Chapter 12: Muscles

asynchronous recruitment

alternation of active motor units to prevent fatigue

sarcomere

arrangement of thin and thick filaments in a myofibril creates a repeating patter of alternating light and dark bands -contractile unit of myofibril

sarcolemma

cell membrane of a muscle fiber

slow wave potentials

cells that exhibit cyclic depolarization and repolarization of their membrane potential -peak of the depolarization reaches threshold, action potentials fire

flexion

centers of the connected bones are brought closer together when the muscle contracts, and the movement

A band

central region of the A band is lighter than the outer edges of the A band because the H zone is occupied by thick filaments only -helles

the entire muscle is enclosed in..

connective tissue sheath that is continous with the connective tissue around the muscle fibers and fascicles and with the tendons holding the muscle to underlying bones

smooth muscle contraction can start with

electrical signals, changes in membrane potential or chemical signals

recruitment

force of contraction in a skeletal muscle can be increased by recruiting additional motor neurons -controlled by nervous system

Cytosol between myofibrils contain..

glycogen, granules and mitochondria -glycogen: storage form of glucose, source of energy -mitochondria: enzymes for oxidative phosphorylation of glucose and other biomolecules, ATP for muscle contraction

I bands

lighest color bands of the sarcomere and represent a region occupied only by thin filaments -isotropic -a Z disk runs through the middle of every I band

crossbridges have two states

low-force (relaxed muscles) and high-force (contracting muscles)

myofibrils

main intracellular structures in striated muscles, highly organized bundles of contractile and elastic proteins that carry out the work of contraction

origin

of a muscle is the end of the muscle that is attached closes to the trunk or to the more stationary bone

relaxation

release of tension created by a contraction

three types of muscle tissue

skeletal, cardiac, smooth

extensor

the bones move away from each other when the muscle contracts, and the movement

proper aligment of filaments within a sarcomere is ensured by two proteins

titin and nebulin

load

weight of force that oposes contraction of muscle

motor unit

-basic unit of contraction in an skeletal muscle -composed of a group of muscle fibers that function together and the somatic motor neuron fires an action potential, all muscle fibers in the motor unit contract

cardiac muscle

-found only in the heart and moves blood through the circulatory system -striated muscles:alternating light and dark bands seen under the light microscope -involuntary -extrensic control: autonomic innervation -modulated by endocrine system

extraocular muscles

-move the eyes or the muscles of the hand -motor unit contains a few as three to five muscle fibers

ligand gated Ca2+ channels

-receptor-operated calcium channels or ROCC -open in response to ligand binding and allow enough Ca2+ into the cell to induce calcium release from SR

muscle fiber types

-slow-twitch fibers: ST or type 1 -fast twitch oxidative-glycolitic fivers: FOG or type 2A -fast-twitch glycolytic fibers (FG or type 2x) found in animals

sarcoplasmic Ca2+ release

-store Ca2+ -modulated by: IP3-channel receptor and ryanodine receptor (RyR)

titin has two functions

1. stabilizes the position of the contractile filaments 2. elasticity returns stretched muscles to their resting length -help by nebulin

store-operated Ca2+ channels

Made from the protein Orai-1. Open to allow more Ca2+ into the cell -SR Ca2+ store decreases, protein sensor (STIM1) on the SR membrane interact with this channel on the cell membrane -Ca2+-ATPase pumps cytosolic Ca2+ into the SR to replenish its stores

single-unit smooth

- connected by one another by gap junctions -intestinal tract -coordinated contraction, the amount of Ca2+ that enters the cell determines the force of the contraction

skeletal muscle transduction of the lectrical signal into a calcium signal requires two key membrane proteins

- t-tubule membrane voltage sensing L-type calcium channel protein called diphydropyridine (DPH) receptor -DPH only found in skeletal muscle, mechanically linked to Ca2+ channels in adjacent sarcoplasmic reticulum -SR Ca2+ release channels are also known as ryanodine receptors (RyR)

thick filament

-250 myosin molecules joint to create -arrange so that myosin heads are clustered at each end of the filament, and the central region of the filament is a bundle of myosin tail

where do muscles get the ATP they need for work?

