A&P chapter 14

RMP of a resting skeletal muscle fiber

about -85mV

myofibrils

cylindrical organelles in skeletal or cardiac muscle fibers which fill most sarcoplasm, leaving little room for other organelles and the cytosol -they are responsible for the muscle fiber's contractility

other names for muscle fibers

myofibers or muscle cells

myosin crossbridges in skeletal muscle fibers

myosin cross bridges on opposite sides of the M line pull the thin myofiaments toward the M line, causing the sarcomere to shorten

H zone

narrow, pale region on either side of the M line (Helle, clear) -contains only thick myofilaments

latent period

a short delay, about 1-2 milliseconds, between initiation of an AP on the sarcolemma and the beginning of crossbridge cycling -the events occurring during this time do not produce any deflection on the myogram

psychological fatigue

a state of mind where a person feels tired but the muscles are still able to contract with full force -likely relates to sensory signals from the muscles and changes in blood pH due to a buildup of lactic acid

acetylcholine (ach)

a type of neurotransmitter, a chemical that transmits an electrical signal from a neuron to another cell -it binds to receptors in the skeletal muscle fiber's motor end plate where it triggers an AP

difference between a skeletal muscle fiber and a typical body cell

a typical body cell is extremely small and cube-shaped, but the typical skeletal muscle fiber is thick, cylindrical shaped

relaxation of the smooth muscle fiber

crossbridge cycling occurs less frequently and the muscle fiber will eventually relax after an enzyme called myosin phosphatase dephosphorylates the MLC

axon

long, fiber-like extension which course through a nerve -inside a skeletal muscle, the axon branches into many fine strands called telodendria

relaxation of muscle fiber

losing its bound calcium ions causes troponin to change shape and move tropomyosin back over the myosin-binding sites which prevents the cross bridges from reattaching to actin after performing recovery strokes and the muscle fiber relaxes

muscle tone

low levels of internal tension sustained by few active motor units

inhibitory stimulation

may chaise relaxation or prevent contraction by 1. halting the movement of calcium ions into the cytosol, 2. removing the calcium ions from the cytosol, or 3. causing hyperpolarization

sarcomeres

repeating subunits inside each myofibril which represent the basic contractile units of striated muscle -extend between two Z discs

buildup of lactic acid

results when prolonged activity depleted the muscle fibers oxygen supply and glycolysis has to continue without ample aerobic respiration -accumulation of lactic acid lowers the pH of the cytosol and interferes with enzyme activity and overall muscle metabolism

recovery stroke

return of the crossbridge into the high-energy straight position

muscles used primarily for endurance activity have more...

slow oxidative fibers

types of skeletal muscle fibers

slow oxidative, fast glycolytic, and fast oxidative fibers

pacemaker cells

small group of specialized cardiac muscle fibers, which transmit electrical signals (APs) to other cardiac muscle fibers, causing them to contract

thin myofilaments

smaller diameter and are pulled by myosin cross bridges to generate tension during a contraction -each resembles two pearl necklaces twisted together -each pearl is called G actin while the double chain of G actin molecules is called F actin

triad

-T tubule and its two adjoining terminal cisternae

sarcoplasmic reticulum

a system of fluid-filled tubes and sacs which expand to form terminal cisternae

striations

alternating light and dark stripes

muscles used primarily for performing tasks that require strength have more...

fast glycolytic fibers

concentric isotonic contraction

-muscle shorten while it is contracting -example: lifting a book off a table requires biceps muscle in the arm to shorten in order to pull the forearm and hand towards the chest

3 energy systems that muscle fibers utilize to convert ADP to ATP

creatine phosphate system, glycogen-lactic acid system, and aerobic respiration

since muscle fibers cannot undergo normal cell division to form new muscle fibers, satellite cells can...

1. fuse to form new muscle fibers 2. fuse with damaged muscle fibers, enlarging the fibers -can only offer skeletal muscles a limited ability to regenerate

4 major steps of excitation-contraction coupling in skeletal muscle fibers

1. generation of the EPP 2. generation fo the AP 3. release of calcium from terminal cisternae 4. crossbridge cycling and development of tension

cardiac muscle cells unique structure

-each has one nucleus and a cell body with many branches -cardiac muscle cells join to one another at special junctions called intercalated discs

3 ways that glycolysis is important to a muscle fiber

1. it generates ATP 2. it supplies substrates and energy to mitochondria 3. it occurs with or without oxygen

3 causes of muscle fatigue

1. lack of nutrients 2. buildup of lactic acid 3. muscle fiber damage

four reasons why slow oxidative fibers can utilize aerobic respiration extensively for ATP synthesis

1. numerous mitochondria 2. many capillaries surround the fibers 3. abundant supply of myoglobin 4. a higher surface area

second messenger

-a chemical produced from reactions in the inside the cytosol -comes back to open calcium channels in the sarcolemma, including caveolae -as calcium ions enter cytosol, sarcolemma depolarizes -if membrane potential reaches threshold, nearby voltage gated calcium channels will open

motor neuron

-a nervous system cell which stimulates movement in other cells -has an axon

smooth muscle tissue

-abundant in the walls of soft, hollow organs, such as the stomach, intestines, bladder, and blood vessels -arranged together in sheets and are tapered on each end -lack striations -involuntary

external tension

-elastic components passively transmit tension from the ends of muscle fibers to a tendon or aponeurosis -in order to move another structure, a skeletal muscle must shorten, and in order for that to happen, the muscle's internal tension must generate external tension that overcomes the load

response of skeletal muscles to exercise

-exercise CANNOT change the type of myosin within the fibers (fast fibers to slow fibers), but some exercises CAN effectively convert fast glycolytic to fast oxidative fibers and vice versa

cardiac muscle tissue

-found only in the heart -striated -branched, and connect end-to-end with other cardiac muscle fibers -involuntary

review of events that occur during the latent period

-ach attaches to ach ligand gated sodium channels on the motor end plate, causing channels to open -sodium ions diffuse into the muscle fiber and generate an end-plate potential -the EPP reaches threshold voltage and causes nearby voltage gated sodium channels to open -more sodium ions diffuse into the muscle fiber and generates an AP -the AP in one region of the sarcolemma causes voltage gated sodium channels in adjacent regions to open, thus an impulse propagates along the sarcolemma and into the T tubules -the AP causes calcium release channels in the terminal cisternae to open -calcium ions diffuse out of the terminal cisternae and into the sarcoplasm where they bind to troponin on the thin myofilaments -the calcium-troponin complex changes shape and moves tropomyosin off the myosin binding sites on actin -myosin crossbridges attach to the actin and crossbridge cycling begins

recruitment

-activating more motor neurons to stimulate skeletal muscles tension -process through which the nervous system controls these factors: number of muscle fibers contracting and types of muscle fibers contracting

phosphorylation of ADP

-adding Pi to a substrate phosphorylation, and in this reaction the ADP becomes phosphorylated -endergonic reaction (required energy) -ADP + Pi + energy --> ATP

excitatory stimulation

-always causes calcium ions to enter the cytosol, most of which come from the ECF at the time of stimulation -calcium ions may enter from ligand gated or voltage gated channels in the sarcolemma (in smooth muscle, voltage gated calcium channels outnumber voltage gated sodium channels)

what may cause treppe

-an inability of calcium pumps to transport all the calcium ions back into the terminal cisternae before the next stimulation occurs -the next stimulation causes the terminal cisternae to release more calcium ions, adding to those remaining in the sarcomere from the first stimulation -the result is that more calcium ions are available to bind with more troponin molecules, freeing up more myosin-binding sites for crossbridge cycling -higher temperature resulting from contraction causes calcium ions to diffuse more rapidly, thereby allowing crossbridge cycling to occur at a faster pace -this is one of the advantages of performing warm up exercises before an athletic event, because warm muscles contract more efficiently than cold muscles

slow oxidative fibers (red fibers, slow-twitch fibers, type I, dark chicken)

