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Biology - Support and Movement in Animals

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    Study Guide Biology – Support and Movement in Animals 1. Human Muscle Muscles allow the body to move, maintain posture, and produce force . Each muscle is made up of thousands of muscle fibers , and each fiber is actually a single muscle cell . These cells are specially 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 the different types of muscles in the human body. 1.1 Structure of a Muscle Fiber Inside every muscle cell are tiny structures called myofibrils . These are long, threadlike units that fill most of the cell. • Each myofibril is divided into repeating sections called sarcomeres . • Sarcomeres are the basic functional units of muscle contraction . Actin and Myosin Filaments Each sarcomere contains two types of protein filaments: • Myosin – thick filaments with small “heads” • Actin – thin filaments These filaments lie parallel to each other , and the myosin heads point toward the actin filaments. In skeletal muscle , the overlapping pattern of actin and myosin creates a striped (banded) appearance , called striations . This is why skeletal muscle is also known as striated muscle .

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    Study Guide 1.2 How Muscles Contract Muscle contraction begins with a nerve impulse . Step - by - Step Contraction 1. A nerve impulse reaches the muscle at the neuromuscular junction . 2. The impulse travels along the muscle cell membrane, called the sarcolemma . 3. It then spreads into the cell’s cytoplasm, known as the sarcoplasm . 4. The impulse causes actin 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 produces contraction . This process is known as the sliding 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: tropomyosin and troponin • Temporary connections called cross - bridges between actin and myosin 1.3 Muscle Relaxation and the All - or - None Rule After contraction: • ATP is used up • Cross - bridges break • Actin and myosin slide back to their original positions • The muscle cell relaxes A muscle cell cannot partially contract . It either contracts fully or not at all. This is called the all - or - none principle . 1.4 Energy for Muscle Contraction ATP: The Main Energy Source Muscle contraction is powered by adenosine triphosphate (ATP) . • ATP is normally produced through cellular respiration , including: ○ Glycolysis ○ Krebs cycle ○ Electron transport system During regular activity, ATP is constantly used and replaced . 1.5 Strenuous Activity and Creatine Phosphate During intense exercise: • ATP is used up very quickly • Creatine phosphate supplies extra energy

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    Study Guide • Creatine phosphate transfers energy to make new ATP molecules This system provides a short burst of power. 1.6 Anaerobic Respiration and Lactic Acid When creatine phosphate runs out: • Muscle cells rely on glycolysis alone • No oxygen is used, so the process is anaerobic • Only 2 ATP molecules are produced per glucose • Pyruvic acid is converted into lactic acid As lactic acid builds up: • Muscles feel tired and sore • Fatigue sets in, preventing overuse Deep breathing after exercise supplies oxygen to repay the oxygen debt . Lactic acid is then converted back into pyruvic acid and used to produce more ATP and creatine phosphate. 1.7 Types of Muscle in the Human Body The human body has three main types of muscle , each with a specific structure and function. 1. Skeletal (Striated) Muscle • Found in the arms, legs, and other body parts • Has clear striations • Attached to bones • Under voluntary control • Allows movement of the skeleton This is the muscle type discussed earlier.

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    Study Guide 2. Smooth Muscle • Has few actin and myosin filaments • Lacks strong striations • Found in: ○ Blood vessel walls ○ Digestive tract ○ Respiratory tract ○ Urinary bladder • Works automatically • Also called involuntary muscle Smooth muscle controls slow, steady movements like digestion and blood flow. 3. Cardiac Muscle • Found only in the heart • Has striations , like skeletal muscle • Is involuntary • Muscle fibers branch and connect, forming a network • This structure allows electrical signals to spread quickly, keeping the heartbeat coordinated 2. Quiz Human Muscle 1. Question Fill in the blank: Which of the following are ultramicroscopic filaments found in muscle cells? Answer Choices • myofibrils • myosin • sarcomeres

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