muscle 1 Flashcards
what is muscle attached to
tendons on either side of joint then tendons attached to bones
what do stripes indicate
underlying molecular mechanisms that enable muscle fiber to contract
what are muscle fibers generated from
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.
why is it good that muscle fiber is long and thin and mutilnucleated
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)
describe myofibrils
make up skeletal muscle fibers
made of protein
dark and light stripes lined up together = molecular machinery
what does myofibrils lined up together cause
allows fiber to contract as single unit, maximizes amount of force and efficiency
describe bands or lines of sarcomere
i band = light
each i band = z line in middle
a band = dark
describe how contract
sarcomere contract = myofibrils contract = muscle fiber contracts = muscle contracts
describe filaments of sarcomere
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
describe cross bridges
part of thick filaments = interact with thin filaments and causes muscle to contract
describe distribution of thick and thin filaments in sarcomere
thick = each surrounded by halo of 6 thin
thin = surrounded by 3 thick
matrix of thin and thick - crystalline arrangement
what is in i band
thin = actin
what is h zone
only think
what is a band
overlap of thick and thin filaments
overlap = critical for contraction of muscle
describe thin filaments
actin - 2 chains of globular actin subunits twisted into helix
sticks to itself and forms long thin fiber
describe thick filaments
myosin
forms long thin filament with head
bundles = thick filament
bundles attached together tightly = m line
describe sliding filament model
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
do thin and thick filaments change in length
nO
stay same but overlap becomes greater
Contraction of sarcomeres
shortens entire myofibril
what does the amount of tension a muscle fiber can develop depend on
fiber length
length-tension relation reflects degrre of overalp between thick and thin filaments
describe length-tension ratio
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
what is cross bridge cycle driven by
atp binding and hydrolysis by myosin head groups
lots of phosphat and energy to drive cycle
describe cross bridge cycle
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
describe mouse trap
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
describe muscle fatigue
concentrations of atp never change - fairly constant
usually to protect muscle - kicks in before atp concentrations drop a lot
How is contraction of voluntary muscle initiated?
motor cortex
Neuron’s activated = fire aps
activates efferent motor neurons
what is motor unit
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
how many fibers innervated by single motor neuron
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).
describe structure of neuromuscular junction
synapse
nicotinic ach receptors
ligand gated ion channels when bind ach
specialized region of muscle - post synaptic membrane of muscle fiber = end plate
describe steps of neuromuscular transmission
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)
describe t tubules
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
what do t tubules and sarcoplasmic reticulum allow
ap to get inside cell
describe sarcoplasmic reticulum
intraceullar membrane network - for calcium ions
storage site
inside cell but still separated from intracellular machinery
describe excitation-contraction coupling - gen
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)
describe excitation-contraction coupling - specifics
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
describe activation of ryanodine receptor
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
describe main role of t tubule
sense depolarization and changes shape and conveys message to ryanodine receptors in sr
what does calcium released from sr do
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
describe tropomyosin
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
what is contraction of muscle fiber
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
describe process of muscle contraction
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
what is summation
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.
what is unfused tetanus
oscillating state
stimulate motor neuron over and over
twicthes and then relaxes
eventually = reaches steady state
what is fused tetanus
as increase aps = adds up a bunch
leads to ca levels being super high
and leads to stable state
more substantial contraction
how to generate force
not due to twitch vs fused tetanus
we do it bu how many individual fibers get activated = recruitment
describe Generation of muscle tension
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.
what is an important mechanism for increasing muscle tension
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
describe skeletal muscle energy metabolism - gen
when relaxed = need not much atp and then suddenly need a bunch
describe skeletal muscle energy metabolism 1
There is only enough premade ATP in a muscle fiber to last for a few twitches
phosphate released cocks head groups
describe skeletal muscle energy metabolism - 2
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
describe skeletal muscle energy metabolism - 3
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
describe glycolysis
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
what do skeletal muscles store energy as
glycogen
describe glycogen
polysaccharide comprising of long chains of glucose molecules
snips glucose off end of glycogen when needed for glycolysis/op