-appear dark red because they have high concentration of myoglobin -relatively thin diameter due to small glycogen reserves -generate ATP primarily through aerobic respiration -large number of mitochondria in their sarcoplasm -can function efficiently with fewer stored glucose molecules -more important for endurance activities

fast glycolytic fibers (white fibers, fast-twitch fibers, type II-B, white chicken)

-appear white due to a low concentration of myoglobin -may be twice as thick as slow fibers due to large glycogen reserves -primarily use glycolysis to make ATP but to continue contracting for a long period of time, there must be an abundance of glucose molecules available -also contain more side-by-side sarcomeres, so glycolytic fibers can generate more tension than the thinner, slower fibers -important in activities requiring strength and or speed -produce less lactic acid quickly

how do skeletal muscle fibers become multinucleate?

-before a person is born, undifferentiated cells are called myoblasts, each only have one nucleus -the nucleus of each myoblast persists inside the newly formed cell, which differentiates into a skeletal muscle fiber -a few myoblasts remain as satellite cells and play a role in muscle fiber regeneration -the number of nuclei depends on the number of myoblasts that fuse

creatine kinase

-catalyzes the conversion of ADP to ATP -transfers Pi from CP to ADP so rapidly that new ATP molecules are available almost instantaneously after the muscle fiber depletes its stored ATP

nutrient utilization within the muscle fiber

-changes when contraction begins -the phosphagen system supplied most of the muscle fibers ATP within the first few seconds of contraction -phosphagen system also provides ritually all ATP for contractions lasting less than about 10 seconds -after a few seconds, glycolysis replaces the phosphagen system as the major source of ATP

thin myofilaments of the smooth muscle fibers

-consist of intertwining actin and tropomyosin, but lack troponin -tropomyosin never covers the myosin-binding sites on actin and serves more for structural support than to regulate contraction -run diagonally instead of parallel to the length of the fiber, forming a spiral pattern through the sarcoplasm -contraction causes the fiber to become globular -contains more thin than thick -ratio of thin to thick is 15:1

perimysium

-continuation of the epimysium and extends deep into a skeletal muscle to bundle muscle fibers into fascicles -fascicles are responsible for the grain of a meat -supports small blood vessels and nerves leading into and out of the fascicles

eccentric isotonic contraction

-muscle lengthens while it is contracting -about twice as powerful -example: slowly lowering the book onto the table requires the biceps muscle in the arm to become longer but still maintain tension to prevent dropping the book

isometric contractions

-generates muscle tension but the muscle's length remains the same -although they do not involve shortening of muscle fibers, they do involve shortening of sarcomeres -example: contracting a muscle to try moving an immovable object that prevents the muscle from shortening

single-unit smooth muscle

-groups of muscle fibers contract together as one unit -also called visceral muscle because it forms walls of hollow visceral organs such as the stomach, intestine, and blood vessels -muscle fibers are organized into sheets and each fiber is linked to its neighboring fiber through gap junctions

superficial fascia

-hypodermis -combination of adipose and areolar tissue that separates dermis of the skin and underlying skeletal muscles -also supports blood vessels and nerves that enter and leave the outermost skeletal muscles

changes within the muscle connected to resistance training

-increased amount of glycogen -increased number of myofibrils -increased glycolysis (fast oxidative fibers becomes fast glycolytic fibers)

changes within the muscle that are connected to endurance training

-increased number of mitochondria -increased amount of myoglobin -increased number of capillaries -increased aerobic respiration (fast glycolytic fibers may become fast oxidative fibers)

fast oxidative fibers (type II-A)

-intermediate fibers that have characteristics of the other 2 types of fibers -appear red due to myoglobin -significant amount of ATP made through aerobic respiration -contain much more glycogen than slow fibers so they make a considerable amount of ATP rapidly through glycolysis

what happens when the nervous system is ready to stimulate a muscle fiber?

-it sends an AP along the motor neuron's axon to the neuromuscular junctions -the AP causes the neuron to release acetylcholine from its axon terminals

intercalated discs

-junctions where cardiac muscle cells join to one another -wavy borders that look like tiny interlocking fingers -gap junctions tunnel across them and allow ions to diffuse from one cardiac muscle cell to another

thick myofilaments

-larger diameter than thin myofilaments and are primarily responsible for muscle movement during contraction -each contains about 250 contractile proteins called myosin and titin

relaxation period

-lasts 5-60 msec when the muscle fiber steadily loses tension causing a downward sloping line on the myogram -positive correlation between contraction period and relaxation period because fibers with the long contraction periods have long relaxation periods and short with short -relaxation results when calcium ions detach from the crossbridges and move back into the terminal cisternae -when calcium ions are no longer available to bind with troponin, the tropomyosin covers the myosin binding sites so the crossbridges are unable to bind to actin -tension that was generated during the contraction period is lost as thin myofilaments slide back to their resting positions and the sarcomeres lengthen -since calcium ions are important in uncovering myosin-binding sites on actin, the amount of tension that a muscle fiber generates is directly proportional to the amount of calcium ions within its sarcomeres

calcium pumps

-located in the terminal cisternae and actively transport calcium ions from the cytosol into the lumen of the SR -inside the SR, they may bind with calsequestrin, allowing the SR to take in even more calcium ions and store them

endomysium

-mostly areolar connective tissue that extends from the perimysium to surround individual muscle fibers within the fascicles -insulates the muscle fibers and supports tiny blood vessels and nerves that lie between the muscle fibers -elastic fibers within endomysium help muscle fibers recoil after they are stretched

neurotransmitters and single-unit smooth muscles

-neurotransmitters bind to only a few muscle fibers within single-unit muscle tissue -if the neurotransmitter is excitatory, it initiates APs, which quickly pass to nearby muscle fibers through the gap junctions -some single-unit muscle fibers can depolarize without an external stimulation because they contain leaky channels which allow enough calcium ions in the cytosol to initiate contraction

intermediate filaments

-noncontractile proteins of the cytoskeleton, which extend from one dense body to the next and help the muscle fiber resist overstitching

multiunit smooth muscle

-not as common -very few gap junctions which allows the brain to have much more control over tension in multiunit smooth muscle -the brain may choose to stimulate only a few or many muscle fibers, depending on amount of tension needed -found inside eyeballs, arrestor pills muscles, walls of tubular passageways in lungs, large blood vessels, and uterus

