BIOL 252 1st Edition Lecture 11 Outline of Last Lecture I Poll Everywhere II Bone Growth and Remodeling III Calcium Homeostasis IV Hypercalcemia V Osteoporosis VI Muscles basic structure of skeletal muscle Outline of Current Lecture I Sarcomere II Transferring contractile forces to whole muscles III Nerve Muscle Relationship IV Muscle Contraction and Relaxation Current Lecture I Sarcomere a Unit of contraction b A Band dark band c In between dark bands are I bands light d M line holds bands of myosin together midline i Myosin molecules pull actin toward M line and opposite side pulls the other way also toward M line e Z disc plate that holds thin filaments on one side and thin filaments on reverse side for neighboring sarcomere i Anchor between two adjacent sarcomeres holds thin filaments together f When muscle contracts and sarcomere shortens which of the following also shortens i Thin filament do not contract do not shrink in size thin slide past thick by sliding past each other make overall sarcomere shorter ii Thick filament same reasoning as thin filament iii I band DO SHORTEN space between myosin and myosin where there is no myosin iv A band does not shrink v M line lines that mark center of A band vi Z disc by itself anchoring point for thin filaments These notes represent a detailed interpretation of the professor s lecture GradeBuddy is best used as a supplement to your own notes not as a substitute II III IV Transferring contractile forces to whole muscles a Accessory proteins b Endomysium dense connective tissue i Connected to tendons connected to bones ii Separates individual muscle fibers c Fascicle wrapped by perimysium d Epimysium around perimysium e Connective tissue makes up tendon attaches to bone f Linking proteins i Bridge from inside to outside of cell g To connect cell membrane proteins dystrophin i Muscular dystrophy 1 Involves faulty dystrophin molecule 2 Weak muscles cannot transfer forces properly Nerve Muscle Relationship a Somatic motor innervation b Motor unit each neuron branches out to a number of muscle fibers c Each neuron controls 1 muscle cell d Smallest ratio is 1 6 e All muscle fibers the neuron is attached to are stimulated contract at the same time f Neuromuscular Junction i Where neuron meets muscle special synapse ii Motor neuron axon terminals make connection w muscle fiber iii Synaptic vesicles contain Ach iv Motor end plate acts like dendrite depolarizations are produced that generate action potentials v Everywhere except motor end plate functions like an axon vi A 20 year old woman exhibits bilateral flaccid paralysis in her facial muscles She is unable to smile frown or squint Which is NOT a viable explanation 1 Myasthenia gravis autoimmune attack on ACh receptors a Cannot get signal across from one cell to the next b Have fewer and fewer ACh receptors 2 ANSWER Organophosphate exposure inhibition of AChE breaks down ACh so muscles aren t constantly contracting a If you inhibit AChE elevated ACh 3 Somatic nerve damage 4 Overexposure to Botox prevents ACh release Muscle Contraction and Relaxation a Excitation muscle receiving electrical stimulus b Contraction results c What connects these two i Excitation contraction coupling ii When you are done contracting want to relax muscles active process d Steps i Excitation of Muscle Fiber 1 Action Potential 2 ACh release 3 Binding of ACh to receptor 4 Opening of ligand regulated ion gate creation of end plate potential type of local potential in muscle cells in neurons it was called EPSP 5 Opening of voltage regulated ion gates creation of action potentials ii Excitation contraction coupling 1 Action potentials stimulate release of calcium from SR 2 Terminal cisternae SR t tubule SR triad 3 What happens to calcium a Calcium binds to troponin and free myosin binding sites iii Contraction 1 Cross bridge formation a Binding causes minor changes in myosin molecule 2 Power stroke a Transfer of force 3 Cross bridge detachment a Requires new molecule of ATP b Rigor mortis no more ATP to detach cross bridges muscles lock up after death 4 Hydrolysis of ATP activation of myosin head a ATP ADP and P b Reactivation of myosin head repeat process again c Process continues so long as calcium present d Take away calcium binding sites no longer available iv Relaxation 1 Absence of excitation leads to diminished calcium and myosinbinding sites become covered w tropomyosin e Will you get contraction 1 2 Calciu m Troponin Tropomyosin ATP Contraction Why NO YES Never contraction w out ATP Because we have actin and no troponin and tropomyosin regulatory binding sites are open 3 YES 4 5 NO but questionable YES Tropomyosin is the one actually covering binding sites W out calcium don t need troponin but tropomyosin still blocks binding sites Troponin and tropomyosin absent so it doesn t matter if calcium is there no blockage of actin
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