B1W3: Skeletal Muscle

Question 1

Organization of Muscles

Answer 1

1. Whole muscle
2. Muscle fiber (muscle cell)
3. Myofibrils (within cell, sarcomeres)
4. Contractile filaments/proteins/structural proteins

Question 2

Titin

Answer 2

Attaches to Z line and keeps thick filaments in line during contraction

Question 3

CapZ

Answer 3

attaches actin filaments to Z line

prevents actin depolarization

Question 4

Nebulin

Answer 4

On thin filament

Maintains constant length of each filament

Question 5

Z line

Answer 5

Boundary of sarcomere

Where thin filaments attch

Question 6

I band

Answer 6

Thin filaments (and z disks)

“I is a thin letter”

Disappears during contraction

Question 7

A band

Answer 7

length of thick filaments

Thhin and thick filaments may overlap here

Question 8

H zone

Answer 8

Thick filaments only

“H is a thick letter”

disappears during contraction

Question 9

M line

Answer 9

Center of the thick filament

Structural protein

Question 10

Label

Answer 10

Question 11

Myosin components

Answer 11

Thick filaments

Two heavy chains for the tail, 4 light chains that form two globular heads

–actin binding site

–ATPase activity

Two of the light chains necessary, other two regulatory for smooth muscle

Question 12

Thin filaments

Answer 12

Two F-actin strands and two strands tropomyosin

Actin contains myosin binding sites

Troponin: 3 subunits, one binds Ca2+ and the other two bind tropomyosin and actin

Tropomyosin: regulatory protein that binds to actin and troponin (blocks active myosin binding sites)

Question 13

Hinges of myosin

Answer 13

One allows head to reach up and grab onto the myosin filament, another is at the myosin head and grabs onto actin

Question 14

Muscle Contraction Steps

Answer 14

1. Mysoin head is attached to actin in rigor state
2. ATP binds to myosin and myosin head releases actin
3. Myosin hydrolyzes ATP to “cock” myosin head
4. Myosin binds actin to form new cross bridge
5. Phosphate is released and myosin head has power stroke
6. ADP released

Question 15

How would no ATP impact skeletal muscle contraction?

Answer 15

1. Myosin head would not release actin
2. Ca2+ not pumped out of cell via (Ca/H+) pump
3. Ca2+ not pumped into SR

Question 16

How are skeletal muscles activated? How many nerve action potentials are needed for a muscle action potential?

Answer 16

Motor nerve impulses

Every nerve action potential will cause a muscle action potential

Question 17

What is the neurotransmitter released and ion that helps release it at neuromuscular junction?

Answer 17

AcH

Ca2+

Question 18

What kind of receptors does AcH in muscle cells bind to?

Answer 18

Ach binds to nicotinic receptor, increasing Na+ and K+ conductance

Depolarization because Na+ conductance has greater effect

Question 19

How does curare block muscle contraction?

Answer 19

Blocks Ach binding to nicotinic receptor completely

Question 20

Are you supposed to see end plate potentials?

Answer 20

NO! Every EPP=AP

if you see one, the neuromuscular transmission is fucked up (maybe Curare?)

Question 21

How does botulinum toxin block muscle contraction?

Answer 21

Cleaves V and T Snares on vesicles of presynaptic neuron

AcH is not released, muscle will not contract

Question 22

How would giving a patient with myasthenia gravis neostigmine (Acetylcholine esterase inhibitor) help treat their condition?

Answer 22

Neostigmine inhibits acetylcholinesterase

By blocking that enzyme, AcH builds up and not deraded, increases likelihood of muscle contraction

Question 23

T Tubules

Answer 23

Network of muscle cell membrane that carries depolarizations from action potentials

Contains DHP receptors that attach to ryanodine receptors on SR

Question 24

Sarcoplasmic reticulum

Answer 24

Stores calcium, releases it and re-uptakes it

Ryanodine receptors are opened by voltage-gated DHP receptors, cause release of Ca2+ into cell

Calsequestrin binds to calcium in SR to maintain low free conc.

SERCA helps pump Ca2+ in

Question 25

Triad

Answer 25

T tubule SR--terminal cisternae

Question 26

Excitation-Contraction Coupling

Answer 26

Action potential due to Na+ current leads to Ca2+ release into the cell from the sarcoplasmic reticulum AP causes depolarization of DHP receptor, which releah opens ryanodine channel and Ca2+ into cell from SR When done, SERCA pumps Ca back into cell

Question 27

Maliganant hyperthermia

Answer 27

SR Ca2+ channels genetically altered, and this appears under anesthesia SR Ca2+ channels do not close properly, Ca2+ leaks into cytoplasm causing sustained contractions, generating heat (NOT GOOD!)

Question 28

Isometric

Answer 28

Same length, contraction without shortening of muscle i.e. lifting bar

Question 29

Isotonic

Answer 29

Same force, muscle contraction with shortening of muscle Lifting dumbell over and over again

Question 30

Quantal summation

Answer 30

As more motor units are recruited, the strength of the muscle contraction increases

Question 31

Temporal summation

Answer 31

Stimulating contractions at a higher frequency, causing increased strength

Question 32

Treppe

Answer 32

after a long period of rest, initial muscle contraction may not be as strong as later stimuli of same strength (i.e. why warm up before working out)

Question 33

Tetanization

Answer 33

Contrations so frequent muscle cannot relax bc Ca2+ not pumped into SR fast enough

Question 34

Twitch contractions

Answer 34

Summate to one steady contraction

Question 35

Passive tension

Answer 35

Tension developed by stretching muscle to diff. lengths

Question 36

Active tension

Answer 36

Total tension-passive tension =degree overap between filaments capable of generating cross bridges

Question 37

What happens to muscle as length increases above normal?

Answer 37

Tension before contraction increases and contractile force decreases at longer lengths At a long enough length, tension before contraction=total force, no contractile force generated

Question 38

Resting length and filaments

Answer 38

Optimal overlap thin and thick filaments

Question 39

Force-Velocity relationships

Answer 39

Velocity decreases as load increases Vmax constant for specific given skeletal muscle Load is so much, V=o at isometric contraction V=max when load is 0

Question 40

When is active force maximum?

Answer 40

Normal length, resting length, or optimal length (all the same)

Question 41

Fast fibers (white)

Answer 41

Larger fibers Fast twitch myosin isoform Less extensive blood supply No myoglobin; abundant glycolytic enzymes, fewer mitochondria

Question 42

Slow fibers (red)

Answer 42

smaller fibers slow twitch myosin isoform more mitochondria, contain myoglobin extensive blood supply adapted for slow, continuous activity