Muscles

Question 1

What are the three types of muscles?

Answer 1

1. Skeletal.
2. Smooth.
3. Cardiac.

Question 2

Definition of antagonistic pairs.

Answer 2

Muscles that work together in opposition to move bones at joints, for example: as one contracts, the other relaxes.

Question 3

What is the advantage of skeletal muscles being arranged in pairs? (2 points).

Answer 3

1. Muscles can only pull on bones when they contract.
2. Muscles cannot push on bones

Question 4

Provide and describe an example of an antagonistic pair.

Answer 4

Biceps contract and the triceps relax.
This pulls the radius and bends the arm at the elbow.
Triceps contract and biceps relax.
This pulls the ulna and straightens the arm at the elbow.

Question 5

Describe the neuromuscular junction ( 10 points).

Answer 5

1. Depolarisation of membrane causes calcium ion channel to open.
2. Ca^2+ ions enter by facilitated diffusion.
3. Causes vesicles to fuse with pre-synaptic membrane.
4. Releasing acetylcholine into the synaptic cleft.
5. Acetylcholine diffuses across cleft.
6. Binds to receptors on the mmebrane of muscle fibre / sarcolemma and muscle contracts.
7. Causes sodium ions channels to open.
8. Sodium ions diffuse in causing depolarisation of membrane of muscle fibre / sarcolemma and muscle contracts.
9. The acetylcholine is hydrolyed by acetylcholinesterase to prevent muscle being overstimulated.
10. The choline and ethanoic acid diffuses back into the presynaptic neuron where they are recombined to synthesise acetylcholine using ATP produced by mitochondria.

Question 6

List the differences between a neuromuscular junction and a cholingeric synapse (5 points).

Answer 6

1. Neuromuscular is only excitatory, cholingeric may be excitatory / inhibitory.
2. Neuromuscular only links neurons to muscles, cholingeric links neurons to neurons, or neurons to other effector organs.
3. Neuromuscular only involves motor neurons, cholingeric involves sensory, motor and intermediate neurons.
4. Neuromuscular is where the action potential ends, cholingeric is where a new action potential may be produced.
5. Neuromuscular: acetylcholine binds to receptors on membrane of muscle fibre. Cholingeric: acetylcholine binds to receptors of post-synaptic neuron.

Question 7

List the similarites between the neuromuscular and cholingeric synapses (4 points).

Answer 7

1. Neurotransmitters are transported by diffusion.
2. Have receptors, that on binding with neurotransmitters, causes an influx of Na+.
3. Uses Na+-K+ pump to repolarise the axon.
4. Use enzymes to breakdown neurotransmitter.

Question 8

Describe actin filaments.

Answer 8

There are two strands of actin coiled around each other like a string of beads.

Question 9

Describe tropomyosin.

Answer 9

A long, thin molecule which lies in a groove between the two chains of actin molecules.

Question 10

Describe the thick filaments that are made up of myosin proteins (3 points).

Answer 10

1. The filament is made from many myosin molecules lying side by side.
2. Each myosine moleculehas two heads which point out to form cross bridges.
3. The tail of the myosin meet in the middle at the M line.

Question 11

Describe the light bands / I bands / isotropic bands.

Answer 11

Produced by actin filaments, with no overlap of myosin filaments.

Question 12

Describe the dark bands / A bands / anisotropic bands.

Answer 12

Produced by myosin filaments- the overlap between myosin and actin filaments which excludes the H zone.

Question 13

Describe the H zone.

Answer 13

The portion of the dark A band where the thick and thin filaments do not overlap.

Question 14

What is the sarcomere?

Answer 14

The contrctile unit of the muscle.

Question 15

Describe the events of muscle contraction- the sliding filament theory (12 points).

