Muscle

Question 1

What are the 3 types of muscle

Answer 1

1. Skeletal
2. Cardiac
3. Smooth

Question 2

What is contraction

Answer 2

Shortening of the cell by interaction of actin and myosin, fuelled by ATP hydrolysis and the rise in the concentration of Ca2+

Question 3

What is the process in skeletal muscle that eventually leads to contraction

Answer 3

1. Motor nerves release acetylcholine
2. Reacts with nicotinic acetyl choline receptor
3. Receptor opens up causing an influx of Na+ ions
4. A wave of depolarisation travels down the T-tubules
5. Causes dihydropyridine receptors to conformationally change
6. This has a physical change on the ryanodine receptor so calcium is released from the sarcoplasmic reticulum
7. The rise in calcium interacts with troponin which leads to contraction

Question 4

What is the difference in the contraction process in cardiac muscle compared to skeletal muscle

Answer 4

There is no physical interaction between the dihydropyridine receptors and the ryanodine receptors
Instead the ryanodine receptors detect the small increase in Ca+ concentration and release more Ca+ from the sarcoplasmic reticulum via calcium-induced-calcium-release
The impulse starts with the SAN

Question 5

What happens to cardiac muscle in heart failure

Answer 5

The sarcoplasmic reticulum dribbles out calcium

Question 6

What is the difference in contraction process in smooth muscle compared to skeletal muscle

Answer 6

There are no T-tubules
Gq/11 muscarinic nicotinic receptors can be activated by acetylcholine
This activates phospholipase C which turns PIP2 into IP3 which releases calcium
CICR causes ryanodine to release more calcium
Calcium binds to calmodulin creating a complex that activates myosin light chain kinase (MLCK)
MLCK will phosphorylate the myosin light chain, allowing the myosin cross-bridge to bind to the actin filament
This allows contraction to begin

Question 7

What is the thick filament in the sarcomere

Answer 7

Myosin

Question 8

What is the thin filament in the sarcomere

Answer 8

Actin

Question 9

What does actin do

Answer 9

It acts as a myosin head binding site, without Ca, tropomyosin covers the binding site

Question 10

What does troponin C do

Answer 10

Binds calcium

Question 11

What does troponin T do

Answer 11

It binds to tropomyosin allowing it to remove it revealing the myosin head binding site once a calcium concentration increase has been achieved

Question 12

What binds the thin filament to the Z disk

Answer 12

Alpha-actinin

Question 13

SFT - Attached

Answer 13

A myosin head lacking a bound ATP or ADP, attached tightly to an actin filament

Question 14

SFT - Released

Answer 14

A molecule of ATP binds to the myosin head, the myosin head unbinds from the actin filament

Question 15

SFT - Cocked

Answer 15

Hydrolysis of ATP occurs, the AD and Pi are still bound to the myosin head but the head moves along the actin filament

Question 16

SFT - Force generation

Answer 16

Weak binding of the myosin head to a new site on the actin filament causes release of the pi, triggering a power stroke. The ADP unbinds

Question 17

SFT - re-attached

Answer 17

Back to the original position of the myosin head tightly bound to the actin however now in a new position

Question 18

Sliding filament theory - SFT

Overview

Answer 18

1. Attached
2. Released
3. Cocked
4. Force-generation
5. Re-attached

Question 19

What is the difference between smooth muscle and skeletal muscle

Answer 19

Contractile proteins are not in regular arrays
Myosin contains a regulatory light chain
Actin is longer in smooth muscle
Phosphatase is required to remove contraction phosphatase is inhibited by many different molecules therefore smooth muscle will remain contracted