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Nerve injury & Structure of Muscle fiber

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Nerve injury & Structure
of Muscle fiber
Dr. Sai Sailesh Kumar G
Associate Professor
Department of Physiology
NRIIMS
Email: dr.goothy@gmail.com
Define following terms
 polarization,
 depolarization,
 hyperpolarization,
 repolarization,
 resting membrane potential,
 threshold potential,
 action potential, refractory period, and all or-none law.
Peripheral nerve injury
Injured nerve fibres may regenerate with restoration of function
Due to presence of endoneurial tube
Nerve injuries may be mainly two types
Crushing or cutting
Regeneration is better in crushing injuries
Stages of degeneration
Distal to the site of injury
Proximal means closer to its origin
Distal means further away
Wallerian or Anterograde degeneration
Axoplasm breaks down into membrane-bound bodies
Degeneration extends from the site of injury to the termination of axon
Stages of degeneration
Myelinsheath disintegrates into droplets of unsaturated fatty acids
The enzymes involved are hydrolytic enzymes
Secreted by lysosomes of schwann cells
Schwann cells proliferate by mitosis
Forms longitudinal columns of cells – Bands of Bunger
They fill the endoneurial tube within the first week
Stages of degeneration
Forms longitudinal columns of cells – Bands of Bunger
They fill the endoneurial tube within the first week
During that period the macrophages derived from surrounding blood
capillaries enter the damaged endoneurial sheaths
Digest the axoplasmic debris and droplets of myelin
After two weeks the macrophages are departed

