Topic 6 - Skeletal Muscles Flashcards
What is an antagonistic muscle pair?
Muscles work together in pairs to bring about movement. These are referred to as antagonistic muscle pairs where one muscle contracts while the other relaxes to move bones at a joint.
What are skeletal muscles for?
They are under voluntary control and are responsible for movement by pulling on bones they are made up of a highly organised structure to ensure efficient contraction and strength.
What are muscle cells and myofibril?
Muscle cells are long cylindrical cells group together for greater strength inside muscle fibres are myofibrils which are specialised protein structures that perform contraction.
What are myofibril made of?
Made of thick filaments (myosin) and thin filaments (actin) that overlap.
What is the structure of actin?
Composed of two actin molecules twisted together to form a filament.
What is the structure of myosin?
Contains myosin heads which bind to specific sites on actin during muscle contraction.
Why does skeletal muscle appear striated under microscope?
The arrangement of microfibrils within the muscle fibre.
What are the steps for examining skeletal muscle?
- Preparation of microscope slide: obtain a thin section of muscle tissue and stain the tissue with a dye.
- Under the microscope: use a light microscope to examine the tissue start at a low magnification and then increased to a higher magnification for detail.
What features can you identify in skeletal muscles?
Striations: alternating light (I-bands) and dark (A-bands) bands caused by the arrangement of actin and myosin.
Nuclei : muscle fibres are multinucleated with nuclei located at the periphery of the fibres.
Sacromeres: visible at higher magnifications as the repeating unit unit along a microfibrils marked by Z-lines.
What is the A-band?
Dark band where actin and myosin overlap.
What is the I-band?
Night band containing only actin filaments.
What is the Z-line?
Marks the boundaries of each sacromere.
What is the H-zone?
Lighter region in the centre of the A-band where there is no overlap of actin and myosin.
What is a sacromere?
Basic contractor unit of a muscle fibre made up of actin and myosin filaments. It is the smallest functional unit of skeletal and cardiac muscle responsible for muscle contraction.
What is a muscle contraction?
Highly coordinated process involving actin and myosin filament within a sarcomere. It is powered by ATP and regulated by calcium ions.
What is the sliding filament model?
- during contraction actin (thin) filaments slide over myosin (thick) filaments causing the sarcomere to shorten.
- I-bands and H-zones become narrower while A-bands remains he same length
What are the six stages of muscular contraction?
- Calcium ions release.
- Binding of calcium to troponin.
- Crossbridge formation.
- Power stroke.
- ATP binding and detachment.
- Reactivation of myosin head.
The first stage of muscular contraction is calcium ion release what is meant by this?
- an action potential travelled along the sarcolemma and into the muscle fibre via T-tubules
- Stimulates the sarcoplasmic rectum to release calcium ions into the sarcoplasm
What is a T-tubule?
A tunnel structure that extends from the surface of a muscle cell deep into its interior.
What is the sarcolemma?
A membrane that surrounds a muscle cell it act as a barrier controlling the entry and exit of substances into an out of the muscle cell. It also helps transmit electrical signals which are essential from muscle contraction.
What is the sarcoplasm?
The cytoplasm of a muscle cell.
What is the sarcoplasmic reticulum?
Specialised type of endoplasmic reticulum found in the muscle cell its main function is to store and release calcium ions during muscle contraction.
The second stage of muscular contraction is binding of calcium to troponin what happens during this stage?
- calcium binds to troponin causing it to change shape
- This pulls tropomyosin away from the actin finding sites exposing them for myosin head attachment
The third stage of muscular contraction is Cross-bridge formation what happens during this stage?
- myosin heads attached to the exposed binding site on actin forming cross-bridges.
The fourth stage of muscular contraction is power stroke what is this?
- The myosin head pivots pulling the actin filament towards the centre of the sarcomere.
- ADP and Pi are released during this movement.
The fifth step of muscular contraction is ATP binding and attachment what happens during this stage?
A new molecule of ATP bind to the myosin head causing it to detach from the actin filament.
The final stage of muscular contraction is reactivation of myosin head what is meant by this?
- ATP is hydrolysed to ADP and Pi providing energy to reset the myosin head into its original position ready for the next cycle.
What are the two energy requirements for contraction?
- ATP hydrolysis: ATP is hydrolysed at each myosin head during the power stroke and resetting the myosin head.
- Calcium ion transport: ATP is also required to pump calcium ions back into the sarcoplasmic reticulum after contraction.
What are the three ATP sources in muscle cells?
- Aerobic respiration: supplies the most ATP during prolonged intensity activity and oxygen is stored in the myoglobin for immediate use.
- Anaerobic respiration: provides ATP when oxygen levels are low leading to lactic acid production.
- Phosphocreatine system: phosphocreatine provides phosphate groups for the rapid regeneration of ATP from ADP ideal for short bursts of intense activity.
What is muscle fatigue?
Occurs when a muscle loses its ability to contract effectively during prolonged activity. It happens due to a reduction in ATP and an accumulation of metabolic by-products such as lactic acid.
What is ATP depletion as a cause of muscle fatigue?
ATP is required for muscle contraction and relaxation prolonged activity reduces ATP levels.
What is lactic acid accumulation as a key cause of muscle fatigue?
Anaerobic respiration during intense exercise produces lactic acid which lowers the pH of muscle cells and inhibits enzyme activity.
What is reduce calcium ion availability as a key cause of muscle fatigue?
Calcium irons are essential from muscle contraction. Fatigue can reduce their release or uptake in muscle cells.
What is neuromuscular junction fatigue?
Prolonged activity may deplete neurotransmitters such as acetylcholine affecting signal transmission.
What is a slow twitch muscle fibre?
- Specialised for endurance activities
- Contract slowly and are resistant fatigue
- adapted for aerobic respiration which is more efficient for prolonged energy supply
What are the key adaptions of slow twitch muscle fibres?
- High myoglobin content: myoglobin store oxygen, giving these fibres a red colour.
- Rich blood supply: insures continuous supply of oxygen and nutrients.
- Numerous mitochondria: site of aerobic respiration to produce ATP
- Low levels: reliance on sustained oxygen supply rather than short term reserves
What are fast twitch muscle fibre types?
- Specialised for short bursts of intense activity.
- Contract quickly and powerfully but fatigue rapidly.
- Adapted for anaerobic respiration which provides quick energy but is less efficient.
What are the adaptations of fast twitch muscle fibre types?
- thicker and more numerous myosin filaments: allows powerful contractions.
- High levels: provides an immediate energy source for anaerobic respiration.
- High concentration of anaerobic enzymes: enables rapid ATP production in the absence of oxygen
- stores of phosphocreatine: allows quickly regeneration of ADP to ATP.
