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Types of muscle fibres Thursday, 21 October 2021 Starter: Look at the images on the right. Are all skeletal muscles the same – discuss with a partner. Key words: slow twitch, fast twitch, myoglobin Learning outcomes: Describe and explain the structural differences between fast and slow twitch muscle fibres Determine the types of fibres mainly present in certain animal muscle tissue. Predict the type of sports a person would be good at based on a muscle biopsy Lets recap – what do we already know? Types of fibres • Skeletal muscles are made up of two types of muscle fibres – slow twitch and fast twitch. • Different muscles have different proportions of these fibres. Task 1 (12 minutes): determining characteristics of the fibres • Using the information in the worksheets around the room, produce a table comparing fast and slow twitch muscle fibres. • Extension: give one reason why fast twitch are likely to tire quickly Characteristic Speed Energy Colour Energy source Type of activity suited to Found in Fast twitch Slow twitch • What can you tell me about these athletes and their muscles now? Task 2: fast or slow twitch quiz? • You will be given information about certain animal muscles. Working with a partner, determine whether the majority of the meat would contain fast or slow twitch muscle. Hint: different parts may have a different ratio Justify your reason! • Chickens spend a lot of time roaming around or standing. Their thigh and leg muscles are used constantly. They rarely fly, and then only for very short distances so their breast and wing muscles aren´t used often. In contrast, wild birds such as ducks fly a lot. • Cattle spend a lot of time standing, and so their muscles are constantly being used. Therefore, beef has a fairly high concentration of myoglobin. • Pigs also can spend quite a bit of time standing and roaming around. However, the animals used for pork are young and small, their muscles are less developed and do less work. • Fish float in water and don't need constant muscle energy to support their skeletons. They do use fins and tail constantly for swimming. “Give me a muscle biopsy and I´ll tell you whether you should be a sprinter or a marathon runner” Use your knowledge of fast and slow twitch muscles to explain this diagram Exam Question • Give three structural differences between slow (Type I) and fast (Type IIb) muscle fibres. • Suggest why successful sprinters have a relatively high percentage of fast fibres in their muscles. Check your answer! • slow / red / tonic / type I, fibres have: • a smaller diameter ; • wider Z lines ; • lower glycogen content ; • more capillaries ; • higher myoglobin content ; • more mitochondria ; • less sarcoplasmic reticulum ; • [accept converse for fast / white / twitch / type II, fibres] • sprinters need fast muscle contraction ; fast fibres produce more power at fast contraction speeds ; fast fibres produce more force than slow fibres ; fast fibres have higher ATPase activity ; fast fibres have large store of creatine phosphate ; as immediate energy source / for ATP production ; even when oxygen is insufficient for aerobic respiration ; Resources to print Speed of contraction • Fast twitch muscles contract very quickly, producing rapid, intense contractions. • Slow twitch muscles are specialised for a slower, sustained contraction. Where do you find them? • Slow twitch muscles are used for posture e.g. in the back • Fast twitch muscles are for fast movement such as in the eyes and legs. Types of activities • Fast twitch muscles are good for short bursts of speed and power e.g. sprinting and weight lifting. They tire quickly • Slow twitch muscles are good for endurance sports such as running long distances. They are slow to tire. Energy • Energy is released slowly through aerobic respiration in slow twitch. They have many mitochondria and blood vessels supplying oxygen, • Fast twitch rely on anaerobic respiration using glycogen. There are few mitochondria and blood vessels. Colour of fibres • Slow twitch fibres are reddish in colour because they are rich in myoglobin ( a red coloured protein that stores oxygen). • Fast twitch fibres are whitish in colour because they don´t have much myoglobin. They respire anaerobically. Glycogen and Creatine phosphate • Slow twitch have low glycogen content and low levels of creatine phosphate, (an organic compound that provides a quick source of energy for muscle fibers to contract). • Fast twitch muscle fibres have high levels of both.