Chapter 14 - Muscle Tissue

motor unit recruitment

- a way the nervous sytem can vary the amount of tension in a skeletal muscle if by stimulating more or fewer msucle fibers -one motor neruon can stimulate more than one muscle fiber -but a single skeletal muscle fiber recieves stimulation from only one motor neuron -an AP traveling along a motor neurons axon stimulates every muscle fiber in the nuerons motor unit -all muscle fibers within the same motor unit contract simultaneously -by stimulating more or fewer units the nervous sytem alters a skeletal muscle tension to perform a specific task

fast oxidative fibers

- characteristics of both slow oxidative and fast glycolytic fibers -aka type 2 A fibers -appear red due to a lot of myoglobin but not as much as slow fibers -make a lot of ATP through aerobic respiration -more glycogen than slow fibers and make considerable amount of ATP rapidly through gylcolysis -powerful and get good gas mileage analogy

lack of nutrients

- doing enduring activities for a long time will diminish the supply of glucose and fatty acids and without these the muscle cant produce ATP

eccentric isotonic contraction

- muscle lengthens while its contracting i.e. slowly lowering the book onto a table -twice as powerful as concentric contractions

muscle fiber damage

- physical damage to the neuromuscular junction or other part of the sarcolemma, myofibrils, or other cellular components -muscle fiber might be less responsive to stimulation or may perform less crossbridge cycling within its sarcomere

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 classified in 2 ways concentric and eccentric

z discs move closer together

- thin myofilaments are attached to z discs therefore they pull z discs towards the center of the sarcomere with thin myofilaments -shortens sarcomere during contraction

3 MAJOR WAYS APS AND EEPS

1. EPPS can vary in intensity & APs are always the same intensity 2. EPPs always remain engative, APs reverse the membrane potential twice 3. EPPs result from ions passing through ligand gated channels while APs result from ions passing through voltage gated channels

Tension in skeletal muscle fibers

1. availibility of Ca2+ ions in myofibrils 2. length of sarcomeres 3. diameter of muscle fiber

why fast glycolytic fibers rely more on glycolysis and less aerboic respiration to generate ATP

1. few mitochondria 2. few capillaries surround the fibers 3. limited supply of myoglobin 4. lower surface area to volume ratio

Treppe is caused by....

1. higher temperature which results from the contraction causing Ca2+ ions to diffuse more rapidly -this allows crossbridge cycling to occur at a faster pace -this is why we must warm up

Treppe is caused by...

1. inability of Ca pumps to transport all the Ca2+ ions back into the terminal cisternae before the next stimulation occurs 2. the next one causes the terminal cisternae to release more Ca2+ ions which adds to the remaining in the sarcomere from the first stimulation -this results in more Ca2+ ions are avalible to bind with more troponin molecules freeing up more myosin binding sites or crossbridge cycling

muscles contraction speed depends on

1. number of muscle fibers contracting 2. types of muscle fibers contracting 3. load being moved -if the first 2 remain constant the speed with which a whole muscle contracts is inversely correlated to the load being moved -greater loads slow the rate of contraction -shortening of a muscle that experiences is inversely proportional to the load - the greater the load the less shortening will occur -first some of your slower muscle fibers are performing isometric contractions and the muscle doesnt shorten and the load doesnt move -by recruiting faster motor units the muscle is able to experience isotonic contraction and lift the object

completely repaying the oxygen debt involves...

1. reestablishing aerobic respiration to pre exercise 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 exercise levels

types of skeletal muscle fibers

1. slow oxidative fibers 2. fast glycolytic fibers 3. fast oxidative fibers slow and fast are related to the rate of ATPase activity on the myosin crossbridges -slow fibers hydrolyze ATP slower than fast fibers therefore have fewer crossbridge cycles in a set amount of time -oxidative and glycolytic refer to the muscles primary energy system for producing ATP -oxidative fibers rely mostly on oxidative phophorlayation of ADP where glycolytic fibers rely mostly on the glycogen - acid acid system

reducing the length of muscle fiber can reduce the tension that the muscle fiber can generate for 2 reasons

1. the thin myofilaments from opposite sides of the sarcomere begin to overlap one another and interfere with crossbridge binding to actin 2. further the shortening of the sarcomere can cause the thick myofilaments to collide with the z lines - in this case z lines are unable to move any closer toward the center of the sarcomere so no tension can develop

contraction according to the sliding filament theory creates the following effects 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 cosntant

connective tissue coverings

5 important functions to muscular system: -separate muscle system from other organ systems -separate and protect and insulate individual muscles -divide inidvidual muscles into several levels of organizations -provide passageways for nerves and blood vessels entering and leaving the muscles -contribute to muscle elasticity

contraction of smooth muscle

JUST READ BOOK!!!!!

movement - cardiac and smooth

THIS IS THE MOST VITAL FUNCTION FOR CARDIAC AND SMOOTH -rthymic contractions of cardiac muscle squeeze blood out of the heart into blood vessels -rthymic contractions of smooth muscle moves food through your digestive system and gametes through the reproductive system - also plays a big part in child birth and goose bumps

contraction

unique ability to generate tension or pulling force through a process -causes muscle to shorten often times -doesnt always cause it shorten but it will ALWAYS generate tension

relaxation

when a contracting muscle lessen its tension

internal extension

when sarcomeres contract they actively generate tension within muscle fibers -this cannot move bones or other body parts because the ends of the muscle fibers do not connect directly to these movable structures -muscle must be able to transmit internal tension to tendons or aponeuroses that do connect directly to movable structures

myosin molecules

bind together at the tips of their tails -the shaft is the tail -all myosin tails within a thick myofilament point toward the sarcomere's M line

axon

branches into many fine strands called telodendria and attached are axon terminals

muscles will shorten if....

contraction force its exceeds load or force that is preventing the muscle from shortening

even though glycosis generates ATP anaerobically a muscle fibers abilitly to contract...

diminishes after a minute or so under anaerobic conditions - in anaerobic conditions enzymes convert the pyruvic acid into LACTIC ACID -as lactic acid accumalates it lowers the PH of the cytosol -acidic condtions begin to disrupt metabolic reactions -lactic acid diffuses into the blood and eventually reaches the liver, heart, or kidney -these organs convert the lactic acid back to pyruvic acid which cant enter their own mitochondria to provide energy for aerobic respiration

triad

each T tubule and its 2 adjoining terminal cristernae collective

muscles used for endurance aka posture

have a higher percentage of slow oxidative fibers

with elbows bent the bicep muscles are shorter and..

