Y3 s1 locomotion muscle dysfunction slideshare

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Y3 s1 locomotion muscle dysfunction slideshare

  1. 1. Mechanisms ofdysfunction of musclesProf. Vajira WeerasingheDepartment of Physiology Lecture is available atwww.slideshare.net/vajira54
  2. 2. Objectives1. Recall the physiology of the motor unit and its neural control2. Outline how disorders at different levels in the control mechanisms affect muscle function
  3. 3. Site of lesions Cortex Internal capsule Brain stem Spinal cordAnterior horn cell Motor nerve Neuromuscular junction Muscle
  4. 4. Motor unit• A single motor neuron and the group muscle fibres supplied by the branches of the axon
  5. 5. motor unit• muscle contraction occurs in terms of motor units rather than by single muscle fibres• a motor unit is defined as – anterior horn cell – motor neuron – muscle fibres supplied by the neuron
  6. 6. motor unit• Innervation ratio – motor neuron:number of muscle fibres• in eye muscles – 1:23 offers a fine degree of control, less strength• in calf muscles – 1:1000 more strength less precise control
  7. 7. Principle of recruitment of motor units• Increase in the tension of a muscle is due to progressive recruitment of motor units• eg. – Mild contraction – few motor units are recruited – mild tension – Moderate contraction – many motor units are recruited – moderate tension – Strong contraction – all the motor units are recruited – maximum tension
  8. 8. The size principle• Ordered recruitment of motor units arise because – Smaller motor units are the easiest to excite – Smaller motor units have low threshold• With progressive recruitment of motor units larger motor units are also recruited
  9. 9. Effect of damage to a nerve• Demyelination• Denervation• Axonal degeneration• Reinnervation• Regeneration• Classified as – Neuropraxia – (mild damage, no significant axonal degeneration) – Axonotmesis – (significant axonal degeneration) – Neurotmesis – (complete nerve section)
  10. 10. Normal innervation Denervation Axonal degenerationReinnervation
  11. 11. Effect of damage to a nerve• Denervation occurs – Features of denervation are the appearance of fibrillations and reduced recruitment pattern • After few weeks muscle fibres start spontaneous contractions on their own called “fibrillations” • This is due to denervation hypersensitivity • Recruitment pattern is reduced because many motor units do not function. Only those remaining motor units will function• Later reinnervation occurs – Later remaining motor units will form new branches and increase their number of muscle fibres therefore with time reinnervation pattern will result
  12. 12. Physiological basis of muscle contraction
  13. 13. Muscle contraction• Excitation - contraction coupling – Excitation : electrical event – Contraction : mechanical event
  14. 14. THIN FILAMENT (Actin)THICK FILAMENT (Myosin)
  15. 15. Muscle fibre typesPhysiological concepts
  16. 16. slow & fast fibres• Slow twitch fibre (type I fibre)• Fast twitch fibre (type II fibre)
  17. 17. Slow twitch fibre (type I fibre)– Slow cross-bridge cycling– slow rate of shortening (eg. soleus muscle in calf)– high resistance to fatigue– high myoglobin content– high capillary density– many mitochondria– low glycolytic enzyme content– They are red muscle fibres
  18. 18. Fast twitch fibre (type II fibre)– rapid cross-bridge cycling,– rapid rate of shortening (eg. extra-ocular muscles)– low resistance to fatigue– low myoglobin content– low capillary density– few mitochondria– high glycolytic enzyme content– fast twitch fibers use anaerobic metabolism to create fuel, they are much better at generating short bursts of strength or speed than slow muscles
  19. 19. fast slow fibres fibresSprinters 63% 37%Marathonrunners 18% 82%Average man 55% 45%
  20. 20. Muscle dysfunction• Muscle fatigue• Muscle cramps• Muscle strain• Muscle disorders
  21. 21. Myopathies• Primary muscle disorders are called myopathies• eg. – Proximal myopathy – Congenital myopathy – Muscular dystrophy – Myositis