-ATP stores in a muscle fiber sufficienty for 8 twitches -ATP converted to ADP and Pi during contraction needs additional energy transfer from high-energy phosphate bonds or by synthesis of ATP through glycolysis and oxidative phosphorylation

Ca2+ to intiate contraction comes from two sources

-The sarcoplasmic reticulum and the extracellular fluid -can create graded contractions whose force varies according to the strength of the Ca2+ signal

Disuse of muscles

-can atrophy -blood supply to muscles diminishes and the muscle fiber gets smaller -somatic motor neuron dysfunction: therapists use electrical impulses to maintain muscle function

cardiac muscle

-cardiac muscle fibers: striated and have a sarcomere structure, shorter than skeletal muscle, may be branches and have a single nucleus -single unit smooth muscle: electrically linked to one another -intercalated disk: gap junctions -pacemaker potentials -sympathetic, parasympathetic and hormonal control

sympathetic neurohormone epinephrine

-causes smooth muscle contraction when it binds to a-adrenergic receptors but relaxation when it binds to B2-adrenergic receptors

muscle with vary contractions

-changing the types of motor units that are active or changing the number of motor units that are responding at any on time

IP3 triggers

-contraction 1. IP3 opens IP3 channels on the SR to release Ca2+ 2. Diacyglycerol (DAG) product of phospholipase C signal pathway, indirectly inhibits myosin phosphatase activity -increasing MLCK/MLCP ratio promotes crossbridge activity and muscle tension

load and velocity (speed) of contraction in muscle fiber

-contraction fastst when the load on the muscle is zero -load of the muscle equals the ability of the muscle to create force, muscle unable to move the load and velocity drops to zero

Myogenic contraction

-contraction from muscle fiber -common in blood vessels that maintain certain amount of tone at all time

legthening (eccentric) contraction

-contribute most to cellular damage after excercise and to lead to delayed muscle soreness

myosin light chain phosphate (MLCP)

-dephiosphorylates myosin light -decreases myosin ATPase activity -does not result in relaxation -always active

length-tension relationship

-direct reflection of the length of individual sarcomeres before contraction begins e. fibers start a contraction at a very long sarcomere length, the thick and thin filaments barely overlap and form few crossbridges c. optimum sarcomere length: filaments begin contracting with numerous crossbridges between the thick and thin filaments, optimum force in that twitch b. sarcomere is shorter than optimum length at the beginning of the contraction, the thick and thin filaments have too much overlap before the contraction begins (no cross bridge) a. sarcomere is too short, thick filaments run into Z disk, myosin is unable to find new binding sites for crossbridge formation and tension decreases rapidly

fascicles

-each skeletal muscle fiber is sheated in connective tissue, with groups of adjacent muscle fibers bundle together into units... -in between: collagen, elastic fibers, nerves and blood vessels are found between fascicles

lever system of the forearm

-elbow joint: fulcrum -rotational movement of the forearm: lever -biceps contract: upward force F1 and pulls down the bone

Myosin ATPase

-energy of power stroke is ATP -myosin: converts the chemical bond energy of ATP into the mechanical energy of crossbridge motion -hydrolyzes ATP to ADP and inorganic phosphate (Pi) -ATP hydrolysis is trapped by myosin and stored as pontential energy -potential energy of the cooked heads become kinetic energy in the power stroke that moves actin

crossbridges

-form: myosin heads of thick filaments bind to actin in the thin filaments -G-actin molecule has a single myosin-binding and each myosin head has one acting binding site and one binding site for ATP

sarcoplasmic reticulum

-formed of modified endoplasmic reticulum that wraps around each myofibril like a piece of lace -concentrates and sequesters: Ca2+ with the help of a Ca2+ -ATPase in the SR membrane -calicum release form the SR creates calcium signals that play a key role in contraction in all type of muscles

phosphocreatine

-is the backup energy source of muscles, whose high-energy phosphate bonds are created from creatine and ATP when muscles are at rest -exercise: high-energy phosphate group of phosphocreatine is quickly transferred to ADP, creating more ATP to power the muscles

smooth muscle actin and myosin

-lacks troponin -less myosin -myosin: longer, surface covered by myosin heads, enables to stretch more -extensive cytoskeleton consisting of intermediate filaments and protein dense boies in the cytoplasm and along the cell membrane -actin filaments attach to dense bodies -cytoskeleton fibers linking dense bodies to the cell membrane help hold actin in place

sarcoplamisc reticulum in smooth muscle

-less organized -network of tubules that extend from just under the cell membrane into the interior of the cell -no t-tubules -associated with membrane invaginations called caveolae participate in cell signaling

actin

-makes up thin filaments of the muscle fiber -globular protein (G-actin): polymerize to form long chains or filaments called F-actin -Two F-actins polymers twist together like a double strand of beads, creating the thin filaments of the myofibril

myofibril proteins include

-motor protein myosin: thick filaments -microfilament actin: thin filamints -regulatory proteins: tropomyosin and troponin -two giant accessory proteins: titin and nebulin

