muscles and movement

  1. sketetal muscle: attached to bones, arranged in antagonistic pair= muscles working in pairs opposite to eachother. 
  • Flexors: contract, and bend joints. e.g. Bicep (contracts and tricep relaxs) 
  • Extensors: contarct, extend/ striaghten a joint. e.g. triceps( contract and biceps relax) striaghten the arm. 
  • composed of myofibrils = actin (thin filaments ) + Myoson ( think filaments)
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Skeletal muscle


  1. sketetal muscle: attached to bones, arranged in antagonistic pair= muscles working in pairs opposite to eachother. 
  • Flexors: contract, and bend joints. e.g. Bicep (contracts and tricep relaxs) 
  • Extensors: contarct, extend/ striaghten a joint. e.g. triceps( contract and biceps relax) striaghten the arm. 
  • composed of myofibrils = actin (thin filaments ) + Myoson ( think filaments)
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contraction of the Skeletal muscle. Sliding Filame

when muscles contracts the thin filaments(light bands/ I bands ) move between the thick myosin filaments( dark bands/ A bands). shortening  length of sacromere, therefore shortening ther muscle. 

  • myosin + actin filaments slide over each other = making sacromere contract- myofibrils do not contract themselves. 
  • the simultaneous contraction of sacromeres myofibrils and therefore muslce fibres contract. 
  • when muscle relaxes they return to their original length. 

Zones of Scaromere : End of Sacromere = Z line, Middle of Sacromere = M-line, around M-line is H zone., which only contains Myosin filaments. 

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sliding filament theory

  • Stages of sliding filament theory

1. Action potential Tiggers influc of calicium ions.

  • action potential from motor neurone, stimulates muscle cell. 
  • this Depolarises the Sarcolemna 
  • depolarisation runs through T- tubles into the Sarcoplsmic reticulum. 
  •  depolarisation causes Releases of Ca2+ ions into sarcoplasm from the sacroplasmic reticulum 
  • calcium ion bind to troponin ( on Actin ), the ion causes the troponin to be pull out of the actin -myosin binding site on to the actin filament. Actin- myosin Binding site now Exposed.
  • mysin head binds to the exposed binding site forming cross bridges = Actin - myosin Bridge
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muscle contraction due to Action potential

Muscles Fibres: Sarcolemna ( cell membrane of muscle fibre calls ) is infolded into the sarcoplasm ( muscle cell cytoplasm ). Theses infolding are tranverse ( T ) tubles.transverse (T) tubles spread electrical impluses throughout the sarcoplasm, which ensures reach of signal through the muscle fibre.

  • for  contraction, you need ATP ( which is provided by Mitochondria  + Calicium ions( releases and stored in the sarcoplasmic reticulum ) 
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Muscle Contration due to action potential

2. ATP Provides Energy for Movement of Myosin Head

Calcuim ions activate ATPase, which breaks down ATP into ADP + Pi +Energy This Energy is used to change the shape os the myosin head and therefore move the myosin head = The power stroke power stroke, results in pulling of the actin filaments.

3 ATP also Breaks the Actin- myosin Bridge.

ATP provides energy to break actin-myosin cross bridge myosin head detaches from actin filament and thenreattaches to a Different binging site which is further alond the actin filament this process is repeated ( ATTACH --> change shape , Detach, reataach to new binding site ) this process will continue as long as Ca2+ ions are attached to the toponin , which changes shape of tropomyosin and exposes binding site

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What happens when Excitation stops.

  • muscles stop being stimulated by action potential 
  • calcuim ions leave binding sites on troponin molecules 
  • calcuim ions are move back to the sarcoplasmic reticulum by active transport ( process Requires ATP
  • troponin molecules return to original shape, pulling tropomyosin mocules with them and blocking the Actin- myosin bind sites
  • Actin filaments slide back to original postion ( RELLAXED POSITION) the sacromere lengthens. 
  • muscles= no contraction, because myosin head not attached to acti filaments. = no actin- myosin cross bridges. 
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Two types of skeletal muscles: Fast Twitch

1. speacialised to porduce rapis, contractions in short burts. 

2.Few mitochondria - ATP comes from Anaerobic respiration( glycolysis) this process consumes gyycogen (stored glucose)

  • 3: little mitocondria    
  • Few Caprillaries
  • therefore cannot stores as much oxygen 
  • whitish in colour 

4. Fatigues quikly

5. High levels of creatine phospahate 

good for sprinting, wieght lifters

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The Two types of Skeletal muscles : Slow Twitch

1. specialised for SLower, sustained contraction 

  • can cope with long period of exercise

2. MANY mitochondira- ATP comes from aerobic respiration ( from the electron transport chain )

3. lots of Myoglobin ( DARK RED PIGMENT) = to store O2

  • lots of capillaries = supply O2.  
  • known as re muscle fibre/ oxidative
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