Johan Dahlin
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180 lines
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# Neuromuskulär transmission och skelettmuskelkontraktion.pdf
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**OCR Transcript**
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- Pages: 16
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- OCR Engine: pymupdf
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- Quality Score: 1.00
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---
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## Page 1
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Skeletal muscle physiology
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Block 2
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Nervcellsfysiologi
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Eric Hanse
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---
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## Page 2
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Motor unit
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The -motorneuron and the muscle fibrers innervated by the -motorneuron
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---
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## Page 3
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The skeletal muscle consists of
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sarcomeres in series and in parallel
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---
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## Page 4
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The neuromuscular junction
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A very large synapse consisting of
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several hundreds of release sites
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High ”safety” – produces a
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suprathreshold postsynaptic
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potential
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AchE hydrolyses most of the Ach
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within 1 ms
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---
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## Page 5
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Pharmacological aspects
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•
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Postsynaptic
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AchR antagonists Curare (Eg. Tubocurarine,
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pancuronium, vecuronium, atracurium)
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Myasthenia Gravis (antibodies against nAChR, α1-
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subunit)
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AchR agonists
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Desensitisation of AChR (Eg. Suxamethonium)
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AchE-inhibitors
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Reversible (eg. neostigmine och physostigmine)
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- Treatment of av mysthenia gravis
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Irreversible –”nerve gases” (eg. sarin, Dyflos,
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ecothiopate, parathion)
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•
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Presynaptic
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Inhibition of choline transport (Ex.
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hemicholinium)
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Lambert-Eatons syndrome (antibodies against
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presynaptic voltage-gated calcium channels)
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Botulinus toxin – proteolysis of SNARE proteins
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---
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## Page 6
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Developmental aspects
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Innervation promotes clustering of
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AChR and switch of subunits
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-reversible upon denervation
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Polyneuronal innervation initially
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---
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## Page 7
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Calcium, from the sarcoplasmatic reticulum, is
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necessary for myosin binding to actin
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---
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## Page 8
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ATP transfer energy to myosin, and decreases
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the affinity between myosin and actin
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The contraction force is proportionell to the number of parallel
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actin-myosin bindings at any given moment
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---
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## Page 9
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The muscle is strongest at an optimal length
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---
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## Page 10
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The higher contraction velocity, the lower force
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Koncentrisk
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Excentrisk
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---
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## Page 11
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M Linari et al. Nature 528:276 10 DEC 2015
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Higher tension recruits more myosin filaments
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---
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## Page 12
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Calcium makes the titin stiffer
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Herzog 2014 J Appl Physiol 116:1407
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---
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## Page 13
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The nervous system regulates contraction force
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by summation and recruitment
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Summation
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-summates contractions mainly because of higher
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calcium concentrations in response to higher
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frequencies of action potentials
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Recruitment
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of motor units according to a pre-
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determined order, type I (S) first
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---
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## Page 14
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Different motor units
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---
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## Page 15
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Fatigue
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Peripheral fatigue
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1) Reduced force
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2) Slower shortening velocity
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3) Slower relaxation
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Central and peripheral fatigue
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---
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## Page 16
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Muscle growth
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---
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