muscle 1

Question 1

what is muscle attached to

Answer 1

tendons on either side of joint then tendons attached to bones

Question 2

what do stripes indicate

Answer 2

underlying molecular mechanisms that enable muscle fiber to contract

Question 3

what are muscle fibers generated from

Answer 3

Muscle fibers are generated during development by the fusion of a large number of small precursor cells called myoblasts. Each myobast has a single nucleus, whereas the fiber is a multinucleated cell.

Question 4

why is it good that muscle fiber is long and thin and mutilnucleated

Answer 4

long and thin = muscles make lots of proteins that fill up fiber and is responsible for contraction
sites of mrna synthesis all down length of muscle fiber = enables proteins to be synthesized locally all down length of fiber (more genes copies = more proteins it can make)

Question 5

describe myofibrils

Answer 5

make up skeletal muscle fibers
made of protein
dark and light stripes lined up together = molecular machinery

Question 6

what does myofibrils lined up together cause

Answer 6

allows fiber to contract as single unit, maximizes amount of force and efficiency

Question 7

describe bands or lines of sarcomere

Answer 7

i band = light
each i band = z line in middle
a band = dark

Question 8

describe how contract

Answer 8

sarcomere contract = myofibrils contract = muscle fiber contracts = muscle contracts

Question 9

describe filaments of sarcomere

Answer 9

thick filaments extending from one end of the A band to the other
thin filaments, attached to the Z lines and extending across the I band-and part way into the A band

Question 10

describe cross bridges

Answer 10

part of thick filaments = interact with thin filaments and causes muscle to contract

Question 11

describe distribution of thick and thin filaments in sarcomere

Answer 11

thick = each surrounded by halo of 6 thin
thin = surrounded by 3 thick
matrix of thin and thick - crystalline arrangement

Question 12

what is in i band

Answer 12

thin = actin

Question 13

what is h zone

Answer 13

only think

Question 14

what is a band

Answer 14

overlap of thick and thin filaments
overlap = critical for contraction of muscle

Question 15

describe thin filaments

Answer 15

actin - 2 chains of globular actin subunits twisted into helix
sticks to itself and forms long thin fiber

Question 16

describe thick filaments

Answer 16

myosin
forms long thin filament with head
bundles = thick filament
bundles attached together tightly = m line

Question 17

describe sliding filament model

Answer 17

head groups of thick reach out and gab thin and pull over thick = pulls z lines closer together and they let go and then pull again = cycle
head groups act independently = has no idea what other groups are doing - all are in diff phases of cycle
driven by atp hydrolysis

Question 18

do thin and thick filaments change in length

Answer 18

nO
stay same but overlap becomes greater

Question 19

Contraction of sarcomeres

Answer 19

shortens entire myofibril

Question 20

what does the amount of tension a muscle fiber can develop depend on

Answer 20

fiber length
length-tension relation reflects degrre of overalp between thick and thin filaments

Question 21

describe length-tension ratio

Answer 21

too contraction = muscle fiber runs into z lines = has no place to go
optimal range
no overlap = no contraction, too spread out, like lift something heavy and arms stretched out
holding something heavy in place - myosin head groups reach out and grab actin and pull but are not getting anywhere and keeps happening, thin filaments not moving, since being pulled apart as strongly as they are being pulled together by head group

Question 22

what is cross bridge cycle driven by

Answer 22

atp binding and hydrolysis by myosin head groups
lots of phosphat and energy to drive cycle

Question 23

describe cross bridge cycle

Answer 23

head group can bind and hydrolyze atp = converts to adp + p and both remain bound to head group, energy used to do something = recock head groups, build up tension, potential energy
head group in place now = stretched out and locked in place
myosin binds to actin, actin has binding sites for myosin head groups
power stroke = pulling, triggers conformational change, adp and p are released = comes off and triggers another step = conformational change
uncocked position = pulls actin over thick filament
atp binds it again and enables head group to let go of filament

Question 24

describe mouse trap

Answer 24

rigor mortis
muscles stiffen up
after a while muscle degenerates
happens due to cycle, since no more atp being made
atp enables head groups to let go, head groups get stuck in position

Question 25

describe muscle fatigue

Answer 25

concentrations of atp never change - fairly constant usually to protect muscle - kicks in before atp concentrations drop a lot

Question 26

How is contraction of voluntary muscle initiated?

Answer 26

motor cortex Neuron’s activated = fire aps activates efferent motor neurons

Question 27

what is motor unit

Answer 27

A motor neuron and the group of muscle fibers it innervates unit = smallest increment of contraction cell bodies in ventral part of grey matter each muscle fiber is only innervated by one motor neuron - one synapse each motor neuron innervates many muscle fibers mutiple muscle Fibers innervated by a single motor neuron

Question 28

how many fibers innervated by single motor neuron

Answer 28

Number of fibers innervated by a single motor neuron may range from 10 size (e.g. extraocular muscles) to 100 (muscles of the hand) to several thousand (large flexor and extensor muscles of leg).

