Topic 6 - Skeletal Muscles

Question 1

What is an antagonistic muscle pair?

Answer 1

Muscles work together in pairs to bring about movement. These are referred to as antagonistic muscle pairs where one muscle contracts while the other relaxes to move bones at a joint.

Question 2

What are skeletal muscles for?

Answer 2

They are under voluntary control and are responsible for movement by pulling on bones they are made up of a highly organised structure to ensure efficient contraction and strength.

Question 3

What are muscle cells and myofibril?

Answer 3

Muscle cells are long cylindrical cells group together for greater strength inside muscle fibres are myofibrils which are specialised protein structures that perform contraction.

Question 4

What are myofibril made of?

Answer 4

Made of thick filaments (myosin) and thin filaments (actin) that overlap.

Question 5

What is the structure of actin?

Answer 5

Composed of two actin molecules twisted together to form a filament.

Question 6

What is the structure of myosin?

Answer 6

Contains myosin heads which bind to specific sites on actin during muscle contraction.

Question 7

Why does skeletal muscle appear striated under microscope?

Answer 7

The arrangement of microfibrils within the muscle fibre.

Question 8

What are the steps for examining skeletal muscle?

Answer 8

1. Preparation of microscope slide: obtain a thin section of muscle tissue and stain the tissue with a dye.
2. Under the microscope: use a light microscope to examine the tissue start at a low magnification and then increased to a higher magnification for detail.

Question 9

What features can you identify in skeletal muscles?

Answer 9

Striations: alternating light (I-bands) and dark (A-bands) bands caused by the arrangement of actin and myosin.
Nuclei : muscle fibres are multinucleated with nuclei located at the periphery of the fibres.
Sacromeres: visible at higher magnifications as the repeating unit unit along a microfibrils marked by Z-lines.

Question 10

What is the A-band?

Answer 10

Dark band where actin and myosin overlap.

Question 11

What is the I-band?

Answer 11

Night band containing only actin filaments.

Question 12

What is the Z-line?

Answer 12

Marks the boundaries of each sacromere.

Question 13

What is the H-zone?

Answer 13

Lighter region in the centre of the A-band where there is no overlap of actin and myosin.

Question 14

What is a sacromere?

Answer 14

Basic contractor unit of a muscle fibre made up of actin and myosin filaments. It is the smallest functional unit of skeletal and cardiac muscle responsible for muscle contraction.

Question 15

What is a muscle contraction?

Answer 15

Highly coordinated process involving actin and myosin filament within a sarcomere. It is powered by ATP and regulated by calcium ions.

Question 16

What is the sliding filament model?

Answer 16

• during contraction actin (thin) filaments slide over myosin (thick) filaments causing the sarcomere to shorten.
• I-bands and H-zones become narrower while A-bands remains he same length

Question 17

What are the six stages of muscular contraction?

Answer 17

1. Calcium ions release.
2. Binding of calcium to troponin.
3. Crossbridge formation.
4. Power stroke.
5. ATP binding and detachment.
6. Reactivation of myosin head.

Question 18

The first stage of muscular contraction is calcium ion release what is meant by this?

Answer 18

• an action potential travelled along the sarcolemma and into the muscle fibre via T-tubules
• Stimulates the sarcoplasmic rectum to release calcium ions into the sarcoplasm

Question 19

What is a T-tubule?

Answer 19

A tunnel structure that extends from the surface of a muscle cell deep into its interior.

Question 20

What is the sarcolemma?

Answer 20

A membrane that surrounds a muscle cell it act as a barrier controlling the entry and exit of substances into an out of the muscle cell. It also helps transmit electrical signals which are essential from muscle contraction.

Question 21

What is the sarcoplasm?

Answer 21

The cytoplasm of a muscle cell.

Question 22

What is the sarcoplasmic reticulum?

Answer 22

Specialised type of endoplasmic reticulum found in the muscle cell its main function is to store and release calcium ions during muscle contraction.

