Muscle Contractions Flashcards
If muscles work in antagonistic pairs what does that mean
As one contracts (agonist) the other muscle relaxes (antagonist).
Label the structure of the muscle
- muscle fibres
- sarcolemma
- transverse ( T) tubule
- sarcoplasm
- mitochondrion
- microfibril
Types of muscles
Cardiac muscles
Smooth muscles
Skeletal muscles
How do the muscles work to move an arm upwards
To bend arm upwards biscept contracts and shortens pulling radius bone upwards, triceps is relaxed
(The opposite occurs to strengthen the arm)
Compare synapse with neuromuscular junctions
- both synapses & neuromuscular junctions are unidirectional due to receptors only being on post-synaptic membrane or muscular cell
- both use acetylcholine as a neurotransmitter
- both use Ca2+ ions to stimulate release of neurotransmitters
- both stimulated by action potential on presynaptic membrane
Contrast the synapse with neuromuscular junctions
- neuromuscular junctions are only excitatory whereas synapses can be excitatory as well as inhibitory
- neuromuscular junctions are the endpoint of action potential whereas synapses generate new action potentials on the next neurone
- neuromuscular junctions only connect motor neurone to muscle cell whereas synapses connect two neurone which could be sensory, relay or motor
Compare the muscle types in terms of size of cell
Smooth muscle
- 400 pm long
- 5 pm wide
Skeletal muscle
- 100 pm long
Cardiac muscle
- 80 pm long
- 5 pm wide
Compare the types of muscles in terms of location/ function
Smooth muscle
- arteries,intestine, bladder, uterus
Skeletal muscle
- attached to bones to bring about movement
Cardiac muscle
- only in the heart used to pump blood
Compare the type of muscle in terms of how they are controlled
Smooth muscle
- controlled by the nervous system but not conscious
Skeletal muscle
- under voluntary control via nervous system
Cardiac muscle
- involuntary muscles can be controlled by AV node but also nervous system
Compare the contraction characteristics of different muscles
Smooth muscle
- contrast more slowly and for longer than skeletal muscle
Skeletal muscle
- contractions occur in short, intense bursts
Cardiac muscle
- intercalated disk allow rapid spread of action potential to ensure contractions are synchronised
Wha are the two types of proteins that are myofibrils in muscle fibers
Thicker myofilaments = myosin
Thin myofilaments = actin
Which together form a sacromere
What are muscle fibres made up of
Muscle fibres made up of million of microfibrils each with contain bundles of thick and thin myofilaments that move past each other other to make muscle contract
Label sacromere diagram
See notes
Sacromere
Myosin
Actin
H zone
I band
A band
What is the I band in muscles
I band is the section of the sacromere with only thin actin filaments
What is the A band in muscle fibre
A band is section of the sarcomere with the overlap of actin filaments and myosin filaments
What is found at the end of each sarcomere
Z band
What is the M line in the muscle fibres
Middle of each sacromere
What is the H zone of muscle fibre
H zone is around the M-line but only myosin filament
Why is ATP important for muscle contraction
Active muscle require high concentration of ATP which is why ^ levels of mitochondria
Apart from aerobic respiration how do muscles gain energy to contract
In time when aerobic respiration cannot create enough ATP to meet this demand, anaerobic respiration also occurs.
The chemical phosphocreatine, which is stored in muscles, assists this process by providing phosphate to regenerate ATP from ADP + Pi
During a muscle contraction what happens to
1. The sacromere
2. I band
3. H zone
In contracted muscles
Sacromere = shorter
I band = shorter
H zone = shorter
What observations do we have to confirm the sliding filament theory
Observations of the shortening of sacromere, i band and H zone in contracted muscles
Is consistent with idea during muscle contractions that the actin and myosin slide between each other, shortening length of microfibril
What is happening/ structure of relaxed muscle
In relaxed muscle
- ADP is bound to myosin heads
- Myosin binding sites on actin = covered with protein troponin & tropomyosin
Sarcoplasmic conc of Ca 2+ is low as being actively transported to sarcoplasmic reticulum
What is happening during the beginning of muscle contraction
(Up to power stroke)
ACTIVATION OF MUSCLE
- arrival of action potential via T-tube causes release of Ca2+ from sarcoplasmic reticulum
- Ca2+ bind to troponin causing change of shape and tropomyosin to be displaced revealing binding sites
- myosin heads bind to actin binding site, forming cross bridge
What happens during and after power stroke in muscle contraction free myosin heads bind
After binding to actin binding sites
Myosin heads change angle from 90o to 45o pulling actin filaments along and releasing bound ADP
(Power stroke)
ATP then binds to myosin heads breaking the cross bridge = heads detach from actin
Ca2+ ions activate ATPas which hydrolyses ATP —> ADP + Pi
Released energy causes myosin heads to return to 90oangle
(ADP remains bound)
How is ATP used for muscle contraction
- hydrolysis of ATP provides energy for movement of myosin head and activate transport of Ca2+ ions back to SR into T-tubes
- resting muscle contains enough ATP for 3-4 secs
- full aerobic respiration is slow & anaerobic respiration is slow
For this reason there are other supply of energy for muscles to work during periods of exercise
How do muscles use phosphocreatine
- muscles contain phosphocreatine which rapidly regenerates ATP from ADP by transfer of Pi to ADP
(This is catalysed by enzyme - creatine phosphokinase - ## ADP + phosphocreatine —> ATP + creatine
Why do muscles not always use phosphocreatine
Supplies of creatine is limited, but can keep contraction until respiration rate reaches demand.
Using anaerobic respiration and phosphocreatine is how a trained athlete sustains activity for about 10 seconds
What is myoglobin
- single chain protein (like single Hb sub-unit)
- has increased affinity of O2 combines at low parietal pressures
Therefore acts as store of oxygen in muscles
What is the features of slow twitch muscle fibres
What is the features of fast twitch muscle fibre
Compare the difference between slow and fast twitch muscle fibre
Slow twitch. Fast twitch
- long contraction. -short contraction
- many mitochondria - fewer mitochondria
- dense network capillaries. - fewer blood capillaries around fibre
- large amount myoglobin. - very little myoglobin
- small store of Ca2+. - large store of Ca2+
- slow rate of ATP hydrolysis. - high rate of ATP hydrolysis in myosin heads
- ATP obtained for aerobic. - ATP obtained from glycolysis
- resistant to fatigue. - lactate accumulates rapidly (quickly fatigued)
