RVC Muscle 2 PDF

Graduate Accelerated BVetMed: Locomotion Muscle 2 Dr Sarah Channon, BSc MSc PhD FHEA Associate Professor in Veterinary Anatomy [email protected] Learning Outcomes ▪ Name and describe the patterns in which muscles are used, coordinated and controlled in animals ▪ Compare the properties of the m...

Graduate Accelerated BVetMed: Locomotion Muscle 2 Dr Sarah Channon, BSc MSc PhD FHEA Associate Professor in Veterinary Anatomy [email protected] Learning Outcomes ▪ Name and describe the patterns in which muscles are used, coordinated and controlled in animals ▪ Compare the properties of the main types of skeletal muscle fibre and describe how these are distributed in the healthy and diseased individual. ▪ Appreciate the concept of a skeletal muscle ‘motor unit’ and how this influences the control of muscle use in the body. ▪ Explain key muscle adaptations and responses which occur due to: exercise, detraining, ageing and injury. ▪ Describe the basic regulatory processes behind skeletal muscle adaptation 2 Recap: Sliding filament theory Images from CCCOnline 3 Types of Muscle Contraction Concentric 4 Patterns of muscle use Agonists and Antagonists Coactivation Synergists Synergies – neural control mechanism whereby groups of muscles neurally ‘wired together’ to produce patterns of specific movements 5 Motor Unit One motor neuron and all the muscle fibres that it innervates Ratio of nerve to muscle fibres varies depending on function of the muscle. Can control muscle force by recruiting more/ fewer motor Strength (e.g. limb) – many units or by controlling force fibres by one nerve; control within a motor unit. (e.g. eye) – few. 6 Muscle Fibre Types Can be classified based on: (i) velocity of shortening (fast vs slow) (ii) main pathway used to form ATP (glycolytic vs aerobic) Smaller diameter Low myosin High Slow Type (weaker); Fatigue ATPase oxidative Oxidative I resistant activity capacity High myosin High Fast Type ATPase oxidative + Oxidative IIa activity glycolytic Glycolytic capacity High myosin Larger diameter High Fast Type ATPase (stronger); glycolytic Glycolytic IIb activity Fatigue easily capacity 7 8 9 Questions? 10 Adaptation of Muscle Area change Hypertrophy of fibres No change in number Length change Change in number of sarcomeres (adding to each end) Not a change in length of sarcomeres Sarcomere 11 11 Regulation: Satellite Cells Between basal lamina and cell membrane Stem cell-like properties Injury/ repair Migrate and form myotubes/ fuse to myofibres Important in hypertrophy Stimulted by IGF/ other growth factors 12  Adaptation to load (exercise) Hypertrophy Fibre type plasticity ▪ Will occur with increased loading/ ▪ Dependant on type of exercise contraction ▪ Specific ‘strength’ training: Fast fibres will hypertrophy X2 as much as Slow fibres Type II Amount of Fibre length change hypertrophy ▪ Through sarcomere addition/ removal Type I ▪ Lengthening (stretch) vs shortening (e.g. casting) 13 Loading Assuming training is appropriate, what MUSCLE ADAPTATIONS WILL YOU SEE? Mr Smith, a Cinnamon McCain’s Mrs Arnold has greyhound trainer racehorse Blue Brandy been prescribed a has decided to has been physiotherapy switch his dog underperforming and regime of gentle Dooley’s Magic to so Cinnamon has stretching and light 800m races (from increased the incline for walks for her 400m). his hill work during spaniel Darcy after training her leg was in a cast for 6 weeks. 14  Detraining/ Immobilisation Reverse changes can also happen Detraining changes happen x2 quickly as training Joint position (muscle tension) influences sarcomere addition – consider when casting Antigravity muscles more at risk Fibre types return to type II – any post immobilisation rehab might restore fibre type, before considering strength training 15 ‘Muscle memory’ 16 Ageing Decreased number Satellite Cells in ageing; reduced proliferative capacity Decreased muscle size and performance ↓ Growth Hormone? Denervation→ muscle atrophy Decreased blood supply Increased fibrous connective tissue – influences passive & contractile properties 17  Injury Burks, Tyesha & Cohn, Ronald. (2011). Role of TGF-β signaling in inherited and acquired myopathies. Skeletal muscle. 1. 19. 10.1186/2044-5040-1-19. 18 Forcina, Laura & Cosentino, Marianna & Musaro, Antonio. (2020). Mechanisms Regulating Muscle Regeneration: Insights into the Interrelated and Time-Dependent Phases of Tissue Healing. Cells. 9. 1297. 10.3390/cells9051297. 19 Summary: One Health Relevance of Topics Discussed ▪ Significance to animal health and welfare Knowledge of muscle and tendon function and response to training important for effective training and rehabilitation ▪ Significance to public health Knowledge of normal muscle structure important for assessing meat quality ▪ Significance to environmental sustainability and ecosystem health 20 Questions? 21