Unit 3.5.3 - Skeletal muscles are stimulated to contract by nerves and act as effectors

Question 1

What are the three types of muscle in the body?

Answer 1

Smooth, cardiac and skeletal

Question 2

What is smooth muscle?

Answer 2

Muscle which contracts without conscious control, it is involuntary

Question 3

What nervous system controls smooth muscle?

Answer 3

The autonomic nervous system

Question 4

Where is smooth muscle found?

Answer 4

In the walls of internal organs

Question 5

In which internal organ is smooth muscle not found?

Answer 5

The heart

Question 6

What is cardiac muscle?

Answer 6

Muscle which contracts without conscious control, it is involuntary, however it is only found in the heart

Question 7

What is skeletal muscle?

Answer 7

Muscle which contracts when you think about it, it is voluntary

Question 8

What nervous system controls skeletal muscles?

Answer 8

Somatic nervous system

Question 9

What are antagonistic muscles?

Answer 9

Muscles which do the opposite to each other, as one contracts one relaxes

Question 10

Skeletal muscles are made up of long bundles of?

Answer 10

Muscle fibres

Question 11

What is the cell membrane of a muscle fibre called?

Answer 11

Sarcolemma

Question 12

What does the sarcolemma look like?

Answer 12

It folds inwards into the sarcoplasm

Question 13

What is sarcoplasm?

Answer 13

A muscle cells cytoplasm

Question 14

What are the It folds in the sarcolemma called?

Answer 14

Transerve (T) tubules

Question 15

What is the function of the transverse (T) tubules?

Answer 15

Helps spread the electrical impulses throughout the sarcoplasm so the impulses can reach all parts of the muscle fibre

Question 16

Why do muscle fibres have lots of mitochondria in them?

Answer 16

To provide the ATP needed for muscle contraction

Question 17

What is the large vesicle inside the muscle cell called?

Answer 17

Sarcoplasmic reticulum

Question 18

What is the function of the sarcoplasmic reticulum?

Answer 18

To store and release calcium ions that are needed for muscle contraction

Question 19

What is meant by muscle fibres are multinucleate?

Answer 19

They have many nuclei

Question 20

What cylindrical organelle makes up muscle fibres?

Answer 20

Myofibrils

Question 21

What are myofibrils made up of?

Answer 21

Bundles of thick myofilaments (myosin) and thin myofilaments (actin)

Question 22

What do you see if you look at a myofibril under an electron microscope?

Answer 22

Alternative patterns of light and dark bands, the I band and A bands

Question 23

What are the A bands made up of?

Answer 23

The thick myosin and some overlapping actin

Question 24

What are the I bands made up of?

Answer 24

Only thin actin

Question 25

What are the short repeating units in myofibrils called?

Answer 25

Sarcomeres

Question 26

What is the end of each sarcomere marked with?

Answer 26

The Z-line

Question 27

What is the middle of each sarcomere marked with?

Answer 27

The M-line

Question 28

What is the middle of a sarcomere called where there is only myosin?

Answer 28

The H-zone

Question 29

What theory explains muscle contraction?

Answer 29

The sliding filament theory

Question 30

Describe the sliding filaments theory simply in two step.

Answer 30

1.) During contraction the sarcomere contracts and the myosin and actin filaments slide over one another 2.) Simultaneous contraction of lots of sarcomeres means the myofibrils and so muscles contract

Question 31

What happens to the size of the A-band, I-band, H-zone and Z-lines during contraction?

Answer 31

The A-band stays the same length, but the I-band and H-zone get shorter, the Z lines get closer together

Question 32

Describe what happens when an action potential arrives at a muscle cell to initiate a muscle contraction in three steps.

Answer 32

1.) The action potential depolarises the sarcolemma 2.) The depolarisation spreads down the T-tubules and to the sarcoplasmic reticulum 3.) This causes the sarcoplasmic reticulum to release calcium ions into the sarcoplasm initiating the muscle contra ion

Question 33

What happens when a muscle contraction is initiated in eight steps?