SR in smooth muscle fibers

-not well developed -does not play major role in supplying calcium ions for contraction -sarcolemma lacks T tubules, but contains numerous caveolae

fatty acids as a source of energy

-pass feely through the phospholipid bilayer sarcolemma and into the mitochondria -the breakdown is a relatively slow process compared to glucose -the surplus ATP made during aerobic respiration using fatty acids help to replenish the phosphagen system and to synthesize glycogen

series elastic components

-passivley transmit tension from thee ends of muscle fibers to a tendon or aponeurosis -noncontractile components that include endomysium, perimysium, and epimysium -stretchable components -tension passes through them one after another -external tension

calmodulin

-protein which calcium binds to, forming a calcium-calmodulin complex

creatine phosphate system

-serves as the primary energy system for converting ADP to ATP -quickest way to convert is with a compound called creatine phosphate or phosphocreatine -an enzyme called creatine kinase catalyzes this reaction, transferring an inorganic phosphate ion from CP to ADP -in this reaction, ADP becomes ATP and CP becomes creatine

epimysium

-sheath of dense irregular connective tissue below deep fascia and covering individual muscles -acts like a girdle to hold muscle fibers together as a group within a skeletal muscle -helps prevent tearing

deep fascia

-sheath of dense irregular connective tissue that lies deep to the superficial fascia and separates individual muscles from one another -blood vessels and nerves course through the deep fascia where they split into smaller branches that enter the muscles

blood supply to muscles

-single artery delivers blood rich in oxygen and nutrients to the skeletal muscle -inside the muscle, the artery branched into many small arteries that course through the perimysium -the small arteries feed the smallest vessels, called capillaries, and into the muscle fiber, while cellular waste diffuse out of the fiber and into the capillaries -these capillaries also absorb heat that the fibers generate during metabolism -numerous capillaries unite to form veins which transports the blood out of the muscle

how do cardiac muscle cells work differently than skeletal?

-skeletal muscle cells only depolarize when motor neuron stimulate a neuromuscular junctions, but some cardiac muscle cells can depolarize automatically and then stimulate other cardiac muscle cells to depolarize -after an AP fires in cardiac muscle cells, about 80% of calcium ions that cause the sliding filaments to move come from the SR and the remaining 20% diffuse into the cardiac muscle cell from ECF in T tubules or across gap junctions between neighboring cardiac muscle cells

dense bodies

-structure which the myofilaments in smooth muscle fibers attach to instead of connecting to Z lines -consist of filamentous actinic proteins -serve same purpose as Z discs, anchoring thin myofilaments in place

how do the organelles in a cardiac muscle cell differ in structure from a skeletal muscle cell?

-the SR folds around each myofibril and the cardiac muscle cell doesn't rely on the SR for all the Calcium ions it needs to contract -mitochondria are larger and more numerous in cardiac muscle cells -number of sliding filaments can vary from thousands to only a few

two sources of oxygen in muscle fibers that can support aerobic respiration

-the blood (hemoglobin which binds oxygen in the lungs and allows oxygen to diffuse through the sarcolemma) -inside the sarcoplasm, some of the oxygen enters the mitochondria, while extra oxygen may bind with myoglobin -when needed for aerobic respiration, the myoglobin releases the oxygen allowing it to diffuse into the mitochondria

before the muscle can shorten what must happen?

-the contractile components (sarcomeres) must generate enough internal tension to make the series elastic components become taut, then the series generates external tension to overcome the load (muscle won't shorten if the external tension does not overcome the load)

I bands

-the light colored striations along a myofibril (isotropic) -each I band extends between the A bands of connected sarcomeres, with a Z line in the middle -I bands contain thin myofilaments only

isotonic contractions

-the muscle's length changes -once the muscle generates sufficient tension to overcome a load, the tension can remain constant throughout the range of movement (the tension within a muscle can remain the same whether the muscle is moving a 10-kg weight 5cm or moving it 10cm) -classified in two ways

cross training

-training regimen of exercises that increases muscle endurance and quickness -muscles rely more on fast oxidative fibers which utilize glycolysis and aerobic respiration for ATP synthesis -includes jogging intermediate distances for endurance and lifting weights to increase strength and quickness

resistance training

-training regimen of exercises that increases muscle strength and quickness -requires strength and short bursts of power -muscles rely on fast glycolytic fibers which make ATP very quickly (produce ATP using CP and glycolysis) -anaerobic -requires muscle to exert tension against large loads for short periods -muscle fibers produce more parallel myofibrils and store more glycogen, resulting in greater muscle size and strength -either isotonic or isometric

endurance training

-training regimen that increases muscle endurance -rely more on slow oxidative muscle fibers which use aerobic respiration to generate ATP -requires muscles to exert tension against relatively small loads for long periods

ATP's building substrates

-usually an ample supply -ADP and Pi -enzymes within the muscle fiber can combine these substrates to form ATP

in what 3 ways do action potentials differ from EPPs?

1. EPPs can vary in intensity, but APs are always the same intensity 2. EPPs always remain negative, but APs revere the membrane potential twice (the inside of the muscle fiber becomes positive then reverts to the RMP) 3. EPPs result from ions passing through ligand gated channels, while APs result from ions passing through voltage gated channels

what effects do contraction have on sarcomeres?

1. Z discs move closer together 2. I bands become narrower 3. zones of overlap become wider 4. H zone becomes narrower 5. width of A bands remains constant

situations that can halt crossbridge cycling

1. a lack of ATP, which prevents crossbridges from detaching from actin at the end of a power stroke 2. an inability of the cross bridges to attach to actin -the second is most responsible for causing muscle fibers to relax

2 reasons why fast glycolytic fibers are faster than slow fibers

1. a twitch begins faster because the myosin ATPase hydrolyzes ATP faster and 2. a twitch ends faster because calcium pumps in the terminal cisternae of the sarcoplasmic reticulum remove calcium ions from the cytosol faster

4 major stages of the crossbridge cycle

1. attachment of myosin to actin 2. crossbridge power stroke 3. detachment of myosin from actin 4. crossbridge recovery stroke

three groups of exercise-training regimens

1. endurance training 2. resistance training 3. cross training

4 reasons why fast glycolytic fibers rely more on glycolysis and less on aerobic respiration to generate their ATP

1. fewer mitochondria 2. few capillaries surround the fibers 3. limited supply of myoglobin 4. a lower surface area

contraction of smooth muscle

1. formation of calcium-calmodulin complex 2. activation of myosin kinase 3. phosphorylation of light-chain region of crossbridge 4. binding of ATP to ATPase site 5. ATPase activity 6. binding of crossbridge to actin 7. crossbridge cycling 8. relaxation of the smooth muscle fiber 9. ATPase site becomes less active

what does completely repaying the oxygen debt involve?

