Muscles

Slow oxidative

• slow in generating force -> suited to endurance events/aerobic exercise e.g. marathon
• adapted for slow rhythmical contractions 
• smaller in size and produce less overall force than fast-twitch fibres
• high aerobic capacity
• high number of mitochondria
• high level of myoglobin
• high capillary density
• high levels of oxidative enzymes 

Fast oxidative glycolytic

• used mainly during short high-intensity endurance events e.g. 400m
• fast contraction
• large force of contraction
• fatigues easily

Fast glycolytic

• used during explosive events e.g. 100m
• very rapid contractions
• very large forces - calcium ions released quicker
• fatigues very easily

• Motor unit -> a motor neurone and its mucle fibres
• Need fast twitch fibres rather than slow twitch fibres
• Spatial summation -> for a greater force of contraction, more and/or bigger motor unit are recruited by the brain
• All or none law -> each muscle fibre within a motor unit contracts maximally or not at all
• Motor unit unable to relax/increase the force
• Muscle spindles detect changes in muscle length/speed of contraction
• Send information to brain/CNS
• Compares information to long term memory to ensure correct force applied

• Receptors/senses detect stimuli and a signal is sent from the medulla oblongata
• Nerve impulse travels down the axon (i.e. spinal cord) to muscle fibres
• Axon is surrounded by a fatty covering (myelin sheath)
• This insulates and protects the nerves
• Nodes of ranvier are the breaks in myelin sheath and allow the nerve to conduct more rapidly
• When the nerve reaches the motor end plate, acetylcholine is released over the nueromuscular junctions 

• Filaments unable to bind due to tropomyosin -> prevents myosin heads attaching
• Nerve impulse -> Releases calcium ions from sarcoplasmic reticulum 
• Calcium ions attach to troponin (on actin filaments) -> causes change of shape of troponin
• Exposes myosin binding site (on actin filament)
• Allows myosin to bind to actin/cross-bridges formed