have more overlap among their myofilaments -the muscle can then exert more tension and it is easier to complete

muscles used primarily that require a lot of strength such as lifting and pushing

higher percentage of fast glycolytic fibers

adding Pi

is phosphorylation and ADP becomes phosphorlayted -that is an endergonic reaction

types of muscle contractions

isotonic or isometric

amino acids are the ________ resort.

last

characteristics of muscle tissue

muscle tissues can perform the functions just describes because of the following four functional characteristics

syanpetic cleft

narrow space between the axon terminal and sarcolemma -

multiunit

not as common as single unit and each muscle fiber lies next to a varicositty or an axon terminal or a motor neuron -very few gap junctions in this tissue -allows the brain to have much more control over tension in multiunit smooth muscle -may choose to stimulate only a few or many muscle fibers depending on the amount of tension needed -found inside eyeballs , arrector pili in the skin, and walls of tubular passageways in the lungs and larger blood vessels and uterus -during pregnancy muscle fibers in the uterus develop gap junctions and effectively function as single unit muscles ex. eye

muscle

organ consisting mostly of muscle tissue made up of cells called muscle fibers aka myofibers aka muscle cells aka myocytes

external extension

passive tension that develops within the series of elastic component exists outside the muscle fibers -generated by a whole uscle at any one time depends on the number of muscle fibers contracting and the types of muscle fibers contracting -nervous system controls these through recruitment

crossbridge cyclilng

repeating the crossbridge cycle many times -repeats as long as the myosin binding sites remain exposed and ATP is availible to cause crossbridge detachment and recovery strokes

intercalated disc

site where two cardiac muscle fibers connect to each other

specific layers of connective tissue that are responsible for the 5 functions

superficial fascia deep fascia epimysium perimysium endomysium

when straight arms the bicep muscles which bend the elbows...

the muscles are stretched and have less overlap among their myofilaments

fast glycolytic fibers

-"white " chicken meat -aka white fibers, fast twitch fibers or type II fibers -appear white because low cocentration of myoglobin -faster than slow fibers because : 1. twitch begins faster because the myosin ATPase hydrolyzes ATP faster 2. a twitch ends faster because CA pumps in the terminal cisternae of the sarcoplasmic reitculum remove Ca2+ ions from the cytosol faster -2 times as thick as slow fibers because large glycogen reserves -primarily use glycolysis to make ATP -to continue contracting for a long period there must be an abundance of glucose molecules availible -store lots of glucose in glycogen -can prolong their ATP production through glycolysis by having an ample supply of glycogen -thicker because contain more side by side sarcomeres -generate more tension than thinner -fatigue more rapidly than slow because produce lactic acid quickly

Zones of overlap- subsection of A bands

-2 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 myofilament with 3 thick myofilaments surround each thin myofilament

myosin crossbridge

-2 sites that are important in contraction -actin-binding site : binding to an actin molecule (proteins in a thin myofilament) -ATPase site: hydrolyzes an ATP to form ADP+ Pi - this provides energy for contraction

Glycogen Lactic Acid System

-2nd fastest system for regenerating ATP -utilizies glycogen as a primary source of glucose which breaks it down to release energy and eventually produces a compound called lactic acid -glucose enters the muscle fiber through facilitated diffusion and stored as glycogen during times of rest -if necessary enzymes cleave glucose molecules from the glycogen

relaxation period

-5-60 msc -muscle fiber steadily loses tension causing a downward sloping line on the myogram -positive correlation between contraction period and relaxation period - while fibers with short contraction periods have short relaxation periods -occurs when Ca2+ ions detach from the crossbridge and move back into the terminal cisternae -when the Ca2+ ions are no longer availible to bind with troponin, the tropomyosin covers the myosin binding ites 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 the Ca2+ ions are important in uncovering myosin binding sites on actin the amount of tenison that muscle fiber generates is directly proportional to the amount of Ca2+ ions within its sarcomeres -treppe and wave summation increase the availibilty of Ca2+

types of motor units

-ALL CONTAIN ONE NEURON -1st they may differ in number of muscle fibers -2nd they do not all contain the same types of skeletal muscle fibers - all muscle fibers within a single motor unit are the same type 3rd- they have muscle fibers of different size - all muscles within the same motor unit are relatively the same size

excitatory stimulation

-ALWAYS causes Ca2+ions to enter the cytosol and most fo these ions come from extracelullar fluid at the time of stimulation -ions may enter the cytosol from the ECF through ligan gated and voltage gated calcium channels in the sarcolemma -ligand normally open up in response to ligand binding to a receptor on the sarcolemma which iniates chemical reactions inside the cytosol

Action Potential in Skeletal Muscle Fibers

-AP is dramatic reversal of the membrane potential that travels as an electrical signal along the sarcolemma -under normal conditions a skeletal muscle fiber wont contract unless an AP passes into sarcoplasm

Generation of the EPP

-AP traveling along a motor neruon's axon causes the axon terminals to release Ach into the synaptic cleft at the neuromuscular junction -Ach binds to Ach gated Na+ channels located on the muscle fiber's motor end plate -open in response to the binding with Ach and allow Na+ ions to diffuse into the muscle fiber thereby generating the EPP -the channels close when acetycholinesterase removes Ach from the channel's receptor

energy for contraction

-ATP is the ONLY molecule that a muscle fiber can use directly as a source of energy to power its crossbridge cycling and operate its Ca pumps and and Na-K pumps -in order to continue functioning a muscle fiber must continually replrenish its supply of ATP -in any moment there are very few ATP molecules inside a muscle fiber -usually an ample supply of its building substrates for ATP - ADP and Pi -enzymes within the muscle fiber can combine the substrates to form ATP -as a muscle fiber works harder its availble ATP falls and its concentration of ADP rises -fiber begins making ATP at a faster rate -muscle fibers utilize three energy systems to convert ADP to ATP : creatine phophate-creatine system, glycogen lactic acid system, and aerobic respirationn

End Plate Potential (EEP)

-Ach iniates a slight electrical change in the sarcolemma of skeletal muscle fibers by opening specific types of membrane channels -attach to ligand gated Na+ channels aka Ach-gate Na+ channels

Release of Ca+ from terminal cisternae

-Ap enters the T tubules where it stimulates voltage sensing receptors in the walls of the t Tubules -Ap causes these receptors to open Ca 2+ release channels in the membrane of the terminal cisternae -Ca2+ ions quickly diffuse out of the terminal cisternae and into the cytosol

