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162 Cards in this Set

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Function of skeletal muscle?(4)


maintain posture/body position

stabilize joints


how does skeletal muscles provide movement?

muscles attach directly/indirectly to bone, pull on bone or tissue when they contract.

How does Skel muscle maintain posture/body position?

muscles are continuously contracting to make adjustments to maintain posture

How does Skel muscles stabilize joints?

tendons crossing joints/muscle tone

how does skel muscle provide thermogenesis?

generate heat when contracting

how are muscles excitable?

respond to nerve stim.

how are muscles contractible?

they shorten when stim.

how are muscles extensible?

they can stretch beyond resting length when relaxed.

how are muscles elastic?

they can recoil/rebound to original resting length after contraction or stretching.

What is endomysium?

CT wrapping that surrounds individual muscle fibers

What is perimysium?

CT wrapping that surrounds bundles of muscle fibers called fascicles

What is epimysium?

Dense irregular CT wrapping that surrounds the entire muscle (final wrapping)

muscle fiber=?

Muscle cell

What is the Sarcolemma?

the plasma mem. surrounding the muscle fiber (cell)

What is the sarcoplasm?

the cytoplasm of the muscle fiber

it uses a lot of ATP

What does it use a lot of?

What does the sarcoplasm contain?

A lot of mitochondria, glycogen, myoglobin and contractile organelles called myofibrils

myoglobin gives muscles what?

their pigment

similar to hemoglobin uses O2

What is a myofibril?

What direction does it run?

long finger-like organelle that fills the sarcoplasm of the cell.

runs parallel to muscle fiber

What is a sarcomere?

A segment on a myofibril

aligned end to end along the length of the myofibril

Has a Z-line

What is a Z-Line?

boundary at the end of each sarcomere

What is a myofilament?

contractile proteins in the sarcomere

arrangement gives muscles its striations

What is Myosin filaments?

Thick filaments

describe myosin filaments

tail with split head

arragned in bundles

What does the head of myosin have?

-ATP binding site

-ATPase enzyme that splits ATP to provide energy during contraction

-Actin binding site

What is Actin filament?

thin filament

What is actin attached to?

attached to Z-line and extends towards the center of sacromere

What does Actin contain?

the active binding site for myosin heads

What proteins regulate the binding of myosin?

Tropomyosin and Troponin

What is Tropomyosin?

a protein that regulates the binding of myosin.

it spirals around actin, blocks active site when muscle is relaxed.

what protein blocks active binding site when muscle is relaxed


What is Troponin?

a protein that regulates the binding of myosin

contains 3 binding sites

What are the 3 things that bind to troponin?


-tropomyosin (controls its position on active binding site)


What are titin (elastic) filaments?

large protien attached to Z-line and runs through the center of thick filaments

What does titin filaments do?

gives muscle elastic property

uncoils when muscle stretches yet stiffens to avoid over extension

recoils when muscle relaxes

What is Sarcoplasmic reticulum (SR)?

specialized smooth endoplasmic reticulum

What does SR sourround?

each myofibril

what is the terminal cisternae?

expanded ends of SR

what does SR store/release?

Ca2+ and releases it when muscle fiber is stim. to contract

When does it release it?

What are transverse tubules (t-tubule)?

deep indentations of the sarcolemma into the muscle fiber

where are t-tubules located?

lie between 2 terminal cisternae

What do t-tubules do?

conduct electrical impulses from sarcolemma into the muscle fiber

coordinates muscle contraction by triggering Ca2+ release from the terminal cisternae

In order to contract a skel muscle must...

-be stim. by somatic motor nueron

-propagate an electrical current, or AP, along

its sarcolemma

-have a rise in intracellular Ca2+ levels(the final trigger for contraction)

3 things

Linking the electrical signal to the contraction is?

excitation-contraction coupling

What is the neuromuscular junction formed from?

Axon terminals

synaptic cleft

motor end plate

what do the axon terminals contain?

they have synaptic vesicles that contain acetylcholine (ACh)

What is the synaptic cleft filled with?

neurotransmitters for ACh

Where is the motor end plate located?

its a specific part of the sarcolemma

What does the motor end plate contain?

ACh receptors

What happens when a nerve impulse reaches the end of an axon at the neuromuscular junction?