McArdle's disease

-muophosphorylase deficiency -enzyme that converts glycogen to glucose 6-phosphate is absent in muscles -muscles lack a usable glycogen energy supply and exercise tolerance is limited

cAMP cause

-muscle relaxation 1. free cytosolic calcium concentrations decrease when IP3 channels are inhibited and the SR calcium -ATPase is activated 2.K+ leaking out of the cell hyperpolarizes it and decreases the likelihood of voltage-activated calcium entry 3. myosin phosphatase activity increases, which causes a decrease in muscle tension

myosin crossbridges move actin filaments

-myosin heads bind to actin molecules -calcium signal initiates the power stroke: myosin crossbridges swivel and push the actin filaments toward the center of the sarcomere -end of power stroke: myosin head releases actin, then swivels back and binds to a new actin molecule for contractio

Phosphate mediated Ca2+ sensitivity

-neurotransmitters, hormones and paracrine molecules alter smooth muscle Ca2+ sensitivity by modulating myosin light chain phosphatase (MLCP) activity -MLCP activity increases dominates causing myosin ATPase dephosphorylate and contraction force decreases even thought cytosolic Ca2+ concentration has not changes -desensitized to calcium -signal molecules that decrease myosin light chain phosphatase activity make the cell more sensitive to Ca2+ and contraction force increases even thought Ca2+ has not changed

how smooth muscle function is influenced by

-neurotransmitters, hormones or paracrine signals -chemical signals: excitatory or inhibitory -modulate contraction by second messenger action at the level of myosin as well as by influencing Ca2+ signals -signal transudction: muscle relaxation and contraction

multi-unit smooth muscle cells

-not linked electrically and they must be stimulated independently to contract -axon terminal or varicosity -selective activation of individual muscle cell -found in iris and ciliary muscle of the eye -in part of the male reproductive tract -uterus except in labor and delievery: becomes single unit at final stages of pregnancy, gap junction connexin proteins turn on under the influence of preganancy hormones -synchronizes electrical signals: allow uterine muscle to contract more effectively while expelling the baby

Z disk

-one sarcomere: two Z disks and the filaments found between them -zig zag protein structures that serve as he attachment for thin filaments -zwischen

IP3-recpetor channel

-open G protein coupled receptors activate phospholipase C signal transductio pathways -second messenger -IP3 binds to the SR IP3-receptor channel, the channel opens and Ca2+ flows out of the SR into the cytosol

Voltage-gated Ca2+ channels

-open in response to depolarizing stimulus -action potentials in muscle cells or from neighboring cells via gap junctions -subtreshold open potentials: open few Ca2+ channels -depolarizes the cell and open additional voltage-gated calcium channels

sliding filament theory

-overlapping actin and myosin filaments of fixed length slide past one another in an energy-requiring process, resulting in muscle contraction -explains: how muscle can contract and create force without creating movement

nitric oxide

-paracrine signal -gas synthesized by the endothelial lining of blood vessels and relaxes adjacent smooth muscle that regulates the diameter of the blood vessels -endothelium-derived relaxing factor or EDRF

Myosin light-chain kinase (MLCK)

-regulatory protein chain -phosphorylation and dephosphorylation of the myosin light chain control contraction and relaxation is smooth muscle -critical factor, depend on Ca2+-calmodulin activity

spincters

-relax when it is necessary to allow material to enter or leave the organ

tropomyosin

-resting skeletal muscle: wraps around actin filaments and partially covers actins myosin binding sites -off-on positioning regulated by troponin

level and fulcrum

-rigid bar that pivots around a point known as the fulcrum -bones form levers and flexible joints form fulcrums -muscle attached to bones create force by ontracting -similar to fishing pole -fulcrum located at one edge of the lever, the load is near the other end of the lever and force is applied between the fulcrum and the load

slow-twitch oxidative; red muscle fibers (type 1)