1. reestablishing aerobic respiration to preexisting rates in all cells that have mitochondria 2. re-synthesizing the phosphagen system to pre-exercise levels in muscle fibers 3. replacing oxygen in the myoglobin of muscle fibers to pre-exercise levels 4. removing all lactic acid and converting it to pyruvic acid 5. replenishing all glycogen stores to pre-exerecise levels

2 major steps of relaxation of the fiber

1. removal of calcium ions 2. relaxation of muscle fiber

5 important functions that layers of connective tissue serve for the muscular system

1. separate the muscular system from other organ systems, 2. separate, protect, and insulate individual muscles, 3. divide individual muscles into several levels of organization, 4. provide passageways for nerves and blood vessels entering and leaving the muscles, and 5. contribute to a muscles elasticity

5 layers of connective tissue covering the muscular system

1. superficial fascia 2. deep fascia 3. epimysium 4. perimysium 5. endomysium

the amount of tension that a skeletal muscle fiber can exert at any one time depends on what 3 factors?

1. the availability of calcium ions in the myofibrils 2. the length of the sarcomeres 3. the diameter of the muscle fiber

a muscle's contraction speed at any one time depends on which 3 factors?

1. the number of muscle fibers contracting 2. the types of muscle fibers contracting 3. the load being moved -greater loads slow the rate of contraction -the greater the load, the less shortening will occur

what does the amount of tension that a skeletal muscle generates at any one time depend on?

1. the tension generates by each contracting muscle fiber 2. the number of muscle fibers that are contracting

two reasons why reducing the length of a muscle fiber can reduce the tension that the muscle fiber can generate

1. the thin myofilaments from opposite sides of the sarcomere begin to overlap one another and interfere with crossbridges binding to actin 2. further shortening of the sarcomere can cause the thick myofilaments to collide with the Z lines

two major ways in which the thick myofilanets are structurally different from those in skeletal and cardiac muscle fibers

1. they have crossbridges along their entire length without any bare central regions 2. the crossbridges have two sites that interact with ATP, instead of just one

while all motor units contain only one neuron, they may differ in what three ways?

1. they may have different numbers of muscle fibers 2. they do not all contain the same types of skeletal muscle fibers 3. they may have muscle fibers of different size

what does the release of Pi by the crossbridge cause?

it causes the crossbridge to bend at its own hinge site and it causes a power stroke

the ONLY molecules that a muscle fiber can use directly as a source of energy to power its crossbridge cycling and operate its calcium pumps and potassium pumps

ATP

what allows a crossbridge cycle to begin?

Calcium ions bind to troponin and cause it to move the tropomyosin off the binding sites

what comes after the creatine kinase transfer Pi from CP to ADP?

CP provides phosphate ions to generate enough ATP for an additional 6-8 seconds of maximum contraction

where does a motor neuron that stimulates a smooth muscle fiber release neurotransmitters?

a motor neuron that stimulates smooth muscle fibers does not release neutransmitter primarily from axon terminals, it releases most of the neurotransmitter molecules from bulb-like regions called variocosities located along the axon

which can exert a greater maximum tension... a muscle fiber that has more myofibrils or a muscle fiber that has fewer myofibrils?

a muscle fiber that has more myofibrils

muscle fatigue (physiological fatigue)

a physiological condition that inhibits contraction which results from prolonged contractions

contraction

a process in which muscle fibers generate tension -often causes muscles to shorten -a contracting muscle may not always shorten but it will always generate tension

what happens if further shortening of the sarcomere causes the thick myofilaments to collide with the Z lines?

Z lines are unable to move any closer toward the center of the sarcomere so no tension can develop

two phases of an AP

a depolarizing phase and a repolarizing phase

nebulin

a filamentous protein which holds the two strands of G actin molecules together in the F actin

smooth muscle tone

a low level tension in smooth muscle fibers that is not due to external stimulation

two sites on the myosin crossbridge that are important to the myosin's functional role in contraction

actin-binding site and the ATPase site

dramatic reversal of the membrane potential that propagates as an electrical signal along the sarcolemma

action potential

calcium-calmodulin complex

activates an enzyme called myosin-light chain kinase

what is glycolysis most important for?

activities involving short bursts of near maximum effort lasting between 10-20 seconds -between these short Burts of activity, the pyruvic acid from glycolysis can enter the mitochondria to undergo aerobic respiration -during the next burst of activity, aerobic respiration is too slow-placed to meet the muscle fibers high demand for ATP and glycolysis comes to the rescue, being able to power up more quickly than aerobic respiration to synthesize ATP

how is the EPP generated?

after the Ach binds to Ach gated sodium channels on the muscle fibers motor end plate, these channels open and allow sodium ions to diffuse into the muscle fiber, which generates the EPP -ach gated sodium channels close when acetylcholinesterase removes ach from the channels receptor

glycogen-lactic acid system

after the CP system, the second fastest system for generating ATP -utilizes glycogen as a primary source of glucose, which breaks down to release energy and eventually produces a compound called lactic acid -glucose enters the muscle fiber through facilitated diffusion and is stored as glycogen during times of rest -when needed, enzymes cleave glucose molecules from the glycogen, making them available for breakdown

what does a high surface area allow?

allows slow fibers to more easily absorb adequate quantities of oxygen from the blood to meet he oxygen demands of the mitochondria

what does an abundant supply of myoglobin allow?

allows slow fibers to remain in an aerobic condition longer, prolonging aerobic respiration -slow fibers can rely less on oxygen diffusing from the blood at the time of contraction because of this

phosphagen system

altogether the stored ATP plus CP makes it up and can provide enough ATP for about 10-15 seconds of maximum concentration

what causes resistance training to increase muscle size?

an increase in myofibrils and stored glycogen, NOT an increase in muscle fibers -muscle fibers may split (does not represent cell division though)

what is a muscle?

an organ consisting mostly of muscle tissue made up of cells called muscle fibers

other than a stimulation by a motor neuron, what else can stimulate the muscle fiber to contract?

an outside electric current applied anywhere along the sarcolemma -however, the electric current must be of sufficient magnitude to depolarize the sarcolemma to threshold voltage in order to generate an AP

threshold stimulus

any stimulus that causes the membrane potential to reach threshold voltage and generate an AP -detectable by an electromyogram

how does a single twitch affect tension?

as a single AP propagates along the sarcolemma, only the depolarized regions will have calcium ions moving into the cytosol from the terminal cisternae, therefore, only the sarcomeres in the depolarized regions will be experiencing crossbridge cycling to generate tension -the terminal cisternae in the polarized regions ahead of the AP are not releasing calcium ions because the AP has not yet arrives -calcium ions in the repolarized regions behind the AP would be moving back into the terminal cisternae and this would cause crossbridge cycling in the repolarized regions to slow down and cease

which organs of other body systems do skeletal muscles contain?