-voltage-regulated Ca2+ channels open and allow Ca2+ to enter axon.

-Ca2+ inside the axon terminal causes vesicles to fuse with the axon membrane and release ACh into the synaptic cleft by exocytosis.

At the neuromuscular junction what diffuses across the cleft?

ACh diffuses across cleft and binds to ACh receptors on motor end plate.

What happens when ACh binds to ACh receptors on motor end plate?

initiates an AP in the muscle

After the AP is initiates in the muscle what happens to ACh?

ACh bound to ACh receptors is quickly destroyed by acetylcholinesterase

ACh binding to receptors at neuromuscular junction opens what kind of channels?

Na+ channels ad Na+ rushes in.

in excitation-contraction coupling:

what happens once the AP is generated?

1)it is propagated along the sarcolemma

2)travels down the T tubules

3)triggers Ca2+ release from terminal cisternae

4)Ca2+ binds to troponin

In excitation-contraction coupling when Ca2+ binds to troponin what happens?

-a conformational change in troponin

-tropomyosin rolls off the actin active binding sites allowing them to be exposed for the myosin to attach

What blocks the actin active binding sites?

(excitation-contraction coupling)


What wants to bind to actin?

(excitation-contraction coupling)


Is there is no Ca2+ can myosin bind?


what is sliding filament theory?

once myosin grabs actin and you have pulling of actin

steps in sliding filament theory

-cross bridge formation

-working (power) stroke

-cross bridge detachment

-"cocking" of the myosin head

what happens in cross bridge formation?

the myosin cross bridge attaches to actin filament

(has energy from ATP)

What happens in the working (power) stroke?

the myosin head pivots and pulls actin filament toward M line

What happens in cross bridge detachment?

new ATP attaches to myosin head and the cross bridge detaches

What happens in cocking of the myosin head?

energy from hydrolysis of ATP cocks the myosin head into the high-energy state.

What happens when nerve stimulation ceases?

(muscle relaxation)

-Ca2+ is removed and actively transported back into SR (requires ATP)

-Tropomyosin roles back over the binding sites and muscle fibers relax (myosin cant grab actin)

Tension definition

force muscle exerts on an object when contracted

what is the opposing force exerted on the muscle?

load or resistance

what must overcome the force of the load in order to shorten?

muscle tension

what are the phases of muscle contraction (3)

-latent period

-period of contraction

-period of relaxation

latent period of muscle contraction

1st few milliseconds, excitation-contraction coupling

period of contraction of muscle contraction

when cross bridge cycling tension increases

(filament are sliding)

period of relaxation of muscle contraction

when Ca2+ is transported back into SR, cross bridge cycling ends, tension decreases

individual mscle fiber contractions are what kind of a response?

"all or none"

whole muscle contactions can vary in _______ produced and ______ of contraction.

tension, length

graded muscle responses are:

-variations in the degree of muscle contraction

-required for proper control of skel movement

graded muscle responses are graded by:

-changing the frequency of stim.

-changing the strength of the stim.

what are the factors that effect muscle tension?


Intensity of stim

frequency of stim

size of muscle

optimal operating length

In factors effecting tension what does the intensity of stim have to do with?

has to do with the number of motor units stim

motor unit?

a single motor neuron and all the muscle fibers that it supplies

what is recruitment?

it has to do with motor units.

it is calling more motor units therefor stim more fibers and increasing muscle tension

what is threshold stim?

it is the min. stim needed to invoke visible contraction

what is max stim?

it is when all motor unit are recruited, strognest contraction produced

what is asychronous recruitment?

its alternating the motor units

In factors effecting tension what is involved in the frequency of stim?


wave summation

complete tetanus

what is twitch?

a single impulse

a contraction followed by relaxation

what is a wave summation?

when impulses are delivered in succession the 2nd twitch will be stronger than the 1st.

What is complete tetanus?

a rapid stimulation results is sustained smooth contraction without periods of relaxtion

Refactory period in skel muscle

contractile response lasts longer, far beyond the refactory period of the AP

importan in skel muscles ability to produce tetaus

what is Treppe?

the staircase effect

its the increased contraction in response to multi stim of the same length

how is treppe different than summation?

relaxation occurs in treppe

in treppe why do contractions increase?