-slow contractile cycles -slow split of ATP -pump Ca2+ to SR slow -contractions last more than 10 times long -maintaing posture, standing or walking -have more mitochondria -more blood vessels in connective tissue to bring oxygen to the cells -myosin: red muscle -smaller diameters

excitation-coupled of Ca2+ entry

-small amount of Ca2+ movement through the DPH receptor -skeletal muscle contraction will still take place if there is no ECF Ca2+ to come through the channel

timing of E-C coupling

-somatic motor neuron action potential followed by skeletal muscle action potential and then contraction -twitch: single contraction relaxation cycle in a skeletal muscle fiber -latent period: short delay, between the muscle action potential and the beginning of muscle tension development. Represents the time required for calcium release and binding to troponin -relaxation phase: tension decreases of the twitch -elastic elements of the muscle return the sarcomeres to their resting length

satallite cells

-stem cells: lie outside the muscle fiber membrane -become active: and differentiate into muscle when needed for muscle growth and repair

Duchene muscular dystrophy

-structural protein dystrophin -links actin to proteins in the cell membrane is absent -muscle fibers lack dystrophin, extracellular Ca2+ enters the fiber through small tears in the membrane or possibly through stretch-activated channels -calcium entry activates intracellular enzymes, resulting in breakdown of the fiber components -progressive muscle weakness -die before age 30 from failure of the respiratory muscles

charley horse or muscle cramp

-sustained painful contraction of skeletal muscles -muscle cramps caused by hyperexcitability of the somatic motor neurons controlling the muscle - neuron fires repeatedly, the muscle fibers of its motor unit go into a state of painful sustained contraction -stretching the muscle inhibits the somatic motor neuron, relieving cramp

fast-twitch oxidative-glycolytic muscle fibers (type 2A)

-tension two to three times faster -split ATP more rapidly -complete multiple contractile cycles more rapidly -faster tension development -pump Ca2+ into their SR more rapidly -twitches last 7.5 msec: playing piano -less fatigue -oxidative phosphorylation for ATP -have more mitochondria -more blood vessels in connective tissue to bring oxygen to the cells -myosin: red muscle -smaller diameters -properties of both oxidative and glycolytic: combination to produce ATP

In 1954 Andrew Huxley and Rolf Niedergerke discovered

-the length of the A band of a myofibril remains constant during contraction -A band represents the myosin filament -shortening of the myosin molecule could not be responsible for contraction

muscle contracts

-thick and thin filaments slide past each other -z disk of the sarcomere move closer together as the sarcomere shortens -I band and H zone where acting and myosin do not olverlap in resting muscle almost disappear -the length of the A band doesn't change

excitation contraction coupling

1. acetylcholine (ACh) is relased from the somatic motor neuron 2. ACh initiates an action potential in the muscle fiber 3. the muscle action potential triggers calcium release from the sarcoplasmic reticulum 4. calcium combines with troponin and initates contraction

series of elastic elements

-when sarcomeres shorten in the first stage of a contraction, elastic elements stretch -stretching: elastic elements allow the fibers to mainatin a relatively constant length even thought the sarcomeres are sortening and creating a tension

myosin head has two protein chains

1-heavy chain: motor domain that binds ATP an uses the energy from ATP high energy phosphate to create movement -motor domain acts as an enzyme considered a myosin ATPase -heavy chain also contains a binding site for actin 2. smaller light chain

contraction cycle

1. ATP binds and myosin detaches: ATP molecules binds to the myosin head -ATP binding decreases the actin-binding affinity of myosin, myosin releases from actin 2. ATP hydrolysis provides energy for the myosin head to rotate abd rettach to actin: ATP binding site on the myosin head closes around ATP and hydrolyzes it to ADP and inorganic phosphate (Pi) -ADP and Pi bound to myosin as energy released by ATP hydrolysis rotates the myosin head until it froms 90 -cooked position actin is 1-3 molecules away from where it started, but weak and low force -rotated position of myosin has stored potential energy and is waiting for calcium signal 3. power stroke: begins after Ca+2 bind to troponin to uncover the rest of the myosin-binding site -crossbridges become strong high-force bonds as myosin releases Pi, and allows myosin to swivel -head swing toward the M line, sliding the attached actin filament along with them -crossbridge tilting: myosin head and hinge region tilt from a 90 to 45 angle 4. myosin releases ADP: end of power stroke -myosin head is again tightly bound to actin in the rigor state -cycle is ready to begin once more as a new ATP binds to myosin

