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 one of the types of muscle contraction?

Answer 2

Isotonic =
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

Ryanodine receptor

Question 5

Describe the process of excitation-contraction coupling of skeletal muscle.

Answer 5

• An action potential propagates along a T tubule and reaches the Dihydropyridine receptor
• Depolarisation causes a conformational change in the DHPR allowing it to make contact with the Ryanodine Receptor on the sarcoplasmic reticulum
• RyR 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

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 > load

Isometric – Tension = load

Question 11

What specialised structure links adjacent cardiomyocytes?

Answer 11

Intercalated Discs

Question 12

What junctions are present in these structures?

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

Describe the process of excitation-contraction coupling of cardiac muscle.

Answer 14

• Action Potential propagates down T-tubules and leads to the opening of VGCCs
• This leads to influx of Ca2+
• Ca2+ then binds to the RyR making them open leading to Ca2+ release from the SR and a further increase in intracellular Ca2+

(Calcium Induced Calcium Release)

Question 15

Describe the process of excitation-contraction coupling of smooth muscle

Answer 15

• Action potential reaches the VGCC and makes it open leading to Ca2+ influx
• Ca2+ binds to Calmodulin forming a Ca2+-CaM complex
• This complex activates myosin light chain kinase
• MLCK phosphorylates myosin light chains and leads to smooth muscle contraction

Question 16

how do myofibrils and myofibrils relate?

Answer 16

myofibres are bundles of myofibril cells

Question 17

describe myofibres?

Answer 17

myofibres are large, cylindrical, multinucleate and packed with myofibrils

Question 18

what does the sarcoplasmic reticulum contain?

Answer 18

• cellular store of Ca2+ that will be released in order to cause contraction

Question 19

what is the sliding filament theory ?

Answer 19

1. presence of Ca2+ causes movement of troponin from tropomyosin which reveals the myosin binding site on the surface of the actin chains
2. the charged myosin heads bind to the exposed binding sites on the actin, (ADP molecules released)
3. The ADP discharge causes the myosin head to pivot in a Powerstroke pulling the actin filament towards the center of the sarcomere
4. Then ATP binds to the myosin head and is hydrolyzed meaning the myosin head is released and recharged

Question 20

what are features of cardiomyocytes?

Answer 20

• striated muscle cells
• linked by intercalated discs
• contains numerous gap junctions
• the gap junctions allow the action potentials to spread rapidly between cells