Muscles, Bones, and Skin

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Muscles, Bones, and Skin
2012-07-16 21:31:14

MCAT Biology
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  1. How do muscles generate force?
    By contracting their cells
  2. What has these roles? 
    1. Movement
    2. Stabilization
    3. Moving substances throughout the body
    4. Heat generation for thermoregulation 
  3. Skeletal muscle
    • Voluntary & Multinucleated 
    • LOTS of mitochondria 
    • Controlled by the somatic NS
    • Squeeze blood & lymph  
  4. Agonist, Antogonist, and synergistic muscles + physics beind contraction 
    • Agonist - contracts 
    • Synergists - help agonist by stabilizing bones involved in movement
    • Antagonist - Stretches

    Muscles apply force at insertion point of bone -- The bone is then rotated about an axis of rotation i.e. joint

    • Muscles DECREASE the body's bulk by INCREASING the force and DECREASING the lever arm --- this allows us to maintain our ROM
  5. Tendons v ligaments 
    Tendons : muscle-bone 

    Ligaments: bone-bone  
  6. What is shivering?
    A thermoregulatory process by the contraction of the skeletal muscles to warm the body 
  7. Slow Twitch Fibers 
    Skeletal muscle fibers 

    • Red
    • LOTS of myoglobin (only 1 O2 molecule)
    • LOTS of mitochondria
    • Slow to tire
    • Postural  
  8. Fast Twitch A Fibers 
    Skeletal Muscle fibers 

    • Red
    • Rapid Contraction
    • Myoglobin
    • Less resistant to fatigue as slow twitch  
  9. Fast Twitch B Fibers
    Skeletal muscle fibers 

    • White
    • Low myoglobin
    • LOTS of glycogen because employ lots of glycogenolysis for energy
    • Very rapid  contraction 
    • Very fast to tire
    • Biceps  
  10. H zone - Thick filaments, gets smaller 

    I band - Actin only, gets smaller, light 

    A band - both thick and thin filaments, doesn't change length, dark
  11. Organization of muscle
    Sarcomere = smallest fxnal unit of muscle 

    2+sarcomeres = myofibril

    Myofibril covered by sarcoplasmic reticulum (filled with Ca2+)

    2+myofibrils = Muscle cell

    Muscle cells wrapped by Sarcolemma
  12. Muscle cell AP genesis 
    • 1. Efferent neuron releases ACh at neuromuscular synapse 
    • 2. ACh generates AP in Sarcolemma
    • 3. AP moves into T-tubules
    • 4. AP reaches SR
    • 5. SR becomes permeable to Ca2+
    • 6. At end of contraction, Ca2+ is pumped back into SR  
  13. Which muscle tissue structure ensures contraction of skeletal muscle is uniform and fast? What about for Cardiac muscle? 

    Gap jxns 
  14. Steps of contraction: 
    1. Tropomyosin covers active site of actin, myosin head is bound to ADP and cocked 

    2. Ca2+ ions cause troponin to pull tropomyosin back, revealing actin's active site

    3. Myosin binds actin

    4. Myosin loses ADP and tugs on actin, contraction and shortening of sarcomere

    5. ATP attached to myosin to release myosin from actin

    6. ATP --> ADP and myosin cocks itself once again  
  15. Rigor mortis 
    ATP needed to dislodge myosin from actin but after death no ATP so muscles initially remain contracted 
  16. Role of ATP in contraction
    ATP BINDING causes myosin to release from active site

    ATP SPLITTING causes myosin head to cock to readiness (this is what requires energy)

    Myosin is like an ATPase because it hydrolyzes ATP to ADP 
  17. Recruitment of motor units 
    The more units that fire, the stronger the contraction 

    Smaller motor units for intricate contractions

    Allows adjustments between picking up dumbell and pencil  
  18. Do myocytes undergo mitosis?
    No. Hypertrophy because too specialized to mitose. 

