ch 6 part 1

• • Function

  to contract or shorten=> responsible for all body movements 

  
  

  Three basic muscle types are found in the body

  • skeletal muscle
  • cardiac muscle 
  • smooth muscle 
• • Skeletal muscle fibers:
  • Packaged into organs called skeletal muscles
  • Largest muscle fibers
  • Soft fragile but exert a lot of power: they are not ripped apart because the connective tissue bundles thousands of their fibers attached together => strengthens and supports muscle
  • Most are attached by tendons and bones
  • Cells are multinucleate 
  • Striated muscle- visible banding
  • Voluntary- subject to conscious control, can be activated by reflexes 
• • Cells are surrounded and bundled by connective tissue

  * endomysium- encloses a singular muscle fiber

  * perimysium- wraps around a fascicle (bundle) of muscle fibers

  * epimysium =fascia- covers the entire skeletal muscle
• • Epimysium blends into a connective tissue (protects, supports, & binds together other tissues)

  Attachment

  * tendons- cord-like structures, mostly collagen fibers, often cross a joint due to toughness and small size 

  * aponeuroses- sheet-like structures, attach muscles indirectly to bones, cartilages, or connective tissue coverings

  • Sites of muscle attachment
  • Bones 
  • Cartilage 
  • Connective tissue coverings 
• SKELETAL MUSCLES

  • Produce movement
  • mobility (biological) and locomotion (organism level)-  allow us to express emotions 
  • Maintain posture and body position
  • Stabilize joints

  -  muscles/tendons reinforce and stabilize joints 

  • Generate heat

  skeletal muscle is at least 40 body mass=>

  • heat is byproduct of muscle activity: ATP used for contraction=>
• PARTS OF CELLS

  • Sarcolemma: “Muscle husk“, covers fibers of skeletal muscles
  • plasma membrane: oval nuclei found underneath it  
  • Sarcoplasm: cytoplasm, rich in oxygen storing myoglobin protein 
  • Myofibrils = Ribbon-like organelles inside muscle cells, composed of muscle filaments
  • Light (I) bandhas midline interruption, darker area=Z-disc 
  • Dark (A) bandhas lighter central area=H-disc with an m line in center which contains protein rods that hold filaments together 
  • sarcoplasmic reticulum: specialised ER that releases Ca2+ on demand
• MYOFILAMENTS

  1. thick filaments=myosin filaments 

  *contains ATPase enzymes (split ATP to release energy for muscle contraction)

  * myosin heads form cross bridges when link to thin filaments during contraction 

  *attached to Z discs by titin (elastic filaments, runs through of core of thick filamentS

  
  

  2. thin filaments=actin filaments

  *contains regulatory proteins (allow or prevent binding of myosin heads to actin)

  *anchored to Z discs

  *light (I) band only has thin filaments 
• Functional Properties:

  1. Irritability=responsiveness=excitability

  • ability to recieve and respond to stimuli

  1. Contractility

           - ability to forcefully shorten when stimulated 

  1. Extensibility

  • Ability to stretch

  1. Elasticity

  •  Ability to recoil and return to resting position 
• • NMJ- contains synaptic vesicles 
  • Acetylcholine (ACh)- specific neurotransmitter that stimulates skeletal muscle fibers 
  • Synaptic cleft: gap between nerve and muscle fiber, nerve and muscle do not make contact 
• • ATP- only energy source that an be used directly to power muscle activity 
  • Muscles store limited amount of ATP, 4-6 seconds worth, to get going
  • ATP must be continuously regenerated for contraction to continue via 3 pathways:

  1. direct phosphorylation of ADP by creatine phosphate 
  2. aerobic respiration 
  3. aerobic glycolysis and lactic acid formation 
• • Muscle fatigue: muscle unable to contract even with stimulus
  • Major contributing factor to muscle fatigue= O2 deficit
• • Muscle tone: continuous partial contractions, resulr of different motor units stimulated by nervous systems in a systematic way 
  • Muscle fibers contract even at rest, involuntary, not visible; necessary for firm, healthy, readiness in muscle  
  • Homeostatic imbalance

  1. Flaccid- muscle no long stimulated due to nerve supply to muscle destroyed = muscle loses its tone = soft, flabby

  i.e. accident

  1. Atrophy- muscle wastes away = flaccid paralysis 
  2. Tetanus- increases muscle tone until muscle no longer controllable= spastic pralysis, due to baterial toxin 
• • Muscle inactivity- due to loss of nerves supply, immobilization, etc. leads to muscle weakness and wasting 
  • Regular exercise increases muscle size, strength, and endurance

  1. Aerobic or endurance exercise

  • Aerobic, jogging, biking=> stronger, more flexible. musles with greater resistance to fatigue, Muscle size not increased much, exercise can go on for hours 

  2. Resistance or isometric exercise

  • increases muscle size/strength due to enlargment of muscle fibers, require little time and equipment, Force muscles to contract with as much 

  force as possible 
• Cardiac muscles

  • Striations
  • Usually a single nucleus
  • Branching cells
  • Involuntary
  • Found only in the heart
• Smooth

  • Lacks striations
  • Spindle shaped cells
  • Single nucleus
  • Involuntary-
  • Found mainly in the walls of hollow organs
• Skeletal

  • Striations
  • Multinucleate
  • long cells
  • Produces movement
  • Maintains posture
  • Stabilizes joints
  • Generates heat