Answer 15

1. Action potential from motor neuron depolarises the sarcolemma.
2. Depolarisation travels deep into the muscle fibre through T-tubules.
3. Calcium ion channels on sarcoplasmic reticulum open.
4. Calcium ions diffuse into the myofibril from sarcoplasmic reticulum.
5. Ca^2+ bind to tropomyosin on actin filament causing it to change shape and move away.
6. Exposes the myosin binding site on the actin.
7. Myosin heads attach to binding site on the actin.
8. Myosin head attaches to binding site on actin forming actinmyosine crossbridge.
9. Hydrolysis of ATP on the myosin head causes myosin head to bend.
10. Pulling actin filament past the myosin filament.
11. Moving further along the actin filament to form new actinmyosin crossbridges.
12. This mechanism causes the sarcomere to shorten in length, therefore causing the myofibril to shorten and the muscle fibre to contract.

Question 16

Describe what happens to the bands / zones when the sarcomere contracts? (6 points).

Answer 16

1. The light I band becomes shorter as there is more overlap.
2. The dark A band stays the same length.
3. The H zone becomes narrower as there’s more overlap.
4. The Z lines move closer together- there is more overlap of thick and thin filaments (actin and myosin).
5. Therefore, length of the sarcomere is shorter.
6. The filaments remain the same length.

Question 17

How does a muscle relax? (7 points).

Answer 17

1. Ca^2+ actively transported back into sarcoplasmic reticulum.
2. Using energy from hydrolysis of ATP.
3. Tropomyosin can now block myosin binding site on actin filaments again.
4. Myosin heads now unable to bind to actin filaments and contraction stops.
5. Muscle relaxes.
6. Force from the antagonistic muscle can pull the actin filaments out from between myosin filaments.
7. Sarcomere lengthens, causing the myofibril to lengthen, causing the muscle fibre to lengthen.

Question 18

Compare slow-twitch and fast-twitch muscle fibres (8 comparisons).

Answer 18

1. Slow: cotracts slower. Fast: contracts faster.
2. Slow: contractions are less powerful. Fast: contractions are more powerful.
3. Slow: adapted for aerobic respiration by avoiding build-up of lactic acid. Fast: easily fatigued due to lactic acid build-up.
4. Slow: adapted to work over a longer period of time, for example: maintaining posture. Fast: adapted to a short period of intense exercise.
5. Slow: most common is calf muscle. Fast: more common in biceps.
6. Slow: rich supply of blood vessels to deliver high concentration of oxygen and glucose for aerobic respiration. Fast: high concentration of enzymes for anaerobic respiration to provide ATP rapidly (lower number of capillaries).
7. Slow: large store of myoglobin to store oxygen. Fast: small store of myoglobin (pale in colour).
8. Slow: numerous mitochondria- produces ATP. Fast: store of phosphocreatine to rapidly generate ATP from ADP in anaeroic conditions.

Question 19

Suggest why there is a high concentration of glycogen required in fast-twitch muscle fibres.

Answer 19

The enzymes hydrolyse glycogen into glucose which releases / provides energy in the form of ATP as the glucose is used as the substrate in glycolysis.

Question 20

Suggest why there is a rich supply of blood vessels required in slow-twitch muscle fibres (3 points).

Answer 20

1. To deliver high concentrations of oxygen for a higher rate of aerobic repsiration.
2. Shorter diffusion pathway for oxygen.
3. Prevents build-up of lactic acids. `

Question 21

Describe how ATP is provided in anaerobic repsiration.

Answer 21

ATP is provided by glycolysis. Very quick supply, but produces lactic acid.

Question 22

Describe how phosphocreatine provide ATP.

Answer 22

Phosphocreatine regenerates ATP. Phosphate group from phosphocreatine combines with ADP to form ATP.

Question 23

Describe phosphocreatine.

Answer 23

A phosphorylated creatine molecule that is stored in skeletal muscle cells and brain cells.

Question 24

Write the equation for the generation of ATP from phosphocreatine and ADP.

Answer 24

ADP + pCr … ATP + Cr