Physiology, Muscles

Front 1

What electromyogram (EMG) can be used for (in connection to muscles)?

Back 1

Can be used to monitor the level of activation of muscle cells in skeletal muscle.

Front 2

What is a motor unit?

Back 2

It is a motor nerve plus all the fibres that the nerve innervates.

Front 3

What is excitation-contraction coupling?

Back 3

The events occurring between the action potential in the muscle fiber and the contraction of the muscle fiber.

Front 4

Myosin is a ... filament. And Actin, tropomyosin and troponin are ... filaments.

Back 4

Myosin is a thick filament. Actin, tropomyosin and troponin are thin filaments.

Front 5

What is the name of a large molecular weight protein that thick filaments comprise?

Back 5

Myosin.

Front 6

Describe the structure of myosin.

Back 6

Myosin is a large molecular weight protein which has six polypeptide chains, including one pair of heavy chains and two pairs of light chains.

Front 7

What forms the "tail" of myosin molecule?

Back 7

The coiled pair of heavy chains.

Front 8

What forms two globular "heads" of the myosin molecule?

Back 8

The four light chains and the N terminus of each heavy chain.

Front 9

What is the myosin molecule globular head necessary for?

Back 9

They have actin-binding site, which is necessary for cross-bridge formation, and a site that binds and hydrolyzes ATP (myosin ATPase).

Front 10

What are the thin filaments composed of?

Back 10

Actin, troponin, tropomyosin.

Front 11

What happens if the myosin binding sites on a thin filament are covered with tropomyosin?

Back 11

The muscle is at rest and actin cannot interact with myosin.

Front 12

What is tropomyosin?

Back 12

The part of thin filaments. this is a filamentous protein that runs along the groove of each twisted actin filament. At rest it covers the myosin-binding sites of actin so the actin and myosin cannot interact, and if contraction must occur, tropomyosin moves away from the binding sites.

Front 13

Name two types of actin.

Back 13

G-actin - globular actin; F-actin - filamentous actin.

Front 14

Explain the role of troponin (T,I,C) in the thin filaments.

Back 14

Troponin is a complex of three globular proteins (T, I, C), located in the regular intervals along the tropomyosin filaments. Troponin T attaches the troponin complex to tropomyosin. Tr.I inhibits the interaction of actin and myosin by covering the myosin-binding site on actin. Tr.C is a Ca++ binding protein that plays major role in the initiation of contraction. Ca binds to TrC and tropomyosin moves away letting actin interract with myosin.

Front 15

Explain the sarcomere (incl.bands).

Back 15

The sarcomere is the basic contractile unit, and it is delineated by the Z disks. Each sarcomere contains a full A band in the center and one half of two I bands on either side of the A band.

Front 16

Describe A band.

Back 16

A bands are located in the center of the sarcomere and contain the thick filaments. Thick and thin filaments may overlap in the A band; these overlaps are potential sites for a cross-bridge formation.

Front 17

Describe I band.

Back 17

The I bands are located on either side of the A band of the sarcomere. They contain thin filaments, intermediate filamentous proteins and Z disks. They have no thick filaments.

Front 18

Describe the M line.

Back 18

The M line is in the middle of the sarcomere, bisects the bare zone and links the central portions of the thick filaments together.

Front 19

Describe the bare zone.

Back 19

The bare zone is in the middle of the sarcomere. There are no thin filaments in the bare zone, so there can be no overlap of thick and thin filaments or cross-bridge in this region.

Front 20

What delineates the ends of each sarcomere?

Back 20

The Z disks, that run down the middle of each I band.

Front 21

What do the cytoskeletal proteins do?

Back 21

They establish the architecture of the myofibrils, ensuring that the thick and thin filaments are aligned correctly and at proper distances from each other.

Front 22

Describe transverse (T) tubules and their function.

Back 22

T tubules are part of the sarcolemmal membrane of the muscle cell. They are responsible for carrying the depolarisation from action potentials at the muscle cell surface to the interior of the fiber.

Front 23

What does transverse tubules and terminal cisternae make together?

Back 23

Triad.

Front 24

What is the name of the muscle cell membrane?

Back 24

Sarcolemma.

Front 25

What is single muscle fiber consists of?

Back 25

Myofibrils.

Front 26

Put in labels.

Back 26

Front 27

Put in labels.

Back 27

Front 28

Fill in labels.

Back 28

Front 29

Which of the sarcomere bands appear to be light and which - dark?

Back 29

I band is light and A band is dark, because I band has no thick filaments, A band does.

