Skeletal Muscle Contraction

Question 1

skeletal muscle

Answer 1

• long striated cells with multiple nuclei
• contraction for voluntary movement
• i band is isotropic-same color
• a is anisotropic- different color
• 40% body mass

Question 2

smooth muscle

Answer 2

• long spindle shaped cells with single nuclei
• hollow organs
• propulsion of substances along internal passageways

Question 3

cardiac muscle

Answer 3

• branching striated cells fused at PM

- pumps blood

Question 4

organization of skeletal muscle

Answer 4

• epimysium
• perimysium surrounds fascicles
• fascicles contain muscle fibers
• muscle fibers are surrounded by endomysium
• muscle fibers contain myofibrils which have sarcomeres
• sarcomere has A, I, H M, Z

Question 5

z line

Answer 5

boundary between two sarcomeres

Question 6

I band

Answer 6

only thin actin filaments (between thick)

Question 7

A band

Answer 7

-entire length of the thick filament

Question 8

H zone

Answer 8

-no overlap between actin and myosin, only myosin present

Question 9

M line

Answer 9

center of sarcomere

-thick filaments linked

Question 10

thick and thin filaments

Answer 10

• arranged in double hexagonal array
• myosin packed in hexagon pattern and each myosin surrounded by six actin filaments in the region where they overlap (A)
• each actin filament surrounded by 3 myosin filaments

Question 11

sliding filament model

Answer 11

• during contraction-
  1. Z lines move closer together
  2. the length of the A band is constant
  3. the length of the I band shortens
  4. as the sarcomere shortens, so does the muscle
• thick and thin slide past each other during contraction

Question 12

muscle myosin

Answer 12

• 6 protein complex with 2 heavy chains and 4 light chains
• arranged into thick filaments with heads sticking out
• there is a hinge region, globular region, and tail region
• heavy chains of 230,000 Da intertwined as double helix and terminates in two globular heads and four light chains (20,000Da)
• total MW 540,000

Question 13

myosin heavy chain

Answer 13

• single protein that contains globular region that binds actin and hydrolyzes ATP
• hinge region and tail region
• two heavy chains wind around each other in each myosin molecule

Question 14

regulatory light chain

Answer 14

• phosphorylated in striated muscles by Ca2+/calmodulin dependent myosin light chain kinase
• in fast twitch remain in phosphorylated form for a prolonged period after a brief tetanus or during low freq repetitive stimulation
• phosphorylation correlates with potentiation of the rate of development and maximal extent of isometric twitch tension

Question 15

essential light chain (alkali)

Answer 15

-fine tuning of the myosin motor function, regulated in an isoform and tissue dependent manner

Question 16

myosin filament (thick)

Answer 16

• 1.6 micron length
• A band
• 200 or more myosin molecules that point outward form the H zone
• successive myosin heads are axially displaced from the previous set by 120 degrees, heads protrude in all directoins
• each myosin head contains an ATPase catalytic site and an actin binding site

Question 17

excitation contraction coupling

Answer 17

1. motor AP travels along motor neuron to the motor endplate of the NMJ
2. nerve endings secrete Ach which acts on a local area of the sarcolemma to open numerous Ach gated channels
3. opening of these channels permits Na in and causes AP in muscle cell
4. AP propagates down T tubule membranes into the interior of the muscle fiber to the triad junction, where is causes release of Ca from SR
5. increased Ca causes the actin and myosin to interact, resulting in sliding motion that shortens the length of the sarcomere
6. the calcium is pumped back into the SR by the Ca-ATPase ion pump located in the SR, reducing the concentration of Ca in the SR, relaxing fiber
7. lengthening of the muscle is achieved by contraction of an antagonistic muscle

Question 18

triad

Answer 18

• 2 cisternae from SR
• 1 T tubule
• T tubules from PM, SR around myofibril
• ensure contraction of whole muscle

Question 19

tropomyosin and troponin

Answer 19

• regulate skeletal contraction
• calcium binds to troponin C and moves troponin T, I, and tropomyosin
• opens myosin binding sites on the actin

Question 20

tropomyosin

Answer 20

• a helical rod protein that covers the myosin binding sites on the thin filament
• blocks myosin from binding

Question 21

troponin

Answer 21

• 3 subunits- C, I ,T
• I has affinity for actin
• T binds to tropomyosin

Question 22

cross bridge cycle

Answer 22

• in presence of calcium and start at attached state
  1. ATP binds to myosin head, causing the dissociation of the actin-myosin complex (released state)
  2. ATP is hydrolyzed, causing myosin heads to return to their resting conformation (cocked state)
  3. cross bridge forms and the myosin head binds to a new position on actin (cross bridge)
  4. P is released and myosin heads change conformation (power stroke)
  5. ADP is released (attached)
• *Rigor mortis- Ca around but no ATP- stay in attached state
• • when no calcium, don’t need ATP to remain detached

Question 23

isometric twitch

Answer 23

• occur at constant muscle length
• muscle in fixed position
• stimulated with AP, force is measured as a function of time
• latent period between stim and contraction- time delay b/n AP and the activation of cross bridge cycle
• tension builds during contraction phase of the twitch and tension declines during relaxation
• contraction and relaxation periods closely parallel the levels of calcium the sarcoplasm that surrounds the sarcomere

Question 24

fast vs slow twitch muscle

Answer 24

• faster to generate tension or slower
• type of myosin heavy chain makes a difference
• speed of sarcoplasmic Ca elevation and clearance
• eye is fast twitch
• soleus is slow twitch

Question 25

Slow twitch

Answer 25

• Type I
• MYH7 gene
• Fatigue Resistant
• Red
• Oxidative
• High mito
• Low glygogen

Question 26

Fast Twitch 1

Answer 26

• Type IIa
• MYH2 gene
• Fatigue resistant
• red
• oxidative
• really high mito
• abundant glycogen

Question 27

Fast twitch 2

Answer 27

• Type IIb
• MYH4 gene
• Fatiguable
• white
• glycolytic energy
• few mito
• high glycogen

Question 28

isometric twitch 2

Answer 28

• can have passive tension from stretching a lot or additional tension from AP
• muscle doesn’t shorten, just makes tension
• difference between passive and additional tension is active tension
• active tension has a bell shaped curve and an optimal stretch because thats the optimum overlap of the thin and thick filaments (number of cross bridges is highest) (thin filaments reach the H zone)

Question 29

muscle fiber growth

Answer 29

• growth mediated by quiescent undifferentiated cells
• satellite cells
• basal lamina at the periphery of mature skeletal muscle fibers
• satellite cells mobilize to proliferate, differentiate, and fuse into multinucleate myofibers
• increases amt of nuclei and myofibril protein production as well as amt of sarcoplasm and CT

Question 30

myostatin

Answer 30

• knockout homoztgotes are body building mice and super baby-myostatin inhibits muscle growth
• altered satellite cell activation and muscle hypertrophy
• exercise and GH decrease myostatin (increase muscle growth)