Biology (Topic 6) Skeletal muscles (2)

What happens when Myosin head bends?

Releases ADP and Pi and pulls actin filaments causing power stroke

What does ATP do in the sliding filament theory ?

Binds to myosin head causing them to release from actin

What does ATP hydrolase enzyme do?

hydrolyses ATP providing energy that allows myosin head to go back to original position

What happens when a nerve impulse is no longer stimulated?

Muscle stops being stimulated:

Calcium ions taken up by sarcoplasmic reticulum

Actin myosin binding sites are blacked , myoxine cannot bind to actin

Filaments can be pulled apart (slide back) to resting

Why is ATP important in muscle contraction?

Resets the position of myosin heads

Return Ca+ to sarcoplasmic reticulum after contraction via active transport

Where does ATP in muscle contraction come from?

Aerobic respiration: due to oxygen supply only sustain low intensity exercise

Anaerobic respiration: small amounts quickly , lactate build up so only short periods

Phosphocreatine: rapid production over short periods

What is phosphocreatine?

stored by muscles , used for rapid regenerate of ATP over short periods

Transfers a pi ion to ADP

ADP + phosphocreatine =

ATP + creatine

What are features of fast twitch muscles?

Contract rapidly

Use anaerobic respiration

Fatigue quickly due to lactate

Few capillaries

Low in myoglobin (due to low oxygen requirements)

What is myoglobin?

Red pigment like haemoglobin, stores oxygen in muscles

Which muscles are better for short bursts of high intensity activities? Why?

Fast twitch

short: anaerobic respiration causes the build up of lactate so fatigue quickly

High intensity: contract rapidly with great force as they generate ATP quickly

What are features of slow twitch fibres?

Contract slower

Aerobic respiration for ATP

Fatigue slowly (less lactate production)

Dense capillary network

High in myoglobin and haemoglobin

Lots of mitochondria

what colours are fast and slow twitch

slow : darker because richer in myoglobin

Fast : lighter - less myoglobin

What are the differences between slow and fast twitch? (5 mark)

Fast vs Slow

Fast have rapid contraction , slow have contract slowly

Fast most ATP from anaerobic , slow most ATP from aerobic

Fast fatigue rapidly (lactate) , slow fatigues slowly

Fast less mitochondria, slow many mitochondria

Fast large glycogen and phosphocreatine stores , slow less

Fast large store of calcium ions in SR, slow small store

Fast fewer capillaries, slow more capillaries

Fast high ATP hydrolase activity , slow lower activity

What happens as a result of repeated contraction of muscles?

Muscle fatigue due to :

Production of lactate during anaerobic respiration

ATP running low

reduction in force over time

Decrease in calcium ion availability

Describe the investigation into rate of muscle fatigue

Apparatus : Hand grip strengthener, stop watch, participant

Method: bring two handles together as many times as possible over 20 seconds

1. Record number of successfully squeezes

2. Rest 10 secs

3. Repeat 3 times

4. Repeat with other people

5. plot graph x - time elapses 20,40 , etc , y - number of successful squeezes

why is there a decrease in calcium ion availability and how does this effect muscle contractions?

Causes muscle fatigue

Less calcium ions released (this is because less are returned to SR)

Less troponin molecules activated

fewer actin myosin cross bridges

weaker contractions

What are limitations of the investigation into muscle fatigue?

Only looks at fatigue in hands:

Other skeletal muscles fatigue at different rates

Intensity may not be high enough to cause fatigue for some individuals

What is troponin?

Protine complex that attaches to actin

Ca+ binds to receptors on it

Causing it to change shape

Causing tropomyosine to move exposing binding sites

What enzyme hydrolises ATP

ATP hydrolase (ATPase)

What is the muscles supply of ATP during vigorous exercise?

phosphocreatine

Phosphorylates ADP

What are features of fast twitch?

Good supply of phosphocreatine

Glycogen stored inside

More enzymes for anaerobic respiration

What are features of slow twitch?

Many mitochondria

high myoglobin

Many capillary ( good supply of blood)

Where is ATPase located in muscle contraction?

myosin head