MOOSKLES

• Types of Muscles:

  • smooth muscles- involuntary, found in walls of internal organs e.g stomach intestines and blood vessels
  • cardiac muscles- involuntary, found in heart
  • skeletal muscles- voluntary and attach to bone by tendons
• tendons: attach skeletal muscles to bones

  ligaments: attach bone to bone
• Antagonistic pairs: one muscle contracts (agonist) whereas the other relaxes (antagonist)

  • muscles work in pairs since they can only pull when they contract
• Skeletal muscle STRUCTURE:

  • composed of long bundles of of long cells - muscle fibres
  • cell membrane of m.f= Sarcolemma - fold inwards across m.f & stick into sarcoplasm
  • Transverse tubules- aid spread of electrical impulses reach all of muscle fibres through all sarcoplasm
  • network of internal membrane- sarcoplasmic reticulum - stores and releases calcium ions for muscle contractions
  • it is multinucleate - contains many nuclei
  • lots of long myofibrils- specialised for contractions
  • m.f lots of atp
• myofibrils: composed of thick and thin myofilaments

  • thick myofilaments- myosin
  • thin myofilaments- actin
  • Dark band- contains thick myosin filaments with some overlapping thin actin filaments -A- bands
  • light band- only thin actin filaments- I -bands
• Myofibrils made up of many short units, SARCOMERES:

  • end of SARCOMERE = Z- line
  • middle of SARCOMERE- M- line in middle of myosin filament, surrounded by H- zone- only containing Myosin
• Sliding filament theory:

  1. actin and myosin slide over eachother to cause SARCOMERES to contract, causing myofibrils and muscle fibres to contract
  2. SARCOMERE returns to original length after muscle
  3. A-bands remain same length, I-bands & H-zone shorten
• Myosin:

  • globular heads that are hinged
  • contain binding site for actin filament and ATP
• Actin:

  • binding sites for Myosin globular heads - actin- myosin binding site
  • tropomyosin found between actin filaments- helps myosin & actin move past eachother
  • Tropomyosin blocks Actin- Myosin binding site when muscle resting
• Muscle Contraction process:

  • arrival of Action potential from motor neurone that causes depolarisation of Sarcolemma
  • depolarisation travels down T-Tubules to Sarcoplasmic reticulum, releasing Calcium ions into Sarcoplasm
  • influx of Calcium ions stimulate muscle contraction
• M.C PT 2:

  • Calcium ions bind to protein attached to tropomyosin, changes protein shape and pulls tropomyosin out of a-m binding site
  • exposed b.s results in bond Actin-Myosin cross bridge formed
  • Calcium ions activate ATP hydrolase, energy for muscle contraction
  • energy released causes M heads to bend, pulling actin filament
  • another ATP provides energy to break a-m cross bridge
  • myosin head returns to starting position, to repeat cycle
• M.C PT3:

  • Many a.m cross bridges formed and broken rapidly, pulling actin filament and sarcomere- causing muscle contraction
  • cycle continues due to calcium ions presence
  • once muscle no longer stimulated, calcium ions leave the binding site of protein attached to tropomyosin, by A.T move back into sarcoplastic reticulum with ATP
  • Tropomyosin moves back into binding site & blocks
  • Actin filament slides back and sarcomere lengthens
• Energy for Muscle Contraction:

  • Aerobic respiration
  • Anaerobic respiration
  • ATP Phosphocreatine system (PCr)
• Energy for Muscle Contraction: Aerobic Respiration

  • ATP generated in oxidative phosphorylation in Mitochondria
  • low intensity- o2 present
• Energy for Muscle Contraction: Anaerobic Respiration

  • ATP made rapidly by glycolysis - pyruvate converted to lactate during fermentation
  • lactate builds up in muscles quickly causing muscle fatigue
  • FOR SHORT PERIOD OF TIME
• Energy for Muscle Contraction: ATP Phosphocreatine system

  • ATP made by phosphorylating ADP- phosphate group from PCr
  • PCr stored inside cell
  • ATP formed quickly
  • PCr runs out quickly - short bursts of vigorous exercise
  • anaerobic + alactic
  • ADP + PCr -> ATP + Cr
• ATP-Phosphocreatine system:

  • Creatine can be broken down into Creatinine and is removed by kidneys
  • high creatinine levels are present in those who regularly exercise, have high muscle mass or may be an indicator of kidney failure
• two types of skeletal muscles:

  • Slow twitch muscle fibres
  • Fast twitch muscle fibres
• Slow twitch muscle fibres:

  • contract slowly, work for prolonged time
  • Aerobically respire
  • endurance based
  • high proportion found in back & calves
  • lots of Mitochondria and Blood Vessels
  • Mitochondria found toward edge of m.f for short diffusion pathway of o2
  • rich in myoglobin- protein storing O2
• Fast twitch muscle fibres:

  • contract quickly, tire quickly
  • short bursts of energy
  • high proportion in legs, arms and eyes
  • low in Mitochondria, Blood Vessels and Myoglobins
  • stores of PCr- energy regenerated fast
  • whitish colour (lack of Myoglobin)