Relaxation of muscle fiber

-Ca+ ions cause the troponin to change shape and move tropomyosin back over the myosin binding sites on the actin -covering binding sites prevents actin from performing recovery strokes and the muscle fiber relaxes

Crossbridge cycling and development of tension

-Ca2+ ions diffuse through the myofibrils where they bind to troponin on the thin myofilaments -troponin then changes shape and moves tropomyosin off of the myosin binding sites on actin -crossbridges quickly attach to the actin and crossbrdige cycling begins -tension develops as the Z discs move toward center of sarcomere

Generation of the AP

-EPP reaches threshold voltage to open the voltage - gated Na+ channels at the edfe of the motor end plate -diffusion of Na+ ions into the cytosol through these channels causes the depolarizing phase of the AP -positive membrane potential closes the gated channels and opends the K+ voltage gated channels -outflow of K+ from cytosol through these channels causes repolarizing phase of AP -following all or nothing principle an AP travel along the sarcolemma and enters the t Tubules

depolarizing phase

-EPP will reach the threshold voltage for nearby voltage gated Na+ channels in the sarcolemma -when that happens voltage - gated Na+ channels open and allow a large number of a Na+ ions to diffuse into the cytosol -cytosol next to the sarcolemma positive and the ECF next to sarcolemma becomes negative -this is the depolarizing phase of the AP and cause the voltage line on the EMG to cross over to the positive side of the graph

cardiac muscle cells

-ONLY HEART -look like skeletal muscle cells but have unique structure -has one nucleus and a cell body with many branches -join together at intercalated discs - wavy boarders that look like tiny interlocking fingers -dont rip apart from each other as the heart beats bc of desmosomes spot weld the discs together -organelles differ in structure and number from those in skeletal muscle cell mitochondria are larger and more numerous -some cardiac cells depolarize automatically and can stimulate others to depolarize - automaticity -after an AP fires in a cardiac muscle cell about 80% of the Ca2+ ions that cause the sliding filaments to move come fro the SR

electromyogram

-RMP of a resting muscle fiber

Sarcoplasmic Reticulum

-T tubules run deep into the sarcoplasm and connect w the system of fluid filled tubes and sacs -AKA sarcoplasmic reticulum -both sides, parallel to a T tubule the SR expands and forms sacs of terminal cristernae -inside CA2+ ions may bind with a calcium binding protein called calsequestrin allowing the SR to take in even more Ca2+ ions and store them

contractility - characteristics of muscle tissue

-ability of a muscle fiber to generate tension -muscle fiber contracts only in response to stimuli that generates APs -contracting muscle fiber generates tension on the structure to which it is attached -skeletal muscle fiber may generate tension on a tendon, cardiac and smooth muscle fibers exert tension on neighboring muscle fibers -contractility is unique to muscle fibers

extensibility - chracteristics of muscle tissue

-ability of a muscle fiber to stretch and beyond a normal length without tearing -kinda like a rubber band -one skeletal muscle stretches when another skeletal muscle shortens -cardiac and smooth muscle fibers are also extensible -blood filling the heart stretches cardiac muscle in the heart's walls while blood coursing through blood vessels may stretch smooth muscle in the vessels' walls -food filling stretches smooth muscle tissue int he walls of these organs

elasticity - characteristics of muscle tissue

-ability of a stretched muscle fiber to recoil to its resting length -passive process and doesnt require energy input -muscle fibers demonstrate elasticity after extensibility

capillaries

-absorb heat that fibers generate during metabolism -numerous capillaries form veins

smooth muscle tissue - TYPE OF MUSCLE TISSUE

-abundant in the walls of soft, hollow organs, aka stomach, intestines, urinary bladder, and blood vessels -arranged in sheets and tapered on each end -lack striations unlike skeletal and cardiac muscle fibers -some connect and affect adjacent smooth muscle fibers through gap junctions -involuntary control

recruitment

-activating more motor units to increase a skeletal muscles tension

during the next burst of activity

-aerobic respiration is too slow paced to meet the muscle fiber's high demand for ATP -gylcolysis comes to the rescue by powering up more quickly than aerobic respiration and synthesize ATP rapidly

opening ligand gated Na+ or Ca2+

-allows these ions to diffuse into the cytosol causing depolarization

actinin

-also extend between adjacent myofibrils all the way to the muscle fiber

length tension relationship

-amount of tension that a skeletal muscle fiber generates is positively correlated to the number of myosin crossbridges that are bound to actin -more tension develops when there is optimum overlap between thick and thin myofilaments when the free ends of the thin myofilaments extend to the edge of the H zone

Wave Summation

-amount of tension that a skeletal muscle fibers exerts is positively correlated to rate of stimulation -as a single AP propogates along the sarcolemma only the depolarized regions will have Ca2+ ions moving into the cytosol from the terminal cisternae -only the sarcomeres in the depolarized regions will be experiencing crossbridge cycling to generate tension -terminal cisternae in polarized regions ahead of the AP are not releasing Ca2+ ions because the AP has not yet arrived -Ca2+ ions in the repolarized regions behind the AP would be moving back into the terminal cisternae -this causes crossbridge cycling in the repolarized regions to slow down and cease

contraction of whole skeletal muscles

-amount of tension that a skeletal muscle generates at any one time depends on 2 major factors 1. tension generated by each contracting muscle fiber 2. number of muscle fibers that are contracting

Muscle Fiber Twitch

-amount of tension that develops within a muscle fiber during a single excitation contraction episode -measuring a fiber's tension from the moment a motor neuron stimulates it until the time the fiber relaxes there are 3 distinct periods 1. latent period 2. contraction period 3. relaxation period these periods are shown on a myogram

tendons and aponeuroses

-anchor the ends of skeletal muscles to other organs

striations

-arrangement of the thick and thin myofilaments causes the myofibrils to display alternating light and dark bands - A bands (dark) and I bands (light)

Zones of overlap become wider

-as the thick myofilaments pull the thin ones toward the center of the sarcomere the 2 types of myofilaments overlap to be wider

anatomy of smooth muscle fibers

-attach to dense bodies - consists of filamentous actinin proteins -intermediate filaments - noncontractile proteins of the cytoskeleton and extend from one dense body to the nexy and help the muscle fiber resist overstretching -caveolae- pocket like indentions that contain extracelulluar fluid

