Muscles

• Types of muscles:

  • Voluntary
  • Cardiac
  • Involuntary
• Similarities between a synapse and neuromuscular junction

  • Neurotransmitters
  • Receptors that bind and open Na+ channels
  • Na+/K+ pumps to repolarise
  • Enzyme breakdown
• Neuromuscular junctions are only excitatory, whereas cholinergic synapses can be inhibitory or excitatory
• Neuromuscular junctions only link neurones to muscles, whereas cholinergic synapses link neurones to neurones and neurones to other effector organs
• Neuromuscular junctions only have motor neurones involved, whereas cholinergic synapses have motor, sensory and relay neurones involved
• In neuromuscular junctions the action potential ends, whereas new action potentials may be produced after cholinergic synapses
• Neuromuscular junctions have acetylcholine bind to the receptors of the muscle fibre membrane, whereas cholinergic synapses have acetylcholine bind to the receptors on the membrane of the postsynaptic neurone
• Neuromuscular transmission

  A) Action potential

  B) Motor neurone axon

  C) Synaptic cleft

  D) Pre-synaptic membrane

  E) Sarcolemma

  F) Mitochondrion

  G) Myofibril

  H) Synaptic knob

  I) Synaptic vesicles containing acetylcholine

  J) Sarcoplasm

  K) Skeletal muscle

  
• Order of neuromuscular junction

  A) Potential

  B) Calcium ions

  C) ACh-containing

  D) Presynaptic

  E) Neuromuscular

  F) Sarcolemma

  G) Sodium ions

  H) Sarcolemma

  I) T-tubules

  J) Calcium ions

  K) Sarcoplasm

  L) Calcium ions

  M) Muscle contraction

  
• Muscle is an organ composed of different tissues (muscle tissue, connective tissue (tendons))
• Muscle tissue is composed of muscle cells called muscle fibres
• Each muscle fibre cell is packed with organelles called myofibrils
• Myofibrils are composed mainly of two muscle filaments called actin and myosin
• Microfibrils can be divided into functional units, each called a sarcomere
• Structure of muscle

  A) T-tubule

  B) Sarcolemma

  C) Mitochondrion

  D) Myofibrils

  
• Structure of myofibrils

  A) Thick filament

  B) Myosin

  C) Thin

  D) Actin

  E) Myofibrils

  F) Cylindrical

  
• Sarcomere

  A) Sarcomere

  B) M line

  C) Z line

  D) Thick myosin filament

  E) z line

  F) I band

  G) A band

  H) H band

  I) I band

  J) Thin actin filament

  K) Sarcomere

  
• In muscle contractions, H band (myosin only) gets narrower
• In muscle contractions, I band (actin only) gets narrower
• In muscle contraction, the Z lines (middle of the actin filaments) get closer together
• In muscle contractions, the M lines (middle of the myosin filaments) get closer together
• In muscle contractions, the A band (the length of the myosin filament) does not change
• The hydrolysis of ATP provides energy for movement of myosin head and the active transportation of calcium ions back into tubules
• Resting muscles only contain enough ATP for 3-4 seconds of intensive exercise
• Mitochondria generate more ATP through the respiration of glucose
• Full aerobic and anaerobic respiration is slow
• Muscle fibres contain phosphocreatine
• Phosphocreatine rapidly generates ATP from ADP by transferring a phosphate ion to the ADP
• ATP synthesis through phosphocreatine is catalysed by the enzyme creatine phosphokinase
• ADP + phosphocreatine -> ATP + creatine
• The supply of phosphocreatine is limited, but enough is present to keep muscles contracting until respiration catches up with muscles demand
• Using anaerobic respiration and phosphocreatine, a trained athlete is able to sustain intense activity for 10 seconds
• Prolonged activity is possible, but the rate of muscle contraction has to be matched to the rate of ATP synthesis
• Myoglobin is a single chain protein
• Myoglobin has a high affinity for oxygen and can act as an oxygen store in muscles
• Slow twitch fibres are designed for aerobic exercise
• Slow twitch fibres use oxygen to produce a small amount of tension over a long period of time
• Slow twitch fibres are resistant to fatigue as the speed of contraction is very slow
• Slow twitch fibres have a higher capacity for aerobic respiration
• Slow twitch fibres are red in colour due to the higher concentration of myoglobin