Muscle Physiology I

Question 1

3 Parts of a Skeletal Muscle

Answer 1

1. Neuromuscular Junction
2. Excitation-contraction coupling cell machinery
3. Sarcomeres (contractile apparatus)

Question 2

Mysium Layers

Answer 2

Epimysium - wraps overall muscle
Perimysium - wraps fascicles
Endomysium - wraps myofibril
Sarcolemma - plasma membrane

Question 3

Myofibril Length

Answer 3

2um

Question 4

Myofibrils uni/multinucleated?

Answer 4

Multi

Question 5

What are T-tubules

Answer 5

Invaginations of the sarcolemma to ensure the AP gets deep into the muscle and hits all myofibrils

Question 6

Triad

Answer 6

Terminal cisternae of SR - T-tubule - Terminal cisternae of SR

Question 7

Where are T-tubules located

Answer 7

Junction of overlap between A and I bands

Question 8

Titin role

Answer 8

Holds F-actin in line with myosin even when muscle is moving

Question 9

Nebulin role

Answer 9

Makes F-actin length consistent by holding G-actin together to form an F-actin

Question 10

F-actin is made from

Answer 10

G-actin

Question 11

A Band

Answer 11

Myosin (thick filament)

Question 12

H Zone

Answer 12

Only myosin (thick filament), no actin

Question 13

M Line

Answer 13

Midline, within the A band / H zone

Question 14

I band

Answer 14

Actin (thin filament)

Question 15

What proteins lie along each actin protein

Answer 15

Tropomyosin and a Troponin Complex

Question 16

Troponin Complex

Answer 16

TnT
TnC
TnI

Question 17

TnT Role

Answer 17

Positions Troponin (Tn) complex on the tropomyosin molecule

Question 18

TnC role

Answer 18

Ca2+ binding sites

Question 19

TnI role

Answer 19

Binds to actin and inhibits myosin from binding to the actin, when there is no Ca2+ in TnC

Question 20

When relaxed what is happening at the actin-myosin binding site

Answer 20

Tropomyosin - Troponin complex blocks it (TnC not bound to Ca2+, so TnI blocks binding site)

Question 21

When Ca2+ binds to TnC what happens at the actin-myosin binding site

Answer 21

TnI moves out of the way, exposing the binding site

Question 22

When ATP binds to Myosin what happens

Answer 22

Actin and myosin dissociate, allowing the cycle to repeat

Question 23

When ATP is hydrolysed by myosin to ADP+Pi, what happens

Answer 23

There is sufficient energy for myosin head to bind to the actin, initiating a cross bridge

Question 24

TnC can bind up to ____ Ca2+ ions

Answer 24

4

Question 25

TnC has __ high affinity binding sites and __ low affinity sites

Answer 25

2, 2

Question 26

Ca2+ binding to TnC is ________ therefore the curve is ____

Answer 26

Co-operative, sigmoidal (ie more forceful when more Ca2+)

Question 27

AP in the T-tubule activates _____ to start the excitation-contraction coupling

Answer 27

DHPR (dihydropyridine receptors)

Question 28

When DHPR has been activated by the voltage, it causes a conformational change in ____ to bring about SR Ca2+ release

Answer 28

RyR1 (Ryanodine receptor)