Question 23

The second stage of muscular contraction is binding of calcium to troponin what happens during this stage?

Answer 23

• calcium binds to troponin causing it to change shape
• This pulls tropomyosin away from the actin finding sites exposing them for myosin head attachment

Question 24

The third stage of muscular contraction is Cross-bridge formation what happens during this stage?

Answer 24

• myosin heads attached to the exposed binding site on actin forming cross-bridges.

Question 25

The fourth stage of muscular contraction is power stroke what is this?

Answer 25

- The myosin head pivots pulling the actin filament towards the centre of the sarcomere. - ADP and Pi are released during this movement.

Question 26

The fifth step of muscular contraction is ATP binding and attachment what happens during this stage?

Answer 26

A new molecule of ATP bind to the myosin head causing it to detach from the actin filament.

Question 27

The final stage of muscular contraction is reactivation of myosin head what is meant by this?

Answer 27

- ATP is hydrolysed to ADP and Pi providing energy to reset the myosin head into its original position ready for the next cycle.

Question 28

What are the two energy requirements for contraction?

Answer 28

- ATP hydrolysis: ATP is hydrolysed at each myosin head during the power stroke and resetting the myosin head. - Calcium ion transport: ATP is also required to pump calcium ions back into the sarcoplasmic reticulum after contraction.

Question 29

What are the three ATP sources in muscle cells?

Answer 29

1. Aerobic respiration: supplies the most ATP during prolonged intensity activity and oxygen is stored in the myoglobin for immediate use. 2. Anaerobic respiration: provides ATP when oxygen levels are low leading to lactic acid production. 3. Phosphocreatine system: phosphocreatine provides phosphate groups for the rapid regeneration of ATP from ADP ideal for short bursts of intense activity.

Question 30

What is muscle fatigue?

Answer 30

Occurs when a muscle loses its ability to contract effectively during prolonged activity. It happens due to a reduction in ATP and an accumulation of metabolic by-products such as lactic acid.

Question 31

What is ATP depletion as a cause of muscle fatigue?

Answer 31

ATP is required for muscle contraction and relaxation prolonged activity reduces ATP levels.

Question 32

What is lactic acid accumulation as a key cause of muscle fatigue?

Answer 32

Anaerobic respiration during intense exercise produces lactic acid which lowers the pH of muscle cells and inhibits enzyme activity.

Question 33

What is reduce calcium ion availability as a key cause of muscle fatigue?

Answer 33

Calcium irons are essential from muscle contraction. Fatigue can reduce their release or uptake in muscle cells.

Question 34

What is neuromuscular junction fatigue?

Answer 34

Prolonged activity may deplete neurotransmitters such as acetylcholine affecting signal transmission.

Question 35

What is a slow twitch muscle fibre?

Answer 35

- Specialised for endurance activities - Contract slowly and are resistant fatigue - adapted for aerobic respiration which is more efficient for prolonged energy supply

Question 36

What are the key adaptions of slow twitch muscle fibres?

Answer 36

- High myoglobin content: myoglobin store oxygen, giving these fibres a red colour. - Rich blood supply: insures continuous supply of oxygen and nutrients. - Numerous mitochondria: site of aerobic respiration to produce ATP - Low levels: reliance on sustained oxygen supply rather than short term reserves

Question 37

What are fast twitch muscle fibre types?

Answer 37

- Specialised for short bursts of intense activity. - Contract quickly and powerfully but fatigue rapidly. - Adapted for anaerobic respiration which provides quick energy but is less efficient.

Question 38

What are the adaptations of fast twitch muscle fibre types?

Answer 38

- thicker and more numerous myosin filaments: allows powerful contractions. - High levels: provides an immediate energy source for anaerobic respiration. - High concentration of anaerobic enzymes: enables rapid ATP production in the absence of oxygen - stores of phosphocreatine: allows quickly regeneration of ADP to ATP.