    Grow in diameter, number of sarcomeres & mitochondria, grow in sarcomere length also  
  19. Cardiac muscle 
    • Striated (having sarcomere) 
    • Connected via intercalated discs and gap jxns
    • Mono-nucleate
    • Involuntary
    • Grows by hypertrophy 

    AP plateau due to slow v-gated Ca2+ channels (serves to lengthen time of contraction)  
  20. Smooth muscle 
    • Involuntary & mono-nucleate 
    • Unstriated 

    Innervated by autonomic NS  

    • Contains intermediate filaments, which are attached to dense bodies
    • When actin and myosin pull together, they pull intermediate filaments and dense bodies together also

    Can be connected via gap jxns for smooth contraction  
  21. What do smooth muscles respond to?
    • Neural stimulus 
    • pH
    • O2
    • CO2
    • Temperature
    • [ions] 
  22. Glands of the skin 
    Sebacious = oil 

    Sudiferous = sweat

    Cereminous = wax 
  23. Types of joints 
    Fibruous - no movement

    Cartilaginous - little movement, ribs

    Synovial - most ROM, synovial fluid contains lymphocytes  
  24. Hardness of bone given by? Tensile strength given by?
    Hardness: Hydroxyapatite crystals Ca10(PO4)6(OH)2

    Tensile strength: Collagen  
  25. What has these roles? 
    1. Protection
    2. Support
    3. Movement
    4. Energy storage 
    5. Blood cell production
    6. Mineral storage  
  26. What has these roles? 
    1. Thermoregulation
    2. Protection
    3. Sensory information
    4. Blood reservoir
    5. Immunity
    6. Vit D 
  27. When skin is burned, what is one of the biggest first aid concerns?
    Water loss
  28. Role of muscle and fat?
    Muscle generates heat, fat insulates 
  29. Skin comes from which germ layer?
    Epidermis = ectoderm 

    Dermis = Mesoderm!!! 
  30. Is epidermis vasculated? Innervated? Alive?

    Innervated by smooth muscle - for thermoregulation & by merkle cells for sensation 

    The outermost part is dead - as keratinocytes move outwards, they die off

    Callous - thickened epidermis 
  31. Dermis d glands 
    • Vascularized 
    • Contain hair follicles
    • Innervated by both nerves an 
  32. SubQ 
    • Fat layer of skin 
    • For thermoregulation  
  33. Vit D and skin 
    • Skin contains melanocytes 
    • UV radiation promotes Vit D synthesis  
  34. Types of thermoregulatory actions of skin 
    • 1. Radiation 
    • 2. Piloerection - goverened by smooth muscles
    • 3. Vasoconstriction/dilation  of blood vessels feeding skin in smooth muscles of arterioles  
  35. Cartilage 
    • Know for: Flexibility and Resiliance 
    • Type of connective tissue 
    • Made of collagen
    • Avascular and un-innervated
    • Hyaline in joints  
  36. Osteoblasts
    • Secrete collagen and matrix 
    • CANNOT mitose
    • Differentiate into Osteocytes
    • Actions upregulated by calcitonin  
  37. Osteocytes
    • Bone cells 
    • CANNOT mitose
    • Exchange nutrients & waste with blood
  38. Osteoclasts 
    • Resorb bone matrix 
    • Release minerals back into blood
    • Thought to develop from monocytes
    • Actions upregulated by PTH 
  39. Effect on osteoclasts and osteoblasts on bone diameter and tips 
    • bones are hollow...osteoclasts make more hollow 
  40. Types of bones 
    1. Long - compact & spongy 

    2. Short - cuboidal, ankle & wrist

    3. Flat - skull, sternum, ribs

    4. Irregular - vertebrae  
  41. In long bone, where is spongy bone? Where is compact bone? Where are the different marrows?
    Spongy bone - at either end, contains red marrow(site of RBC synthesis) 

    Compact bone - in diaphysis, surrounds yellow marrow(adipocytes)
  42. Mineral homeostasis in bones
    Ca2+ in blood - bound to proteins or as salt/phosphates 

    • Too much Ca2+ = fatigue & lethargy
    • Too little = cramps

    Most Ca2+ stored as hydroxyapatite in bone  - this makes bone a storage site for both Ca2+ and phosphates
  43. Haveresian canals - tunneled by osteoclasts and contain blood + lymph vessels

    Volkmann canals: interconnect H canals

    Lamellae - matrical rings within H canals laid by osteoblasts

    Canaliculi - pores that allows osteocytes to exhange nutrients with blood, within H canals  
  44. Osmoregulation of skin 
    sweat excretes salts and nitrogenous wastes! 

    Also insulated bady against water loss  
  45. Heat homeostasis skin 
    Too cold: piloerection + vasoconstriction 

    Too hot: vasodilation, sweat (evaporative cooling)  
  46. Protection against abrasions, chemicals, bacteria
    1. Keratin makes tight seal to form barrier against pathogens and protect from abrasion 

    2. Sweat is ACIDIC, contains Abs

    3. Sebum kills bacteria

    4. Natural flora
  47. Different types of heat exchange mechanisms
    • 1. Radiation 
    • 2. Conduction
    • 3. Evaporative cooling