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BIO 2500 Exam 3 Muscle Physiology • There are 2 sets of intracellular tubules in skeletal muscle fibers that are important for muscle contractionso Sarcoplasmic reticulum – smooth endoplasmic reticulum – stores and regulates Intracellular Calcium that is necessary for contractiono Has interconnecting tubules that surround each myofibril o Moat tubules run longitudinally along myofibril• Terminal cisternae – 2 larger tubules that run perpendicular to myofibril at junction of A band and I band• Also associated with Sarcoplasmic reticulum are mitochondria and glycosomes to provide energy for contraction• T (Transverse) tubules – found at each A band/I band junction, are elongated tubes *****• Invaginations of sarcolemma • Lumen of t-tubule continuous with extracellular space • A t-tubule runs between the 2 terminal cisternae forming the triad • Allow electrical impulses to be transmitted deep into muscle fiber and to every sarcomere! Stimulate adjacent terminal cisternae of SR to release Ca needed for muscle contraction!! • ***AND THEY ARE responsible for contraction of myofibrils at virtually the same time
2 • Sarcoplasmic reticulum – stored & regulates intracellular Cao Terminal cisternae –at each A band/I band junction• T tubules – invaginations of sarcolemma 1. Integral proteins protruding t-tubule into space between t-tubule and terminal cisternae act as voltage sensors2. Also integral proteins in terminal cisternae that form Ca channelsForm triads**
3 Sliding Filament Model of Contraction 1. Thin filaments slide past thick filaments a. Due to cross-bridge formation 2. The I-bands shorten 3. Sarcomeres shorten 4. H-zones disappear 5. A-bands move closer together but length is same How do muscles contract? 1. Muscle fiber stimulated by nerve ending 2. Generate & propagate electrical impulse 3. Increase in intracellular Ca • Stimulation by nerve ending causes a change in membrane potential• An electrical impulse has to be generated and propagated along the muscle fibers • Increase in intracellular Ca is the trigger for contraction to occur • So it takes both the nervous and the muscular system for contraction to occur o Each muscle fiber has a single neuromuscular junction*****
4 Neuromuscular Junction • Where axon terminal meets a muscle fiber • Consists of: a. Axon terminal – end of neuron o Synaptic vesicles – contain acetylcholine (ACh) b. Synaptic cleft – space between axon terminal and sarcolemma [Asks question about this]c. Motor end plate – specialized area of muscle fiber that synapses with axon terminal or makes contact with axon terminal o Junctional folds – folds IN SARCOLEMMA at motor end plate that contain acetylcholine receptors
5 Channels • Channels formed from the integral membrane proteins (specifically, transmembrane integral proteins)1. Voltage gated channel – open when membrane potential changes 2. Chemically (Ligand) gated channel –opens when a chemical bindsa. Ex. Ca or P; Na or K3. Mechanically gated channel –opens in response to mechanical movement *****Be able to draw and label picture ****Asks when/what kind of channel opens? Stage 2; Voltage-gated channel *****Could switch exocytosis with endocytosis in step 3
6 How do muscles contract? 1. Muscle fibers are stimulated by nerve ending 2. Generate & propagate electrical impulse 3. Increase in intracellular Ca• Membrane potential – difference in electrical charge across the plasma membrane• Resting membrane potential –at rest; ~-70 mVo Inside the cell has overall negative charge relative to outside• **Muscle & nerve cells are “excitable”, meaning they can receive and respond to stimuli; in other words, resting membrane potential can change!
7 • Depolarization – membrane potential becomes less negative • End plate potential –initial depolarization of motor end plate • Repolarization – after a wave of depolarization passes one area, the sarcolemma there changes permeability again & K channels open while N channels closeAction Potential • Large, transient depolarization event, including polarity reversal, that is conducted along the plasma membrane of a muscle or nerve fiber • Action potential only generated if stimulus strong enough • Refractory period – occurs during repolarization****Graph is always on the test Excitation-Contraction Coupling**** • Sequence of events whereby action potential propagation leads to sliding of myofilamentso All events from stimulus to binding of myosin & actin, forming cross-bridges
8 • Action potential is generated and propagates to t-tubules and them down the t-tubules • AP propagates down t-tubule causes voltage sensitive proteins of t-tubule to change shape, which mechanically opens Ca channels of terminal cisternae • Calcium: more highly concentrated in Sarcoplasmic Reticulum than in Sarcoplasm so Ca passes through the channel out of SR & into the sarcoplasm
9 Finally…Contraction! • Repetitive cyclical process of cross bridge formation, myosin propelling thin filaments toward M line, and cross bridge detachment • Requires ATP and Calcium • Hydrolysis of ATP provides energy for contraction 1. Myosin bridges alternately attach to actin and detach (pulls actin myofilaments toward center of sarcomere) • Release of energy by hydrolysis of ATP powers cycling process 1. Hydrolysis – ATP cleaved into ADP and inorganic phosphate THIS IS THE END OF EXCITATION CONTRACTION COUPLING.
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Join more than 18,000+ college students at Auburn University who use StudySoup to get ahead
School: Auburn University
Course: Anatomy and Physiology 1
Professor: Zachary Farris
Term: Fall 2016
Tags: anatomy, and, and Physiology
Name: Exam 3 Study Guide
Description: This covers all the muscle physiology, nervous system physiology, and central nervous system physiology material that will be on the 3rd exam.