Tissues 7 (Muscle)

Question 1

What are the two types of muscle contraction and how do they differ?

Answer 1

• Isotonic: tension stays the same and length changes - Isometric: tension changes and length remains the same

Question 2

What are the two subtypes of isotonic contraction?

Answer 2

• Concentric (shortening) - Eccentric (lengthening)

Question 3

What is the Z-line made up of?

Answer 3

• Alpha-actinin - CapZ

Question 4

What are the two types of receptors involved in excitation-contraction coupling of skeletal muscle?

Answer 4

• Dihydropyridine receptor (DHPR) - Ryanodine receptor (RyR)

Question 5

What is the process of excitation-contraction coupling of skeletal muscle?

Answer 5

• AP propagates along T tubule and reaches DHPR
• Depolarisation causes conformational change in the DHPR allowing it to make contact with RyR
• RyR (on sarcoplasmic reticulum) opens causing Ca2+ release from the SR
• This triggers the muscle contraction

Question 6

What are the different components of a sarcomere?

Answer 6

Z-line Actin filaments CapZ and Tropomodulin Nebulin Titin Myosin Tropomyosin

Question 7

What is the structure of actin?

Answer 7

Two twisted alpha helices

Question 8

What does Titin do?

Answer 8

It holds the myosin in place (anchors to Z line) It is very large

Question 9

Where are CapZ and Tropomodulin found?

Answer 9

At the ends of the actin filaments

Question 10

What is the relationship between tension and load in isotonic and isometric contraction?

Answer 10

Isotonic – Tension > Force

Isometric – Tension = Force

Question 11

What specialised structure links adjacent cardiomyocytes?

Answer 11

Intercalated Discs

Question 12

What junctions are present in intercalated discs?

Answer 12

• Desmosomes (holds membrane structures together)
• Gap Junctions (allows electrical communication between cells)

Question 13

Which receptors are involved in excitation-contraction coupling of cardiac muscle?

Answer 13

• Voltage Gated Calcium Channels - Ryanodine Receptors

Question 14

What is the process of excitation-contraction coupling of cardiac muscle?

Answer 14

• AP propagates down T-tubules and leads to the opening of VGCCs (influx of Ca2+)
• Ca2+ binds to RyR making them open
• Ca2+ released from SR further increase in intracellular Ca2+ (Calcium Induced Calcium Release)

Question 15

What is the process of excitation-contraction coupling of smooth muscle?

Answer 15

• AP reaches VGCC and makes it open (Ca2+ influx)
• Ca2+ binds to Calmodulin forming Ca2+-CaM complex
• complex activates myosin light chain kinase
• MLCK phosphorylates myosin light chains and leads to smooth muscle contraction

Question 16

What are T-Tubules?

Answer 16

membrane invaginations that contract the extracellular fluid

Question 17

What is the sarcoplasmic reticulum?

Answer 17

extensive network of Ca2+ stores surrounding each myofibril

Question 18

What is the sliding filament theory?

Answer 18

• Ca2+ moves troponin, exposing myosin binding site, allowing charged myosin head to bind to actin filament
• ADP discharged on binding causes power stroke of myosin head
• power stroke pulls actin filament to sarcomere centre
• ATP binding releases myosin head
• ATP hydrolysis provides energy to recharge myosin head

Question 19

Label the sarcomere

Answer 19

1. Myosin Heads
2. Actin Filament
3. Titin
4. Myosin
5. Nebulin
6. Z-line
7. Tropomodulin
8. Tropomyosin
9. CapZ

Question 20

What is a sarcomere?

Answer 20

Functional unit of muscle that lies between 2 Z-lines

Question 21

What part of myofibrils gives a striated appearance?

Answer 21

• A band (dark band: length of myosin - contains H zone)
• I line (light band: length not containing myosin, intersected by Z lines)