Steps of a Crossbridge Cycle

-attachment of myosin to actin -crossbridge powerstroke -detachment of myosin from actin -crossbridge recovery stroke *watch APR

sarcomere

-basic contractile subunit of a striated muscle -connect to one another like a soft drink cans stacked -extends between 2 thin dark lines - Z discs or Z lines -contains assortment of proteins that group together to form thick and thin myofilaments

occurs with or without oxygen

-because its an anaerobic process it doesnt require oxygen -allows a muscle fiber to continue making ATP even when oxygen isnt available -due to ample supply of glucose glycosis can provide enough ATP to sustain maximum contractions for up to a minute or so after aerobic respiration can no longer meet the demand for ATP

Transverse (T) tubules

-before skeletal muscle fiber can contract APs must pass into the interior of the fiber -tiny invanginations in the sarcolemna provide a pathway for this to happen -linings are continuous with the rest of the sarcolemma -the openings dot the entire length of the skeletal muscle at regular interval -extracellular fluid fills the T tubules but does not mix with the cytosol

glucose breakdown

-begins in glycosis - a series of 10 reactions that converts one glucose molecules into 2 molecules of pyruvic acid -glycolysis represents only the initial stages of glucose breakdown and converts the glucose to a variety of compounds before finally forming pyruvic acid

aponeuroses

-broad sheet like tendons that attach a flat skeletal muscle to above or to another skeletal muscle -ex. epicranial aponeurosis that covers the top of a skull like a helmet

inhibitory stimulation

-cause relaxation or prevent contraaction by 1. halting the movement of ions in to the cytosol 2. removing ions from cytosol 3. causing hyperpolarization

opening a voltage gated Na+ channel

-causes more voltage gated Na+ channels to open -depolarization at one site on the sarcolemma initiates depolarization at an adjacent site -this results in a wave of depolarization that travels along the sarcolemma

Ach-gated Na+ channels

-channels open up Ach binds to them and allows Na+ ions to diffuse into the cytosol from the ECF -this leads to the membrane potential of the motor end plate become less negative - this is local depolarization called end plate potential -they can generate EPP they do not allow enough Na+ ions into the cytosol to reverse the membrane's polarity -that happens bc the channels only stay open for a small period -Ach is broken down by an enzyme called acetycholinesterase located in the synaptic cleft -this causes the channel to close -if other channels didnt open then channels would stop depolarizing and stop moving to 0

superficial fascia aka subcutaneous tissue or hypodermis

-combination of adipose and areolar connective tissue that separates the dermis of the skin from the underlying skeletal muscle -lies closest to the body's outer surface -adipose tissue acts like insulating blanket to keep muscle warm and provide the muscle with trigylcerides for energy -also support blood vessels and nerves that enter and leave the outermost skeletal muscles

anatomy of skeletal muscle

-complex organ consisting of skeletal muscle tissue and connective tissue -contains other organs of other body systems - blood vessels, lymphatic vessels, and nerves -come in a variety of shapes and sizes -size depends on number of skeletal muscle fibers present -small ones (aka face) contain only few hundred muscle fibers -large ones (chest or back) contains thousands of muscle fibers

Sarcolemma of skeletal muscle fiber

-contains 2 types of voltage gated channels -voltage gated Na+ -voltage gated K+ -located near the edge of the motor end plate and all along the remainder of the sarcolemma including the t Tubules -they open in repsonse to a certain level of change in the membrane potential

perimysium

-continuation of the epimysium and extends deep into a skeletal muscle to bundle muscle fibers into groups called fasicles -supports small blood vessels and nerves leading into and out of the fasicles

Maintaining Posture - functions of muscle tissue

-contracting skeletal muscles can prevent movement of your neck and back -brain can control skeletal muscles both voluntarily and involuntarily

myofibrils

-cylindrical organelles that the SR surrounds -responsible for the muscle fiber's contractility -the end of each one is bound to the inner surface of the sarcolemma -organelles and inclusions occupy the limited space between myofibrils -consists of repeating subunits called sarcomeres

Sarcoplasm

-cytoplasm of the cell -skeletal and cardiac fibers have some unique organelles called myofibrils -myofibrils fill most of the sarcoplasm -gylcogen releases the glucose molecules that can provide enrgy for ATP synthesis

A bands

-dark striations -"anisotropic" -occupies the central portion of the sarcomere and contains both thick and thin myofilaments -divided into 3 regions M line, H zone, and zones of overlap

subthreshold stimulus

-depolarizes the sarcolemma but the membrane potential does not reach threshold voltage

AP has 2 phases

-depolarizing -repolarizing phase

Tropomyosin

-double stranded filamentous protein that spirals through F actin -covers the mysoin binding sites on actin when muscle fiber is relaxed to prevent the crossbridges to actin

high surface area to volume ratio

-due to being narrower than larger diameter fibers, this means slow fibers have a relatively larger percentage of their total mass exposed to the ECF -the high ratio allows slow fibers to more easily absorb adequate quantities of O2 from the blood to meet the O2 demands of the mitochondria

Z disc

-each one consists of interwining proteins called actinin - these form net-like pattern extending across the myofibril -the interconnection between Z discs helps keep the sarcomeres of adjacent myofibrils in line withe each other

AP's in wave summation

-each successive AP iniates a contaraction wave that is larger than the previous wave -due to having additional Ca2+ ions entering the cytosol before all of those released during a previous AP can be pumped back into terminal cisternae -More Ca2+ ions in the cytosol at any ont time allow more crossbridge to attach to actin -this is so successive stimulations cause more forceful contractions than the first

