Muscles Flashcards
Describe the structure of skeletal muscle - 6
- Muscle
- Bundle of muscle fibres
- Muscle fibre
- Myofibrils
- Sarcomere
- Protein filaments : actin and myosin
Describe a muscle fibre 4
- Muscle cells fuse to form a very long multinucleated cell
- Surrounded by a cell membrane called sarcolemma
- Have lots of mitochrondia - provides ATP for muscle contraction
- Contains sarcoplasm : cytoplasm of striated muscle cells
Why are the muscle fibre cells multinucleated? 3
- Single nucleus not enough to control metabolism of long cell
- Time taken for protein to be made in cell is too long
- To reach furthest parts of the cell
What does the sacroplasm contain? 2
- Folds called transverse tubules [T] help to spread electrical impluses throughout the sacroplasm
- To reach all parts of the muscle fibres
What runs through the sacroplasm?
Sarcoplasmic reticulum
What is the sarcoplasmic reticulum?
A network of internal membranes running through the sarcoplasm
What does the sarcoplasmic reticulum do?
Stores and releases calcium ions needed for muscle contraction
What word is used to describe the muscle fibre patterns?
Striated - pattern of light and dark bands
What are bundles of muscle fibres?
Bundles bound together by connective tissue continuous with tendons
How long across is each bundle of muscle fibres?
2cm across
What does the connective tissue in bundle of muscle fibres contain?
Blood vessels
Where are myofibrils found?
Sacroplasm
What are myofibrils?
Long cylinderal organelles highly specialised for contraction
What are myofibrils made up of?
Repeated contracile units arranged end to end (sacromeres]
What are sacromeres made up of?
Protein filaments:
- Actin
- Myosin
Is actin thin/thick?
Thin
Is myosin thin/thick?
Thick
How does the sacromere contract?
Through the co-ordinated sliding of protein filaments past each other
How does the sacromere return to its original shape?
Through the returning of sliding protein filaments to their original length when the muscle relaxes
When labelling an actin and myosin diagram what should be labelled? 5
- Z line
- M line
- A band
- I band
- H Zone
What is the z line?
Marks the ends of the sacromere, where sarcomeres joined together sideways
What is the m line?
The middle of each sacromere in the middle of the myosin filaments
What are the A bands?
Dark bands where the actin and myosin is overlapping
What are the I bands?
Light bands with thin actin only
What do the intermediately coloured bands contain?
Myosin only
What do the actin and myosin do in contraction?
- Actin moves within myosin, sliding over each other
- Sacromere shortens in length
- Muscle length shortens
- Actin and myosin DO NOT shorten themselves
What are the 2 proteins between actin filaments?
- Troponin
- Tropomyosin
Troponin and tropomyosin are…
…attracted to each other
What are the myosin filaments made up of?
- Hinged globular heads that move back and forth
- With binding sites for actin and ATP
What do actin filaments have?
Actin-myosin binding sites for myosin heads
Part 1 of sliding filament theory - myosin binding to actin 10
- Nerve impulsive [action potential] arrives from a motor neurone at a neuromuscular junction
- Stimulates muscle cell
- Depolarises sacrolema
- Depolarisation spreads down T tubules to sacrcoplasmic reticulum
- SR releases stored calcium ions into sacroplasm
- Calcium ions bind to troponin
- Causes it to change shape
- Pulls attached tropomyosin out of actin myosin binding site
- Exposes actin myosin binding sites on actin filaments
- Allows myosin head to bind to actin filament forming an actin myosin cross bridge
Part 2 of sliding filament theory - the role of ATP 10
- Calcium ions activate ATPase enzyme when actin and myosin bind
- Causes breakdown of ATP into ADP and Pi to provide energy needed for contraction
- Myosin changes shape
- Myosin head moves forward
- Pulls actin filament along over it
- ATP molecule binds to myosin head
- Causes it to detach from the actin filament, breaking the actin myosin bridge
- An ATPase on the myosin head hydrolyses ATP to form ADP and Pi
- Causes change in myosin head shape, returning it to its upright position
- Enables cycle to start again
Explain how muscle contraction stops
- Muscle stopped being stimulated by nerve impulses
- Calcium ions leave binding sites on troponin molecules
- Moved by active transport back into sarcoplasmic reticulum
- Troponin molecules return to original shape
- Pulls attached tropomyosin molecules with them
- Block actin-myosin binding sites
- Muscles not contracted
- No myosin heads attached to actin filaments - no cross bridges
- Actin filaments slide back to relaxed position
- Lengthens sacromere
What is skeletal muscle used for?
