Nerve & muscle final

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  1. 1. Muscles are effectors which enable movement to be carried out
  2. 2. Muscles are responsible for all types of body movements they contract or shorten and are the machine of the body
  3. 3. Muscle comprises the largest group of tissues in the body accounting for approximately half of the bodys weight. Skeletal muscles __________ 40% of body weight Cardiac and smooth muscle ____ 10% of body weight
  4. 4. 3 types : Skeletal Muscles attached to skeleton Cardiac Muscles heart Smooth Muscles internal organs
  5. 5. The muscles have 4 important functions: 1. Production of movement-External and internal 2. Maintaining posture 3. Stabilizing joints 4. Generating heat
  6. 6. 1.1. ExcitabilityExcitability the ability to receive and respond to stimuli for e.g. Can respond to chemical neurotransmitters. 2.2. ContractilityContractility Contracts when it is excited 3.3. ExtensibilityExtensibility The ability of muscles to be stretched 4.4. ElasticityElasticity The ability of muscle to resume a resting length after it has been stretched.
  7. 7. 1. Depending upon striations: Striated: e.g. cardiac muscle and skeletal muscle Non striated: smooth muscle 2. Depending upon the control: Voluntary: Skeletal muscles Involuntary: Cardiac and smooth muscles 3. Depending upon situation: Cardiac: in heart Skeletal: attached to bones Smooth or visceral: present in visceras
  8. 8. Skeletal muscleSkeletal muscle striated with light & dark bands visible with scope voluntary control of contraction & relaxation Makes up 40% of body weight Responsible for locomotion, facial expressions, posture, respiratory movements, other types of body movement Voluntary in action; controlled by somatic motor neurons 8
  9. 9. Cardiac muscleCardiac muscle striated in appearance involuntary control Auto rhythmic because of built in pacemaker (SA node) Innervated by autonomic nerves 9
  10. 10. Smooth muscleSmooth muscle non-striated in appearance Involuntary In the walls of hollow organs, blood vessels, eye, glands, uterus, skin Some functions: propel urine, mix food in digestive tract, dilating/constricting pupils, regulating blood flow, Controlled involuntarily by endocrine and autonomic nervous systems 10
  11. 11. Connective tissue components of the muscle include epimysium = surrounds the whole muscle perimysium = surrounds bundles (fascicles) of 10-100 muscle cells endomysium = separates individual muscle cells All these connective tissue layers extend beyond the muscle belly to form the tendon 11
  12. 12. Muscle attachments Most skeletal muscles run from one bone to another One bone will move other bone remains fixed Origin less movable attach- ment Insertion more movable attach- ment
  13. 13. Composed of muscle cells (fibers), connective tissue, blood vessels, nerves Fibers are long, cylindrical, and multinucleated and abundant mitochondria Tend to be smaller diameter in small muscles and larger in large muscles. 1 mm- 4 cm in length Develop from myoblasts; numbers remain constant Striated appearance Nuclei are peripherally located Satellite cells are stem cells which normally stay dormant but are activated when the muscle is injured
  14. 14. Cell membrane = sarcolemma Cytoplasm = sarcoplasm SER = sarcoplasmic reticulum
  15. 15. Deep structures of a sceletal muscle
  16. 16. Microscopic Anatomy of Skeletal Muscle fiber The predominant structural feature of a skeletal muscle fiber is numerous Myofibrils (80% of volume of muscle fiber) Myofibrils are aligned to give distinct bands I band = light band A band = dark band
  17. 17. Myofibrils are densely packed, rod like cylindrical contractile elements They make up most of the muscle volume (80%) Each muscle fiber has several hundred to several thousand myofibrils. The arrangement of myofibrils within a fiber is such that a perfectly aligned repeating series of dark A bands and light I bands is evident
  18. 18. Myofibril Each myofibril is composed of 1500 adjacent myosin filaments and 3000 actin filaments which are large polymerized protein molecules made up of polymerization of proteins myosin and actin molecules respectively that are responsible for the actual muscle contraction.