Excitation - Contraction Coupling

-electrical signals ultimately cause contraction, which is a mechanical event 1. generation of the EPP 2. generation of the AP 3. release of the Ca2+ 4.Crossbridge cycling and developmenet 5.Removal of Ca2+ 6. Relaxation of Muscle Fiber

sphincters

-encircle short segments of a soft tubular organ -contracting sphincter can squeeze so tightly that materials cant get through the tube -relaxing a sphincters cause the tubular organ to expand allowing materials to pass freely through it -some contain smooth muscle while others contain skeletal -latter type allow one to control urination and defecation -feces movement

supplies substrates and energy to mitochondria

-following glycosis most of the stored energy in glucose exists in the chemical bonds of 2 pyruvic acid molecules -when oxygen is present the pyruvic acids enter the mitochondria where they provide energy for the synthesis of many more ATPs

myoglobin

-found in sarcoplasm -red colored pigment that binds oxygen molecules

Cardiac Muscle Tissue - TYPE OF MUSCLE TISSUE

-found only in the heart -striated -branched and connect end to end with other cardiac muscle fibers -involuntary - not under councious control

terminal cristernae

-function as reservoirs for storing calcium ions which play a vital role in contraction -concentration of CA2+ is 40,000 times higher here than it is in the cytosol -release Ca2+ ions that play an important role in the contraction process

glycosis is important to a muscle fiber in 3 ways

-generates ATP -supplies substrates and energy to mitochondria -occurs with or without oxygen

isometric contractions

-generates muscle tension but the muscles length remains the same -contracting a muscle to try moving an immovable object that prevents the muscle from shortening is an example of isometric -triceps muscles also perform isometric during stages of push ups -although they do not involve the shortening of muscle fibers they do involve shortening of sarcomers -internal and external -sarcomeres represent a skeletal muscles contractile component because they are directly responsible for the muscle fibers ability to generate tension

distribution of Muscle fibers

-genetics is the primary factor that determines the realtive percentages of different muscle fiber in a particular skeletal muscle - certain activities can modify existing fibers

during long periods of activity

-glycogen isn't available and glucose becomes less important and fatty acids become more important as a source of energy for ATP synthesis -if a muscle fiber does not have any glucose or fatty acids it will use amino acids as a source of energy for ATP synthesis

Creatine Phosphate System

-glycogen lactic acid and aerobic respiration systems require just a few seconds to gear up -this system serves as the primary energy system for converting ADP to ATP -in a fully rested skeletal muscle fibbers there is only enough stored ATP available to generate about 8 twitches -quickest system : creatin phosphate or phosphocreatine reacting with ADP -creatin kinase catalyzes this reaction transferring an inorganic phosphate ion Pi from CP to ADP -ADP becomes ATP and CP becomes creatine -creatine kinase transfers Pi from CP to ADP so fast that new ATP molecules are available almost immediately after the muscle fiber depletes its stored ATP -CP provides phosphate ions to generate enough ATP for additional 6-8 seconds -stored of ATP plus CP makes up the muscle fibers phosphagen system - this provide enough ATPfor about 10-15 seconds of maximum contraction

after a few seconds of contraction

-glycolysis replaces the phosphagen system as the major source of ATP -glycolysis is most important for activities that need short bursts of near maximum effort i.e. tennis, football, and the 100 meter sprint

Generates ATP

-glycosis makes only 2 ATPs for each glucose molecule that it breaks down but this happens very rapidly -after about 4seconds of maximum contraction glycosis takes over for DP as primary synthesizer of ATP

Treppe

-gradual increase in tension resutling from successive stimulations

single unit

-groups of fibers contract toegther as one unit -aka visceral muscle - forms the walls of hollow visceral organs like the stomach, intestine, and blood vessels

motor neruon

-has long fiber like extensions called axons which course through a nerve

mucles used for requiring a combination of endurance and stregnth

-higher percentage of slow and fast oxidative fibers

ALL or Nothing principle

-if it reaches threshold it will always each action potential

Protection and support of visceral organs- functions of muscle tissue

-important function of skeletal muscle tissue -the skeletal muscles form walls and floor of the abdominopelvic cavity and protect and support visceral organs within that cavity -abdominal muscles offer more protection when they contract bc it makes the muscle firm

regulating movement of food and liquid - functions of muscle tissue

-important homeostatic function of smooth and cardiac muscle -not only does it force material through but it can restrict movement --restricts through use of sphincters -regulates movement of blood through blood movement -walls of blood vessels contain smooth muscle that respond to chemicals in the blood or signals from the nervous system

fasicles

-in the skeletal muscles theyre responsible for the grain -small parallel ridges ont he surfaces of the skeletal muscles

response to skeletal muscle exercise

-increase muscle strength and endurance -doesnt change the type of myosin within the fibers therefore no type of exercise is able to convert fast fibers to slow fibers and vise versa -some exercises effectively convert fast glycolytic fibers to fast oxidative fibers or vise versa

# of ways it changes muscle

-increased amount of glycogen -increased number of myofibrils -increased glycolysis

# of changes

-increased number of mitochondira -increased amount of myoglobin -increases number of capillaries -increased aerobic respiration

endurance

-jogging, swimming, long distance running, and cross country -muscles must contract repeatedly for long periods -muscles must rely more on slow oxidative muscle fibers which uses aerobic respiration for ATP -training regimen that increases muscle endurance -muscles to exert tension against realtively small loads for long periods -does very little for increasing the size or strength of a muscle but results in # of changes

slow oxidative fibers

-known as the "dark" chicken -aka red fibers, slow twitch fibers or type 1 fibers -appear a dark red because they have a high concentration of myoglobin -thin diameter because relatively small glycogen reserves -generate ATP primairly through aerobic respiration -numerous mitochondria in their sarcoplasm -can function efficently with fewer stored glucose molecules -heavily rely on aerobic respiration of fatty acids -important for endurance activities like marathons and jogging because they use aerobic respiration extensively for ATP synthesis because : numerous mitochondria , many capillaries surround the fibers, abundant supply of myoglobin , higher surface area volume ratio

types of smooth muscle

-lack motor ends plates to which neurortransmitters can bind -receptors that bind nerurotransmitters may be found all along the sarcolemma -motor neuron that stimulates smooth muscle fibers doesnt release neurotransmitter primarily from axon terminals -releases most of its neurotransmitters moecules from bulb like regions- variscosities- located along axon either single unit or multiunit

thick myofilaments

-larger diameter than thin myofilaments -primarily responsible for muscle movement during contraction -contains about 250 contractile proteins called myosin -& elastic, structural protein called titin -each myosin molecule within a thick myofilament consists of 2 subunits -thick myofilament in skeletal and cardiac muscle fibers are smooth bc no crossbridges

contraction period

-last 4-40 msec -muscle fiber steadily increase tension - causes an upward sloping line on the myogram -tension develops as myosin crossbridges pull the thin myofilaments toward the central portion of the sarcomere -the thin myofilament overlap the thick even more allowing more crossbridges to bind with actin -tension reaches a maximum height on the myogram when no more crossbridges can bind to actin during the excitation contraction epidsode -primarily due to the limited number of Ca2+ ions that enter the cytosol in response to a single AP -not all skeletal fibers contract at the same pace -reason being that myosin crossbridges in some muscle fibers can perform crossbridge cycling faster than others do

axon terminals

-lays very close to the sarcolemma but doesnt touch it

Width of A bands remains constant

-length of thick myofilaments determines width of A bands therefore contraction doesnt change width of A bands

abundant supply of myoglobin

-lets slow fibers remain in aerboic respiration -due to this storage slow fibers can rely less on O2 diffusing from the blood at the time of contraction

I Bands

-light colored striations along a myofibril -"isotropic" -extends between the A bands of connected sarcomeres with a Z line in the middle -2 sarcomeres share half of one I brand -contain thin myofilaments but NO thick myofilaments

calcium pumps

-located in the terminal cisternae actively transport CA2+ from the cytosol into the lumen

3 types of muscle tissue that differ in...

