thedifferent types of muscles in the human body.1.1 Structure of a Muscle FiberInside every muscle cell are tiny structures calledmyofibrils. These are long, threadlike units that fillmost of the cell.•Each myofibril is divided into repeating sections calledsarcomeres.•Sarcomeres are thebasic functional units ofmuscle contraction.Actin and Myosin FilamentsEach sarcomere contains two types of protein filaments:•Myosin–thick filaments with small “heads”•Actin–thin filamentsThese filaments lieparallel to each other, and the myosin heads point toward the actin filaments. Inskeletal muscle, the overlapping pattern of actin and myosin creates astriped (banded)appearance, calledstriations. This is why skeletal muscle is also known asstriated muscle.

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Study Guide1.2How Muscles ContractMuscle contraction begins with anerve impulse.Step-by-Step Contraction1.A nerve impulse reaches the muscle at theneuromuscular junction.2.The impulse travels along the muscle cell membrane, called thesarcolemma.3.It then spreads into the cell’s cytoplasm, known as thesarcoplasm.4.The impulse causesactin filaments to slide over myosin filaments.5.As the filaments slide, the ends of the muscle cell are pulled closer together.6.This shortening of the muscle cell producescontraction.This process is known as thesliding filament mechanism.What Is Needed for Contraction?Muscle contraction requires:•Calcium ions•Energy in the form of ATP

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Study Guide•Two regulatory proteins:tropomyosinandtroponin•Temporary connections calledcross-bridgesbetween actin and myosin1.3Muscle Relaxation and the All-or-None RuleAfter contraction:•ATP is used up•Cross-bridges break•Actin and myosin slideback to their original positions•The muscle cellrelaxesA muscle cellcannot partially contract. It either contracts fully or not at all. This is called theall-or-none principle.1.4Energy for Muscle ContractionATP: The Main Energy SourceMuscle contraction is powered byadenosine triphosphate (ATP).•ATP is normally produced throughcellular respiration, including:○Glycolysis○Krebs cycle○Electron transport systemDuring regular activity, ATP is constantlyused and replaced.1.5Strenuous Activity and Creatine PhosphateDuring intense exercise:•ATP is used up very quickly•Creatine phosphatesupplies extra energy

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Study Guide•Creatine phosphate transfers energy to makenew ATP moleculesThis system provides a short burst of power.1.6Anaerobic Respiration and Lactic AcidWhen creatine phosphate runs out:•Muscle cells rely onglycolysis alone•No oxygen is used, so the process isanaerobic•Only2 ATP moleculesare produced per glucose•Pyruvic acidis converted intolactic acidAs lactic acid builds up:•Muscles feel tired and sore•Fatiguesets in, preventing overuseDeep breathing after exercise supplies oxygen to repay theoxygen debt. Lactic acid is thenconverted back into pyruvic acid and used to produce more ATP and creatine phosphate.1.7Types of Muscle in the Human BodyThe human body hasthree main types of muscle, each with a specific structure and function.1. Skeletal (Striated) Muscle•Found in thearms, legs, and other body parts•Hasclear striations•Attached to bones•Undervoluntary control•Allows movement of the skeletonThis is themuscle type discussed earlier.

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Study Guide2. Smooth Muscle•Hasfew actin and myosin filaments•Lacks strong striations•Found in:○Blood vessel walls○Digestive tract○Respiratory tract○Urinary bladder•Worksautomatically•Also calledinvoluntary muscleSmooth muscle controls slow, steady movements like digestion and blood flow.3. Cardiac Muscle•Foundonly in the heart•Hasstriations, like skeletal muscle•Isinvoluntary•Muscle fibersbranch and connect, forming anetwork•This structure allows electrical signals to spread quickly, keeping the heartbeat coordinated2. Quiz Human Muscle1. QuestionFill in the blank:Which of the following are ultramicroscopic filaments found inmuscle cells?Answer Choices•myofibrils•myosin•sarcomeres

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