Answer 33

1.) Calcium ions bind to the troponin and changes its shape 2.) This pulls the attached tropomyosin with stand exposes the actin-myosin binding site 3.) The myosin head binds to it and forms an actin-myosin actin bridge 4.) Calcium ions also activate the enzyme ATPase which breaks down ATP into ADP and Pi releasing energy 5.) Some of this energy is used to make the myosin head kick and push the actin past the myosin 6.) After this the rest of the energy is used to break down the actin-myosin bridge and detach the myosin head from the binding site 7.) The head is re - cocked and is attached to another actin-myosin binding site further down 8.) The process is repeated shortening the sarcomere and causing the muscle contraction

Question 34

What happens during muscle contraction when the muscle stops being stimulated?

Answer 34

1.) The calcium ions leave the binding sites on the troponin molecule and return back to the sarcoplasmic reticulum by active transport 2.) The troponin returns to its original shape 3.) Pulling the tropomyosin with it and blocking the actin-myosin binding sites 4.) The actin filaments then slide back to their original position relaxing the muscle

Question 35

What are the three ATP can be generated for muscle contraction?

Answer 35

Aerobic respiration, anaerobic respiration and ATP-phosphocreatine system

Question 36

How is most of the ATP produced in aerobic respiration?

Answer 36

In the electron transfer chain

Question 37

What is aerobic respiration good for? Any why?

Answer 37

Long periods of low intensity exercise because you need a constant supply of oxygen

Question 38

How is most of the ATP produced in anaerobic respiration?

Answer 38

In glycolysis

Question 39

What is the end product of glycolysis? And what happens to it?

Answer 39

Pyruvate, it undergoes lactate fermentation which produces lactate

Question 40

Why is a build up of lactate bad?

Answer 40

It causes muscle fatigue

Question 41

What is anaerobic respiration good for? And why?

Answer 41

Short periods of high intensity exercise, doesn't require oxygen however lactate does build up so it isn't good for too long

Question 42

How is ATP made in the ATP-phosphocreaitne system?

Answer 42

Phosphorylating (adding a phosphate group) to ADP

Question 43

What does PCr stand for?

Answer 43

Phosphocreaitne

Question 44

Where does the phosphate group come from to add to ADP?

Answer 44

PCr

Question 45

What is ATP-phosphcreatine system good for? And why?

Answer 45

Short bursts of vigorous exercise as the PCr runs out after a few seconds

Question 46

What is the equation which produces ATP in the ATP-phosphocreaitne system?

Answer 46

ADP + PCr → ATP + Cr

Question 47

What are two types of muscle fibres?

Answer 47

Slow twitch and fast twitch

Question 48

What are slow twitch muscle fibres?

Answer 48

Muscle fibres that contract slowly and work for a long tie before getting tired

Question 49

What are slow twitch muscle fibres good for?

Answer 49

Long distance running and maintaining posture

Question 50

Where are high proportions of slow twitch muscles found? And why?

Answer 50

In the back and calves to maintain posture

Question 51

How is energy released in aerobic respiration?

Answer 51

Through aerobic respiration

Question 52

What do slow twitch muscle fibres have lots of? And why?

Answer 52

Lots of mitochondria and blood vessels to supply oxygen and produce ATP

Question 53

Why are the mitochondria found mainly near the edge of slow twitch muscle fibres?

Answer 53

So theres a short diffusion pathway for oxygen from the blood vessels to the mitochondria

Question 54

What colour do slow twitch muscle fibres appear? And why

Answer 54

Red - they have lots of a red coloured protein myoglobin which stores oxygen

Question 55

What are fast twitch muscle fibres?

Answer 55

Muscle fibres that contract very quickly and don't work of long before getting tired

Question 56

What are fast twitch muscle fibres good for?

Answer 56

Short bursts of power like in sprinting and eye movement

Question 57

Where are high proportions of fast twitch muscles found? And why?

Answer 57

In the muscles you use for fast movement like your arms and legs

Question 58

What do fast twitch muscle fibres have lots of? And why?

Answer 58

Stores of PCr to produce energy quickly when needed

Question 59

What colour do fast twitch muscle fibres appear? And why?

Answer 59

Whitish they don't have many myoglobin

Question 60

Draw a muscle cell, muscle fibre and microfibril.

Answer 60

Question 61

Draw a diagram for the cross section of the A-band and H-zone.

Answer 61

Question 62

Label the different zone and bands of this sarcomere.

Answer 62