Structural Support and Movement Chapter 36
Impacts, Issues Pumping Up Muscles Increasing muscle size and strength with drugs such as andro has unwanted side effects and can damage other organ systems
36.1 Invertebrate Skeletons Hydrostatic skeleton An enclosed fluid that contracting muscles act upon (as in sea anemones, earthworms) Exoskeleton A hardened external skeleton found in some mollusks and all arthropods Endoskeleton An internal skeleton, as in echinoderms
Hydrostatic Skeleton: Sea Anemone
Hydrostatic Skeleton: Earthworm
Exoskeleton: Fly
Exoskeleton: Spider
36.1 Key Concepts Invertebrate Skeletons Contractile force exerted against a skeleton moves animal bodies In many invertebrates a fluid-filled body cavity is a hydrostatic skeleton Others have an exoskeleton of hard structures at the body surface Still others have a hard internal skeleton, or endoskeleton
36.2 The Vertebrate Endoskeleton All vertebrates have an endoskeleton Usually consists primarily of bones Supports the body, site of muscle attachment Protects the spinal cord The vertebral column (backbone) is made up of individual vertebrae separated by intervertebral disks made of cartilage
Axial and Appendicular Skeleton Axial skeleton Skull Vertebral column Ribs Appendicular skeleton Pectoral girdle Pelvic girdle Limbs
Skeletal Elements: Fish and Reptile
The Human Skeleton Some features of the human skeleton are adaptations to upright posture and walking Foramen magnum at the base of the skull allows brain and spinal cord to connect Vertebrae stacked one above the other in an S curve
Bones of the Human Skeleton
36.3 Bone Structure and Function Bones have a variety of shapes and sizes Long bones (arms and legs) Flat bones (skull, ribs) Short bones (carpals) The human skeleton has 206 bones ranging from tiny ear bones to the massive femur
Bone Anatomy Bones consist of three types of living cells in a secreted extracellular matrix Osteoblasts build bones Osteocytes are mature osteoblasts Osteoclasts break down bone matrix Bone cavities contain bone marrow Red marrow in spongy bone forms blood cells Yellow marrow in long bones is mostly fat
Bone Anatomy: Long Bone
Bone Functions
Bone Formation and Remodeling The embryonic skeleton consists of cartilage which is modeled into bone, grows until early adulthood, and is constantly remodeled Bones and teeth store the body s calcium Calcitonin slows release of calcium from bones Parathyroid hormone releases bone calcium Sex hormones encourage bone building Cortisol slows bone building
Long Bone Formation
About Osteoporosis Osteoporosis ( porous bones ) When more calcium is removed from bone than is deposited, bone become brittle and break easily Proper diet and exercise help keep bones healthy
Osteoporosis
36.4 Skeletal Joints Where Bones Meet Joint Area of contact or near contact between bones Three types of joints Fibrous joints (teeth sockets): no movement Cartilaginous joints (vertebrae): little movement Synovial joints (knee): much movement
Synovial Joints In synovial joints, bones are separated by a fluidfilled cavity, padded with cartilage, and held together by dense connective tissue (ligaments) Different synovial joints have different movements Ball-and-socket joints (shoulder) Gliding joints (wrist and ankles) Hinged joints (elbows and knees)
Three Types of Joints
Three Types of Joints
36.5 Those Aching Joints We ask a lot of our joints when we engage in sports, carry out repetitive tasks, or strap on a pair of high heels
Joint Injuries and Diseases Common joint injuries Sprained ankle; torn cruciate ligaments in knee; torn meniscus in knee; dislocations Arthritis (chronic inflammation) Osteoarthritis; rheumatoid arthritis; gout Bursitis (inflammation of a bursa)
36.2-36.5 Key Concepts Vertebrate Skeletons Vertebrates have an endoskeleton of cartilage, bone, or both Bones interact with muscles to move the body; they also protect and support organs, and store minerals Blood cells form in some bones A joint is a place where bones meet; there are several kinds
36.6 Skeletal Muscular Systems Muscle fibers Long, cylindrical cells with multiple nuclei that hold contractile filaments Tendons attach skeletal muscle to bone Muscle contraction transmits force to bone and makes it move Muscles and bones interact as a lever system Many skeletal muscles work in opposing pairs
