Muscle fibres Flashcards
What are the properties of slow twitch muscle fibres?
- These fibres are red and contain large amounts of myoglobin and many blood capillaries.
- They respire aerobically and store glycogen as a metabolic fuel
- They split ATP at a slow rate
- they have the ability to function over long periods of time and the ability to aspire fat stores in the body.
What are the properties of fast twitch muscle fibres?
- These fibres are white and contain a low content of myoglobin
- few mitochondria
- few blood capillaries
- large amounts of glycogen
- geared to generate ATP by anaerobic metabolic processes
- can only function for short periods of time due to the production of lactate
- have storage for creatine phosphate and anaerobic respiration.
What are the proportions of muscle fibre types?
The proportion of slow twitch fibres to fast twitch fibres is genetically determined
The average person has approximately 60% fast muscle fibres and 40% slow twitch fibres
What happens to muscle fibres with training?
With consistent endurance training muscle fibres can develop more mitochondria and surrounding capillaries so can transform into slow-twitch fibres to improve endurance.
How is a tendon made up?
- tendons are at the end of the muscle and connect the muscle to the bone
- these tendons are made up of bundles of muscle fibres bound together by connective tissue (2cm)
- each muscle fibre is a single muscle cell surrounded by a cell surface membrane (0.01cm in diameter)
- within each muscle fibre there are also numerous myofibrils
- these myofibrils are each composed of sarcomeres
How is the sarcomere made up?
Made up of two types of filaments:
- myosin: a thick filament
- actin: a thin filament
The sliding of these filaments brings about the contraction of the muscles
What do the two types of filaments form?
Actin - forms thin filaments (I bands)
Myosin - forms thick filaments (A bands)
What is the sliding filament theory? summary
When a muscle contracts, the actin moves across the myosin filaments, shortening the sarcomere
What is the structure of myosin?
- two long polypeptide chains twisted together
- at the end of each chain is a globular head which has ADP and Pi bound to it
- myosin filament: lots of these molecules bundled together,, with heads sticking out
What is the structure of actin?
- two chains of actin monomers joined together
- its shape produces sites where the globular heads of the myosin can fit and bind
- around the monomer chains it tropomyosin, along the tropomyosin is troponin bound at regular intervals
- when the muscle is relaxed the tropomyosin covers the binding sites
What is the sliding filament theory - steps
- A nerve impulse arrives at a neuromuscular junction and calcium ions are released
- the calcium ions diffuse through the myofibril
- this initiates the movement of the protein filaments:
- calcium ions attach to the troponin molecules causing them to move
- as a result the tropomyosin on the actin filament moves, exposing myosin binding sites on actin filaments
- myosin heads bind with myosin binding sites on the actin filaments forming cross bridges
- when the myosin head binds to the actin, ADP and Pi on the myosin head are released
- the myosin changes shape, causing the myosin head to nod forward. This movement results in the movement of the filaments. The attached actin moves over the myosin
- an ATP molecule binds to the myosin head, this causes the myosin head to detach
- an ATPase on the myosin head hydrolyses the ATP forming ADP and Pi
- This hydrolysis causes a change in the shape of the myosin head. It returns to its upright position, enabling the cycle to start again
What is creatine phosphate?
- Also known as phosphocreatine, is found stored in high levels in fast twitch muscle fibres
- It is an immediate energy system and a high energy compound
- when exercise intensity is high, or energy needs are instantaneous, creatine phosphate stored in muscle is broken down to provide energy to make ATP
- when the high-energy bond PCr is broken, the energy it releases is used to resynthesise ATP
- in this process, ATP is usually made without the presence of oxygen
- maximum intensity can only be achieved for short periods of time as the supply of PCr is very limited
What is the creatine phosphate system?
ADP + creatine phosphate –> ATP + creatine
At rest ATP is hydrolysed to ADP and the phosphate is transferred to creatine to make phosphocreatine
- this occurs in the mitochondria, where ATP levels are high
- during exercise, phosphocreatine is hydrolysed and the phosphate is released to make ATP from ADP
- this occurs in the muscles where ADP levels will be high
What are creatine supplements?
Creatine supplements can be taken to try and increase the amount of creatine phosphate stored in the muscles. This could be beneficial to athletes as it would allow athletes who work anaerobically to be able to work for longer.
What are diets of endurance?
Endurance athletes should eat protein at 1.4kg per day
Athletes taking part in longer endurance events need more protein than those running shorter distance