-location, microscopic structure, function, and control

buildup of lactic acid

-long times of activities takes away the fiber's O2 supply and glycolysis has to continue without aerobic respiration which results in a build up of lactic acid -this lowers the pH of the cytosol and interferes with enzyme activity and overall muscle metabolism -makes your muscles burn

smooth msucle tone

-low level of tension in these fibers that is not due to external stimulation

Stabilizing Joints

-major function of skeletal muscles -contracting skeletal muscles can help stabilize the joint

diameter tension relationship

-maximum tension that a fiber can generate is directly proportional to the number of sarcomeres in the fiber -it is NOT simply the total number of sarcomeres lying end to end that is important in dtermining the maximum tension possible but instead the number of sarcomeres lying side by side -basically muscle fibers that has more myofibrils can exert a greater maximum tension than a fiber with fewer myofibrils -a thick steel rod is stronger than a thin

skeletal muscle tissue - TYPE OF MUSCLE TISSUE

-most abundant type of muscle tissue -mostly bound indirectly by way of tendons, to bones of the skeletal system -the fibers are long and cylindrical and high striations -each end is connected to firbous connective tissue which is bound to another organ-typically bone -SKELETAL MUSCLE FIBERS ARE THE LONGEST MUSCLE CELLS IN THE BODY -the only muscle fibers that a person can counciously control - aka voluntary -sometimes it is necessary that the nervous system controls skeletal muscle fibers involuntarily

endomysium

-mostly areolar connective tissue that extends from the perimysium to surround individual muscle fibers within the fascicle -insulates the muscle fibers as a thin rubber coating insulates electrical wires -supports tiny blood vessels and nerves that lie between the muscle fibers -elastic fibers here also help muscle fibers recoil after stretched

Removal of Ca2+

-motor neruon stops stimulating the muscle fiber no APs pass into the t Tubules so the Ca2+ release channels in the terminal cisternae close -Ca pumps actively transport Ca2+ ions from the cytosol back into the terminal cisternae -Ca2+ ions diffuse off of troponin

sliding filament theory

-muscle fiber contracts when myosin crossbridgess on the thick myofilaments attach to and pull the thin myofilaments -thin myofilaments slide past the thick myofilaments (thick remain stationary) lengths dont change -explanation of contraction

Concentric isotonic contraction

-muscle shortens while contracting i.e. picking up a book

contraction and relaxation of skeletal muscle fibers

-myofilaments interact to cause contraction

H zone - subsection of A bands

-narrow pale region on either side of the M line -contains only thick myofilaments

muscle tone

-nervous system constantly stimulates small numbers of motor units in skeletal muscles even though they muscle as a whole is relaxed -few active motor units sustain a low level of internal tension - if anerve leading to a muscle is cut the muscle loses its tone and becomes flaccid -does not generate enough external tenions to cause the muscle to shorten - muscle tone doesnt move other structures -can be useful in preventing movement -nervous sytem avoids fatiguing its motor units by constantly switching its stimualtion to different motor units -regular exercise can increase this - allows muscle tension to increase or decerase in order to make adjustments to posture -increasing muscle tone increases the muscles metabolic activity at rest -increase metabolic activity is more motor units are consuming . more ATP

Regulation of Muscle Contraction

-nervous system regulates the availability of Ca2+ ions inside the sarcomere -specific site where a neuron stimulates the muscle fiber

movement of thick myofilament

-occurs when it bends at 2 hinge sights -when both sides are bent the myosin is in its low energy position -when ATPase site hydrolizes ATP, the myosin become cocked in . straight high energy position -removing of ADP and P from the crossbridge causes it to spring and back to low energy position

Triad

-one T tubule and 2 terminal cisternae - covers each zone of overlap hence 2 triads cover each sarcomere

motor unit

-one motor neuron plus all the skeletal muscle fibers that is stimulates -skeletal muscle has multiple of these -a particular muscle contains 3 motor units - 1 has 3 muscle fibers a 2nd has 6 muscle fibers and a 3rd has 9 fibers -by stimulating different combinations of motor units the nervous system can stimulate 3,6,9,12,15,or 18 muscle fibers depending on the tasks

blood supply

-only a single artery delivers blood rich in oxygen and nutrients to the skeletal muscle -artery then branches into many small arteries that course through the perimysium -small arteries feed the smallest vessel aka capillaries -run along side each muscle fiber -oxygen and nutrients diffuse out of the capillaries and into the muscle fiber while cellular wastes diffuse out of the fiber and into the capillaries

size principle

-order of recruitment of different size motor units is directly proportional to the amount of force required to perform a particular muscle activity -the relationship between the size of a motor units and its order of recruitment -very important to precise motor control

first few seconds of contraction

-phosphagen system supplies most of the muscle fiber's ATP -phosphagen system provides virtually all the ATP for contractions lasting less than about 10 seconds i.e. throwing a baseball , sprinting to first base, jumping out of the path of an oncoming truck

oxygen debt

-prolonged contractions deplete oxygen from myoglobin so more O2 must diffuse into the muscle fiber from the blood -concentration of O2 in the blood drops -leads to the blood being unable to supply enough O2 to the muscle fibers to sustain aerobic respiration at a rate adequate to meet the high demands for ATP -during anaerobic reactions muscle fibers rely on glycolysis for ATP and also produces lactic acid -lactic acid accumulates in the blood and is a major stimulus causing the brain to speed up a person's breathing rate -the body must take in extra oxygen to reestablish aerobic respiration and restore the cells to their resting condition -defintion: extra oxygen that a person must breathe into the body after exercise

muscle fatigue / physiological fatigue

-prolonged contractions that result in physiological condition that inhibits contraction -can result from continual contractions wihtout relaxation such as in the hand and arm muscles while playing tug of war -can also occur from repeated contraction and relaxation like rowing a boat -its causes : lack of nutrients, buildup of lactic acid, muscle fiber damage

