Muscle Contraction

Question 1

What kind of receptor does skeletal muscle have?

Answer 1

Nicotinic

Question 2

Motor nerves release ____

Answer 2

acetylcholine

Question 3

The acetylcholine-nicotinic receptor interaction results

Answer 3

in the nicotinic receptor opening as a sodium channel

Question 4

Skeletal muscle depolarization causes activation of __________

Answer 4

L calcium channels (dihydropyridine receptors)

Question 5

Calcium entry into muscle releases calcium from intracellular storage sites (sarcoplasmic reticulum) via ___________

Answer 5

calcium-induced calcium release (ryanodine receptors - physically coupled, don’t actually need Ca to go into cell)

Question 6

Elevated intracellular calcium concentrations result in _______

Answer 6

calcium binding to troponin C

Question 7

calcium binding to troponin C

—-> ____________

Answer 7

releases inhibition of actin-myosin interactions

Question 8

______ heads then contact ________ to create muscle shortening and force generation, provided ________ is present

Answer 8

Myosin - actin

Requires ATP

Question 9

acetylcholinesterase

Answer 9

breaks down acetylcholine into choline and acetate to stop signal

Question 10

______ indicate borders of sarcomere

Answer 10

Z lines indicate borders of sarcomere

Question 11

Muscle __ band remains same size but ____ bands decrease in width

Answer 11

A band

I band

Question 12

Power stroke occurs as a result of _______

Answer 12

Release of Phosphate after cleaving ATP –> ADP + Pi which cocked the myosin head

Question 13

When is ADP released during muscle contraction?

Answer 13

During/because of power stroke

Question 14

_______ allows myosin head to be released from actin

Answer 14

Binding of ATP

Question 15

Amyotrophic lateral sclerosis

Answer 15

degeneration of motor neurons

Question 16

Lambert-Eaton syndrome

Answer 16

antibodies against Ca channels in motor neurons resulting in inability to release Ach

Question 17

Botulism toxin

Answer 17

prevents Ach release by cleaving synaptic associated proteins (SNAPs)

Question 18

Myasthenia gravis

Answer 18

autoantibodies against nicotinic receptors in skeletal muscle

Question 19

Malignant hyperthermia

Answer 19

caused by mutation of ryanodine receptor allowing excessive release of Ca - usually triggered by anesthetics

Question 20

Duchenne’s muscular dystrophy

Answer 20

mutation in dystrophin, skeletal muscle support protein

Question 21

Pesticides and nerve gases

Answer 21

Pesticides and nerve gases are anticholinergics (acetylcholinesterase inhibitors) → overstimulation of nicotinic receptors

Question 22

Amount of force generated by muscle directly proportional ______

Answer 22

to number of actin-myosin crossbridges per cross-sectional area

Work best when considerable overlap between actin and myosin
Stretched muscle → actin/myosin no longer interacting → no strength
As shorten muscle → actin and myosin interacting, force increases linearly
Maximal point - maximal # cross bridges (no more in center)
If go past that - disordered by no more cross bridges

Question 23

Force-velocity relationship

Answer 23

Muscles contract most rapidly when there is no load on the muscle

Question 24

Isotonic contraction

Answer 24

Load on muscle is constant

Question 25

Isometric contration

Answer 25

Load is larger than muscle’s ability to move it (shorten tendon, but can’t move bony attachment)

Question 26

Type I muscle Fiber

Answer 26

Slow twitch
Slower myosin ATPase enzyme
High proportions in distance runners or in postural muscles (soleus)
Contain lots of myoglobin → “Red Fibers”
Need myoglobin because they require a lot of oxygen to maintain contractions

Question 27

Type II muscle fiber

Answer 27

High proportions in extraocular muscles of eye
Faster myosin ATPase
White fibers (less myoglobin)
Anaerobic metabolism

Question 28

Concentric contractions

Answer 28

Muscle contracts resulting in shortening

Typical biceps curl in weightlifting

Question 29

Eccentric contractions

Answer 29

Muscle lengthens while attempting to shorten
Much more damage to muscle with this type of contraction 
Running downhill (trying to contract while stretching)

Question 30

Muscle conduction to contraction

Answer 30

AP depolarization opens presynaptic VG Ca channels inducing NT release –> Postsynaptic ligand binding leads to muscle cell depolarization in motor end plate –> depolarization travels along muscle cell and down Ttubule –> Depolarization at Voltage-sensitive DHP receptor, mechanically coupled to ryanodine receptor on SR, induced conformational change causing Ca release from SR –> release Ca binds to troponin C causing conformational change that moves tropomyosin out of myosin-binding groove on actin filaments –> myosin releases bound ADP and Pi - displacement of myosin on actin filament (power stroke) –> binding of new ATP molecule causes detachment of myosin head from actin filament, hydrolysis of ATP to ADP + Pi cocks head

Question 31

Contraction of muscles results in what of bands

Answer 31

H and I bands shorten between Z lines (HIZ shrinkage)

A band is Always same length

Question 32

Darker regions contain ______

Lighter regions contain ______

Answer 32

dark - myosin

lighter - actin

Question 33

Motor neurons release _____

Answer 33

acetylcholin

Question 34

Cardiac muscle has ___ channels, more reliant on

Answer 34

L channels, ca-induced-ca-release (not physically coupled)

Question 35

Smooth muscle contraction controlled by

Answer 35

Ca interacting w/ calcium dependent myosin light chain kinase