blood vessels (cardiovascular), lymphatic vessels (lymphatic), and nerves (nervous)

why does a muscle fibers ability to contract diminish after a minute or so under anaerobic conditions?

because under anaerobic conditions, enzymes convert the pyruvic acid into lactic acid and as the lactic acid accumulates, it lowers the pH of the cytosol and the acidic conditions begin to disrupt metabolic reactions -lactic acid diffuses into the blood and eventually reaches the liver, heart, or kidneys and these organs convert lactic acid back to pyruvic acid which can enter their own mitochondria to provide energy for aerobic respiration

glucose breakdown

begins in a process called glycolysis, a series of ten chemical reactions that converts one glucose molecules into two molecules of pyruvic acid -glycolysis represents only the initial stages of glucose breakdown, and converts the glucose to a variety of compounds before formally forming pyruvic acid

aponeuroses

broad, sheet-like tendons that attach a flat skeletal muscle to a bone or to another skeletal muscle

axon terminals

bulb-like endings which lie very close to the sarcolemma of a muscle fiber but does not touch it

how does the nervous system avoid fatiguing its motor units?

by constantly switching its stimulation to different motor units -as a result, motor units get a chance to rest while the amount of muscle tone remains fairly constant

how does a muscle fiber respond when a motor neuron stimulates the skeletal muscle fiber with one AP?

by initiating a series of crossbridge cycles

how does ach initiate a slight electrical change in the sarcolemma of skeletal muscle fibers?

by opening specific types of membrane channels (ach-gated Na+ channels) -the channels open when ach binds to them and allows sodium to diffuse into the cytosol from the ECF, which causes the membrane potential of the motor end plate to become less negative

how does the nervous system alter a skeletal muscles tension to perform a specific task

by stimulating more or fewer motor units

one way the nervous system can vary the amount of tension isn a skeletal muscle

by stimulating more or fewer muscle fibers -each axon within a nerve has multiple axon terminals, and each terminal stimulates a single muscle fiber -one motor neuron can stimulate more than one muscle fiber -a single skeletal muscle fiber receives stimulation from only one motor neuron

calcium pumps during relaxation

calcium pumps actively transport calcium ions back into the terminal cisternae

actin-binding site

capable of binding to an actin molecule, one of the proteins in a thin myofilament

if the stimulation rate is so rapid that no relaxation occurs between stimulations

complete tetanus

how are isotonic contractions classified

concentric isotonic contraction and eccentric isotonic contraction -depends on how the muscle changes length

what might muscle fatigue result from?

continual contractions without relaxation or repeated contraction and relaxation

in order to continue functioning what must a muscle fiber do?

continually replenish its supply of ATP

myosin

contractile proteins in thick myofilaments -two myosin molecules bind to one another at the tips of their tails and the shaft of the myosin is the tail and all myosin tails within thick myofilaments point towards the sarcomeres M line -the protruding knobs at one end of each myosin molecule are the myosin heads

A bands

dark striations along a myofibril -anisotropic, which means this region scatters unevenly -occupies the central portion of the sarcomere and contains both thick and thin myofilaments -further divides into M line, H zone, and zones of overlap

end-plate potential

depolarization of skeletal muscle fibers caused by the Ach binding to the ligand gated sodium channels

sub threshold stimulus

depolarized the sarcolemma but the membrane potential does not reach threshold voltage -detectable by an electromyogram

tropomyosin

double stranded, filamentous protein that spirals through F actin -when the muscle is relaxed, it covers the myosin-binding site, preventing the cross bridge from attaching to actin

electromyogram

drawing where the resting membrane potential of a resting muscle fiber can be illustrated -it can depict the relative electrical condition of the inside of the muscle fiber compared to the outside

what prevents the loss of tension when the crossbridge detaches from actin?

during contraction, not all cross bridges are in the same stage of crossbridge cycling. some are performing power strokes while others perform recovery strokes

how can crossbridge cyclings continue for any considerable time?

during stimulation, more calcium ions enter the cytosol causing more calcium calmodulin complexes to form, which activates more MLCK -eventually the concentration of activated MLCK exceeds the concentration of myosin phosphatase, causing phosphorylation of the light-chain regions to occur more often than dephosphorylation, resulting in prolonged contractions

titin

elastic, structural protein in thick myofilaments -extends through the core of the thick myofilanent and attaches to proteins in the Z disc, thus titin anchors the thick myofilament to a Z disc

acetylcholinesterase (AchE)

enzyme located in the synaptic cleft which breaks down Ach shortly after it binds to the channel

4 functional characteristics of muscle tissue

excitability, contractility, extensibility, elasticity

classification of stimulations of smooth muscle

excitatory or inhibitory

pacemaker cells

fibers found in the stomach and other parts of the digestive tract -can depolarize without external stimulation because of their leaky channels which allow calcium ions to diffuse into the cytosol which initiates contraction

telodendria

fine strands that have small bulb-like endings called axon terminals

primary factor that determines the relative percentages of different muscle fiber in a particular skeletal muscle

genetics, however certain types of physical activity van modify existing fibers

the only part of the body that contains cardiac muscle cells

heart

ATPase site

hydrolyzed an ATP to form ADP + P, which provides the energy for contraction

when will a muscle shorten?

if its contraction force exceeds the load (force that is preventing a muscle from shortening)

incomplete tetanus

if the stimulation rate allows at least partial relaxation between contractions

under normal circumstances when does a skeletal muscle contract?

in response to APs from the nervous system, then the APs reach the muscle through a single nerve and the nerve penetrates the epimysium near the center of the muscle then divides extensively -the branches course through the perimysium between the muscles fascicles

when do these channels open?

in response to a certain level of change in the membrane potential

contractile unit

in the smooth muscle fiber, it consists of two dense bodies and the myofilaments extending between them

types of muscle contractions

isotonic and isometric

does having many nuclei provide any benefits to the cell?

it allows gene transcription to occur at many locations in the fiber simultaneously

what does it mean to say a muscle fiber is excitable?

it can respond to stimulation by generating electrical signals along its sarcolemma -these electrical signals ultimately cause contraction, which is a mechanical event

what happens when a skeletal muscle fiber is stretched?

it pulls the Z lines further apart, narrowing the zones of overlap between the thick and thin myofilaments, and fewer crossbridges can grab hold of the actin and the muscle fiber is unable to generate maximum tension

what happens after AP enters the T tubules?

it stimulates voltage-sensing receptors in the walls of T tubules and the AP causes these receptors to open calcium release channels in the membrane of the terminal cisternae -calcium ions quickly diffuse out of the terminal cisternae and into the cytosol

what happens after myosin-light chain kinase is activated?