-there is increasing availability of Ca2+ in the sarcoplasm (keeps sending AP)

-reduced slack of the elastic series component

-muscle enzyme systems become more effiecient because heat is increased as muscle conteracts

In factors effecting tension the size of the muscle has to with?

-# of muscle fibers per muscle

-size of individual muscle fibers-fibers produce more myofilaments in response to demands placed on them.

In factors effecting tension the optimal operating length has to do with?

the resting length in which max contraction an be generated (70-130%)

occurs when muscle is slightly stretched and filaments barley overlap


same tension

-muscle tension remains constant during contraction

-muscle length changes during contraction, shortens or legnthens

types of isotonic contractions



concentric isotonic contraction

muscle shortens and does work

eccentric isotonic contraction

muscle contracts as it legnthens

helps counteract gravity or prevent joint injury "muscle braking"

what are isometric contractions?

same legnth

-tension increases but muscle legnth remains the same

-muscle in unable to produce enough force to overcome the load

what is muscle tone?

-constant low level of tension in relaxed mucles

-maintained by spinal reflexes that activate alternating motor units

-keeps muscles firm and ready to respond to stim.

Role of ATP in skel muscle?

muscles need constant supply of ATP to carry out contractions.

-cross bridge formation, power stroke

-disconnecting cross bridges

-active transport of Ca2+ back into terminal cisternae

-Na+/K+ pump

how much ATP do muscles store?

for a 4-6 second contraction

what must be constantly regenerated for muscle contractions?


what are the 3 pathways tat supply additional ATP for muscle contraction?

-Creatine phosphate (direct phosphorylation)

-oxidative phosphorylation


what happens in direct phosphorylation?

Creatine phosphate transfers energy and a phosphate to ADP forming ATP

(Creatine phosphate + ADP*-----* creatine + ATP)


Where is Creatine phosphate stored?

in muscle fibers

how much energy is produced from diect phosphorylation (Creatine phosphate)

provides a rapid source of energy 10-15 seconds of contraction

howdo muscles prefer to get ATP?

through Oxidative phosphorylation (aerobic respiration)

where does Oxidative phosphorylation occur?

in the miochondria

what is the main source of ATP when O2 is present?

Oxidative phosphorylation

what fuels Oxidative phosphorylation?

glycogen stores and glucose and fatty acids delivered by the blood

how much energy is produced from Oxidative phosphorylation?

can provide hours of muscle contraction for prolonged moderate activity.

is Oxidative phosphorylation fast or slow?

slower because it requires the delivery of O2 and glucose

Are there any limits to the amount of nutrients that can be delivered to mucles?

yes, there are cardiovascular limits.

-CV cant keep up with O2 demands

-BV in the muscles are compressed during max contraction (hinders nutrient delivery)

-Oxidative phosphorylation may not be able to keep up and produce enough ATP to keepup with demands

is glycolysis anaerobic or aerobic?

anaerobic (NO O2)

what happens in glycolysis?

glucose is broken down to pyruvec acid and produces 2 ATP

with no O2 pyruvec acid is converted to lactic acid

glycolysis creates how much ATP

produces minimal amounts of ATP but does it quickly

provides 30-60 seconds of high level activity

define fatigue

decline in muscle tension as a result of previous activity

when are muscles unable to contract despite being stim?

in fatigue

what does fatigue result from?

deficient amount of ATP

what is the process that happens in fatigue?

-anaerobic respiration becomes less efficient as lactic acid accumulates and pH drops in the muscle fiber

-muscle fibers lose K+ as the Na-K pump is unable to restore ion balance since it requires ATP

what is neuromuscular fatigue?

not caused by a shortage of ATP but a shortage of neurotransmitters at the neuromusclar junction

what is oxygen debt?

its the amount of extra O2 the body must take in to restore muscle chemistry back to a resting state

how does Oxygen debt occur?

-liver converts lactic acid i blood to pyruvate acid which can be converted into glucose to enter aerobic respiration now that O2 is available

-glycogen stores are replenished in muscles and liver.

-creatine is re-phosporylated into creatine phosphate and stored in muscles

-O2 rebinds to myoglobin

how do muscle fibers differ in their methods of metabolism?

