Chapter 12 Muscular System Types of muscle tissue Smooth involuntary muscle found in hollow organs and vessels Cardiac involuntary muscle found in the heart Skeletal voluntary muscle that is attached to the skeleton Functions Support the body by allowing us to stay upright Allow for movement by attaching to the skeleton Help maintain a constant body temperature Assist in movement in the cardiovascular and lymphatic vessels by contraction Protect internal organs and stabilize joints How do skeletal muscles work Antagonistic muscles that work in opposite pairs Synergistic muscles working in groups for a common action to move elbows or wrists there are different muscles to assist in that common action Movement movement of specific parts of the body Locomotion movement of the whole body from one place to another Sarco muscle cells Ligaments the point of connection of a bone to another bone by fibrous connective tissue Tendon fibrous connective tissue that attach a muscle to a bone Why is the magnitude of contraction of the previous response added to the next response Why is the magnitude increasing gradually Once the calcium ions have been released from the sarcoplasmic reticulum there is already some calcium in the cytoplasm which has not been re uptaken into the cytoplasmic reticulum And before that you re applying the second stimulus ultimately releasing more calcium more actin sites being exposed more contraction Terminology for muscle cell tissue structure The plasma membrane is called the sarcolemma The cytoplasm is called the sarcoplasm The SER of a muscle cell is called the sarcoplasmic reticulum and stores calcium Terminology for structure within a whole muscle Muscle fibers are arranged in bundles called fascicles Myofibrils are bundles of myofilaments that run the length of a fiber Myofilaments are proteins actin and myosin that are arranged in repeating units Sarcomeres are the repeating units of actin and myosin found along a myofibril Known as the muscle unit or contraction unit o Made of 2 protein myofilaments o A thick filament is composed of several hundred molecules of the protein myosin Each myosin molecule is shaped like a golf club o Primarily a thin filament consists of 2 intertwining strands of the protein actin o These filaments slide over one another during muscle contraction The beginning of a muscle contraction The beginning of muscle contraction The sliding filament model 1 Nerve impulses travel down a motor neuron to a neuromuscular junction 2 Acetylcholine ACh neurotransmitter is released from the neuron and binds to the muscle fiber 3 This binding stimulates the fiber causing calcium to be released from the sarcoplasmic reticulum 4 Released calcium combines with troponin a molecule associated with actin 5 This causes the tropomyosin threads around actin to shift and expose myosin binding sites 6 Myosin heads bind to these sites forming cross bridges 7 ATP binds to the myosin heads and is used for energy to pull the actin filaments towards the center of the sarcomere contraction occurs What role does ATP play in muscle contraction and rigor mortis ATP is needed to attach and detach the myosin heads from actin After death muscle cells continue to produce ATP through fermentation and muscle cells can continue to contract When ATP runs out some myosin heads are still attached and cannot detach causing rigor mortis Rigor mortis and body temperature may be used to estimate time of death The three phases of a single muscle twitch and how summation and tetanus increase the force of contraction Terms to describe whole muscle contraction Motor unit a nerve fiber and all of the muscle fibers it stimulates Latent period when the muscle id preparing to contract when all the process is being conducted Contraction period when actin and myosin filaments slide Relaxation period fresh ATP molecules detach the myosin heads of the actin sites Muscle twitch a single contraction lasting a fraction of a second Summation an increase in muscle contraction until the maximal sustained contraction is reached sum of remaining muscle contraction they keep adding Tetanus maximal steady sustained contraction Fatigue constant contraction of muscle provokes the muscle to give up because the muscle hasn t Muscle tone a continuous partial contraction of alternate muscle fibers causing the muscle to look relaxed completely firm less when asleep Fuel sources for muscle contraction Stored in the muscle Glycogen In the blood Fat Glucose Fatty acids Importance of exercise They are broken down to produce ATP through glycolysis electron transport and Krebs cycle It increases muscle strength endurance and flexibility Increases cardiorespiratory endurance increases ATP increases contraction and relaxation of muscles We are burning the fuels glycogen and fats stored in the muscle Protein increases by breakdown of those fuels stored The proportion of protein to fat increases favorably May prevent certain cancers colon breast cervical uterine and ovarian Improves density of bones thus decreasing the likelihood of osteoporosis because there is constant absorption and reabsorption of calcium in between the ones and blood Enhances mood and may relieve depression Common muscle disorders Spasms sudden involuntary muscle contractions that are usually painful Convulsions seizures multiple spasms of skeletal muscles Cramps strong painful spasms often of the leg and foot Strain stretching or tearing of a muscle Sprain twisting of a joint involving muscles ligaments tendons blood vessels and nerves Muscle diseases weaken Myalgia achy muscles due to injury or infection Myo muscles algia pain Muscular dystrophy group of genetic disorders in which muscles progressively degenerate and Myasthenia gravis autoimmune disorder that attacks the ACh receptor and weakens muscles of the face neck and extremities Amyotrophic lateral sclerosis ALS commonly known as Lou Gehrig s disease motor neurons degenerate and die leading to loss of voluntary muscle movement Sarcomas cancers that originate in muscle or the connective tissue associated with muscle Homeostasis The skeletal and muscular systems Both systems are involved with movement that allows us to respond to stimuli digestion of food return of blood to the heart and moving air in and out of the lungs Both systems protect body parts Bones store and release calcium needed for muscle contraction and nerve impulse conduction Blood cells are produced in the bone Muscles
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