Muscular System- Part 1 Unit 5 Miss Wheeler
Fun Facts! The tongue is the strongest muscle in your body The smallest muscles in the body are in the middle ear The largest muscle in the body is the gluteus maximus It takes 17 muscles to smile, and 43 muscles to frown The heart is the only muscle that never gets tired
Muscle Functions 1. Produce movement 2. Maintain posture 3. Stabilize joints 4. Generate Heat
Characteristics of Muscles Muscle cells (called muscle fibers) are elongated All muscles share some terminology: Myo - muscle Mys - muscle Sarco flesh Epi- upon Peri- around Endo- inner
Muscle Tissue Three muscle types (you already know these): 1. Smooth Muscle 2. Cardiac Muscle 3. Skeletal Muscle
Smooth Muscle How blood and food move No striations Single nucleus Involuntary Spindle-shaped cells Found in walls of hollow organs (intestines, blood vessels)
Cardiac Muscle Makes your heart beat Striations Single nucleus Involuntary Cells jointed to each other at intercalated discs Found only in the heart
Skeletal Muscle Moves your bones Striated Multi-nucleated Voluntary Cells are surrounded and bundled by connective tissue Most are attached to bones by tendons
Try This! A. Smooth B. Cardiac C. Skeletal involuntary striated moves bones voluntary this picture à
Structures of Skeletal Muscle Epimysium- covers the entire skeletal muscle Perimysium- covers a bundle of fibers (fascicle) Endomysium- covers a single muscle fiber (cell)
Structures of Skeletal Muscle Sarcolemma- muscle fiber membrane Sarcoplasm- cytoplasm of muscle fiber Sarcoplasmic Reticulum- transport (ER). Store calcium Myofibrils- organelle structure that takes up most of the space in a muscle fiber Myofilaments- threadlike proteins that make up a myofibril
Structure of Skeletal Muscle
Structure of Skeletal Muscle Myofibrils are made of myofilaments that form a unit called a sarcomere with light and dark bands. ACTIN = thin filaments; form light band (I band) MYOSIN = thick filaments; form dark band (A band)
Try This! Muscle composed of bundles composed of cells composed of fibrils composed of filaments light Individual types dark
Twizzler Analogy Many packages of Twizzlers together = fascicle Find a fascicle on your diagram
Twizzler Analogy 1 package of Twizzlers = The packaging =
Twizzler Analogy 1 bundle of Twizzlers = 1 Twizzler strand =
Twizzler Analogy
Try This! Now try making your own model of a skeletal muscle using only the materials you are given.
Muscle Contraction How muscles contract to move the skeleton
Review Muscle fiber à myofibrils à myofilaments Myofibrils are made of units called sarcomeres, made of thick (myosin) and thin (actin) filaments Sarcomeres stretch from Z line to Z line
Muscle Contraction THE BIG PICTURE Thick (myosin) and thin (actin) filaments slide over one another to shorten the muscle during contraction
Where Does It Start? Skeletal muscle contraction begins at the neuromuscular junction. What do you think the neuromuscular junction is?
Neuron Axon terminal Cell body Axon
Motor unit = motor neuron & muscle fiber that it activates More motor units = stronger contractions of the muscle
Acetylcholine Sarcoplasmic Reticulum
Muscle Contraction 1. Nerve impulse releases acetylcholine (neurotransmitter) into neuromuscular junction 2. Sends action potential through T-tubules to the sarcoplasmic reticulum (SR) 3. Ca 2+ (calcium) is released from SR to sarcomeres 4. Calcium binds to troponin on thin filaments, which then shift the tropomyosin to expose binding site on actin 5. Myosin head from thick filaments binds to actin thin filaments using energy from ATP (cross-bridge) 6. Thick filament pulls thin filament toward the center, shortening the sarcomere and causing muscle contraction
Steps #1-3 Acetylcholine Sarcoplasmic Reticulum
Sarcomere Contraction Steps #4-6
Sliding Filament Theory Actin and myosin filaments slide past each other as a muscle contracts
Contraction Video https://www.youtube.com/watch?v=bmt4ptxrcva
Sliding Filament Analogy Boat = myosin (thick filament) Oar/paddle = myosin arm Water = actin (thin filament) Life ring = calcium
Resting Muscle 1. ATP binds to myosin arm 2. ATP breaks down into ADP + P, reading to be activated
Step 1. Action Potential 1. A nerve action potential releases acetylcholine 2. Signal gets sent to sarcoplasmic reticulum, which releases calcium
Step 2. Myosin-Actin Binding 1. Calcium binds to troponin 2. Causes tropomyosin to move out of the way of the actin binding site 3. Actin and myosin bind using energy from ATP
Step 3. Row, row, row your boat 1. Myosin arm pivots so myosin and actin slide past each other, shortening the sarcomere 2. ADP and P released
Quick Write 1. What chemical helps expose the binding site on actin? 2. What is the source of energy for a contraction? 3. What happens to the length of the sarcomere during a contraction?
Types of Muscle Contractions Isotonic Contractions- the myofilaments are successful in their sliding movements. The muscle shortens, and movement occurs Ex. Bending the knee, smiling Isometric Contractions- contractions in which the muscles do not shorten. Tension develops in the muscle and it attempts to slide the filaments Ex. When you push against a wall or try to lift a very heavy object
Types of Muscle Contractions Isotonic Contractions Isometric Contractions