Functions of the skeletal system. Bone, Muscle and Moving. Bone comes in 2 forms Articular cartilage. Bones are alive!

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1 Bone, Muscle and Moving Separately neither bone or muscle is able to produce movement Muscles contract (get shorter) when the muscle shortens, it pulls on the bone Pulling on one bone causes movement at the accompanying joint Functions of the skeletal system Moves the body working together with the muscles Supports the body Protects internal organs Produces blood cells Stores minerals (calcium and phosphate) Bones are alive! Articular cartilage Bone comes in 2 forms Articular cartilage A typical bone: a tube of dense compact bone spongy bone as the inner support Growth plate at the ends of the bones Articulating cartilage where two bones meet prevents bone from grinding against bone at a joint growth plate periosteum blood vessel at the ends Red bone marrow a specialized tissue that makes blood cells in the shaft Filled with yellow bone marrow stores fat Bone tissue is served by blood vessels and nerves growth plate periosteum blood vessel More detail on bone Concentric rings of mineralized matrix containing living bone cells called osteocytes These cells secrete the surrounding material, or matrix Made of plates with spaces filled with red bone marrow Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display. osteocyte in lacuna concentric lamellae central canal osteon 100 µm Osteocyte lacuna osteocyte osteocytes nucleus How do bones grow? Bones first form as cartilage. The cartilage gradually changes into bone tissue - or ossifies blood vessels 1

2 How do bones grow? A "" of cartilage (called a growth plate) remains as long as the bone is growing Bones increase in length as these cartilage cells continue to reproduce and ossify Bone is constantly being replaced A dynamic process old bone is removed from the skeleton and new bone is added. Bones continue to change shape throughout life in response to blood calcium levels amount of stress placed on the bones Usually, the removal and formation of bone are in balance and maintain skeletal strength. Bone tissue is constantly being replaced Bone remodeling Large cells called osteoclasts dissolve bone tissue Adds calcium and other minerals to the bloodstream Osteoblasts build the mineral structure back up, pulling calcium and minerals from the bloodstream Bone resorption Osteoclasts break down bone erode the bone surface Adhere to the surface of bone and release acids and enzymes Bone remodeling Bone formation Osteoblasts form new bone repair the surface They secrete bone matrix and promote calcium deposition into the matrix Why remodel bones? Growth and repair Bones able to respond to stress by changing size, shape and strength Allows the body to regulate the amount of calcium in the blood Calcium is required for muscle contraction and nerve impulse transmission Bone remodeling 4:40 2

3 Exercise plays an important role in maintaining bone mass Bone repair Treating a fracture involves Putting the bone back into its natural shape Immobilizing it Repair involves remodeling old bone tissue is replaced by new bone tissue Osteoporosis: Bone destruction > formation What do you do to help your bones? Bones are thinner, more porous and easily broken Do you exercise? Drink milk or eat foods high in calcium? Get enough vitamin D? Wear helmets and knee pads when you ride a bike or skateboard? What do we need calcium? Skeletal Muscle Transmits nerve impulses Strengthens bone 3

4 Skeletal muscle is built like a cable Muscle Nuclei Bundle of muscle fibers Single muscle fiber (cell) Bundle of muscle fibers Each fiber is a single cell with many nuclei Striped Muscle Structure of skeletal muscle Nuclei Bundle of muscle fibers Single muscle fiber (cell) Dark Within each fiber (or cell) are bundles of protein fibers, or myofibrils Striped appearance due to alternating light and dark s Dark Structure of skeletal muscle Dark Sarcomere Sliding filament model of muscle contraction s are made of two proteins Myosin: thick filaments shaped like a golf club Actin: thin filaments These filaments slide over one another during muscle contraction Sarcomere TEM Thick filaments (myosin) Dark Thin filaments (actin) Sarcomere contractile units region between 2 dark lines (called Z lines) Figure 27.31b Contraction starts with a nerve impulse Nerve Motor neuron Contraction shortens the sarcomere But does not change the length of the thin and thick filaments Contraction starts with a nerve impulse Nerve impulses travel down motor neurons to a neuromuscular junction Muscle fibers (cells) Muscle Tendon Bone Nerves send a contraction impulse across the synapse via chemicals called neurotransmitters 4

5 Contraction starts with a nerve impulse A change in electrical charge (the action potential) sweeps down the membrane of the muscle cell What exactly happens when signal is received? End of Neuron Muscle Nucleus End of Neuron ACh Released Muscle contraction 0:42 Muscle contraction Sliding filament model of muscle contraction Myosin Pulls on Actin to Shorten Muscle Actin Calcium ion Binding sites are exposed Thick filament (myosin) 1. Action Potential Arrives Thin filament (actin) 2. ER Releases Calcium Myosin head 3. Calcium exposes binding sites on Actin 4. Myosin binds to actin power stroke Key events 5. Releases Myosin for Another Round Heads of the myosin molecules bind to Actin molecules in the thin filaments Myosin head bends and pulls the thin filament Contraction requires energy supplied by. Myosin Thick filament (myosin) Thin filament (actin) Myosin head (low-energy configuration) The myosin head attaches to an actin filament. binds to a myosin head, which is then released from an actin filament. The power stroke ADP + P Myosin head (high-energy position ) The myosin head bends back, pulling the actin filament toward the center of the sarcomere. As long as is available, the process can be repeated until the muscle is fully contracted. The breakdown of cocks the myosin head. Need to detach myosin head Figure 27.33a 5

6 Where does the energy for contraction come from? Sliding filament model Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Aerobic glycogen or fatty acids 2. Cock releases energy to myosin 3. Attach Myosin head binds, drops actin Myosin attaches to actin creating a crossbridge CO2 + H2 O + 34 Power stroke Sliding filament 3:00 [show 1st part only] c. Anaerobic glycogen White fibers are suited for bursts of activity fermentation b. Contain lots of mitochondria, myoglobin (red, oxygen-carrying molecule), and fat droplets Endurance events Most efficient way to make Requires oxygen Aerobic respiration Where does the energy for contraction come from? 2 Red fibers are geared for aerobic respiration 1. Detach 4. Bend O2 Muscle fibers need to contract lactate + Weight lifting, sprinting Make energy faster and without oxygen (anaerobic) Use glucose as fuel Fast-acting but results in lactate build up Does lactate buildup cause muscle fatigue? Once thought that lactate causes muscle fatigue and muscle burn Lactic acid isn t the culprit Muscle soreness is caused by actual muscle cell damage and inflammation Glycolysis What are the functions of skeletal muscles? Skeletal muscles work in pairs Posture Joint Stabilization Making Heat Triceps relaxed Tendon Biceps relaxed Biceps contracted Movement Triceps contracted Figure

7 The skeletal and muscular systems work together How Do Muscles Change When Exercised??? Both are involved with movement Both protect body organs Bones store and release calcium needed for muscle contraction and nerve impulse conduction Muscles help maintain body temperature Aerobic Exercise Muscles Get: Blood Mitochondria How Do Muscles Change When Exercised??? Anaerobic Exercise More Myosin & Actin Filaments Muscles Get: Do athletes need more protein? What fuel(s) are needed for athletic performance? Glucose Primary fuel for strengthand-power events Glycolysis rapid syn. Fatty acids Primary fuel for endurance events Aerobic metabolism Protein X Usually not metabolized to fuel cell activity 7