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NMP-5.pptx

  • 1. Nerve injury & Structure of Muscle fiber Dr. Sai Sailesh Kumar G Associate Professor Department of Physiology NRIIMS Email: dr.goothy@gmail.com
  • 2. Define following terms  polarization,  depolarization,  hyperpolarization,  repolarization,  resting membrane potential,  threshold potential,  action potential, refractory period, and all or-none law.
  • 3. Peripheral nerve injury Injured nerve fibres may regenerate with restoration of function Due to presence of endoneurial tube Nerve injuries may be mainly two types Crushing or cutting Regeneration is better in crushing injuries
  • 4. Stages of degeneration Distal to the site of injury Proximal means closer to its origin Distal means further away Wallerian or Anterograde degeneration Axoplasm breaks down into membrane-bound bodies Degeneration extends from the site of injury to the termination of axon
  • 5. Stages of degeneration Myelinsheath disintegrates into droplets of unsaturated fatty acids The enzymes involved are hydrolytic enzymes Secreted by lysosomes of schwann cells Schwann cells proliferate by mitosis Forms longitudinal columns of cells – Bands of Bunger They fill the endoneurial tube within the first week
  • 6. Stages of degeneration Forms longitudinal columns of cells – Bands of Bunger They fill the endoneurial tube within the first week During that period the macrophages derived from surrounding blood capillaries enter the damaged endoneurial sheaths Digest the axoplasmic debris and droplets of myelin After two weeks the macrophages are departed
  • 7. Stages of degeneration After two weeks the macrophages are departed Endoneurial tube is filled with proliferating Schwann cells The macrophages are mitogenic to Schwann cells and provide trophic (feeding) and  tropic (guidance) Factors for regenerating axons
  • 8. Stages of degeneration Proximal to the site of injury Retrograde degeneration Extends up to the next node of Ranvier Within 48 hours of injury, the cell bodies of affected neurons show chromatolysis Chromatolysis occurs due to axon reaction
  • 9. Stages of degeneration Chromatolysis Nissl bodies disappear Soma increases in size Nucleus becomes eccentric in position
  • 10. Stages of Regeneration During the process of regeneration Nissl bodies reappear Protein synthesis takes place by the cytoplasmic RNA For the regrowth of axon in the proximal segment
  • 11. Stages of regeneration When cell body recovers from axon reaction The axon of proximal stump sprouts Divides into multiple branches with swollen tips called growth cones Explores the distal stump In the distal stump, Schwann cells send processes in the direction of growth cones
  • 12. Stages of regeneration The cones develop filopodia Filopodia convey surface receptors for anchorage with complementary cell surface adhesion molecules of Schwann cells Actin filaments within the filopodia attaches to the surface receptors Filopodia of motor and sensory neurons can recognize Schwann cell basement membranes previously occupied by axons of similar kind
  • 13. Stages of regeneration Guided by the strands of Schwann cells Successful fibres reach the distal portion of the nerve Under favourable conditions the time taken by regenerating axons to extend from proximal to distal stump is about 7 or 8 days Growth proceeds in the distal stump at the rate of 3 or 4 mm a day The growth rate falls as it approaches target cells
  • 14. Stages of regeneration How do the regenerating axons recognize target cells? Release of nerve growth factor from target cells Eg: Skeletal muscle
  • 15. Stages of regeneration Functional restoration takes place within a week after the restoration of structural continuity Myelin sheath begins to develop in about 15 days Myelination completes within one year
  • 16. Stages of regeneration Functional restoration takes place within a week after the restoration of structural continuity Myelin sheath begins to develop in about 15 days Myelination completes within one year
  • 18. Hazards in regeneration In a mixed nerve fibre, the motor axon may enter in the endoneurial tube which was originally occupied by sensory axon Reach a wrong destination No functional achievement
  • 19. Hazards in regeneration  Sometimes penetrating wound of parotid gland damages the auriculo- temporal and greater auricular nerves During the process of healing Secreto-motor fibres of auriculo-temporal nerve grow out and join with the distal end of greater auricular nerves Fibres reach sweat glands in the facial skin
  • 20. Hazards in regeneration  When patient eats Beads of perspiration appear on skin covering parotid gland Stimulus intended for saliva secretion produce sweat Frey’s syndrome
  • 21. Muscle Physiology  Muscles are contraction specialists.  The three types of muscle are skeletal,  smooth, and cardiac. Skeletal muscle attaches to the skeleton.  Contraction of skeletal muscles moves bones to which they are attached, allowing the body to perform a variety of motor activities. Skeletal muscles that support homeostasis  chewing, and swallowing food and those essential for breathing. Also, heat-generating muscle contractions help regulate body temperature.  Skeletal muscles are further used to move the body away from harm.  Skeletal muscle contractions are also important for non-homeostatic activities, such as dancing or operating a computer
  • 22. Muscle Physiology  Smooth muscle is found in the walls of hollow organs and tubes.  Controlled contraction of smooth muscle regulates movement of blood through blood vessels, food through the digestive tract, air through respiratory airways, and urine to the exterior
  • 23. Muscle Physiology  Cardiac muscle is found only in the walls of the heart, whose contraction pumps life-sustaining blood throughout the body
  • 24. Structure of skeletal muscle  Muscle comprises the largest group of tissues in the body, accounting for approximately half of body weight. Skeletal muscle alone makes up about 40% of body weight in men and 32% in women, with smooth and cardiac muscle making up another 10% of total weight
  • 25. Structure of skeletal muscle  Although these three muscle types are structurally and functionally distinct, they can be classified in two ways according to common characteristics.  striated (skeletal and cardiac muscle) or  unstriated (smooth muscle), depending on whether alternating dark and light bands, or striations (stripes), can be seen when the muscle is viewed under a light microscope
  • 26. Structure of skeletal muscle  muscles are categorized as voluntary (skeletal muscle) or involuntary (cardiac and smooth muscle), depending on whether they are innervated by the somatic nervous system and subject to voluntary control or are innervated by the autonomic nervous system and not subject to voluntary control, respectively
  • 27. Structure of skeletal muscle  muscles are categorized as voluntary (skeletal muscle) or involuntary (cardiac and smooth muscle), depending on whether they are innervated by the somatic nervous system and subject to voluntary control or are innervated by the autonomic nervous system and not subject to voluntary control, respectively
  • 29. Structure of skeletal muscle  Myofibrils are specialized contractile elements that constitute 80% of the volume of the muscle fiber. Each myofibril consists of a regular arrangement of highly organized cytoskeletal microfilaments the thick and the thin filaments The thick filaments, which are 12 to 18 nm in diameter and 1.6 mm in length, are special assemblies of the protein myosin, whereas the thin filaments, which are 5 to 8 nm in diameter and 1.0 mm long, are made up primarily of the protein actin
  • 31. A and I bands  Viewed with an electron microscope, a myofibril displays alternating dark bands (the A bands) and light bands (the I bands) The bands of all the myofibrils lined up parallel to one another collectively produce the striated appearance of a skeletal muscle fiber visible under a light microscope.
  • 32. A band  An A band is made up of a stacked set of thick filaments along with the portions of the thin filaments that overlap on both ends of the thick filaments. The thick filaments lie only within the A band and extend its entire width The lighter area within the middle of the A band, where the thin filaments do not reach, is the H zone
  • 34. A band Supporting proteins that hold the thick filaments together vertically within each stack can be seen as the M line, which extends vertically down the middle of the A band within the center of the H zone
  • 35. I band An I band consists of the remaining portion of the thin filaments that do not project into the A band.  Visible in the middle of each I band is a dense, vertical Z line. The area between two Z lines is called a sarcomere, which is the functional unit of skeletal muscle.
  • 37. Functional unit A functional unit of any organ is the smallest component that can perform all functions of that organ. Accordingly, a sarcomere is the smallest component of a muscle fiber that can contract
  • 38. Titin Single strands of a giant, highly elastic protein known as titin extend in both directions from the M line along the length of the thick filament to the Z lines at opposite ends of the sarcomere  Titin is the largest protein in the body, being made up of nearly 30,000 amino acids
  • 39. Cross bridges With an electron microscope, fine cross-bridges can be seen extending from each thick filament toward the surrounding thin filaments in the areas where the thick and thin filaments overlap  A single muscle fiber may contain an estimated 16 billion thick and 32 billion thin filaments, all arranged in this precise pattern within the myofibrils.
  • 40. Myosin forms the thick filaments Each thick filament has several hundred myosin molecules packed together in a specific arrangement. A myosin molecule is a protein consisting of two identical subunits, each shaped somewhat like a golf club The tail ends of the two subunits are intertwined around each other like golf-club shafts twisted together, with the two globular heads projecting out at one end
  • 41. Myosin forms the thick filaments Myosin can bend at hinge points in two locations: one along the tail and the other at the “neck” or junction of the tail with each head The heads form the cross-bridges between the thick and thin filaments. Each cross-bridge has two sites crucial to the contractile process: (1) an actin-binding site and (2) a myosin ATPase (ATP- splitting) site.