Skeletal Muscular Action
Opposing Muscle Groups
Muscles and Tendons
Muscles and Tendons
36.6 Key Concepts The Muscle Bone Partnership Skeletal muscles are bundles of muscle fibers that interact with bones and with one another Some cause movements by working as pairs or groups; others oppose or reverse the action of a partner muscle Tendons attach skeletal muscles to bones
36.7 How Does Skeletal Muscle Contract? Myofibrils (bundles of contractile filaments) run the length of the muscle fiber Myofibrils are divided into bands (striations) that define units of contraction (sarcomeres) Z-bands attach sarcomeres to each other Sarcomeres contain two types of filaments Thin, globular protein filaments (actin) Thick, motor protein filaments (myosin)
Fine Structure of Skeletal Muscle
The Sliding Filament Model Sliding filament model Interactions among protein filaments within a muscle fiber s individual contractile units (sarcomeres) bring about muscle contraction A sarcomere shortens when actin filaments are pulled toward the center of the sarcomere by ATP-fueled interactions with myosin filaments
The Sliding Filament Model
36.8 From Signal to Response: A Closer Look at Contraction Like neurons, muscle cells are excitable Skeletal muscle contracts in response to a signal from a motor neuron Release of ACh at a neuromuscular junction causes an action potential in the muscle cell
Nervous Control of Contraction Action potentials travel along muscle plasma membrane, down T tubules, to the sarcoplasmic reticulum (a smooth endoplasmic reticulum) Action potentials open voltage-gated channels in sarcoplasmic reticulum, triggering calcium release that allows contraction in myofibrils
Nervous Control of Contraction
The Roles of Troponin and Tropomyosin Two proteins regulate bonding of actin to myosin Tropomyosin prevents actin from binding to myosin Troponin has calcium binding sites Calcium binds to troponin, which pulls tropomyosin away from myosin-binding sites on actin Cross-bridges form, sarcomeres shorten, and muscle contracts
Interactions of Actin, Tropomyosin, and Troponin
36.9 Energy for Contraction Multiple metabolic pathways can supply the ATP required for muscle contraction Muscles use any stored ATP, then transfer phosphate from creatine phosphate to ADP to form ATP With ongoing exercise, aerobic respiration and lactic acid fermentation supply ATP
Three Metabolic Pathways Supply ATP
36.10 Properties of Whole Muscles Motor unit One motor neuron and all of the muscle fibers its axons synapse with Muscle twitch Contraction produced by brief stimulation of a motor unit Tetanus A sustained contraction caused by repeated stimulation of a motor unit in a short interval
Muscle Twitch and Tetanus
Motor Units and Muscle Tension Muscle tension The mechanical force exerted by a muscle The more motor units stimulated, the greater the muscle tension A load opposes muscle tension Isotonic contraction: muscle shorten and move the load Isometric contraction: muscles tense but do not shorten or move the load
Isotonic and Isometric Contraction
Fatigue, Exercise, and Aging Muscle fatigue Decrease in capacity to generate force; muscle tension declines despite repeated stimulation Aerobic exercise makes muscles more resistant to fatigue (increases blood supply, mitochondria) Intense exercise increases actin and myosin All muscle fibers form before birth; number and size of muscle fibers decline as people age
36.11 Disruption of Muscle Contraction Some genetic disorders, diseases, or toxins can cause muscles to contract too little or too much Muscular dystrophy (X-linked disorder) Motor neuron disorders (polio, ALS) Botulism (Clostridium botulinum toxin) and tetanus (C. tetani toxin)
Muscular Dystrophy Muscle fibers break down, muscles fail death results from respiratory failure
Tetanus C. tetani infection, preventable by tetanus vaccine
36.7-36.11 Key Concepts Skeletal Muscle Function Muscle fibers contract in response to signals from a motor neuron A muscle fiber contains many myofibrils, each divided crosswise into sarcomeres ATP-driven interactions between protein filaments shorten sarcomeres, causing muscle contraction