Movement
How do the arms move? 5
- Bicep stimulated
- Bicep contracts
- Tricep relaxes
- Pulls on tendon
- Bends/flexes the arm
How do muscles work? 4
- Muscles contract/relax
- To pull on bones at joints
- Joints bent [flexed]/straightened [extended]
- Muscles can only pull
What are antagonistic pairs/why do muscles work in antagonistic pairs? 3
- Muscles can only work in one direction
- Therefore there is a need to create opposite forces
- Two muscles : extensor and flexor are needed to move bone
What is an extensor?
Muscle causing the extension of a joint when it contracts
What is a flexor?
Muscle causing the flexing of a joint when it contracts
What are ligaments?
- Attach bone to other bone
- Allow some movement
- Provides stability
How do ligaments provide stability?
They have lots of elastic tissue
What are tendons?
- Attach muscles to bones
- Enable muscles to move joints
- Relatively inelastic
Why are tendons relatively inelastic?
So all the force is transmitted to the bone
What is a joint?
Point where two bones meet
What are the synovial joints?
Joints allowing for bone movement
What are synovial joints separated by?
A cavity filled with synovial fluid
What is the synovial fluid?
A viscious and sticky lubricant allowing for free movement of bones
What is the cartilage like?
White, hard and rubbery
What does the cartilage do?
Protects bones within joints and is a shock absorber
What are the two types of muscle fibres?
- Slow twitch
- Fast twitch
What affects proportion of slow twitch to high twitch muscle fibres?
- Genetics
- Endurance training
- Type of muscles
What proportion of muscle fibres do endurance trainers/endurance muscles [e.g back muscles] have?
High slow twitch to fast twitch proportion
List the properties of slow twitch fibres compared to fast twitch 9
- More aerobic respiration
- Darker muscle fibres: higher myoglobin levels
- High amounts of respiratory enzymes
- More capillaries
- Lower glycogen content
- More mitochondria
- Less sarcoplasmic reticulum
- Fatigues less quickly
- Lower levels of creatine phosphate
List the properties of fast twitch fibres compared to slow twitch 9
- More anaerobic respiration
- Higher levels of creatine phosphate
- Higher glycogen content
- Less mitochondria
- Less capillaries
- More sarcoplasmic reticulum
- Fatigues more quickly
- Less respiratory enzymes
- Ligher muscle fibres: lower myoglobin levels
- Higher levels of creatine phosphate
Why are slow twitch muscle fibres darker? 3
- Higher myoglobin levels
- Higher O2 store
- Ensures sufficient supply of O2 for aerobic respiration
Why do slow twitch muscle fibres have more capillaries? 3
- Better blood supply
- Facilitates faster supply of glucose and oxygen for aerobic respiration
- Faster removal of CO2
Why are slow twitch muscle fibres have more mitochondria?
Krebs Cycle and oxidative phosphorylation take place here for aerobic respiration
Why do slow twitch muscle fibres have lower glycogen content? 3
- Slow twitch in use fairly constantly
- No need to store glucose
- Just needs continual supply
Why do slow twitch muscle fibres have less sarcoplasmic reticulum? 3
- Less Ca+ needed to be released
- Actin/myosin don’t need as quick initiation
- Muscle contraction is slower
Why do slow twitch muscles fatigue less quickly?
Less anaerobic respiration so less lactic acid
Why are fast twitch muscle fibres lighter? 2
- Lower myoglobin levels
- Anaerobic respiration occurs so no oxygen needs to be stored in these fibres
Why do slow twitch muscle fibres have less capillaries? 3
Mostly anaerobic respiration so no oxygen supply needed
Why do slow twitch muscle fibres higher glycogen content? 3
- Only used occasionally
- When used to large supply of glucose needed
- Stored there in preparation
Why do slow twitch muscle fibres less mitochondria? 3
- Mostly undergoes anaerobic respiration
- Involves glycolysis
- Occurs in cytoplasm
Why do slow twitch muscle fibres have more sarcoplasmic reticulum? 3
- Releases more Ca+ ions
- Initiates movements of actin and myosin
- Faster muscle contraction
Why do slow twitch muscle fibres fatigue more quickly? 3
Anaerobic respiration releases lactic acid
What is the purpose of slow twitch fibres? 2
- Specialised for slower, sustained contraction
- Long periods of exercise and endurance activities: marathons/posture
What is the purpose of fast twitch fibres? 2
- Specialised for rapid, intense contraction
- Short bursts of speed and power: eye movement and sprinting
What is myoglobin? 4
- Similar to haemoglobin
- Has a high affinity for oxygen
- Only releases it when O2 concentration falls very low
- Therefore acts as oxygen store