Troponin

-protein consisting of 3 polypeptide chains -1 of them hold the troponin to actin -2nd holds the troponin to tropomyosin to form troponin-tropomyosin complex -3rd calcium ions bind with the remaining polypeptide causing it to change shape and move tropomyosin away from the myosin binding sight

myosin heads

-protruding knobs at end of each myosin molecule -collectively called myosin crossbridge

between short bursts of activity

-pyruvic acid from glycolysis can enter the mitochondria to undergo aerobic respiration

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

-regenerating CP requires ATP -resting muscle fiber produces a surplus of ATP molecules primarily through the other 2 energy systems -an enzyme transfers Pi from some of these extra ATPs to creatine molecules -ATP becomes ADP and creatine becomes CP -CP serves as a temporary storage site for Pi -if necessary CP gives the Pi to an ADP

motor end plate

-region of the sarcolemma that borders the snynaptic cleft

stimulation of smooth muscle

-respond to neurotransmitters from motor neruons, hormones from endocrine glands, celllular waste products, and stretching of sarcolemma -either excitatory or inhibitory

nutrient utilization and levels of activity

-resting skeletal muscle fibers usually have plenty of O2 available for aerobic respiration and primarily utilize fatty acids as a source of energy for this process -resting muscle fiber needs only a steady supply of ATP not necessarily a quick source of ATP -stores most of its glucose in glycogen -surplus of ATP made during aerobic respiration using fatty acids helps to replenish the phosphagen system to synthesize glycogen -nutrient utilization changes when contraction begins

Sarcolemma

-sarcolemma : cell membrane of a muscle fiber - consists of phospholipid bilayer containing integral and peripheal proteins -contains special channels that allow certain ions to pass into and out of the fiber at a rapid pace -movement of ions changes the elcetrical conidtion of the membrane and ultimately leads to contraction of the fiber

regeneration of muscle fibers

-satellite cells in the event of an injury fuse to form new muscle fibers or fuse with damaged muscle fibers which enlarges the fibers -satellite cells can only offer skeletal muscles only a limited ability to regenerate

Crossbridge Cycle

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

epimysium

-sheath of dense irregular connective tissue below the deep fascia and covers individual muscles -glistening membrane on the muscles surface -acts like a girdle to hold muscle fibers together as a group within a skeletal muscle -when muscles contract the epimysium helps prevent it from tearing

deep fascia

-sheath of dense irregular connective tissue that lies deep to the superficial fascia and separates individual muscles from another ex. separates muscles int he brachial region of the upper limb -a lot like strands of cotton spanning the gap between muscles -blood vessels and nerves course through the deep fascia where they split into smaller branches that enter the muscles

Latent Period

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

generating body heat- functions of muscle tissue

-significant function of skeletal muscle -muscles generate heat when they release energy from food molecules -some heat is lost in the external enviroment and some maintains the body -if external enviroment is cold then the nervous system stimulates skeletal muscles to shiver or contract and relax in a vibrating pattern -shivering generates heat and helps prevent a drop in the internal body temp.

I bands become narrower

-since the z discs of shortening sarcomere are moving toward the thick myofilaments, the width of the I band becomes narrower

numerous mitocondria

-site for oxidation of fatty acids -having a lot of mitochondria allows slow fibers to oxidize fatty acids very efficently wihtout having to rely on the supply of pyruvic acid from glycolysis function

neuromuscular junction

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

movement - functions of muscle tissue (skeletal)

-skeletal are responsible for all bone movement -other skeletal muscles cause movement of soft organs - like making faces

Neuromuscular Junction

-skeletal muscle fibers contraact in response to stimulation from a the nervous system called motor neuron -when its ready to stimulate a muscle fiber it sends an AP along the motor neurons axon to the neuromuscular junction -AP causes the neuron to release a chemical - acetylchloline- from its axon terminals

EPP in muscles

-skeletal muscle fibers: depolarize -other types depolarize or hyperpolarize

aerobic respiration or oxidative phosphorylation

-slowest form of converting ADP to ATP -proceeds only when O2 is present -occurs inside the mitochondria and respresents the final stages of glucose breakdown -also breaks down fatty acids from triglycerides and amino acids from proteins -all of these substrates release energy for ATP synthesis but this only occurs when oxygen is present -muscle fibers have 2 sources of O2 1. is the blood - RBC contain hemoglobin whichs binds O2 to the lungs - the hemoglobin releases the O2 which diffuses through the sarcolemma - some of the O2 enters the mitochondria while extra binds with myoglobin 2. myoglobin releases the O2 allowing it to diffuse into the mitochondria

Thin Myofilament

-smaller diameter than thick -pulled by myosin crossbridges to generate tension during a contraction -resembles 2 pearl necklaces that are twisted together -each pearl is G actin and the double chain is called F actin -neubulin holds the 2 strands of G actin molecules together in the F actin -each G actin contains myosin binding site -2 regulatory proteins are found : tropomyosin, troponin - these control when myosin crossbridges can attach to g actin

series elastic component

-some of a skeletal muscle's noncontractile components passively trasnmit tension from the ends of muscle fibers to a tendon or aponeurosis -leadings away from a muscle fiber : endomysium, perimyisum,epimysium -these components are stretchable and tension passes through them one after the other -in order to pass through a skeletal muscle must shorten for this to happen a muscles internal tension must generate external tension that overcomes a load -initial stages of contraction do not cause the muscle to shorten

tetanus

-stimulate a muscle fiber so frequently that complete relaxation cannot occur between stimulations -state of contraction

incomplete tetanus (unfused)

-stimulatio rate allows at least partial relaxation between contractions

complete tetanus (fused)

-stimulation rate so rapid that no relaxation occurs between stimulations

Titin

-structural protein inside thick myofilaments -extends through the core of thick myofilament and attaches to proteins in the Z disc -titin anchors the thick myofilament to a Z disc much like a mooring rope secures a boat to a pier -if a force reaches a sarcomere the titin will stretch also -removing the pressure causes the titin to recoil and pull the Z discs closer together -when the past procedure happens the sarcomere then reverts to its original position

cross training

-tennis, soccer, boxing, and basketball -muscle endurance and quickness -fast oxidative fibers which utilize glycolysis and aerobic respiration for ATP synthesis -increases muscle endurance and quickness -incorporates both endurance and resistance

excitability or irratibility - characteristics of muscle tissue

-the ability of a muscle fiber to respond to a stimulus by generating APs that propagate along its cell membrane -the APs then initiate chemical reactions that cause the fiber to contract -chemicals released from the nervous and endocrine systems are the major stimuli that cause muscle fibers to generate APs

