structure and function of exercising muscle

Question 1

what are the functions of skeletal muscle

Answer 1

• force generation for locomotion and breathing
• force generation for postural support
  -heat production during cold stress
  -communication

Question 2

describe the 3 types of muscle

Answer 2

-smooth: involuntary, slow, spindle shaped and 1 nuclei
-cardiac: heart, involuntary, in between, branched, 1 or 2 nuclei, striated
-skeletal: attached to bone, voluntary, fast, straight, many nucleis, striated

Question 3

what are the 4 properties of muscle

Answer 3

Excitability: Capacity to respond to a stimulus
* Contractility: ability to shorten and generate force
* Extensibility: ability to stretch
* Elasticity: ability to recoil to original resting
length after stretched

Question 4

what surrounds the entire muscle

Answer 4

-epimysium
-consists of many bundles (fasciculi)

Question 5

what is the fasciculi surrounded by

Answer 5

perimysium
it consists of individual muscle cells

Question 6

what is the muscle fiber surrounded by and what does is consists of

Answer 6

surrounded by endomysium
consists of myofibrils divided into sacromeres

Question 7

what is the function of the plasmalemma(cell membrane)

Answer 7

-fuses with tendon
-conducts action potential
-maintains pH, transports nutrients

Question 8

what is the function of the sarcoplasm

Answer 8

– Cytoplasm of muscle cell
– Unique features: Glycogen storage, myoglobin

Question 9

what is the function of the t tubules

Answer 9

– Extensions of plasmalemma
– Carry action potential deep into muscle fiber

Question 10

what is the function of the sarcoplasmic reticulum

Answer 10

calcium (Ca2+) storage

Question 11

what are the sarcomeres?

Answer 11

– Basic contractile element of skeletal muscle
– End to end for full myofibril length

Question 12

what are the 4 different striped appearances of the sarcomeres?

Answer 12

– A-bands: dark/blue stripes (actin + myosin)
– I-bands: light/pink stripes (only actin)
– H-zone: middle of A-band (only myosin)
– M-line: middle of H-zone
* Common boundary structure: Z-disk (or Z-line)

Question 13

what are the 3 proteins of actin

Answer 13

– Actin: contains myosin-binding site
– Tropomyosin: covers active site at rest
– Troponin: anchored to actin, moves tropomyosin

Question 14

what is the structure of myosin

Answer 14

• Two intertwined filaments with globular heads
• Globular heads
  – Protrude 360° from thick filament axis
  – Will interact with actin filaments for contraction

Question 15

what is the process of actin and myosin in a relaxed state ?

Answer 15

– No actin-myosin interaction at binding site
– Myofilaments overlap a little

Question 16

what is the process of actin-myosin contraction in a contracted state ?

Answer 16

– Myosin head pulls actin toward sarcomere center (power stroke)
– Filaments slide past each other
– Sarcomeres, myofibrils, muscle fiber all shorten

Question 17

what happens after the power stroke ?

Answer 17

– Myosin detaches from active site
– Myosin head rotates back to original position
– Myosin attaches to another active site farther down

Question 18

the process continues until

Answer 18

– Z-disk reaches myosin filaments or
– AP stops, Ca2+ gets pumped back into SR

Question 19

what happens when AP arrives at SR from T tubule

Answer 19

– SR sensitive to electrical charge
– Causes mass release of Ca2+ into sarcoplasm

Question 20

what happens when Ca2+ binds to troponin on actin

Answer 20

– At rest, tropomyosin covers myosin-binding site
– Troponin-Ca2+ complex moves tropomyosin
– Myosin binds to actin, forming a cross-bridge, allowing a
contraction to occur

Question 21

when ATP binds to myosin head, what does ATPase on myosin breaks ATP to?

Answer 21

– ATPase on myosin head
– ATP  ADP + Pi + energy

Question 22

what are the steps of excitation contraction coupling

Answer 22

1. Action potential (AP) starts in brain
2. AP arrives at axon terminal, releases acetylcholine (ACh)
3. ACh crosses synapse, binds to ACh receptors on plasmalemma
4. AP travels down plasmalemma, T-tubules
5. Triggers Ca2+ release from sarcoplasmic reticulum (SR)
6. Ca2+ enables actin-myosin contraction

Question 23

what happens when the muscle relaxes

Answer 23

• AP ends, electrical stimulation of SR stops

Question 24

where does the Ca2+ go when the muscle relaxes

Answer 24

• Ca2+ pumped back into SR
  – Stored until next AP arrives

Question 25

without___, troponin and tropomyosin return to resting conformation

Answer 25

Ca2+

Question 26

what is the resting conformation of troponin and tropomyosin

Answer 26

– Covers myosin-binding site
– Prevents actin-myosin cross-bridging