Muscle Contractions

Question 1

If muscles work in antagonistic pairs what does that mean

Answer 1

As one contracts (agonist) the other muscle relaxes (antagonist).

Question 2

Label the structure of the muscle

Answer 2

• muscle fibres
• sarcolemma
• transverse ( T) tubule
• sarcoplasm
• mitochondrion
• microfibril

Question 3

Types of muscles

Answer 3

Cardiac muscles
Smooth muscles
Skeletal muscles

Question 4

How do the muscles work to move an arm upwards

Answer 4

To bend arm upwards biscept contracts and shortens pulling radius bone upwards, triceps is relaxed
(The opposite occurs to strengthen the arm)

Question 5

Compare synapse with neuromuscular junctions

Answer 5

• 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

Question 6

Contrast the synapse with neuromuscular junctions

Answer 6

• 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

Question 7

Compare the muscle types in terms of size of cell

Answer 7

Smooth muscle
- 400 pm long
- 5 pm wide

Skeletal muscle
- 100 pm long

Cardiac muscle
- 80 pm long
- 5 pm wide

Question 8

Compare the types of muscles in terms of location/ function

Answer 8

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

Question 9

Compare the type of muscle in terms of how they are controlled

Answer 9

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

Question 10

Compare the contraction characteristics of different muscles

Answer 10

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

Question 11

Wha are the two types of proteins that are myofibrils in muscle fibers

Answer 11

Thicker myofilaments = myosin
Thin myofilaments = actin
Which together form a sacromere

Question 12

What are muscle fibres made up of

Answer 12

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

Question 13

Label sacromere diagram

Answer 13

See notes
Sacromere
Myosin
Actin
H zone
I band
A band

Question 14

What is the I band in muscles

Answer 14

I band is the section of the sacromere with only thin actin filaments

Question 15

What is the A band in muscle fibre

Answer 15

A band is section of the sarcomere with the overlap of actin filaments and myosin filaments

Question 16

What is found at the end of each sarcomere

Answer 16

Z band

Question 17

What is the M line in the muscle fibres

Answer 17

Middle of each sacromere

Question 18

What is the H zone of muscle fibre

Answer 18

H zone is around the M-line but only myosin filament

Question 19

Why is ATP important for muscle contraction

Answer 19

Active muscle require high concentration of ATP which is why ^ levels of mitochondria

Question 20

Apart from aerobic respiration how do muscles gain energy to contract

Answer 20

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

Question 21

During a muscle contraction what happens to
1. The sacromere
2. I band
3. H zone

Answer 21

In contracted muscles
Sacromere = shorter
I band = shorter
H zone = shorter

Question 22

What observations do we have to confirm the sliding filament theory

Answer 22

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

Question 23

What is happening/ structure of relaxed muscle

Answer 23

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

Question 24

What is happening during the beginning of muscle contraction
(Up to power stroke)

Answer 24

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

Question 25

What happens during and after power stroke in muscle contraction free myosin heads bind

Answer 25

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)

Question 26

How is ATP used for muscle contraction

Answer 26

- 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

Question 27

How do muscles use phosphocreatine

Answer 27

- 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 -

Question 28

Why do muscles not always use phosphocreatine

Answer 28

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

Question 29

What is myoglobin

Answer 29

- 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

Question 30

What is the features of slow twitch muscle fibres

Question 31

What is the features of fast twitch muscle fibre

Question 32

Compare the difference between slow and fast twitch muscle fibre

Answer 32

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)