H zone becomes narrower

-the free ends of the thin myofilaments mark the outer boundaries of the H zone -since the pulling thin myofilaments toward center sarcomere causes their free ends to move to the M line causing the H zone to be narrower

membrane potentials of muscle fibers

-the inside of a boarder of the sarcolemma is 85 mV more negative than the outside boarder

if a muscle fiber stretches 70% longer than its optimum length

-then there is no overlap between the thick and thin myofilaments -muscle fiber is unable to contract -tension can still exist withtin the muscle fiber due to the elasticity of the titin filaments within the sarcomeres

opening ligand gated K+ and Cl-

-these ions diffuse out of the cytosol causing hyperpolarization

many capillaries surround the fibers

-they also increase the amount of oxygen that is available from diffusion from the blood -this provides more oxygen to the fiber and allows aerobic respiration to continue longer during maximum exertion

anatomy of skeletal muscle fiber

-thick and cylindrical cell -normally extend the entire length of the muscle in which they are found -multinucleate (more than 1 nucleus) -each nucleus is a diploid containing 2 complete sets or 46 chromosomes -myoblasts fuse with one anothers which causes the multinucleate -some myoblasts remain as satellite cells between the muscle fibers LARGET CELL IN BODY

Myofilaments

-thick and thin

tendons

-thick cord like bands of dense regular connective tissue that anchor a skeletal muscle to a bone

M line - subsection of A bands

-thin line located int he center of the A band -contains proteins of myomesin that extend across the width of the myofibril and keep the thick myofilaments in line -the proteins keep the thick myofilaments an equal distance apart within the sarcomere

relaxation of skeletal muscle fiber

-things that halt crossbridging 1. lack of ATP which prevents crossbridges from detaching from actin at the end of the power stroke 2. inability of the crossbridges to attach to actin -Ca2+ ions are bound to troponin and it keeps tropomyosin off the myosin binding sites on actin -when the Ca2+ detaches from troponin the troponin changes shape and moves tropomyosin over the myosin binding site -this happneing prevents the crossbridge to retach to actin and remains in the high energy position at the end of a recovery stroke -when tropomysoin covers all binding sites thick filaments cant generate any tension to the thin -Ca-pumps actively transport Ca2+ ions back into their terminal cisternae

refractory period

-time when AP is at a specific site on the sarcolemma that site will not respond to another stimulus until the repolarizing phase is complete -unresponsive period

what effects the stretch of muscles?

-titin filaments and postition of bones

pacemaker cells

-transmits electrical signals called APs to other cardiac muscle fibers causing them to contract -these are a small group of of specialized cardiac cells

acetylcholine aka ACH

-type of neurotransmitter a chemical that transmits an electrical signal from a neuron to another cell -it then binds to receptors in the skeletal muscle fiber's motor end plate wher it triggers an AP -the AP travels along the sarcolemma and into the sarcoplasm where it iniates contraction

nerve supply

-under normal circumstances muscles contract only in response to APs from the nervous system -APs reach this through a single nerve -nerve penetrates the epimysium near the center of the muscle then divides extensively -course through the perimysium between the muscles fasicicles -the nerve that penetrates a skeletal muscle not only conducts the APs into the muscle but also out

smooth muscle tissue

-very unique shape -tapered one each end -single oval shaped nucleus resides in center of sarcoplasm -secrete their own endomysium , consisting of fine collagen fibers and glycoproteins -endomysium supports blood vessels and nerves

threshold voltage

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

resistance training

-weight lifting, bodybuilding, and sprinting -require strength but for short busts of power -muscles must rely more on ffast lycolytic fibers -called anaerobic -must store large quantities of glycogen -muscles to exert tension against large loads for short periods -muscle fibers produce more parallel mofibrils and store more glycogen resulting in greater muscle size and strength -either isotonic or isometric - isometric is more effective -does very little for muscle endurance but can change muscle -increases muscle size due to an increase in myofibrils ands tored glycogen not an increases in muscle fibers -may cause some muscle fibers to split

load velocity relationship

-when lifting the same size load fast fibers contract faster than slow fibers -moving different size loads the speed of contraction is inversely correlated with the load

repolarizing phase

-when membrane +30mV the voltage gated Na+ channel close -positive membrane potential allows voltage-gated K+ channels to open -when these channels open a large number of positive K+ ions diffuse out of the cytosol causing the voltage to return to the resting membrane potential -repolarzing phase AP -repolarization always follow depolarization

Wave summation cont.

-when the Ap and contraction bulge reach end of muscle fiber, that region repolarizes crossbridge cycling ceases the contraction bulge disappears and fiber releases -sarcolemma must respect the refractory period responding the stimulation only after repolarization occurs and relaxation isnt needed -if a 2nd stimulus is applied before the first contraction bulge disappears the muscle fiber will develop a wave of contraction -the 2nd contraction adds to the tension generated by the first contraction budlge -effects of succesive stimulations on muscle fiber tension is wave summation

stretching to a skeletal muscle fiber pulls the z lines farther apart

-which narrows the zones of overlap between thick and thin -this also has fewer crossbridges to grab hold of the actin and the muscle fiber is unable to generate maximum tension

events that occur during latent period

1. Ach attaches to ach gated Na+ channels on the motor end plate causing these channels to open 2. Na+ ions diffuse into the muscle fiber and generate and end plate potential -EPP 3. EPP reaches threshold voltage and causes nearby voltage gated Na+ channels to open 4. more Na+ ions diffuse into the muscle fiber and generates an AP 5. the AP in one region of the sarcolemma causes voltage gaged Na+ channels in adjacent regions to open- thus an impulse travels along the sarcolemma and into the T tubules 6. the AP causes Ca2+ ions diffuse out of the terminal cisternae and into the sarcoplasm where they bind to troponin on the thin myofilaments 7. the Ca-tropnin complex changes shape and moves tropomyosin off the myosin binding sites on actin 8. myson crossbridges attach to the actin and crossbridge cycling begins