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The Muscular System and Homeostasis What are muscles? • Muscles act like rope pulling bones and other muscles together • They convert chemical energy into kinetic energy (movement) • There are 3 types of muscle tissues in the body Types of Muscles Skeletal Muscles • Responsible for voluntary movement • Attached to bones Skeletal muscle Actin Myosin Bundle of muscle fibers Sarcomere •Striated/Stripped •600 in the body Z disc Myfibril •Long Muscle fiber (cell) Types of Muscles Smooth Muscles • Not voluntary control • Found in hollow structures: stomach, intestines, veins • Not striated Types of Muscles Cardiac Muscle • voluntary contractions • Found only in the heart • Striated/Stripped • Does not fatigue easily How do muscles contract? • Muscles contract when thin filaments in the muscle fiber slide over the thick filaments Relaxed Muscle Myosin Movement of Actin Filament Actin Z disc Actin Sarcomere Binding sites Myosin Contracted Muscle Cross-bridges Z disc Crossbridge Where are calories burned? • The ATP provides the power to move the Myosin • ATP to cell: gas to car • ATP come from food you eat • It combines with O2 to burn and give energy Steps of muscle contraction • 1. Myosin head binds to actin. • 2. ATP causes bend in myosin head • 3 myosin contracts muscle • Actin binding sites are blocked by tropomyosin when the muscles is relaxed • When calcium ion concentrations in the muscle fiber increase, they form a troponin-tropomyosin complex that shifts away from the binding sites on the actin allowing the muscle to contract • Calcium ions are regulated by the nerves that connect to the sarcoplasmic reticulum surrounding the muscle fiber • The calcium ions are removed by active transport when the nerve impulse stops, relaxing the muscle Creatine Creatine phosphate phosphate builds builds up up and and is is stored stored in in resting resting muscle muscle (purple (purple box). box). For For the the muscle muscle to to contract contract (green (green area), area), it it needs needs to to acquire acquire ATP. ATP. (A) (A) When When the the muscle muscle starts starts contracting, contracting, it it breaks breaks down down stored stored creatine creatine phosphate. phosphate. This This generates generates some some ATP ATP that that is is used used immediately. immediately. (B) (B) To To continue continue contracting, contracting, the the muscle muscle carries carries out out aerobic aerobic cellular cellular respiration respiration as as long long as as oxygen oxygen is is available. available. When When the the oxygen oxygen has has been been used used up, up, the the muscle muscle can can carry carry out out fermentation fermentation for for aa limited limited period period of of time. time. Fermentation Fermentation results results in in only only aa small small amount amount of of ATP ATP compared compared with with the the amount amount produced produced by by aerobic aerobic cellular cellular respiration, respiration, and and lactate lactate builds builds up. up. Once Once the the muscle muscle resumes resumes resting resting (purple (purple box), box), creatine creatine phosphate phosphate builds builds up up again. again. Muscle Energy • ATP provides energy for the flexing of the myosin heads • The ATP is produce in one of three ways • 1) Creatine Phosphate Breakdown –the creatine gives up a phosphate to DPTÆATP • 2) Aerobic Respiration – glucose and oxygen are required in the muscle for this to occur, the products are carbon dioxide and heat • 3) Fermentation – If oxygen is consumed faster then it can be supplied aerobic respiration is replaced by fermentation the product of which is lactic acid Controlling Muscle Contraction • Nerve cells (motor neurons) control muscle contraction Muscle fiber neuron Muscles, Health and Homeostasis Muscle & Bone Interaction • Muscles are attached to tendons. • Tendons anchor to bone • pull on the bone to allow for movements Movement Movement Biceps (relaxed) Triceps (relaxed) Biceps (contracted) Triceps (relaxed) Complications and Disorders • Most are caused by sudden pressure and intense pressure place onto the muscles and tendons. • Many can be caused by a lack of use if the muscles (atrophy) • Complete Though Lab 10.2 • These graphs show the force of muscle contraction with time. (A) A simple muscle twitch has three periods: latent, contraction, and relaxation. (B) When a muscle is not allowed to relax completely between stimuli, the contraction gradually increases in intensity until it reaches a maximum, which is sustained until the muscle fatigues. • Skeletal muscles have different proportions of fasttwitch and slow-twitch fibres. Thus, the force and response times of their contractions differ. Importance of Physical Activity