Unit 6: Muscles

Question 1

What are skeletal muscles

Answer 1

striped/striated muscle

consists if numerous long muscle fibres/cells

Question 2

What are properties of muscle fibres

Answer 2

• cylindrical in shape and enclosed by a cell surface membrane (sarcolemma)
• many nuclei (multinucleate)
• contain many microfibris with cross-striations
• arranged in parallel to give striped appearance

Question 3

Which microscope can see muscle

Answer 3

electron microscope

Question 4

What are the repeating bands in a muscle called

Answer 4

sarcomere

Question 5

What is actin

Answer 5

thin filaments which possess binding sites for myosin heads

Question 6

What is myosin

Answer 6

thick filaments composed of many myosin molecules bundled together

myosin heads have ATP hydrolyse activity to provide energy for contraction

Question 7

What does the A band represent

Answer 7

dark band
length of myosin filaments

Question 8

What does the outer region of the A band represent?

Answer 8

overlapping myosin and actin filaments
- these are darker

Question 9

What is the H zone

Answer 9

only contains myosin filaments

• not as dark and at the centre of the A band

Question 10

What is the M line?

Answer 10

connects myosin filaments in the A band

Question 11

What is the I band

Answer 11

light band
contains only thin actin filaments

Question 12

What is the Z line?

Answer 12

connects actin filaments and is the boundary of the sarcomere

Question 13

Outline the sliding hypothesis

Answer 13

during contraction actin filaments are pulled between myosin filaments resulting in the shortening of the muscle fibre and changes in banding pattern

Question 14

What happens to the H zone during contraction?

Answer 14

Narrows

Question 15

What happens to the outer regions during contraction

Answer 15

become wider

Question 16

What happens to the A band during contraction?

Answer 16

stays the same length of myosin filaments dont change

Question 17

What happens to the I band during contraction

Answer 17

narrows the non overlapping actin filaments

Question 18

What happens to the Z band during contraction

Answer 18

move closer together

Question 19

What happens to the length of the sarcomere during contraction

Answer 19

decrease

Question 20

What is tropomyosim

Answer 20

a protein that covers the binding site of actin

Question 21

How do mucles contract

Answer 21

by the formation of cross bridges between actin and myosin filaments

Question 22

Outline the mechanism of muscle contraction

Answer 22

• contraction is activated by Ca2+ ions released from the sarcoplasmic reticulum
• when released Ca2+ binds to tropomyosin causing it to change shape and move from the binding site
• enables actinomyosin bridges to form as myosin heads attach to actin filaments
• Ca2+ stimulate ATP hydrolase to hydrolyse ATP providing energy to move the myosin head which pulls the actin filament and to detach the myosin head which breaks actinomyosin bridges
• Bridges rapidly break and reform as the myosin heads attach further along the filaments pulling past the myosin filaments causing shortening of each sarcomere
• mitochondria in muscle fibres supply ATP via aerobic respiration
• when the muscle is no longer stimulated the Ca2+ ions are actively moved back into the sarcoplasmic reticulum

Question 23

What is a Neuromuscular junction?

Answer 23

a specialised synapse between a motor neurone and the sarcolemma
- synapses with a muscle fibre & sarcolemma represents postSM

Question 24

Outline transmission across a Neuromuscular junction

Answer 24

• action potential arrives and synaptic know stimulating depolarisation of preSM
• stimulates Ca+ channels to open in the preSM and diffuse into the synaptic knob
• cause synaptic vesicles to fuse with preSM and break open
• acetylcholine is released and diffuse across synaptic cleft

- acetylcholine attach to specific receptor sites on the sarcolemma

• stimulates entry of Na+ causing depolarisation

- results in action potential along sarcolemma into muscle fibres stimulating release of Ca2+ which initiate muscle contraction

• acetylcholine is broken down by cholinesterase
• choline and acetyl is taken up by active transport into synaptic knob and acetylcholine is resynthesised using ATP

Question 25

What are the two muscle fibres skeletal muscles are made up of

Answer 25

slow and fast fibres

Question 26

What are the properties of slow fibres?

Answer 26

- contract slowly - many mitochondria - energy released slowly thru aerobic respiration - high resistance to fatigue (work for long time without tiring) - good for endurance events - low concentration of glycogen as lots of energy released per glucose molecule - red in colour due to myglobin - low conc of phospocreatine

Question 27

What are the properties of fast fibres

Answer 27

- contract quickly - few mitochondria - energy released quickly thru anaerobic respiration - low resistance to fatigue (tire easily) - good for short bursts of speed/power - high concentration of glycogen to provide lots of glucose as less energy is released per glucose - white due to no myglobin - high conc of phospocreatine

Question 28

Why is ATP required during muscle contraction

Answer 28

- to move myosin head which pulls actin filament - to detach myosin head which breaks actin-myosin bridges - for reabsorption of Ca2+ into sarcoplasmic

Question 29

How is ATP produced by the phosphocreatine system

Answer 29

**phosphocreatine is stored in muscle** and used as a **reserve for the supply of phosphate** to combine with ADP to form ATP - helps produce ATP quickly in anaerobic conditions

Question 30

Why is the phosphocreatine system used during short periods of vigorous exercise

Answer 30

it generates ATP but phosphocreatine is **used up after a few seconds** the process is anaerobic but doesn't produce lactic acid

Question 31

How is phosphocreatine reformed?

Answer 31

using phosphate from ATP when the muscle is relaxed

Question 32

How can ATP be produced?

Answer 32

- phosphocreatine system - anaerobic respiration - aerobic respiration

Question 33

How is ATP produced by Anaerobic respiration

Answer 33

by glycolysis which produces **pyruvate** when O2 is in short supply pyruvate is converted to lactate which builds up in muscle causing fatigue

Question 34

How is ATP produced by Aerobic respiration?

Answer 34

produced during oxidative respiration in mitochondria this process is rapidly uded up

Question 35

How do skeletal muscles attatch to bones

Answer 35

By inelastic tendons

Question 36

How do the biceps and triceps work antagonistically?

Answer 36

- bicep muscle contracts pulling lower arm up - simultaneously the triceps muscle relaxes and lengthens - triceps muscle contracts to return lower arm to its original position - at same time biceps muscle relaxes and lengthens