Skeletal Muscle Contraction Flashcards
1
Q
skeletal muscle
A
- long striated cells with multiple nuclei
- contraction for voluntary movement
- i band is isotropic-same color
- a is anisotropic- different color
- 40% body mass
2
Q
smooth muscle
A
- long spindle shaped cells with single nuclei
- hollow organs
- propulsion of substances along internal passageways
3
Q
cardiac muscle
A
- branching striated cells fused at PM
- pumps blood
4
Q
organization of skeletal muscle
A
- 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
5
Q
z line
A
boundary between two sarcomeres
6
Q
I band
A
only thin actin filaments (between thick)
7
Q
A band
A
-entire length of the thick filament
8
Q
H zone
A
-no overlap between actin and myosin, only myosin present
9
Q
M line
A
center of sarcomere
-thick filaments linked
10
Q
thick and thin filaments
A
- 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
11
Q
sliding filament model
A
- 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
12
Q
muscle myosin
A
- 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
13
Q
myosin heavy chain
A
- 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
14
Q
regulatory light chain
A
- 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
15
Q
essential light chain (alkali)
A
-fine tuning of the myosin motor function, regulated in an isoform and tissue dependent manner
16
Q
myosin filament (thick)
A
- 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
17
Q
excitation contraction coupling
A
- motor AP travels along motor neuron to the motor endplate of the NMJ
- nerve endings secrete Ach which acts on a local area of the sarcolemma to open numerous Ach gated channels
- opening of these channels permits Na in and causes AP in muscle cell
- 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
- increased Ca causes the actin and myosin to interact, resulting in sliding motion that shortens the length of the sarcomere
- 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
- lengthening of the muscle is achieved by contraction of an antagonistic muscle
18
Q
triad
A
- 2 cisternae from SR
- 1 T tubule
- T tubules from PM, SR around myofibril
- ensure contraction of whole muscle
19
Q
tropomyosin and troponin
A
- regulate skeletal contraction
- calcium binds to troponin C and moves troponin T, I, and tropomyosin
- opens myosin binding sites on the actin
20
Q
tropomyosin
A
- a helical rod protein that covers the myosin binding sites on the thin filament
- blocks myosin from binding
21
Q
troponin
A
- 3 subunits- C, I ,T
- I has affinity for actin
- T binds to tropomyosin
22
Q
cross bridge cycle
A
- 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
23
Q
isometric twitch
A
- 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
24
Q
fast vs slow twitch muscle
A
- 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
25
Q
Slow twitch
A
- Type I
- MYH7 gene
- Fatigue Resistant
- Red
- Oxidative
- High mito
- Low glygogen
26
Q
Fast Twitch 1
A
- Type IIa
- MYH2 gene
- Fatigue resistant
- red
- oxidative
- really high mito
- abundant glycogen
27
Q
Fast twitch 2
A
- Type IIb
- MYH4 gene
- Fatiguable
- white
- glycolytic energy
- few mito
- high glycogen
28
Q
isometric twitch 2
A
- 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)
29
Q
muscle fiber growth
A
- 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
30
Q
myostatin
A
- 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)