  22. 22. Congenital myopathy (floppy baby)Congenital myopathy produces floppy baby
  23. 23. Muscular dystrophyPrimary muscle disorder produces gross muscle wasting
  24. 24. Duchenne Muscular dystrophy• Duchenne muscular dystrophy is a lethal degenerative disease of muscles in which the protein dystrophin is absent• Gower’s sign is seen• Dystrophic muscles are more susceptible to stretch-induced muscle damage
  25. 25. Dystrophin• Dystrophin is a rod-shaped cytoplasmic protein, and a vital part of a protein complex that connects the cytoskeleton of a muscle fiber to the surrounding extracellular matrix through the cell membrane• It provides an anchoring function to the muscle proteins
  26. 26. Myotonia• Some muscle disorders could be due to derangement of electrical activity in the muscle membrane – Na+, K+ Cl- channel derangements – Called channelopathies – Myotonia dystrophica, myotonia congenita • Lack of K+ or Cl- channels • Depolarisation is normal • Repolarisation will not take place normally
  27. 27. Anterior horn cell diseases• SMA (Spinal muscular atrophy) • Affect infants • Poor prognosis • Several types are present SMA type I, II etc• DSMA (Distal spinal muscular atrophy) • Affect adolesecents • Main feature is a wasting of small muscles of the hand • Non-progressive and benign• MND (Motor neuron disease) or ALS (amyotrophic lateral sclerosis) • Affect adults (after 40 years) • Features include weakness and wasting of limb muscles, tongue fasciculations, dysarthria, dysphagia • Slowly progressive and poor prognosis
  28. 28. DSMA (distal spinal muscular atrophy)SMA (spinal muscular atrophy) MND (motor neuron disease)
  29. 29. Neuromuscular junction disorders• eg. myasthenia gravis• Muscle fatiguability• Ptosis
  30. 30. Electromyography• This is a neurophysiological test done in order to detect muscle disorders• Recording electrodes are needles (EMG needles)• They contain cathode and anode in the form of a needle• This is inserted into the muscle• Motor unit recording pattern is recorded visually in the screen and sound pattern is recorded from a loudspeaker
  31. 31. EMG MachineEMG Needle EMG recording
  32. 32. EMG recording - normal• At rest – No activity• Ask the subject to make a voluntary contraction – Motor unit action potentials amplitude and duration are calculated – Recruitment pattern is recorded
  33. 33. Normal resting Motor unit action potentials Normal full recruitment
  34. 34. EMG recording – denervation pattern• At rest – Fibrillations• Ask the subject to make a voluntary contraction – Motor unit action potentials amplitude and duration normal – Recruitment pattern is reduced
  35. 35. fibrillationsReduced recruitment
  36. 36. EMG recording – denervation with reinnervation pattern• At rest – Fibrillations, fasciculations• Ask the subject to make a voluntary contraction – Motor unit action potentials amplitude and duration increased • (in motor neuron disease – anterior horn cell disease – giant motor units are seen) – Recruitment pattern is reduced
  37. 37. Giant motor units
  38. 38. EMG recording – myopathic pattern• At rest – No activity or fibrillations• Ask the subject to make a voluntary contraction – Motor unit action potentials amplitude and duration are reduced – Early full recruitment pattern
  39. 39. Myopathic EMG pattern
  40. 40. EMG recording – myotonia• Rest: – Prolonged continuous activity – Triggered by needle position or percussion – “Bomb diver sound” – Myopathic pattern
  41. 41. Myotonia - Bomb diver pattern
  42. 42. Single fibre EMG• This is a specialised EMG technique• This is useful to diagnose myasthenia gravis
  43. 43. Clinical use of needle EMG• Investigation of nerve injuries and their recovery – Denervation pattern – Reinnervation pattern• Diagnosis of anterior horn cell diseases – SMA, DSMA, MND (or ALS)• Diagnosis of muscle disorders – Myopathy and myositis – Muscular dystrophy – Myotonia dystrophica• Diagnosis of myasthenia gravis – Single fibre EMG

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