muscle physiology

Question 1

What makes up muscle fibres

Answer 1

Myofibrils

Question 2

What makes up myofibrils

Answer 2

sarcomeres containing myofilaments

Question 3

What proteins make up thin filaments

Answer 3

Actin, myosin and tropomyosin

Question 4

What are the thin filaments of a sarcomere tethered to?

Answer 4

Z - disk

Question 5

What is the A band

Answer 5

The length of the thick myosin filament, does not change in contraction

Question 6

What is the I band

Answer 6

Length of thin actin filaments not overlapped by myosin/thick filament

Shortens with muscle contraction

Question 7

What is the structure of the thin filaments

Answer 7

Backbone is a double stranded alpha helix polymer of F actin, with troponin and tropomyosin on it

Question 8

Describe the structure of thick filaments

Answer 8

Bipolar assemblies of myosin II molecules, These have 2 heavy chains intertwined, 2 regulatorylight chains, and 2 alkali/essential light chains

Question 9

What role does Ca2+ play in initiating cross-bridge cycling

Answer 9

Troponin C binds to Ca2+, causinf troponin I to move away from actin filament, and Troponin T pushes tropomyosin away from actin binding site

Question 10

What are the 5 steps of the cross bridge cycle in skeletal msucle?

Answer 10

1: ATP binding (dissociates actin-myosin complex)
2: ATP hydrolysis (myosin heads reach resting position)
3: Cross bridge forms, myosin head binds to new position on actin
4: release of Pi from myosin, myosin head changes shape, resulting in the power stroke
5: ATP is released

Question 11

How do muscle cells regulate the contraction cycle

Answer 11

Regulating step 3: the access of Ca2+ to thr tropomyppsin

Question 12

Describe the neuromuscular junction

Answer 12

Motor neurons flattened to form motor end plate, acetylcholine released into synaptic cleft, attaches to nicotinic ach receptors. Acetylcholinesterase rapidly breaks down Ach in synaptic cleft

Question 13

What are transverse tubules

Answer 13

Plasma membranes of muscle cells which invaginate tthe muscle cell

Question 14

Describe excitation-contraction coupling

Answer 14

Action potentail travels from skeletal muscle membrane down T tubules. Depolarisation opens voltage gated L-type calcium channels in tetrads

Increase in calcium leads to cross-bridge cycling

Question 15

How is contraction terminated

Answer 15

Calcium must be removed,

Minor: Na-Ca exchanger, Ca pump at membrane

Major: Ca reuptake into SR by SERCA-type Ca pump