Physiology of skeletal muscle

Question 1

Muscle organization

Answer 1

Muscle + epimysium

Facicle + perimysium

Muscle fibre + endomysium

Myofibril

Sarcomere

Question 2

sarcolemma has many _________

Answer 2

ion channels

Question 3

H zone
A band 
I band
M line
Z line

Answer 3

H zone = only myosin
A band = both, d/p on myosin
I band = only actin
M line = in between myosin fiaments
Z line = sarcomere

Question 4

When muscle contracts, then only _____ lines/zones change

Answer 4

Z line and A band and I band

Question 5

Muscle is made of water and solids. Solids include

Answer 5

1. proteins
   a. structural:
   α- Actinin
   Titin
   Myomesin

b. contractile:
Actin
Myosin
Troponin
Tropomyosin

c. others: Myoglobin

2. other constituents:
Fat
CHO
Inorganic salt
Nitrogenous substances
Non nitrogenous substances

Question 6

Lightest band

Darkest band

Answer 6

I band

A band / H band

Question 7

Actin has tropomyosin (long covering molecule) with troponin binding site on it. Troponin has 3 subunits:

Answer 7

Troponin has 3 subunits
1. T subunit – binds to tropomyosin
2. I subunit – binds to actin
Both of them blocking the myosin binding site
3. C subunit – binds to calcium (Ca2+)
When Ca2+ binds to the C subunit, the myosin binding site is uncovered

Question 8

Each myofibril is surrounded by _________ and has __________

Answer 8

SR (with Ca2+ ions)

and has

T tubules

Question 9

normally tropomyosin is blocking the actin molecules from binding to myosin. in presence of high Ca2+ (>0.01 micrometer)

Answer 9

ca2+ binds to troponin at C site, which moves tropomyosin out of the way, so myosin heads can bind to the actin

Question 10

Process of action potential into muscle fibre

inititiation and contraction phase

Answer 10

1. ca2+ must increase in IC, either through SR or from outside
2. in presence of AP, Ca2+ channels on t-tubules open (called LTCC - L-type VGCC).
3. SR has some ca. LTCC is near to RyR2 (Rynedein receptor). when LTCC opens, it causes change to RyR2 receptors casuing it open. exit of ca into the sarcoplasm. mechanical gated.
4. ca2+ binds onto troponin C, tropomyosin is moved.
5. actin-myosin binding allowed.
6. myosin heads execute power stroke
7. actin filament slides toward centre of sarcomere

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Question 11

Sliding filament theory/the cross-bridge cycle

Answer 11

in attached m+a state:

1. atp binds to myosin head - weakens crossbridge which is formed with actin
2. ATP –hydrolysis–> ADP + Pi
   myosin heads return to their resting conformation –> cocked/relaxed/straightened
3. a crossbridge forms, myosin head binds to a new position on acgin = weak crossbridge as long as ADP + Pi is attached to it
4. Pi is released (hydrolysis) only ADP attached now –> straightens crossbridge
5. conformational change of myosin heads - power stroke
6. adp is released

Question 12

What happens during contraction?

Answer 12

HIZ = decrease
A = same

Question 13

Process of relaxation of muscle fiibres

relaxation phase

Answer 13

IT IS ENERGY DEPENDENT

1. (SERCA) sarcoplasmic Ca-ATPase pumps calcium back into the SR

**PLB protein = modulator of SERCA

2. extrusion of ca into ECF by the Na-Ca exchanger (NCX) = antiport, Ca out, 3Na in.
   Na then removed by Na-K pump
3. release of ca from tpnn-c

Question 14

During contraction:
L type LTCC
RyR2

Answer 14

During relaxation:
SERCA
PLB
NCX

Question 15

summary of CBC:

Answer 15

From c to r
ATP has to bind, and then it will release the bound state

Again, another ADP+Pi will bind
this can casue contraction

to strenthgetnh contraction and cause powerstroke Pi has to be released.

only ADP= strongest bound state

ADP unbinds, ATP binds

cycle repeats