Tissues 7

Question 1

What are the features of skeletal muscle structure?

Answer 1

• Long and cylindrical cells
• Multinucleate
• Dark and light bands give striated appearance

Question 2

What is the sarcomere?

Answer 2

The functional unit of muscle which lies between two Z lines.

Question 3

What are T-tubules?

Answer 3

Invaginations of the myofibril that come into contact with the extracellular fluid

Question 4

What is the sarcoplasmic reticulum?

Answer 4

Specialised network of intracellular calcium stores that surround each myofibril.

Question 5

What is actin?

Answer 5

Thin polymeric filament that is composed of two alpha helices twisted together. It displays polarity.

Question 6

What is myosin?

Answer 6

Thick filaments that contain globular heads that can interact with actin to facilitate muscle contraction.

Question 7

What is titin?

Answer 7

Very large and spring-like filament that anchors actin to the Z lines.

Question 8

What is nebulin?

Answer 8

A large filament associated with actin.

Question 9

What is tropomyosin?

Answer 9

An elongated protein bound to actin.

Question 10

What is CapZ?

Answer 10

Filament associated with positive end of actin.

Question 11

What is tropomodulin?

Answer 11

Filament associated with negative end of actin.

Question 12

How is calcium release initiated in muscle contraction?

Answer 12

1) AP propagates along myofibril
2) Depolarisation activates dihydropyridine receptors, causing conformational changes
3) Change is transmitted to ryanodine receptors on SR, opening ryanodine receptor causing Ca2+ to be released.
4) Depolarisation further increase Ca2+ influx.

Question 13

What happens in the presence of calcium?

Answer 13

Troponin moves to the tropomyosin chain, exposing the myosin binding sites on the surface of actin.

Question 14

How does the sliding filament theory work?

Answer 14

1) In the presence of calcium, calcium binds to the troponin, causing a conformational change of the troponin-tropomyosin complex, causing it to move into a groove of the actin chain, revealing open binding sites
2) Charged myosin heads bind to exposed actin sites
3) Discharge of ADP results in power stroke, pulling actin towards centre of sarcomere
4) ATP binding releases myosin from actin
5) ATP hydrolysis provides energy to re-energise and re-orientate the myosin heads for the next contraction

Question 15

What is isotonic contraction?

Answer 15

Where the muscle length changes but tension remains the same.

Question 16

What is isometric contraction?

Answer 16

Where the muscle length or tension does not change.

Question 17

What are two types of pacemaker cells in the heart?

Answer 17

Sinoatrial node (spontaneously active) and the atrioventricular node (base of RA).

Question 18

What are two types of conducting cells?

Answer 18

Bundle of His and Purkinje fibres.

Question 19

What do they intercalated disks do?

Answer 19

Connect individual myocytes to one another.

Question 20

What do gap junctions do?

Answer 20

Allow action potentials to spread rapidly from one cell to another.

Question 21

How does EC coupling work in smooth muscle cells?

Answer 21

1) Depolarisation opens Ca2+ channels
2) Ca2+-CAM complex activates myosin light chain kinase (MLCK)
3) MLCK phosphorylates myosin light chains
4) Cross bridges are formed with actin, resulting in contraction

Question 22

Where is smooth muscle found?

Answer 22

In the walls of hollow organs.