Exicatory Contraction Coupling

Question 1

Dantrolene method of action

Answer 1

Inhibits ryanodine receptors in the sarcoplasmic reticulum and blocks the release of calcium
Used to treat malignant hyperthermia that occurs after exposure to succinylcholine; (succinylcholine can cause excessive Ca release from SR causing skeletal muscle contractions, rapid increase in temperature, renal failure)

Question 2

What happens after skeletal muscle cell is stimulated at the NMJ

Answer 2

AP spreads over surface and down T tubules
Causes DHP receptors to physically alter the state of ryanodine receptors, causing Ca channels to open
Ca diffuses out of SR and binds to troponin
This interaction causes tropomyosin to pull off of binding sites of actin, allowing myosin to bind

Question 3

Each myosin molecule is associated with _ actin molecules

Answer 3

6

Question 4

Nebulin

Answer 4

Long molecule which helps align actin

Question 5

Titan

Answer 5

Large/long elastic protein associated with myosin and anchors it within the sarcomere. Also helps return a stretched sarcomere to its resting length

Question 6

Dystrophin

Answer 6

Huge protein that connects the muscle cell cytoskeleton including actin to the EC matrix and CT
Works like a shock absorber during contraction
Stabilizes the sarcolemma and prevents contraction induced injury. Without dystrophin- muscle fibers are easily injured

Question 7

Myosin/Actin interaction process during contraction

Answer 7

Myosin, bound to ADP and Pi, bind the actin site
Pi is released causing myosin head to pull actin past it
ADP is replaced by ATP, causing myosin head to unbind
ATP hydrolyzed, causing the myosin head to recock
Cycle continues until Ca is resequestered into the SR

Question 8

Peripheral fatigue

Answer 8

Contraction requires the availability of ATP

Question 9

Central fatigue

Answer 9

Perception of fatigue or loss of motivation possibly brought on by increasing levels of byproducts of contraction such as lactic acid or free hydrogen ion

Question 10

Force of contraction

Answer 10

Dependent on the starting length of sarcomere
Maximum force can be generated near middle of length extremes, which is where you get most efficient binding of actin/myosin
Force is depended on how fast the fiber is stimulated by nerve

Question 11

Length-tension dependent force

Answer 11

If sarcomere is very short, the myosin cannot pull the actin very far before it hits the Z-line.
If sarcomere is very long, many myosin heads will have been pulled away from proximity of the actin molecule- bigger H-zone

Question 12

Stimulation dependent force of contraction

Answer 12

If second twitch is initiated before complete relaxation, the second twitch generates a larger force
The greater the frequency of stimulation, the greater the potential force
Overlap of twitches without complete relaxation is referred to as tetanus

Question 13

A neuron that innervates more fibers will generate a greater or lesser force than one that innervates fewer fibers

Answer 13

Greater

Question 14

Actin polymerization and ATP

Answer 14

ATP is not required for polymerization, but it occurs faster when it is present instead of ADP

Question 15

Rate of actin subunit association/dissociation in relation to monomer concentration

Answer 15

Rate of association is proportional to the concentration of free monomers, while the rate if dissociation is independent of concentration

Question 16

Actin filaments are particularly abundant where

Answer 16

Beneath the plasma membrane

Question 17

Fimbrin

Answer 17

Forms actin into tight parallel bundles aligned with the same polarity, preventing myosin II from entering bundle

Question 18

a-actinin

Answer 18

Forms actin into loose contractile bundles, allowing myosin II to enter bundle
Forms contractile ring used in mitosis to cause cell division

Question 19

Filamin

Answer 19

Creates 3-D meshwork of actin that is needed in cells that need to withstand a lot of force

Question 20

Filopodia

Answer 20

Thin projections of plasma membrane supported and created by actin

Question 21

Lamellipodia

Answer 21

Broad, sheet like extension at leading edge of cell, containing actin

Question 22

Pseudopodia

Answer 22

Based on actin linking into 3-D network, responsible for phagocytosis

Question 23

Spectrin

Answer 23

Actin binding protein that forms a network which creates a cortical cytoskeleton that interacts with membrane proteins
Mutation in spectrin, ankyrin, protein 4.1 all cause hereditary spherocytosis- impaired deformability and reduced stability of RBCs
Membranes break down, RBCs damaged and die
-anemia, jaundice, splenomegaly

Question 24

Myosin I

Answer 24

Membrane association, endocytosis

Question 25

Myosin II

Answer 25

Contraction

Question 26

Myosin V

Answer 26

Organelle transport

Question 27

Power-stroke of myosin head is proportional to

Answer 27

Length of neck domain

Question 28

Duchene muscular dystrophy

Answer 28

X-linked recessive- affects boys
Progressive muscle wasting
Wheelchair by 12, death by 22