7.1.3 - Muscle Fibres

Question 1

Describe A Muscle Fibre Bundle
(4 Points)

Answer 1

~ Contains contractile proteins, mitochondria and myofibrils in the sarcoplasm.

~ Surrounded by the sarcolemma.

~ Multi-nucleated.

~ Has a sarcoplasmic reticulum.

Question 2

Describe The Sarcolemma
(3 Points)

Answer 2

~ Outer membrane of the muscle fibre.

~ Folds inwards to make structures called transverse tubules (T tubules).

~ The t-tubules run close to the sarcoplasmic reticulum and helps spread electrical impulses throughout the muscle fibre for muscle contraction.

Question 3

Describe The Sarcoplasm

Answer 3

Contains mitochondria, myofibrils and contractile proteins.

Question 4

The Sarcolemma Contains Mitochondria, What Is It Used For?

Answer 4

Aerobic respiration to generate ATP for muscle contraction.

Question 5

The Sarcolemma Contains Myofibrils, What Are They?
(4 Points)

Answer 5

~ Cylindrical.

~ Made up of contractile proteins called actin and myosin.

~ Contain bundles of thick and thin myofilaments that move past each other and cause the muscle to contract.

~ The two myofilaments are arranged in a particular order, creating different types of bands and lines.

Question 6

What Are The Thick Myofilaments Made Up Of?

Answer 6

Myosin.

Question 7

What Are The Thin Myofilaments Made Up Of?

Answer 7

Actin.

Question 8

Describe The Sarcoplasmic Reticulum (SR)
(2 Points)

Answer 8

~ Acts as a store of calcium ions (CA2+), released during muscle contraction.

~ The membranes of the SR contain protein pumps that transport calcium ions into the lumen of the SR.

Question 9

What Are Calcium Ions Needed For?

Answer 9

Muscle contraction.

Question 10

Describe The H Band Part Of The Myofibril
(2 Points)

Answer 10

~ Thick myosin filaments present.

~ Does not shorten during contraction.

Question 11

Describe The I Band Part Of The Myofibril
(2 Points)

Answer 11

~ Thin actin filaments present.

~ Does not shorten during contraction.

Question 12

Describe The A Band Part Of The Myofibril
(2 Points)

Answer 12

~ Contains areas where only myosin filaments are present and areas where myosin and actin filaments overlap.

~ Increases during contraction as filaments overlap more.

Question 13

Describe The M Line Part Of The Myofibril

Answer 13

Attachment for myosin filaments.

Question 14

Describe The Z Line Part Of The Myofibril

Answer 14

Attachment for the actin filaments.

Question 15

Describe The Sarcomere Part Of The Myofibril

Answer 15

The section of myofibril between two Z lines.

Question 16

What Happens When Muscles Contract In Terms Of Myofibrils?

Answer 16

Sarcomeres slide over each other.

Question 17

Describe The Skeletal Muscle
(6 Points)

Answer 17

~ Striated.

~ Tubular.

~ Multi-nucleated, to enhance tissue repair.

~ Moves voluntarily.

~ Attached to the skeleton.

~ Fatigues quickly.

Question 18

Describe The Cardiac Muscle
(9 Points)

Answer 18

~ Striated

~ Myogenic.

~ Found in the heart tissue.

~ Contracts involuntarily.

~ Branched.

~ Binucleated.

~ Has intercalated discs which join muscle fibres together.

~ Covers the walls of the heart.

~ Doesn’t fatigue quickly.

Question 19

Describe The Smooth Muscle
(7 Points)

Answer 19

~ Non-straited.

~ Spindle shaped.

~ Binucleated.

~ Contracts involuntarily.

~ Controlled by the autonomic nervous system.

~ Covers the wall of internal organs.

~ Fatigues slowly.

Question 20

What Are The 2 Types Of Muscle Fibres Found In Muscles?
(2 Points)

Answer 20

~ Fast twitch fibres.

~ Slow twitch fibres.

Question 21

Describe Myoglobin
(3 Points)

Answer 21

~ A type of iron and oxygen binding protein found in skeletal and cardiac muscle.

~ Functions as a store of oxygen in muscles.

~ Red pigment molecule.

Question 22

Describe Fast Twitch Muscle Fibres
(7 Points)

Answer 22

~ Contract quickly.

~ Anaerobic respiration as its main metabolic pathway.

~ Produce short intense bursts of force.

~ Fatigue quickly.

~ Lower capillary and myoglobin density, makes them pink.

~ Low mitochondrial density.

~ Faster rate of ATP hydrolysis in myosin heads.

Question 23

Why Do Fast Twitch Muscle Fibres Contract Quickly?

Answer 23

Their rapid contraction-relaxation cycle means they need large amounts of calcium ions present to stimulate contraction.

Question 24

Why Do Fast Twitch Muscle Fibres Rely On Anaerobic Respiration?

Answer 24

For ATP supply.

Question 25

Why Do Fast Twitch Muscle Fibres Fatigue Quickly?

Answer 25

Due to the lactate produced from anaerobic respiration.

Question 26

Why Do Fast Twitch Muscle Fibres Appear Pinker / Paler In Colour?

Answer 26

Due to lower capillary and myoglobin density.

Question 27

What Are Fast Twitch Muscle Fibres Better Suited For?

Answer 27

Power.

Question 28

What Are Slow Twitch Muscle Fibres Better Suited For?

Answer 28

High endurance.

Question 29

Describe Slow Twitch Muscle Fibres
(7 Points)

Answer 29

~ Contract slower.

~ Aerobic respiration for ATP.

~ Fatigue less quickly.

~ Perform repetitive, low force movements.

~ Higher capillary and myoglobin density, makes them red.

~ High haemoglobin and mitochondria density.

~ Slower rate of ATP hydrolysis in myosin heads.

Question 30

Why Do Slow Twitch Muscle Fibres Fatigue Less Quickly?

Answer 30

Due to less lactate production.

Question 31

Why Do Slow Twitch Muscle Fibres Appear Red?

Answer 31

Due to a high capillary and myoglobin density.

Question 32

What Are Striations Caused By?

Answer 32

A and I bands.