it transfers a phosphate ion from ATP to a special site on the crossbridge, called the myosin-light chain region (MLC)

contraction period

lasts 4-40 msec when the muscle fiber steadily increases tension, which causes an upward sloping line on the myogram -during this period, tension develops as myosin crossbridges pull the thin myofilaments toward the central portion of the sarcomere -thin myofilaments overlap the thick myofilaments men more which allows more crossbridges to bind with actin -tension reaches maximum height on the myogram when no more crossbridges can bind to actin during this excitation-contraction episode (primarily due to the limited number of calcium ions that enter the cytosol) -not all skeletal muscles contract at the same speed because myosin crossbridges in some muscle fibers can perform crossbridge cycling faster than others do

repolarizing phase

membrane potential reaches about +30mV and the voltage gated sodium channels close -this allows voltage gated potassium channels to open, and a large number of K+ ions diffuse out of the cytosol, causing the voltage to return to the resting membrane potential (-85mV) -a wave of repolarization follows immediately behind the wave of depolarization

what happens when voltage gated sodium channels open?

more voltage gated sodium channels will open which causes a wave of depolarization that propagates along the sarcolemma

the region of the sarcolemma that borders the synaptic cleft

motor end plate

6 important functions of all muscle tissues

movement, maintaining posture, stabilizing joints, regulating movement of food and liquids, protection and support of visceral organs, generating body heat

what make up muscle tissue?

muscle fibers

inclusions in muscle fibers

muscle fibers contain glycogen and myoglobin -glycogen releases the glucose molecules that can provide energy for ATP synthesis and myoglobin binds oxygen molecules -when needed, oxygen detaches and can enter the mitochondria to participate in ATP synthesis

what does it mean to tone up a muscle?

muscles are firm even at rest -the nervous system continually stimulates small numbers of motor units in skeletal muscles, even thought the muscle as a whole is relaxed

the site where an axon terminal and a motor end plate meet at the synaptic cleft

neuromuscular junction

all-or-nothing principle

principle that muscle fibers normally abide by -an AP either occurs at full strength or it does not occur at all

can Ach gated sodium channels reverse the membranes polarity (make the inside of the fiber become positively charged)?

no, because they do not allow enough sodium ions into the cytosol for it -Ach gated channels remain open for only a brief period

can muscle tone move other structures?

no, it does not generate enough external tension to cause the muscle to shorten, but it can be useful for preventing movement

motor unit

one motor neuron plus all the skeletal muscle fibers that it stimulates -a skeletal muscle has multiple motor units

stress-relaxation

phenomenon in which sudden stretching of smooth muscle causes the muscle to contract but then slowly relaxes over the next few minutes

what must occur before the ATPase site can use ATP to perform crossbridge cycle?

phosphorylation of the MLC must occur

resting skeletal muscle usually have...

plenty of oxygen available for aerobic respiration and primarily utilize fatty acids as a source of energy for this process -they also need a steady source of ATP, not necessarily a quick source -stores most of its glucose in glycogen

caveolae

pocket-like indentations that contain ECF -ECF within them has a higher than normal concentration of calcium ions due to the action of calcium pumps within the caveola's membrane -serves as important calcium ion storing structures that are important in the contraction process

muscle fiber damage

prolonged activity may result in physical damage to the neuromuscular junction or other parts of the sarcolemma, myofibrils, or other cellular components -muscle fiber may be less responsive to stimulations or may perform less crossbridge cycling within its sarcomeres

why does a person breathe heavily during vigorous exercise?

prolonging contractions depletes oxygen from myoglobin, so more oxygen must diffuse into the muscle fiber from the blood, as a result, the concentration of oxygen in the blood drops and the blood is unable to supply enough oxygen to the muscle fibers to sustain aerobic respiration at a rate adequate for high demands for ATP

troponin

protein consisting of three polypeptide chains -one of the polypeptides holds the troponin to the actin and the second one holds the troponin to tropomyosin to form a troponin-tropomyosin complex -calcium ions can bind with the remaining polypeptide causing it to change shape and move tropomyosin away from the myosin-binding site

activating more motor units to increase a skeletal muscle's tension

recruitment -the nervous system is recruiting more muscle fibers to contract

is a muscle fiber uses CP to generate ATP, how does a muscle fiber replenish its CP?

regenerating CP requires ATP -a resting muscle fiber produces a surplus of ATP molecules primarily through the other two energy systems -an enzyme transfers Pi from some of these extra ATPs to creatine molecules and in the process, ATP becomes ADP, and creatine becomes CP -CP serves as a temporary storage site for Pi and when needed, the CP gives back the Pi to an ADP

what can increase muscle tone?

regular exercise -allows muscle's tension to either increase or decrease in order to make adjustments in body position, posture, and movement -also increases the muscle's metabolic activity at rest because motor units are consuming more ATP

sphincters

rings of muscle tissue that encircle short segments of a soft tubular organ -contracting a sphincter can squeeze the tube so tightly that materials can no longer move through the tube, but relaxing the sphincter causes the organ to expand allowing materials to pass freely through

terminal cisternae

sacs of the SR -function as a reservoir for storing calcium ions, which plays a vital role in contraction

represents a skeletal muscle's contractile components since they directly responsible for the muscle fiber's ability to generate tension

sarcomeres

automaticity

self-triggering property in the heart

myosin-binding site

site in G actin where a myosin cross bridge can attach

nuclei of a skeletal muscle fiber

skeletal muscle fibers are multinucleate -each nucleus is diploid, containing two complete sets, or 46 chromosomes

three types of muscle tissue

skeletal, cardiac, smooth

muscles used for tasks requiring a combination of endurance and strength have more...

slow and fast oxidative fibers

the narrow space between the axon terminal and sarcolemma

synaptic cleft

pulling force

tension -muscles have the ability to generate different levels of tension

myosin crossbridge

term given to the time during contraction when the two myosin heads bind to the thin myofilament and form a cross over with the thin myofilament

what happens after ach triggers an AP?

the AP propagates along the sarcolemma and into the sarcoplasm where it initiates contraction

what comes after the power stroke?

the ATPase releases the ADP and another ATP binds to the ATPase site, causing the crossbridge to detach from the actin -ATPase hydrolyzes the ATP, causing the crossbridge to perform a recovery stroke and return to high energy position

what happens after dephosphorylation of the MLC?

the ATPase site becomes less active -the crossbridge may remain bound to the actin for some time after detaching which is called the latch state (enables smooth muscle to maintain tension for long periods without the need for ATP)

what happens after AchE breaks down Ach?

the Ach gated channel closes, preventing further diffusion of sodium ions through the channel

contractility

the ability of a muscle fiber to generate tension

extensibility

the ability of a muscle fiber to stretch beyond a normal length without tearing

elasticity

the ability of a stretched muscle fiber to recoil

excitability or irritability

the ability of muscle fiber to respond to a stimulus by generating APs that move along its cell membrane

the order of recruitment of different size motor units is directly proportional to...

the amount of force required to perform a particular muscle activity -to generate a small amount of tension to move a small load, the nervous system first recruits small motor units and as the load increases, the nervous system recruits larger and larger motor units

muscle fiber twitch

the amount of tension that develops within a muscle fiber during a single excitation contraction episode

the amount of tension that a skeletal muscle fiber exerts is positively correlated to...

