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Chapter 12 Muscular System Skeletal Muscles A. Functions 1) support the body – oppose gravity, upright posture 2) make bones move 3) help maintain constant body temperature – produce heat through cellular respiration 4) assist movement in cardiovascular and lymph systems 5) protect internal organs and stabilize joints cardiac muscle function = smooth muscle function = study page 263, Fig. 12.1 for muscle comparison B. Skeletal muscle structure...muscle tissue is covered by layers of fibrous connective tissue called fascia which extends to become tendons. C. Each muscle has an origin tendon and an insertion tendon. origin = insertion = - muscles can only contract or shorten - muscles usually work in groups to do actions so no one muscle does all the work D. Muscles work in pairs to do opposing movements.. prime mover = antagonist = synergist = Examples: E. Naming muscles: 1) by size 2) by shape 3) by location 4) by direction of fibers 5) by number of attachments 6) by action 7) for origin & insertion F. Skeletal Muscles to know on diagram page 266... trapezius latissimus dorsi external oblique *rectus abdominis *quadriceps femoris group tibialis anterior gastrocnemius *biceps brachii *triceps brachii pectoralis major *deltoid *sternocleidomastoid – flexes head *masseter *biceps femoris Achilles tendon (not a muscle) gluteus maximus gluteus medius – not in book, on diagram at the end of notes F. know the function of the (*) muscles above, found on page 266 Mechanism of Muscle Fiber Contraction A. Overview.. (page 268, Fig. 12.6) 1. muscle fiber = muscle cell *transverse tubules (T tubules) are extensions of the plasma membrane down into the cytoplasm * T tubules contact the sarcoplasmic reticulum (E.R.) which contain Calcium ions *myofibrils = contractile proteins in muscle fiber (actin and myosin) 2. Sarcomere = contractile unit of a muscle fiber (many per cell) 3. Sliding Filament Theory describes how muscles contract... * each sarcomere shortens but protein stay the same length *contraction requires both ATP and Ca+2 ions B. Nerves are needed to tell muscles when to contract 1. motor nerve fibers branch at the ends of axons to form a neuromuscular junction. * synaptic cleft = space between nerve fiber and muscle fiber Know parts: synaptic cleft synaptic vesicles receptors neurotransmitter nerve muscle see Fig. 12.7, page 269 2. Sequence of events in a muscle cell contraction.. nerve impulse >> neurotransmitter released from synaptic vesicles >> neurotransmitter travels across synaptic cleft >> neurotransmitters attach to receptors on muscle cell >> muscle cell membrane transfers message down T tubules >> sarcoplasmic reticulum releases calcium ions around fibers >> sarcomeres shorten (ATP is required) >> muscle cell contracts **when nerve impulse stops, calcium is reabsorbed and sarcomeres relax Rigor Mortis – “stiffness in death” (page 276) - muscles contract after death and stay contracted until cells deteriorate Because… Whole Muscle Contraction A. Myogram = graph of muscle contraction B. Muscle twitch = a single muscle contraction drawing >> 3 stages: latent, contraction, relaxation * motor unit = one motor neuron and the muscle cells it controls ( may be a few or 1,000) C. Each muscle cell contracts all the way or not at all – All or None D. Tetanus = maximum sustained contraction of a muscle E. Muscle tone = some fibers are always contracting (taking turns) to maintain posture and position F. Recruitment and Strength * recruitment = using more motor units as the task requires Increase the strength of a contraction by using more motor units or by keeping motor units contracted by constant stimulation (tetanus) G. Exercise is beneficial because...see page 275 * it increases muscle strength (resistance exercises) * it increases muscle endurance (sustained effort) * it increases cardiorespiratory endurance (heart and lungs) * it increases HDL * it increases lean body mass and reduces fat * it increases bone density (if you have enough calcium and hormones) * it relieves depression (releases endorphins) Energy for Muscle Contraction A. Fuel Sources – where do cells get glucose for cellular respiration? 1. some stored in muscle… 2. some comes from blood…. B. Muscles get ATP for muscle contraction from three places.. (Fig. 12.11) 1) creatine phosphate breakdown to creatine - fastest source - used up quickly - resupplied when muscles are at rest 2) fermentation of glucose to lactate (acid) without oxygen - pH of muscle drops and enzymes don’t work - fatigue and cramping after a few minutes due to acid buildup - 2 ATP per glucose 3) cellular respiration: equation (can use glycogen or fatty acids, too) - most efficient at producing most ATP (36 ATP per glucose) - provides most of ATP and body heat - requires oxygen - myoglobin is an oxygen “magnet” in muscle cells ** training increases muscle’s ability to do cellular respiration (most efficient) by increasing the number of mitochondria in cells and efficiency of heart at delivering oxygen to muscle C. Oxygen Debt – oxygen is “owed” to muscles after heavy exercise * other tissues cannot do this as well repaying oxygen debt involves: resupplying creatine phosphate and disposing of lactic acid D. Athletics and Muscle Contraction 1) size of muscles can be increased by resistance exercises atrophy = shrinking of muscle due to lack of use or stimulation hypertrophy – increase in muscle size due to heavy lifting see page 280 for performance enhancing drug information possible dangers (?) E. Muscle Disorders 1) spasms – sudden and involuntary muscular contractions Includes…seizures, convulsions, cramps, twitches and intestinal Spasms 2) strain = stretching or tearing a _________________ Sprain = twisting a joint leading to damage to __________________________ 3) myalgia refers to achy muscles (viruses, inflammation, etc.) Fibromyalgia = 4) tendinitis – caused by strain of repeated activity 5) muscular dystrophy – progressive degeneration and weakening of muscles due to a genetic defect 6) myasthenia gravis – autoimmune disease causing muscle weakness 7) Amyotrophic lateral sclerosis (ALS) –a deterioration of neurons that control muscle (page 277)
