SKELETAL PT 2

Question 1

describe how muscle fiber type shifts

Answer 1

with loading (exercise training), IIX goes down and with unloading (like a space flight or spinal cord injury), IIX amount goes up

Question 2

why do IIX fibers increase with inactivity

Answer 2

because I and IIA use a lot of oxygen, so it’s a lot of work to keep them up

Question 3

describe aerobic training and muscle fiber type

Answer 3

less IIA, more I

Question 4

describe motor units

Answer 4

vary in size; consists of a motor neuron and all muscle fibers they supply

Question 5

how are muscle fibers dispersed through a muscle

Answer 5

muscle fibers from a motor unit spread throughout the whole muscle, so stimulation of a single motor unit causes only weak contraction of muscle

Question 6

what principle so motor units follow

Answer 6

all or none principle

Question 7

what are the three types of muscle fibers

Answer 7

type I (slow), type IIA (fast fatigue-resistant), type IIX (fast fatiguable)

Question 8

describe type IIX motor fibers

Answer 8

fast fatiguable, large motor units with high innervation ratio, fast twitch

Question 9

describe IIA motor fibers

Answer 9

large motor units, more sustained but less dramatic twitch; more fatigue resistant but still fatiguable

Question 10

describe type I fibers

Answer 10

small motor neurons, low innervation ratio, slow twitch and fatigue resistant

Question 11

what is excitation-contraction coupling

Answer 11

process of pairing electrical events (motor neuron AP) to mechanical events (muscle contraction); aka events that occur between excitation and coupling

Question 12

where does EC coupling occur

Answer 12

synapse of junction of motor neuron axon terminal with muscle fiber motor end plate (very excitable region of muscle fiber plasma membrane)

Question 13

what neurotransmitter is released at neuromuscular junction

Answer 13

acetylcholine

Question 14

describe the first step of EC coupling process

Answer 14

have signal that sent do somatic motor neuron,
which is a depolaorizing event

Question 15

describe the second step in EC process

Answer 15

at neuromuscular junction, we release Ach, which binds
to receptors on skeletal muscle membrane, which allows for depolairzation
of skeletal muscle membrane

Question 16

describe the third step in EC process

Answer 16

opening of Na channels, which causes influx of Na which causes depolirzation

Question 17

describe the fourth step in the EC process

Answer 17

depolariization goes down t-tubules; along t-tubules on either side is a bunched up
part of the sarcoplasmic reticulum

Question 18

describe the 5th step in the EC coupling process

Answer 18

ca binds to tropnin, which tells tropomyosin to move from actin

Question 19

describe the sixth step of EC process

Answer 19

myosin can bind to actin and allow for contraction

Question 20

whats the cross bridge

Answer 20

binding site of ATP on each molecule

Question 21

what is cross bridge formation triggered by

Answer 21

Ca2+ cycle

Question 22

whats the first step in cross bridge formation

Answer 22

active site on actin is exposed as Ca binds to troponin

Question 23

whats the second step in cross bridge formation

Answer 23

myosin head forms a cross-bridge with actin

Question 24

whats the third step of cross bridge formation

Answer 24

during power stroke, myosin head bends and ADP and phosphate are released

Question 25

whats the fourth step in cross bridge formation

Answer 25

a new molecule of ATP attaches to the myosin head, causing the cross-bridge to detach

Question 26

whats the fifth step in crossbirdge formation

Answer 26

ATP hydrolyzes to ADP and phosphate, which returns myosin to cocked position

Question 27

describe the skeletal muscle length-tension relationship

Answer 27

describes the amount of tension that is produced by a muscle as a feature of it's length

Question 28

what are skeletal muscle satellite cells

Answer 28

skeletal muscle stem cells, that are multipotent and give rise to more satellite cells, differtnited skeletal muscle cells, myonuclei

Question 29

how much nuclear material belongs to true myonuclei

Answer 29

85 - 95% (i.e. located inside plasma membrane)

Question 30

how much of nuclear material are satellite cells

Answer 30

5 - 15%; located between basement membrane and plasma membrane

Question 31

how many nuclei per fiber length do satellite cells have

Answer 31

approx. 200 - 300 nuclei per mm of fiber length (contrast to many other cells in our body which are usually single nucleus)

Question 32

why are satellite cells/myonuclei important

Answer 32

growth + development of muscle adaptive capacity of skeletal muscle recovery from injury or neuromuscular disease

Question 33

where is nuclear material located

Answer 33

between myofiber basement and plasma membrane

Question 34

describe satellite cell role in myofiber hypertrophy

Answer 34

not completely known; but as fiber grows, there is need for new myonuclei to maintain myonuclear domains

Question 35

whats the myonuclear domain theory

Answer 35

every nuclei within the muscle fiber is responsible for a specific amount of volume within the cell, so we can only make muscle grow if we get more nuceli involved so satellite cells donate

Question 36

describe the first step in myonuclear donoation

Answer 36

untrained muscle fiber

Question 37

describe the second step in myofiber donation

Answer 37

training muscle fiber increases in size; each myonuclei is near its domain ceiling

Question 38

describe the third step in myonuclei donation

Answer 38

satellite cells fuse to the muscle fiber, donating nuclei

Question 39

describe the fourth step of myofiber / myonuclear donation

Answer 39

muscle fiber now has more nuclei; therefore, it's growth capacity has increased

Question 40

different between the two possible response to fiber stress

Answer 40

hypertrophy (fibers grow in size - humans); hyperplasia (fibers grow in number)

Question 41

describe regenerating normall musclle fiber

Answer 41

myonuclei + satellite cell

Question 42

describe regenerating damaged muscle fiber

Answer 42

activated + proliferating satellite cells

Question 43

describe regenerating repairing muscle fibers

Answer 43

muscle precursors cells derive from satellite cells have fused

Question 44

describe generating regenerated muscle fibers

Answer 44

with new satellite cell and centrally-placed, newly-generated myonuclei

Question 45

describe the calcium/tropnonin/tropomyosin relationship

Answer 45

Ca connects to troponon, which tells tropomyosin to get off binding sites so myosin can attach

Question 46

where is calcium stored and what happens when that thing is depolarized

Answer 46

Ca stores in sarcoplasmic reticulum; when depolaorized, Ca ion channels open up and let Ca into sarcoplasm which lets everything happen

Question 47

what are the three parts of the power stroke

Answer 47

- adp and P on myosin = myosin can grab actin - adp and P leave myosin, nothing on myosin and can pull in - atp on myosin, myosin releases actin