the rate of stimulation

after exercise stops, why does the breathing rate remain fast for some time?

the body must take in extra oxygen to reestablish aerobic respiration and restore the cells to their resting condition

sarcolemma

the cell membrane of a muscle fiber -consists of a phospholipid bilayer, but also contains special channels that allow certain ions t pass into or out of the fiber at a rapid pace

what happens when ATP attaches to the ATPase site on the crossbridge?

the crossbridge changes shape and detaches from the actin, then the crossbridge hydrolyzes the ATP into ADP + Pi which releases energy that enables the crossbridge to bend back to its high energy position

crossbridge cycling

the crossbridge cycle repeated many times

before a crossbridge cycle begins, what has to happen?

the crossbridge holds an ADP and P on its ATPase site and is spring loaded in the high-energy position. in this position, the crossbridge attempts to bind with actin but tropomyosin prevents it by blocking the myosin-binding sites

wave summation

the effect of successive stimulations on muscle fiber tension

oxygen debt or excess-post exercise oxygen consumption

the extra amount of oxygen after exercise

what happens if a muscle fiber is stimulated so frequently that complete relaxation cannot occur between stimulations?

the fiber remains in a state of contraction known as tetanus

what does the nutrient that a skeletal muscle fiber uses as a primary source of energy for ATP synthesis depend on?

the fiber's activity level

treppe

the gradual increase in tension resulting from successive stimulations -if a skeletal muscle contracts and completely relaxes, the second contraction generates slightly more tension than the first contraction -if the fiber completely relaxes again then quickly receives a third stimulation, the third contraction generates slightly more tension than the second contraction -this pattern may repeat up to 50 stipulations before the tension of each subsequent contraction remains constant

myogram

the graph that shows the 3 periods

3 distinct periods between the time a motor neuron stimulates until the time the fiber relaxes

the latent period, contraction period, and relaxation period

what happens if an inhibitory ligand decreases the concentration of calcium ions in the cytosol?

the ligand binds to a receptor on the sarcolemma, which causes the formation of a second messenger -the second messenger stimulates calcium pumps in the sarcolemma and SR to work faster -the action of the calcium pumps decreases the cytosol calcium ion concentration and without calcium ions to bind to calmodulin, crossbridge cycling ceases

size Principle

the relationship between the size of a motor unit and its order of recruitment -very important for precise motor control of skeletal muscles

skeletal muscle tissue

the most abundant type of muscle tissue, most is bound indirectly (by tendons) to bones of the skeletal system -long and cylindrical and have striations -skeletal muscle fibers are usually the longest cells in the body -voluntary

muscle fiber and glycogen

the muscle fiber utilizes glycogen as a source of glucose, but thirty minutes of moderate exercise can deplete the glycogen supply, thereafter, the muscle fiber must rely on the blood for glucose -during long period of activity, when glycogen is no longer available, glucose becomes less important and fatty acids become more important as a source of energy for ATP synthesis

what do the terms oxidative and glycolytic refer to?

the muscle fiber's primary energy system for producing ATP -oxidative fibers rely mostly on oxidative phosphorylation of ADP, whereas glycolytic fibers rely mostly on glycogen-lactic acid systems

sarcoplasm

the muscle fibers cytoplasm which is surrounded by the sarcolemma

what happens when there is not enough oxygen in the blood?

the muscle fibers rely on glycolysis for ATP, but they also produce lactic acid, which accumulates in the blood and is a major stimulus causing the brain to speed up a person's breathing rate

what happens after ATP binds to the myosins ATPase site?

the myosin ATPase site hydrolyzes the ATP to form ADP + Pi, causing the crossbridge to become cocked in the high energy position, then the spring loaded crossbridge binds to the actin, causing the Pi to detach from the ATPase site

crossbridge cycling repeats as long as...

the myosin-binding sites remain exposed and ATP is available to cause crossbridge detachment and recovery strokes

what does the external tension generates by a whole muscle at any one time depend on?

the number of muscle fibers contracting and the types of muscle fibers contracting

the amount of tension that a muscle fiber generates is positively correlated to...

the number of myosin crossbridges that are bound to actin

what does the size of the muscle depend on?

the number of skeletal muscle fibers present

what do the terms slow and fast refer to?

the relative speed of contraction, which is directly proportional to the rate of ATPase activity on the myosin crossbridges -slow fibers hydrolyze ATP slower than fast fibers and have fewer crossbridge cycles in a set amount of time

what causes thecrossbridge power stroke?

the release of Pi from the ATPase site

crossbridge cycle

the sequence of events by which a myosin crossbridge binds to actin, generates tension, then detaches from actin

excitation-contraction coupling

the sequence of events leading from the stimulation of a muscle fiber to the resulting contraction of that fiber

neuron

the site where a nervous system cell stimulates the muscle fiber

intercalated disc

the site where two cardiac muscle fibers connect to one another

what happens after the myosin cross bridges attach to and pull the thin myofilaments?

the sliding filament theory: the thin myofilaments slide past the thick myofilaments, which remain stationary, but the lengths of the myofilaments do not change

aerobic respiration or oxidative phosphorylation

the slower method for converting ADP to ATP -a series of chemical reactions -proceeds only when oxygen is available -occurs inside mitochondria and represents the final stages of glucose breakdown -also breaks down fatty acids and amino acids -altogether releases 36 ATP molecules

when calcium ions detach from troponin...

the troponin changes shape and moves tropomyosin over the myosin-binding sites, and when this happens, a crossbridge is unable to reattach to actin and remains in high energy position at the end of a recovery stroke

while calcium ions are bound to troponin...

the troponin keeps tropomyosin off the myosin binding sites on actin

what does the direction of the voltage gated channel depend on?

the type of ligand gated channel causing the change -opening of ligand gated sodium or calcium channels allow sodium or calcium to diffuse into he cytosol, resulting in depolarization -opening ligand gated potassium channels allows potassium to diffuse into the cytosol, resulting in hyperpolarization -opening chlorine gated channels allows chlorine ions to diffuse into the cytosol, resulting in hyperpolarization

EMG of depolarizing phase

the voltage line crosses over to the positive side of the graph

threshold voltage

the voltage that causes a particular type of voltage-gated channel to open

the most obvious and unique anatomical feature of smooth muscle fibers

their shape -tapered on each end -single oval nucleus in center of sarcoplasm -secrete their own endomysium (consists of fine collagen fibers and glycoproteins) -endomysium supports blood vessels and nerves

M line

thin line located in the center of the A band (mittel, middle) -contains myomesin that extend across the width of the myofibril and keep the thick myofilaments in line -these keep the thick myofilaments an equal distance apart within the sarcomere

if a skeletal muscle fiber stretched 70% longer than its optimum length...

