UMass Amherst KIN 460 - Neural signals- the neuromuscular junction Handout (5 pages)

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Neural signals- the neuromuscular junction Handout



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Neural signals- the neuromuscular junction Handout

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5
School:
University of Massachusetts Amherst
Course:
Kin 460 - Motor Control
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Questions Neural signals The neuromuscular junction Postural Control in Multiple Sclerosis Stability and Complexity Analyses Brief review of muscle structure Nerve stimulus and the neuromuscular junction University of Massachusetts Amherst Department of Kinesiology Connective tissue sheaths of skeletal muscle epimysium perimysium and endomysium Microscopic anatomy of a skeletal muscle fiber Photomicrograph of portions of two isolated muscle fibers 700x Notice the obvious striations alternating dark and light bands Bone Nuclei Dark A band Light I band Epimysium Epimysium Fiber Perimysium Tendon Endomysium Muscle fiber in middle of a fascicle Diagram of part of a muscle fiber showing the myofibrils One myofibril extends from the cut end of the fiber Sarcolemma Mitochondrion Myofibril Blood vessel Perimysium wrapping a fascicle Endomysium between individual muscle fibers Dark A band Thin actin filament Nucleus Z disc H zone Z disc Small part of one myofibril enlarged to show the myofilaments responsible for the banding pattern Each sarcomere extends from one Z disc to the next Thick myosin filament Z disc Muscle fiber Light I band I band A band Sarcomere M line I band Enlargement of one sarcomere sectioned lengthwise Notice the myosin heads on the thick filaments M line Z disc Thin actin filament Elastic titin filaments Thick myosin filament Fascicle Perimysium 2013 Pearson Education Inc Cross sectional view of a sarcomere cut through in different locations Myosin filament Actin filament I band thin filaments only H zone thick filaments only M line thick filaments linked by accessory proteins Outer edge of A band thick and thin filaments overlap 1 Microscopic anatomy of a skeletal muscle fiber Microscopic anatomy of a skeletal muscle fiber Diagram of part of a muscle fiber showing the myofibrils One myofibril extends from the cut end of the fiber Sarcolemma Mitochondrion Myofibril Dark A band Light I band Nucleus Sarcolemma plasma membrane Sarcoplasm cytoplasm of muscle cell large glycosomes and hemoglobin Z disc H zone I band A band Sarcomere Z disc I band M line Muscle contraction 1 Sarcomere shortens 2 I band shortens 3 H zones disappear 4 A bands move closer together but length stays the same Muscle structure Microscopic anatomy of a skeletal muscle fiber Z disc Thin actin filament Small part of one myofibril enlarged to show the myofilaments responsible for the banding pattern Thick Each sarcomere myosin extends from one Z filament disc to the next Sarcomere M line Z disc Enlargement of one sarcomere sectioned lengthwise Notice the myosin heads on the thick filaments Sliding filament model during contraction myosin and actin slide past each other intermittently through cross bridges Thin actin filament Elastic titin filaments Thick myosin filament Muscle contraction is controlled by the nerve initiated electrical impulses that travel along the sarcolemma T tubules continuations of sarcolemma signal travels to the deepest parts of muscle Sarcoplasmic Reticulum regulates intracellular calcium 2 Questions Relationship of the sarcoplasmic reticulum and T tubules to myofibrils of skeletal muscle Part of a skeletal muscle fiber cell I band Z disc A band H zone Brief review of muscle structure I band Z disc M line Sarcolemma Myofibril Nerve stimulus and the neuromuscular junction Triad T tubule Terminal cisterns of the SR 2 Sarcolemma Tubules of the SR Myofibrils Mitochondria Tubules of SR blue T tubules white The phases leading to muscle fiber contraction 1 of 2 The phases leading to muscle fiber contraction 2 of 2 Action potential AP arrives at axon terminal at neuromuscular junction AP travels across the entire sarcolemma ACh released binds to receptors on sarcolemma Phase 1 Motor neuron stimulates muscle fiber see Figure 9 8 Ion permeability of sarcolemma changes Local change in membrane voltage depolarization occurs Local depolarization end plate potential ignites AP in sarcolemma AP travels along T tubules Phase 2 Excitation contraction coupling occurs SR releases Ca2 Ca2 binds to troponin myosin binding sites active sites on actin exposed Myosin heads bind to actin contraction begins 3 When a nerve impulse reaches a neuromuscular junction acetylcholine ACh is released 1 of 3 When a nerve impulse reaches a neuromuscular junction acetylcholine ACh is released 2 of 3 Myelinated axon of motor neuron Axon terminal of neuromuscular junction Sarcolemma of the muscle fiber Action potential AP 5 ACh binding opens ion channels in the receptors that allow simultaneous passage of Na into the muscle fiber and K out of the muscle fiber More Na ions enter than K ions exit which produces a local change in the membrane potential called the end plate potential action potential Ca2 release 1Action potential arrives at axon terminal of motor neuron 2 Voltage gated Ca2 channels open Ca2 enters the axon terminal moving down its electochemical gradient Axon terminal of motor neuron Synaptic vesicle containing ACh Synaptic cleft Fusing synaptic vesicles 3Ca2 entry causes ACh a neurotransmitter to be released by exocytosis ACh 4ACh diffuses across the synaptic cleft and binds to its receptors on the sarcolemma Junctional folds of sarcolemma Sarcoplasm of muscle fiber 6 ACh effects are terminated by its breakdown in the synaptic cleft by acetylcholinesterase and diffusion away from the junction Postsynaptic membrane ion channel opens ions pass Action potential arrives at axon terminal Voltage gated Ca2 channels open ACh Degraded ACh Release of Ach through by exocytosis Ach diffuses across synaptic cleft Acetylcholinesterase Ion channel closes ions cannot pass Binds to receptors Na into muscle cell K out of cell endplate potential action potential Ca2 release Ach is broken down by enzyme Acetylcholinesterase 4 The phases leading to muscle fiber contraction 2 of 2 AP travels across the entire sarcolemma AP travels along T tubules Phase 2 Excitation contraction coupling occurs SR releases Ca2 Ca2 binds to troponin myosin binding sites active sites on actin exposed Myosin heads bind to actin contraction begins Excitation contraction coupling transmission of action potential along sarcolemma causes myofilaments actin myosin to slide This is not direct but indirect through release of calcium removes inhibitory action of tropomyosin regulatory protein on the actin filament Questions Brief review of muscle structure Nerve stimulus and the neuromuscular junction 5


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