Skeletal Muscles

Question 1

Functions of skeletal muscles

Answer 1

• Movement
• Maintaining posture
• Stabilising
• Storage of substances
• Heat generation

Question 2

Structure of myofibril

Answer 2

• Actin (Thin filament)
• Myosin (Thick filament)
• Sarcomere

Question 3

Order of membranes in a muscle starting with most outer membrane:

Answer 3

• Epimysium
• Perimysium
• Fasciculus
• Endomysium
• Sarcolemma

Question 4

what does a muscle fibre/muscle cell look like?

Answer 4

• multinucleated
• striated
• contains lots of myofibrils

Question 5

What 3 components make up Actin?

Answer 5

• Troponin
• Actin
• Tropomyosin

Question 6

job of Troponin and Tropomyosin

Answer 6

Troponin - Acts like a gate keeper removing tropomyosin from binding sites so Actin can bind and the muscle contract
Tropomyosin - Blocks the binding sites on actin where myosin binds during contraction

Question 7

structure of actin:

Answer 7

subunits bound in a double helix strand, with tropomyosin wrapped around

Question 8

Structure of Myosin:

Answer 8

Made of 2 substructures

• Globular Head which binds to actin binding site
• Flexible region

Question 9

What is the sarcoplasmic reticulum?

Answer 9

• A blue netlike membrane that surrounds each myofibril

- It stores and releases Ca2+ into the muscles for contraction

Question 10

What is the cross bridge cycle?

Answer 10

• AP arrives
• Ca2+ is released from sarcoplasmic reticulum
• Ca2+ attaches to Troponin which moves Tropomyosin
• Tropomyosin moves uncovering an actin binding site
• Myosin globular head moves to binding site via hydrolysis of ATP forming a cross bridge
• Pi released from myosin head, moves angle of myosin head ‘like a swimming stroke’
• Myosin head then breaks the crossbridge/bond using ATP
• This repeats until CA2+ or ATP levels drop

Question 11

What is isometric contraction?

Answer 11

being able to hold a force but not over power is

Question 12

what makes the muscle fibres striated?

Answer 12

• light zones where there is only actin

- dark zones where there is myosin all align

Question 13

Describe a slow twitch fibre:
X-section:
Colour:
Endurance:
Myosin chain:

Answer 13

X-section: small
Colour: Red
Endurance: High
Myosin chain: MHC1

Question 14

Describe an oxidative fast twitch muscle:
X-section:
Colour:
Endurance:
Myosin chain:

Answer 14

X-section: medium
Colour: pink
Endurance: intermediate
Myosin chain: MHC2A

Question 15

Describe a glycolytic fast twitch fibre:
X-section:
Colour:
Endurance:
Myosin chain:

Answer 15

X-section: large
Colour: white
Endurance: low
Myosin chain: MHC2X

Question 16

what 3 different fibre types are there?

Answer 16

type 1: Slow twitch
type 2A: fast twitch oxidative
type 2X: fast twitch glycolytic