there is no overlap between the thick and tin myofilaments, the muscle fiber is unable to contract, but tension cans till exist within the muscle fiber due to the elasticity of the Titian filaments within the sarcomeres

how are smooth muscle tissues classified?

they are classified depending on whether a neuron stimulates the muscle fibers individually or relies on gap junctions between fibers to transmit APs -either single unit or multiunit

what happens after calcium ions enter the cytosol?

they diffuse through the myofibrils where they bind to troponin on the thin myofilaments -the troponin changes shape and moves tropomyosin off the myosin-binding sites on actin which allows myosin cross bridges to attach to the actin, and crossbridge cycling begins -Z discs move toward center of the sarcomere

capillaries function in slow oxidative fibers

they increase the amount of oxygen available through diffusion from the blood which provides more oxygen to the fiber, allowing aerobic respiration to continue longer during maximum exertion

what happens when tropomyosin covers all binding sites?

thick myofilaments cannot generate tension on the thin myofilaments and the muscle fiber loses tension as the thin myofilaments slide back to their resting position, returning the sarcomeres to their resting length

myofilaments

thick or thin -the two types run parallel along the sarcomere's long axis and interact to shorten the sarcomere during contraction -the arrangement of the thin and thick myofilaments causes myofibrils to display striations -the different colored striations are A bands and I bands

tendons

thick, cordlike bands of dense regular connective tissue that anchor a skeletal muscle to a bone

Z discs

thin, dark lines which consists of intertwining proteins called actinic that form a net-like pattern extending across the myofibril -the interconnection between the Z discs helps keep the sarcomeres of adjacent myofibrils in line with one another

why does each successive AP initiate a contraction wave that is larger than the previous wave?

this is due to having additional calcium ions entering the cytosol before all of those released during a previous AP can be pumped back into the terminal cisternae -more calcium ions in the cytosol at any one time allow more crossbridges to attach to actin, so successive stimulations cause more forceful contractions than the first

what would happen if that crossbridge cycling in the depolarized region creates a small bulge that moves along the muscle fiber like a wave following the AP?

this single contraction bulge would generate the same amount of tension at any location along the fiber -when the AP and contraction bulge reach the end of the muscle fiber, that region repolarizes, crossbridge cycling ceases, the contraction bulge disappears, and the fiber relaxes

T tubules (transverse)

tiny invaginations in the sarcolemma which provide a pathway for APs to pass into the interior of the fiber -ECF fills the inside of the T tubules but does not mix with the cytosol

under normal circumstances, what limits the distance that muscles can stretch?

titin filaments, elastic tissues in the muscle and tendons, and the position of bones -even if a muscle seems to be stretched, there is still almost optimum overlap between the myofilaments

two situations that increase the availability of calcium ions within a sarcomere

treppe and wave summation

two regulatory proteins found on the thin myofilament

tropomyosin and troponin

zones of overlap

two dark regions extending from either side of the H zone to the edge of the A band -contain overlapping thick and thin myofilaments -6 thin myofilaments surround each thick myofilaments, while 3 thick myofilaments surround each thin myofilament -a triad covers the zone of overlap

where are neurotransmitters in the smooth muscle fibers?

unlike skeletal muscle fibers, smooth muscle fibers lack motor end plates to which neurotransmitters can bind -instead, receptors that bind neurotransmitters may be found all along the sarcolemma

the normal working length of sarcomeres in a contracting muscle fiber

usually +-20% of this optimum length

what 2 voltage gated channels do the sarcolemma of a skeletal muscle fiber contain?

voltage gated sodium channels and voltage gated potassium channels -these are located near the edge of the motor end plate and all along the remainder of the sarcolemma, including T tubules

depolarizing phase

voltage gated sodium channels open and allow a large amount of sodium ions to diffuse into the cytosol when an EPP reaches the threshold voltage for nearby voltage-gated sodium channels in the sarcolemma -cytosol next to the sarcolemma becomes positive and the ECF next to the sarcolemma becomes negative

what happens when the sarcolemma hyperpolarizes in smooth muscle fibers?

voltage-gated calcium channels remain closed, preventing calcium ions from entering the cytosol

relaxation

when a contracting muscle lessens its tension

when can hyperpolarization result?

when a ligand opens potassium channels, allowing potassium ions to diffuse out of the fiber, or opens chloride channels, allowing chloride ions to diffuse into the fiber -in either case, the membrane potential increases

removal of calcium ions

when a motor neuron stops stimulating the muscle fiber, no APs pass into the T tubules, so calcium release c channels in the terminal cisternae close -at the same time, calcium pumps actively transport calcium ions from the cytosol back into the terminal cisternae and as the calcium concentration in the cytosol drops, calcium ions diffuse off of troponin

refractory period

when an AP is at a specific site on the sarcolemma, that site will not respond to another stimulus until the repolarizing phase is complete -voltage gated sodium channels cannot re-open until the region around them repolarizes

low energy position

when both sites of the myosin cross bridge are bent

when is the speed of contraction inversely correlated with the load?

when moving different sized loads

when does a muscle fiber contract?

when myosin cross bridges on the thick myofilaments attach to and pull the thin myofilaments

internal tension

when sarcomeres contract, they actively generate tension within muscle fibers -internal tension alone cannot move bones or other body parts because the ends of muscle fibers do not connect directly to these moveable structures -muscle transits internal tension to tendons or aponeuroses that do connect directly to moveable structures

high energy position

when the ATPase site hydrolyzes ATP, the myosin becomes cocked in this straight position

how is the AP generated?

when the EPP reaches theshold voltage to open the voltage gated sodium channels at the edge of the motor end plate, sodium ions diffuse into the cytosol through these channels which causes depolarizing phase of the AP -the positive membrane potential closes the voltage gated sodium channels and opens potassium channels and the outlaw of potassium ions from the cytosol through these channels causes the repolarizing phase of the AP -AP propagates along sarcolemma and enters the T tubules

power stroke

when the crossbridge pulls the thin myofilament -at the end, the crossbridge releases the ADP, creating stiffness

when does more tension develop?

when there is optimum overlap between thick and thin myofilaments, that is, when the free ends of the thin myofilaments extend to the edge of the H zone

what do smooth and cardiac muscles respond to?

whereas skeletal muscle fibers normally contract in response to stimulation from neurons, smooth and cardiac muscle fibers respond to a number of different stimuli, including neurotransmitters from motor neurons, hormones from endocrine glands, cellular waste products, and stretching of the sarcolemma

what happens if a muscle fiber is stimulated two times in rapid succession?

while the sarcolemma must respect the refractory period, responding to stimulation only after repolarization occurs, relaxation need not occur -if a second stimulus is applied before the first contraction bulge disappears, the muscle fiber will develop a wave of contraction and the second contraction bulge adds to the tension generated by the first contraction bulge

lack of nutrients

without an adequate supply of nutrients, the muscle fiber lacks the sources of energy needed to synthesize adequate amounts of ATP -a deficiency in ATP decreases the number of crossbridge cycles possible which results in weaker contractions