Study Guide for Exam 5 Lessons 26 32 3 11 18 24 Lesson 26 Describe which muscles are under the control of the motor system and which are under the control of the autonomic nervous system The PNS has two efferent components o The motor system carries signals to skeletal muscles and is voluntary Controls skeletal muscles o The autonomic nervous system regulates smooth and cardiac muscles and is generally involuntary Controls smooth muscles cardiac muscles and glands Explain the function of skeletal muscles Vertebrate skeletal muscle moves bones and the body and is characterized by a hierarchy of smaller and smaller units Attached to skeleton in antagonistic pairs o The skeleton provides a rigid structure to which muscles attach o Skeletons function in support protection and movement What are antagonistic muscles Muscles that work in correspondence with each other o Biceps and triceps One contracts while the other relaxes for a given motion Describe the organization of skeletal muscles A skeletal muscle consists of a bundle of long fibers each a single cell running parallel to the length of the muscle Bundles of long fibers running parallel to the length of the muscle The functional unit of a muscle is called a sarcomere and is bordered by Z lines o Thin filaments are anchored to the ends of the sarcomere at the Z line o Thick filaments are anchored in the middle of the sarcomere at the M line Each muscle fiber is itself a bundle of smaller myofibrils arranged longitudinally What is a muscle fiber What is a sarcomere What is a myofibril What is a myofilament The myofibrils are composed of two kinds of myofilaments o Thin filaments consist of two strands of actin and two strands of a regulatory protein o Thick filaments are staggered arrays of myosin molecules Why is skeletal muscle striated Skeletal muscle is also called striated muscle because the regular arrangement of myofilaments creates a pattern of light and dark bands It is striated to aid in the contraction of the muscles Describe how thick and think filaments are arranged Thin filaments are anchored to the ends of the sarcomere at the Z line Thick filaments are anchored in the middle of the sarcomere at the M line What are the thick thin filaments composed of Thin filaments consist of two strands of actin and two strands of a regulatory protein Thick filaments are staggered arrays of myosin molecules Explain the sliding filament model According to the sliding filament model filaments slide past each other longitudinally producing more overlap between thin and thick filaments The sliding of filaments relies on interaction between actin and myosin How are cross bridges formed and why are they important The head of a myosin molecule binds to an actin filament forming a cross bridge and pulling the thin filament toward the center of the sarcomere Muscle contraction requires repeated cycles of binding and release What are the stages of the muscle contraction cycle Where is ATP used Sustained muscle contractions are fueled by ATP generated through glycolysis and aerobic respiration Study figure 50 28 to see exactly where ATP is used Describe how an action potential in a muscle cell causes contraction of the muscle The stimulus leading to contraction of a muscle fiber is an action potential in a motor neuron that makes a synapse with the muscle fiber The synaptic terminal of the motor neuron releases the neurotransmitter acetylcholine Acetylcholine depolarizes the muscle causing it to produce an action potential Action potentials travel to the interior of the muscle fiber along transverse T tubules o The action potential along T tubules causes the sarcoplasmic reticulum SR to release Ca2 The calcium binds to the troponin after this occurs How is calcium involved For a muscle fiber to contract myosin binding sites must be uncovered This occurs when calcium ions Ca2 bind to the troponin complex and expose the myosin binding sites Contraction occurs when the concentration of Ca2 is high muscle fiber contraction stops when the concentration of Ca2 is low What does calcium bind onto The Ca2 binds to the troponin complex on the thin filaments This binding exposes myosin binding sites and allows the cross bridge cycle to proceed Describe the function of the calcium ATPase pump Not described in slides o Study figure 50 30 and watch video explaining pump to answer this part Why is this pump important to muscle function Important for cells to maintain low concentrations of Ca 2 ions for proper cell signaling Describe ALS and myasthenia gravis Amyotrophic lateral sclerosis ALS formerly called Lou Gehrig s disease interferes with the excitation of skeletal muscle fibers this disease is usually fatal Myasthenia gravis is an autoimmune disease that attacks acetylcholine receptors on muscle fibers treatments exist for this disease Explain how muscle tension can be modified Contraction of a whole muscle is graded which means that the extent and strength of its contraction can be voluntarily altered There are two basic mechanisms by which the nervous system produces graded contractions o Varying the number of fibers that contract o Varying the rate at which fibers are stimulated How are motor units involved in varying muscle tension In vertebrates each motor neuron may synapse with multiple muscle fibers although each fiber is controlled by only one motor neuron A motor unit consists of a single motor neuron and all the muscle fibers it controls summation What is summation and tetanus A twitch results from a single action potential in a motor neuron More rapidly delivered action potentials produce a graded contraction by Tetanus is a state of smooth and sustained contraction produced when motor neurons deliver a volley of action potentials Describe the different types of skeletal muscle fiber There are several distinct types of skeletal muscles each of which is adapted to a particular function They are classified by the source of ATP powering the muscle activity or by the speed of muscle contraction Oxidative and glycolitic fibers Fast and slow twitch fibers What are the differences between oxidative and glycolytic fibers How about fast and slow twitch fibers Oxidative fibers o Rely mostly on aerobic respiration to generate ATP o Have many mitochondria a rich blood supply and a large amount of myoglobin a protein that binds oxygen more tightly than hemoglobin does o In poultry and fish dark meat is composed of oxidative fibers Glycolytic fibers
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