Front 30

How many units of actin have binding site which myosin can interact with?

Back 30

All of them.

Front 31

Which proteins maintain the architecture of the myofibrils?

Back 31

Cytoskeletal proteins, like titin (associated with thick filaments, goes from M line to Z line through the myosin, makes sure that the thick filament is positioned in the right place to give the max.active tension) and nebulin (associated with thin filaments, it extends from one end of the actin to the other, controls the length of thin filaments).

Front 32

Which bands on the sarcomere shorten during contraction of the muscle cell?

Back 32

H band (bare zone) and I band.

Front 33

Which band does not change its length during contraction of the muscle?

Back 33

A band.

Front 34

During muscle contraction why does the sarcomere shorten?

Back 34

Because the actin filaments slide along between the myosin filaments.

Front 35

What is the function of the sarcoplasmic reticulum?

Back 35

The sarcoplasmic reticulum is an internal tubular structure, which stores and releases Ca ions for excitation-contraction coupling.

Front 36

Finish the statement:
Total force generated by a single sarcomere is proportional to ....

Back 36

... the total number of cross-bridges formed between the thick and thin filaments.
AND
... the overlap between the thick and thin filaments.

Front 37

Each cross-bridge generates force .... of other cross-bridges.

Back 37

Each cross-bridge generates force independent of other cross-bridges.

Front 38

What are the roles of ATP in the cross-bridge cycle?

Back 38

- Energy source: ATP hydrolysis provides the energy for cross-bridge cycle;
- Allosteric regulator: Binding of ATP to myosin breaks the link between actin and myosin. This allows the cycle to be repeated.

Front 39

What is the function of the Calsequestrin protein in the sarcoplasmic reticulum?

Back 39

It binds Ca ions, so Ca can be stored in sarcoplasmic reticulum.

Front 40

Name functions of sarcoplesmic reticulum.

Back 40

- Storage of high concentrations of Ca ions;
- rapid release of Ca ions into the myoplasm in response to an action potential;
- rapid removal of Ca ions from the myoplasm.

Front 41

Ca ions is accumulated in the sarcoplasmic reticulum by the action of what?

Back 41

Of Ca++ ATPase.

Front 42

When the muscle fibre is at rest what is the situation of Ca ions in the ICF?

Back 42

Intracellular concentration of Ca ions is very low, because the Ca++ ATPase pumps the Ca ions from the ICF into the the interior of the sarcolasmic reticulum.

Front 43

How is Ca stored in the sarcoplasmic reticulum?

Back 43

It is stored bound to the protein called calsequestrin. so the concentration of free Ca ions in the intrasarcoplasmic reticulum is extremely low.

Front 44

What are the functions of the T tubules?

Back 44

- The conduction of action potential from the sarcolema deep into the muscle fibre;
- The conduction of action potential to the sarcoplasmic reticulum causing the release of calcium.

Front 45

Which triad receptors are involved in sensing the action potentials and releasing Ca ions?

Back 45

- The dihydropyridine (DHP) receptor in the T tubules (only) functions as a voltage sensor;
- The ryanodine receptor in sarcoplasmic reticulum functions as a Ca release channel.

Front 46

What makes muscle relax?

Back 46

The removal of Ca from troponin -> inhibition of tropomyosin.

Front 47

Define tension.

Back 47

Tension is a force exerted on an object by a contracting muscle.

Front 48

Define load.

Back 48

Load is a force exerted on a muscle by the weight of an object.

Front 49

What is isometric contraction?

Back 49

When muscle develops tension without changing length.

Front 50

What is isotonic contraction?

Back 50

When muscle shortens, while load remains constant.

Front 51

What is eccentric (lengthening) contraction?

Back 51

When load exceeds muscle tension, load pulls muscle to a longer length.

Front 52

There are two types of smooth muscle organisation. Name and explain them.

Back 52

Unitary: Muscle fibres act together as a functional unit.
Multiunit: Muscle fibres act independently.

Front 53

What are the gap junctions for in the smooth and cardiac muscles?

Back 53

They permit coordinated contraction; ions move through them ensuring signalling and communication between cells.

Front 54

What is the Ca++ sensor in muscles?

Back 54

In cardiac and skeletal muscle it is troponin, but in smooth muscle it is calmodulin.

Front 55

What is the name of tension developed by simply stretching a muscle to different lengths.

Back 55

Passive tension.

Front 56

What is the name of tension developed when a muscle is stimulated to contract at different preloads?

Back 56

Total tension. It is the sum of the active tension developed by the cross-bridge cycling in the sarcomeres and the passive tension caused by stretching the muscle.