-pathways to produce ATP

duration of muscle contrction

-how quickly their ATPases work

speed of contraction

slow--oxidative muscle fibers


slow to contract but most resistant to fatigue

-good for endurance/continuous contraction

-better equipped for oxidative phosphorylation

lots of mitochondria/smaller in diameter

high myoglobin content

-slow myosin ATPase activity

Fast--oxiative muscle fibers


fast to contract but resistant to fatigue

-equippd for oxidative posphorylation

-fast myosin ATPase activity

(better at adaptation)

fast--glycolytic fibers


fast to contract but fatigue quickly

-good for power and speed for short duration

-high glycogen reserves and relie mainly on glycolysis

-fatigue quicky cause of lactic acid build up

-large fibers geneneate more force but poor nutrient diffusion

-light in color due to reduced myoglobin

-fewer capillaries and mitochondria

Aerobic exercise

(effects of exercise on muscle fibers)

results in more efficient muscle metabolism and resistance to fatigue

-increases capillaries, mitochondria and myoglobin

-also increases efficiency of the heart, lungs, body metabolism and neuromuscular coordination

resistance-weight lifting and isometric contractions

(effects of exercise on muscle fibers)

fibers produce more myofilaments and myofibrils causing muscle fibers to hypertrophy

-increases glycogen stores

results in increased muscle size and strength

What is smooth muscle composed of?

spindle-shaped fibers

organized into 2 layers (longitudinal and circular)

except stomach has 3 layers

Where is smooth muscle found?

in walls of hallow organs (except heart)

smooth muscle lack what?

neuromuscular junctions

smooth muscle have innervating nerves that have __________ swellings called_______ that release ________

bulbous,varicosities, neurotransmitters

Are smooth muscle nuerotransmitters excitatory or inhibitory?

some are excitatory and some are inhibitory depending on the receptor

what is the difference of SR in smooth muscle compared to skel muscle?

the SR in smooth muscle is less developed and lacks a certain pattern with in the cell

Do Smooth muscles have t-tubules?


what is the difference in the thin filaments of smooth muscle compared to skel muscle?

the thin filaments only have tropomyosin, there is NO troponin.

in smooth muscle how are thick and think filaments arranged?

diagonally, which causes the smooth muscle to contract in a corkscrew manner

how do actin and myosin interact in smooth muscles?

they interact according to the sliding filament theory

in smooth muscle what triggers Ca2+'s release from the SR?

a calcium influx from the extracellular space triggers it.

what triggers contraction in smooth muscle?

a rise in intracellular Ca2+

In smooth muscle what does Ca2+ bind to?


in smooth muscle what does activated calmodulin activate?

myosin light chain kinase enzyme which transfers phosphate from ATP to myosin cross bridges

in smooth muscles the phosphorylated cross bridges ineract with?

actin to produce shortening

visceral smooth muscle is________


Smooth muscle ____________ cells display rhythmic spontaneous __________ in membrane potentials.

Known as _______ ________ potentials

pacemaker, variations

slow wave

(depolarize and cause other cells to contract)

myogenic (smooth muscles)

self excitable- they can produce spontaneous AP without external stimulation.

(they can be stim by NS as well)

in smooth muscle how are cells electrically coupled to one another?

via gap junctions and contract rythmically as a unit

pacemaker smooth muscle cells AKA?

interstial cells of cajal

pacemaker smooth muscle cells membrane potentials ________ closer and ________ away from threshold

oscillates, further

in smooth muscles what happens if threshold is reached?

a burst of AP is triggered causing rhythmic smooth muscle contractions

what do pacemaker smooth muscle cells drive?

several digestive processes

what effects smooth muscle activity?

Hormones, paracrines, mechanical stress, and nerve stim determines the starting point of the slow wave potentials

smooth muscle exhibits a phenomenon called stress-relaxation response in which:

-smooth muscle responds to stretch only briefly, and then adapts to its new length

-the new length however retains its ability to contract

-this enables organs such as stomach and bladder to temporarily store contents

multiunit smooth muscles are found:

in large airways to the lungs, large arteries,arrector pili muscles attached to hair follicles and the internal eye muscles

what are the characteristics of multiunit smooth muscles?

-rare gap junctions

-structurally independent muscle fibers

-a rich nerve supply, forms motor units

-graded contractions in response to neural stim

single unit smooth muscle is what type of contraction?

all or none

multiunit smooth muscle acts like what?

skel muscle, there is a graded response