Question 29

describe structure of neuromuscular junction

Answer 29

synapse nicotinic ach receptors ligand gated ion channels when bind ach specialized region of muscle - post synaptic membrane of muscle fiber = end plate

Question 30

describe steps of neuromuscular transmission

Answer 30

1-action potential in motor neuron = ca channels open up in presyn terminal, ca flows in and vesicles fuse 2-ach release at presynap term into synaptic cleft 3-na influx through activated nicotinic ach receptors 4 - enplate potential (epsp, very large depolarization, motor neuron gets past threshold) 5 - fiber action potential (whole rest of fiber has na voltage gated, specialized, ap starts at end plate and shoors out rapidly = single contracted unit)

Question 31

describe t tubules

Answer 31

tubes that extend into muscle fiber but are continuations of outside of cell hole in membrane and forms tube inside muscle cell - connects inside to outside of cell

Question 32

what do t tubules and sarcoplasmic reticulum allow

Answer 32

ap to get inside cell

Question 33

describe sarcoplasmic reticulum

Answer 33

intraceullar membrane network - for calcium ions storage site inside cell but still separated from intracellular machinery

Question 34

describe excitation-contraction coupling - gen

Answer 34

t tubule = essential for ability of action potential to communicate with contractile machinery and cause muscle to actually contract DHP receptor= calcium channels, ion channels, binds dihydropyridines (in t tubule) ryanodine receptor = ion channel permeable to calcium, different kind of channel - in sr (stores calcium)

Question 35

describe excitation-contraction coupling - specifics

Answer 35

ap comes along activates voltage gated ca channels if these plug up = muscle still contracts = doesnt trigger contarction bc not enough ca but still critical DHP receptors activated and change shape and pushes on channels - linkage so calcium flows out inside sr = small calcium level --> big increase of caclium inside muscle due to sr releasing rapidly muscle contratcs due to calcium

Question 36

describe activation of ryanodine receptor

Answer 36

ca activates dhp receptor and changes conformation and pushes on ryanodine receptor and opens channel and ca flows out into cytoplasm of cell physical linkage

Question 37

describe main role of t tubule

Answer 37

sense depolarization and changes shape and conveys message to ryanodine receptors in sr

Question 38

what does calcium released from sr do

Answer 38

binds troponin on thin filaments Causes conformational chnage in troponin = moves tropomyosin molecule away from myosin binding site on actin = then can bind heads of thick filaments

Question 39

describe tropomyosin

Answer 39

long thin protein wraps around actin filaments covers up binding sites for myosin head groups when muscle is relaxed all troponin binds at same time and then pushes tropomyosin away from binding sites

Question 40

what is contraction of muscle fiber

Answer 40

in response to a single ap = twitch twitch lags behind muscle ap - because of delays with excitation contratcion coupling duration of contraction reflects time it takes for ca in cell to return to baseline

Question 41

describe process of muscle contraction

Answer 41

fiber doesn't begin to contract until ap over delay before fiber begins to contract = 5-6 ms = many steps between ap and contraction muscle contraction very rapidly = 30-40ms starts to relax = 120,140ms back to og state relaxing = amountof time it takes to pump ca back into sr

Question 42

what is summation

Answer 42

applies to individual muscle fibers Single action potentials in the motor neuron, spaced more than a few hundred milliseconds apart, cause a transient twitch of the muscle fiber. if the action potentials are applied more rapidly, the twitches begin to add together. Motor neurons typically fire in bursts, resulting in, sustained contraction of the muscle fiber, called tetanus.

Question 43

what is unfused tetanus

Answer 43

oscillating state stimulate motor neuron over and over twicthes and then relaxes eventually = reaches steady state

Question 44

what is fused tetanus

Answer 44

as increase aps = adds up a bunch leads to ca levels being super high and leads to stable state more substantial contraction

Question 45

how to generate force

Answer 45

not due to twitch vs fused tetanus we do it bu how many individual fibers get activated = recruitment

Question 46

describe Generation of muscle tension

Answer 46

Force generated by a muscle is called tension. The tension exerted by a whole muscle is controlled by recruitment (an increase in the number of active fibers) and by summation (the additive effects of several closely spaced twitches) Skeletal muscle is adapted for large force generation over a narrow operating range.

Question 47

what is an important mechanism for increasing muscle tension

Answer 47

recruitment of additional motor units more neurons and more fibers = even more contraction varies in diff amounts = ex eye = 1 neurone innervates 5 muscles so varies in increment of 5 in leg = vary in steps of 1000 muscle fibers

Question 48

describe skeletal muscle energy metabolism - gen

Answer 48

when relaxed = need not much atp and then suddenly need a bunch

Question 49

describe skeletal muscle energy metabolism 1

Answer 49

There is only enough premade ATP in a muscle fiber to last for a few twitches phosphate released cocks head groups

Question 50

describe skeletal muscle energy metabolism - 2

Answer 50

Transfer of a P from creatine phosphate to ADP creates enough ATP for a few seconds of muscle activity creatine phosphate - high energy molecule has phosphate stuck to it - high energy bond lots in muscle fiber atp converted to adp = triggers creatine phosphate to stick phosphate onto adp to make atp concentrations of creatine phosphate goes down and converted to creatine creatine phosphate concentrations go down and can sustain atp concentrations and contract for a few seconds

Question 51

describe skeletal muscle energy metabolism - 3

Answer 51

Levels of ATP are sustained during prolonged muscle activity by glycolysis and oxidative phosphorylation. Glycogen in the muscle and glucose and fatty acids from the blood provide the fuel. glycolysis = anaerobic, muscle stores glycogen/get glucose from blood (slower, if longer period of time) and generates a few atp molecules (2) and waste = lactic acid oxidative phosphorylation = in mitochondria, needs o2 from bloodstream, generates many aps, more time consuming

Question 52

describe glycolysis

Answer 52

takes glucose - 6 carbons and breaks into 2 3c moleculss and that releases energy = makes atp molecules, v fast 2 3c molecules called pyruvate get fed into op = makes lots of atp and uses up all energy in molecules, takes more time

Question 53

what do skeletal muscles store energy as

Answer 53

glycogen

Question 54

describe glycogen

Answer 54

polysaccharide comprising of long chains of glucose molecules snips glucose off end of glycogen when needed for glycolysis/op