Front 57

What is the name of tension which is determined by subtracting the passive tension from the total tension? It presents the active force developed during the cross-bridge cycle.

Back 57

Active tension.

Front 58

The active tension developed is proportional to the number of cross-bridges that cycle. What does that mean in terms of sarcomere length?

Back 58

The active tension is maximal when there is maximal overlap of thin and thick filaments and maximal cross-bridges. When muscle is stretched to longer lengths (the sarcomere is too) the active tension is reduced. Likewise, when the sarcomere length is reduced, the thin filaments collide with each other in the centre of sarcomere and reducing the number of possible cross-bridges, active tension.

Front 59

Fill in blanks:
The amount of tension is determined for a muscle undergoing an ... contraction, in which the muscle is allowed to develop ... at a present ... (called ...) but is not allowed to ... .

Back 59

Fill in blanks:
The amount of tension is determined for a muscle undergoing an isometric contraction, in which the muscle is allowed to develop tension at a present length (called preload) but is not allowed to shorten .

Front 60

In isotonic contraction the ... is fixed, and the muscle is allowed to ... .

Back 60

In isotonic contraction the force is fixed, and the muscle is allowed to shorten.

Front 61

Why there is no striations in the smooth muscles?

Back 61

Because the muscle the thin and thick filaments are not organized in sarcomeres.

Front 62

Which type of smooth muscle has gap junctions between cells, which allow the electrical activity to spread quickly throughout the organ, followed by coordinated contraction?

Back 62

Unitary smooth muscle.

Front 63

Which type of smooth muscle has no coupling between cells, no gap junctions?

Back 63

Multiunit smooth muscle.

Front 64

Which type of muscle is found in the vascular smooth muscle?

Back 64

The combination of unitary and multiunit smooth muscle.

Front 65

In excitation-contraction coupling of the smooth muscle Ca++ binds to which protein to allow cross-bridge cycling?

Back 65

Calmodulin.

Front 66

To start the cross-bridge cycle in smooth muscle what does Ca++ binds to and activates it?

Back 66

Myosin-light-chain kinase.

Front 67

In smooth muscle process of contraction what happens after Ca++ binds and activates Myosin-light-chain kinase?

Back 67

Myosin-light-chain kinase uses ATP to phosphorylate myosin cross-bridges, which allows them to bind to actin. Contraction happens.

Front 68

What are other sources of Ca++ in the smooth muscle except the voltage-gated Ca channels?

Back 68

Ligand-gated Ca++ channels in the sarcolemmal membrane and IP3-gated Ca++ channels in the sarcoplasmic reticulum membrane.

Front 69

Why does the summation of twitches not occur in cardiac muscle?

Back 69

Because cardiac muscle must contract just once with each heart beat and must relax fully between contractions.

Front 70

Does the smooth muscle contract fast or slowly? What advantage does it have?

Back 70

Slowly. It can be shortened in much greater degree than striated muscle, as a result it can produce large and sustained movements of organs such as intestine.

Front 71

Which three pathways cause an increase in the myoplasmic Ca++ concentration in smooth muscle?

Back 71

- Ca entry via voltage-gated Ca channels in response to cell depolarisation;
- Ca release from the SR;
- Ca entry via voltage-independent Ca channels.

Front 72

What are myofibrils? Organisation and components.

Back 72

Myofibrils are cylindrical organelles. They are bundles of actomyosin filaments (sarcomeres) that run from one end of the cell to the other and are attached to the cell surface membrane at each end. The filaments of myofibrils, myofilaments, consist of two types, thick and thin.
Thin filaments consist primarily of the protein actin, coiled with nebulin filaments.
Thick filaments consist primarily of the protein myosin, held in place by titin filaments.

Front 73

What are muscle fibres? Organisation and components.

Back 73

Muscle fibres - muscle cells. Within the cells are myofibrils. Individual muscle fibres are surrounded by endomysium. Muscle fibers are bound together by perimysium into bundles called fascicles.

Front 74

Describe organisation and components of a muscle.

Back 74

Muscle is mainly composed of muscle cells. Within the cells are myofibrils; myofibrils contain sarcomeres, which are composed of actin and myosin. Individual muscle fibres are surrounded by endomysium. Muscle fibers are bound together by perimysium into bundles called fascicles; the bundles are then grouped together to form muscle, which is enclosed in a sheath of epimysium. Muscle spindles are distributed throughout the muscles and provide sensory feedback information to the central nervous system.

Front 75

Label.

Back 75

Front 76

Label.

Back 76