Skeletal Muscle Cell and Contraction

Question 1

sarcolemma membrane

Answer 1

skeletal muscle cell membrane

contains T-tubles = invaginations

Question 2

T-tubules

Answer 2

dihydropyridine receptors = Ca channels

cell surface on T-tubules

Question 3

sarcoplasmic reticulum

Answer 3

intracellular calcium storage space

ryanodine receptors = Ca channels

Question 4

skeletal muscle cell contractile apparatus

Answer 4

sarcomere

Question 5

sarcomere

Answer 5

H-zone = only myosin thick filament (length changes with contraction)
A-band = length of the myosin thick filament (remains constant)
I band = contains actin thin filament (length changes with contraction)
Z-lines = demarcate sarcomere borders

Question 6

A band

Answer 6

length of myosin thick filament

DOES NOT change in length

Question 7

H zone

Answer 7

area of only myosin thick filament

length changes with contraction as Z-lines come together

Question 8

I band

Answer 8

contains actin thin filament

length changes with contraction as filaments move together

Question 9

skeletal muscle cell contraction

Answer 9

AP from nerve –> opens VG-Ca channels –> ACh released into synapse
ACh binds ACh receptors on muscle cell (muscle cell end plate)
muscle cell depolarizes –> travels down cell to T-tubules –> open dihydropyridine receptors

Question 10

dihydropyridine receptor

Answer 10

voltage-gated Ca channel activates and opens after depolarization of muscle cell from AP
causes Ca induced Ca release from the sarcoplasmic reticulum (ryanodine receptor activation)

Question 11

ryanodine receptor activation

Answer 11

increase in Ca release from sarcoplasmic reticulum where Ca is being stored
Ca leaves SR through ryanodine receptors

Question 12

Calcium in muscle cell contraction

Answer 12

Ca binds to troponin C
tropomyosin moves –> allows actin and myosin to bind each other = myosin-actin binding site (actin cross-bridge) revealed
myosin cross-bridge binds to actin cross bridge

Question 13

resting muscle

Answer 13

tropomyosin blocks actin-myosin binding site

Question 14

phases of actin-myosin crossbridging

Answer 14

1. resting muscle = actin-myosin unbound
2. binding of cross bridge to actin (Ca-binding to troponin causes conformational change in tropomyosin = exposes cross bridging site)
3. power stroke
4. release

Question 15

muscle cell contraction

Answer 15

I band = shortens
H zone = shortens
actin filaments pulled closer together
sarcomere length shortens

Question 16

power stroke muscle contraction

Answer 16

myosin in cocked state by binding ATP and hydrolyzes to ADP and inorganic phosphate

Question 17

dissociation of actin and myosin

Answer 17

binding of ATP to cross bridge causes loss of affinity for actin

Question 18

rigor mortis

Answer 18

stiffened state after death

absence of ATP in the dead = muscle remains contracted because myosin can’t release from actin

Question 19

Type I muscle fibers

Answer 19

slow twitch - red muscle fibers
long term aerobic metabolism - low ATPase activity
increased myoglobin (red color)
increased mitochondrial content
best for slow, posture-maintaining muscles (ex: back)

Question 20

Type II muscle fibers

Answer 20

fast twitch fibers - fast contraction
high ATPase activity - increased capacity for anaerobic glycolysis
decreased mitochondrial content
decreased myoglobin (white color0
best for fast, short-term, skilled muscles of eye, sprinter’s legs, hands
hypertrophies with weight training

Question 21

skeletal muscle denervation atrophy

Answer 21

muscle tissue atrophies
muscle fiber type grouping on histology and occurs with reinnervation (nerve repair) - Type I and Type II muscle fibers grouped together

Question 22

skeletal muscle disuse atrophy

Answer 22

prolonged disuse (bedridden)
angular atrophy - smaller muscle fibers with angular shape
primarily type II

Question 23

smooth muscle contraction

Answer 23

AP –> opens VG-Ca channels in sarcolemma

hormones and NTs –> open VG-Ca channels in SR

Question 24

Cardiac muscle contraction

Answer 24

inward Ca current during plateau –>

Ca release from SR

Question 25

phosphorylated myosin

Answer 25

more likely to interact with actin = more likely to have muscle contraction

Question 26

smooth muscle contraction Ca increase

Answer 26

1. increased intracellular Ca 2. Ca binds calmodulin 3. Ca-calmodulin bind to and activates myosin light chain kinase (MLCK) 4. myosin is phosphorylated 5. myosin-P binds actin and shortening occurs 6. dephosphorylation of myosin --> relaxation (by myosin light chain phosphatase)

Question 27

effect of alpha 1 and M3 muscarinic receptor stimulation on smooth muscle

Answer 27

increases IP3 increases intracellular Ca smooth muscle contraction

Question 28

beta 2 stimulation effect on smooth muscle contraction

Answer 28

increases cAMP inhibits MLCK (myosin light chain kinase) smooth muscle relaxation

Question 29

nitrate effects on smooth muscle contraction

Answer 29

nitrates converted to nitric oxide (NO) NO activates guanylate cyclase increase cGMP cGMP causes smooth muscle relaxation of blood vessels