  19. 19. With an electron microscope , a myofibril displays alternating dark bands (A band) and light band (I band) . The bands of all the myofibrils lined up parallel to one another collectively producing the striated appearance of skeletal muscle fibers visible under light microscope Alternate stacked sets of thick and thin filaments that slightly overlap one another are responsible for the A and I band
  20. 20. A microscopic photo and a scheme of
  21. 21. Different polarization characteristics throughout A bands: a dark band; full length of thick filament & the portions of thin filaments that overlaps on both ends of the thick filaments
  22. 22. H zone - thick but NO thin filaments M line system of supporting proteins which hold the thick filaments together vertically within each stack (protein to which myosins attach)
  23. 23. Having like properties in all directions (singly refractive) I bands: a light band; it is the remaining of the actin filament that do not project into A band Thin but NO thick filaments In the middle of I band is a Z line The area b/w 2 Z lines is called sarcomere which is the functional unit of the skeletal muscle
  24. 24. Z disk: filamentous network of protein. Serves as attachment for actin filaments of the two adjoining sarcomeres So I band extends from A band of one sarcomere to A band of the next sarcomere
  25. 25. Figure 9.3c,d
  26. 26. The distance between two successive Z lines is called sarcomere which is the functional unit of the skeletal muscle. Each relaxed sarcomere is 2.5 m in width and consists of one whole A band and half of each of the two I bands located on either side. About 10,000 sarcomeres per myofibril
  27. 27. T h ic k f ila m e n ts ( m y o s in ) T h in fila m e n t s ( a c tin ) M lin e Z lin e Z lin e p r o t e in s in t h e Z lin e ju s t th in fila m e n t o v e r la p z o n e - b o th th ic k & th in fila m e n ts ju s t th ic k f ila m e n t m y o s in b a r e z o n e - n o c r o s s b r id g e s p r o te in s in th e M lin e
  28. 28. Titin filaments: single strand of giant, elastic protein called titin extend in both direction from the M line along the length of the thick filament to the Z lines it is the largest protein in the body with 30,000 amino acids
  29. 29. 1. Along with M line proteins titin helps stabilize the position of the thick filaments. 2. By acting like a spring , it greatly augments a muscles elasticity 3. Gets stiffer as it is stretched (uncoiled) which keeps sarcomeres from overstretching.
  30. 30. These are small projections from the sides of the myosin filaments towards the surrounding thin filaments in the areas where the thick and thin filaments overlap.
  31. 31. Each thick filament is surrounded by six thin filaments and each thin filament is surrounded by 3 thick filaments
  32. 32. Myosin forms the thick or myosin filament Each thick filament is formed by the polymerization of 200 or more myosin molecules
  33. 33. It is a protein containing 2 identical subunits , each shaped like a golf club. The tails or 2 heavy chains of myosin molecules wound together to form a rod portion lying parallel to the myosin filament and two heads or 4 light chains projecting out at one end so it is a (hexamer)
  34. 34. The tails of the myosin molecules bundled together to form the body of myosin filament while heads of the molecules hang outward to the sides of the body Mirror image of each other Also part of the body of each myosin molecule hangs to the side along with the head thus providing an arm
  35. 35. The protruding arm and heads are called cross bridges. There are no cross bridge heads in the centre of myosin filament Each cross bridge is flexible at 2 points called hinges
  36. 36. 1. Hinged Arms: it is present where arm leaves the body of the myosin filament . It allows the head either to be extended far outward from the body of the myosin filament or to be brought close to the body
  37. 37. Hinged heads: This hinge is present where head attaches to the arm. The hinge heads in turn participate in the actual contraction process.
  38. 38. 1. Actin binding site : Can bind to active sites on the actin molecules 2. Have ATPase activity: activity that breaks down adenosine triphosphate (ATP), releasing energy.
  39. 39. Actin filament Thin filaments = actin filaments Composed of 3 proteins
  40. 40. Thin filaments are chiefly composed of the protein actin (back bone of thin filament) Each actin molecule is a helical polymer of globular or spherical subunits called G actin which are linked to create the F actin filaments The subunits contain the active sites to which myosin cross bridge attach during contraction Tropomyosin (stiffener and blockade) and troponin (TnI, TnT, TnC) are regulatory subunits bound to actin
  41. 41. TnI bound to the actin fiber and is inhibitory, by blocking the binding site TnT bound to the tropomyosin fiber holding it in place TnC will bind to Ca++ ions to cause a position shift that exposes the actin binding site so that cross-bridging can occur, resulting in contraction
  42. 42. In a relaxed muscle contraction does not take place; actin cannot bind with cross bridge because of the way the troponin and tropomyosin are positioned within the thin filament. When no Ca bound to troponin , it stabilizes tropomyosin in its blocking position over active sites of actin filament. But when Ca binds to troponin, the shape of this protein is changed in such a way t