Lecture 4 - Excitation-Contraction Coupling

Question 1

Characteristics of skeletal muscle

Answer 1

Striated, multiple nuclei and an abundance of mitochondria

Question 2

Characteristics of a skeletal muscle cell

Answer 2

Relatively large, elongated and cylindrical in shape

Question 3

Why are multiple mitochondria required in skeletal muscle

Answer 3

As the muscle has high energy demands

Question 4

What are the muscle fibres formed by during embryonic development

Answer 4

Fused myoblasts

Question 5

What are the specialised contractile elements within skeletal muscles

Answer 5

Myofibrils

Question 6

What does each myofibril consist of

Answer 6

Thick and thin filaments

Question 7

What protein makes up the thick filaments

Answer 7

Myosin

Question 8

What protein makes up the thin filaments

Answer 8

Actin

Question 9

What are the different areas a myofibril can be split into

Answer 9

A band, I band, Z line, M line and the H zone

Question 10

What is the A band composed of

Answer 10

A stacked set of thick filaments and the thin filaments that overlap

Question 11

In what area(s) of the myofibril are the thick filaments found

Answer 11

The A band

Question 12

What is the lighter area within the A band known as

Answer 12

The H zone

Question 13

What causes the lighter portion within the A band

Answer 13

It is the point where the thin filaments do not overlap with the thick

Question 14

What holds the thick filaments together

Answer 14

A system of supporting proteins

Question 15

The proteins that hold the thick filaments together form the

Answer 15

M line

Question 16

What is the I band composed of

Answer 16

The portions of the thin filaments that don’t overlap with the thick filaments

Question 17

What is the dense vertical line present in the I band called

Answer 17

The Z line

Question 18

What is the area between two Z lines called

Answer 18

A sarcomere

Question 19

What is the functional unit of skeletal muscle

Answer 19

The sarcomere

Question 20

What is the Z line

Answer 20

Flat, cytoskeletal discs that connect the thin filaments

Question 21

What is the smallest functional unit that can undergo contraction

Answer 21

A sarcomere

Question 22

If a muscle is to grow, how does it do this

Answer 22

By adding new sarcomeres onto the ends of the myofibrils

Question 23

What is excitation-contraction coupling

Answer 23

How the muscle converts an electrical stimulus, action potential, into a mechanical response, contraction

Question 24

What cycle brings about contraction

Answer 24

The cross-bridge cycle

Question 25

What are the two main proteins involved in the cross bridge cycle

Answer 25

Actin and myosin

Question 26

The cross bridge interactions cause

Answer 26

The sliding filament mechanism

Question 27

Why is calcium so important

Answer 27

As it is the link between excitation and contraction

Question 28

The release of what stimulates skeletal muscle to contract

Answer 28

Acetylcholine

Question 29

Where is acetylcholine released

Answer 29

The neuromuscular junction

Question 30

What does the binding of ACh cause

Answer 30

A change in the membrane permeability which results in an action potential being fired

Question 31

What are the two important membranous structures that help to ensure conduction of the AP over the whole muscle

Answer 31

The transverse (T) tubules and the sarcoplasmic reticulum (SR)

Question 32

Within the muscle where are T tubules found

Answer 32

At the junction between the A band and the I band

Question 33

Where do the T tubules run from

Answer 33

The muscle cell membrane into the central portion on the muscle fibre

Question 34

What does the presence of an AP in the T tubules cause

Answer 34

A change in permeability of the sarcoplasmic reticulum

Question 35

What is the sarcoplasmic reticulum (SR)

Answer 35

A modified endoplasmic reticulum that consists of a fine network of interconnected membrane enclosed compartments surrounding each myofibril

Question 36

What are the sac like regions at the ends of the SR known as

Answer 36

The lateral sacs (terminal cisternae)

Question 37

What is stored within the lateral sacs

Answer 37

Ca2+

Question 38

What does the spread of an AP down a T tubule trigger

Answer 38

The release of Ca2+ from the SR (lateral sacs) into the cytosol

Question 39

What serves as Ca2+ release channels

Answer 39

Foot proteins

Question 40

What are foot proteins also known as

Answer 40

Ryanodine receptors

Question 41

WHat are the foot proteins made up of

Answer 41

Four subunits

Question 42

What is ryanodine

Answer 42

A plant chemical that holds open the calcium release channels

Question 43

What are the T tubule receptors made up of

Answer 43

Four subunits

Question 44

What is another name for T tubule receptors

Answer 44

Dihydropyridine receptors

Question 45

What effect does the drug dihydropyridine have on T tubule receptors

Answer 45

It blocks them

Question 46

What type of sensors are the dihydropyridine receptors

Answer 46

Voltage-gated

Question 47

What occurs to the ryanodine receptors when an AP is propagated down the T tubule

Answer 47

The local depolarisation causes the receptors to open

Question 48

Opening of the Ca2+ channel in direct contact with the T tubule causes what

Answer 48

The other half of the receptors that aren't connected to the T tubule to open

Question 49

Once all the receptors are opened what happens

Answer 49

Calcium is released into the cytosol

Question 50

During the cross-brigde cycle what does the released Ca2+ cause

Answer 50

For the binding sites on actin to be exposed

Question 51

When the binding sites of actin are exposed, what does this signal the beginning of

Answer 51

The cross bridge cycle

Question 52

What is unique about the APs of cardiac muscle

Answer 52

The exhibit a prolonged positive phase accompanied by a prolonged period of contraction

Question 53

The AP of cardiac muscle has a characteristic shape due to

Answer 53

The plateau phase

Question 54

What happens during the plateau phase of a cardiac muscle AP

Answer 54

Calcium is constantly entering the muscle cells

Question 55

Where does the calcium, required for contraction, in cardiac muscle come form

Answer 55

The external environment

Question 56

What is activated to allow calcium to move from the external environment into the cardiac muscle cells

Answer 56

The activation of L-type Ca2+ channels

Question 57

What does the entry of the Ca2+ from the external environment cause

Answer 57

The release of more Ca2+ from the sarcoplasmic reticulum

Question 58

What leads to cross bridge cycling and contraction within cardiac muscle

Answer 58

Ca2+ induced Ca2+ release

Question 59

What causes variation in cross bridge activity

Answer 59

The amount of cystolic Ca2+ present