Muscle Contraction

Question 1

What causes Myasthenia gravis?

Answer 1

It is autoimmune and it is caused by defects in signalling from nerve to muscle at neuromuscular junctions

Question 2

What is contraction ?

Answer 2

The ability of a muscle to actively shorten and develop tension

Question 3

What is skeletal muscle attached to?

Answer 3

Bone via a tendon

Question 4

What makes up muscle ?

Answer 4

Muscle
Fasciculus
Fibre/Cell
Myofibril
Sarcomere
Filaments

Question 5

What are the thick and thin filaments ?

Answer 5

Thick - myosin

Thin - actin

Question 6

When are H bands and I bands at maximum width?

Answer 6

In a relaxed muscle

Question 7

What disappears in a fully contracted muscle ?

Answer 7

The H zone

Question 8

What remains unchanged during muscle contraction and relaxation ?

Answer 8

A band width

Question 9

What are T tubules important for ?

Answer 9

Spread of the AP across the membrane

Question 10

What is stored in the sarcoplasmic reticulum ?

Answer 10

Calcium ions

Question 11

Where do ATP and actin bind to myosin ?

Answer 11

At the double head

Question 12

How could you describe the actin filament ?

Answer 12

Double stranded F-actin molecules comprising polymerised G-actin molecules

Question 13

What regulatory protein is on the actin filament ?

Answer 13

Tropomyosin

Question 14

What regulatory proteins lies on the tropomyosin ?

Answer 14

Troponin

Question 15

Why is troponin important ?

Answer 15

This is where calcium binds enabling the muscle to contract

Question 16

What happens when there is low Ca++ in the cell?

Answer 16

Tropomyosin blocks access to the myosin binding site of actin

Question 17

What happens when troponin binds to Ca++?

Answer 17

There is a structural change which allows myosin to access its binding site on actin

Question 18

What does the hydrolysis of ATP produce ?

Answer 18

ADP and Pi

Question 19

What is released and what forms when myosin head attaches to myosin-binding site on actin?

Answer 19

Phosphate is released

Cross-bridge forms and myosin head pivots from 90-45

Question 20

In the sliding filament hypothesis what causes actin to slide past myosin?

Answer 20

After the release of ADP, the cross-bridge generates force which causes actin to slide past myosin

Question 21

What causes the cross bridge to detach ?

Answer 21

When another ATP is bound

Question 22

What is the optimal length of a sarcomere ?

Answer 22

2.1-2.2 microns

Question 23

Why are sarcomere usually at optimal length in the body ?

Answer 23

Tendon attachment

Question 24

What happens at the neuromuscular junction?

Answer 24

Nerve and muscle cells are meeting and that incites that excitation which generates the high calcium conditions

Question 25

What does acetylene choline bind to and what does this cause?

Answer 25

Nicotinic receptor Opens receptor-operated channels, inward current produces local depolarisation (a graded potential)

Question 26

How does the local currents depolarise the muscle membrane ?

Answer 26

Influx of Na+ ions

Question 27

Where does the AP flow?

Answer 27

Via the T-tubules

Question 28

What senses the T tubules during muscle contraction ?

Answer 28

Dihydropyridine receptors (L-type channels)

Question 29

What do L-type channels trigger?

Answer 29

Ca++ release channels on sarcoplasmic reticulum to open and realise Ca++ init sarcoplasm The channels are called ryanodine receptors

Question 30

What happens during Rigor Mortis?

Answer 30

Ca++ leak out after death of the SR into the cell enabling actin-myosin binding however no ATP is synthesise and therefore cross-bridges cannot detach

Question 31

What does the total force produced by single muscle fibre depend on?

Answer 31

The rate of muscle fibre stimulation by motor nerve

Question 32

What does 2 close APs cause ?

Answer 32

Wave summation

Question 33

What do a number of APs that are relatively close together cause?

Answer 33

Unfused tetanus

Question 34

What do a number of APs that are very very close together cause?

Answer 34

Fused tetanus

Question 35

What is an isotonic contraction ?

Answer 35

Constant tension | Change in length

Question 36

What are the two types of isotonic contractions ?

Answer 36

Concentric - muscle shortens | Eccentric - muscle lengthens

Question 37

What is an isometric contraction ?

Answer 37

Constant length | Produces tension

Question 38

What are the 3 types of skeletal muscle fibres ?

Answer 38

Type I - slow Type IIA - fast Type IIB - fast

Question 39

Describe slow twitch type I muscle fibre.

Answer 39

- postural muscle of back - slow, sustained contractions required - oxidative metabolism - many mitochondria - red - myoglobin - resist fatigue

Question 40

Describe fast twitch type IIA muscle fibre.

Answer 40

- soleus in calf - fast contraction - oxidative metabolism - many mitochondria - red-pink myoglobin - intermediate fatigue resistance

Question 41

Describe fast twitch type IIB muscle fibre.

Answer 41

- extraocular muscle - rapid contractions - anaerobic glycolysis - few mitochondria - white - little myoglobin - high glycogen content

Question 42

What are the two types of smooth muscle ?

Answer 42

Single unit smooth muscle | Multi unit smooth muscle

Question 43

What are T-tubules called in smooth muscle ?

Answer 43

Caveolae

Question 44

What does Ca++ bind to in smooth muscle contraction ?

Answer 44

Calmodulin

Question 45

What type of muscle doesn’t have spontaneous activity ?

Answer 45

Skeletal muscle

Question 46

What muscle has MLCK?

Answer 46

Smooth muscle

Question 47

List the types of muscles from fastest and slowest contraction speed.

Answer 47

Skeletal Cardiac Smooth

Question 48

Where can CA++ be found in Cardiac and smooth muscle ?

Answer 48

SR and ECF