excitation contraction coupling detail

1. acetylcholine released into the synapse at a neuromuscular junction bind to ACh receptor-channels on the motor end plate of the muscle fiber -ACh open: allow Na+ (influx exceeds-electrochemical gradient force bigger) and K+ 2. depolarization: creating an end-plate potential (EPP) -action potential travels: t-tubules by opening voltage gasted Na channels 3-4. action potential moves down the t-tubules causes Ca2+ release from the sarcoplasmic reticulum -free cytosolic Ca2+ levels in a resting muscle are low, after action potential increases 100 fold -depolarization reaches DHP receptor: changes conformation and opens RyR Ca2+ release channels in the sarcoplasm reticulum 5. Ca2+ high binds to to tropinin, tropomyosin moves to the ON position 6. contraction occurs

different types of smooth muscle

1. by location: humans- vascular (blood vessels), gastrointestinal (walls of digestive tract and associated organs, such as the gallbladder), urinary (walls of bladder and ureters), respiratory (airway passages), reproductive (uterus in females and other reproductive structures in both females and males) and ocular (eye) 2. by contraction pattern: if it alternates between contraction and relaxation states or whether is is continuously contracted 3. by their communication with neighboring cells: electrically connected by gap junctions, they contract as a coordinated unit

troponin and tropomyosin in contraction

1. concentration begins in response to calcium signal, protein of troponin C binds reversibly to Ca2+ 2. calcium troponin C complex pulls trypomyosin completely away from actins myosin binding sites 3. on position enables myosin heads to form strong, high force corssbridges and carry out their power strokes 4. moves acting filament 5. contractile cycles repeat as long as the binding site are uncovered

smooth muscle contraction

1. contraction begins: cytosolic Ca2+ concentrations increase follow Ca2+ entry from the extracellular fluid and Ca2+ release from the SR 2. Ca2+ binds to calmodulin (CaM) 3. Ca2+-calmodulin complex activates an ezyme myosin light chain kinase (MLCK) 4. Ca2+-calmodulin activates MLCK, enzyme phosphorylates the myosin light protein chains 5. phosphorylation of myosin enhances myosin ATPase activity. Myosin ATPase activity is high, actin binding and crossbridge cycling increase tension in the muscle (very slow)

steps in muscle contraction

1. events in the neuromuscular junction: convert an acetylcholine signal from a somatic motor neuron into an electrical signal in the muscle fiber 2. excitation-contraction (E-C) coupling: muscle action potentials initiate calcium signals that in turn activate a contraction-relaxation cycle 3. sliding filament theory of contraction: contraction-relaxation cycle, intact muscles, one contraction-relaxation cycle is called a muscle twitch

two principles

1. force is created by actin-myosin crossbridge interaction between sliding filaments 2. contraction in smooth muscle, skeletal and cardiac muscle is initiated by an increase in free cytosolic Ca2+ concentrations

The total rotational force* created by the biceps depends on two things:

1. force of the muscle contraction and 2. distance between the fulcrum and the point at which the muscle inserts onto the radius

theories in fatigue

1. increased levels of Pi: producen when ATP and phosphocreatine are used for energy in the muscle fiber, can slow down myosin and alter power stroke 2. elevated phosphate levels decrease Ca2+ release from the SR 3. ion imbalances: K+ efflux, changes in Na+-K+-ATPase

electromechanical coupling

Contraction caused by electrical signaling

pharmacomechanical coupling

Contractions initiated by chemical signals without a significant change in membrane potential -can relax muscle tension whithout a change in membrane potential

tetanus

action potentials continue to stimulate the muscle fiber repeatdly at short intervels, relaxation between contraction dimishes until the muscle fiber achieves a state of maximal contraction

central fatigue

arise from the central nervous system. Includes subjective feelings of tiredness and a desire to cease activity. Low pH from acid production during ATP hydrolysis is often mentioned as a possible cause of fatigue, but only in cases of maximum exertion. failure of the CNS command neurons.

flexor

bones attached to a muscle or connected by a flexible joint, contraction of the muscle moves the skeleton

skeletal muscles are usually attached to bones

by tendons made of collagen

troponin

calcium binding complex of three proteins -troponin controls the positioning of an elongated protein polymer tropomyosin

nebulin

inelastic giant protein that lies alongside thin filaments and attaches to the Z disk -nebulin helps align the actin filaments of the sarcomere

summation

interval of time between action potentials is shortened, the muscle fiber does not have time to relax between stimuli, resulting in a more forceful contraction

tonic smooth muscle in the walls of some blood

maintain an intermediate level of contraction -under tonic control by the nervous system -vascular smooth muscle contracts and relaxes as the situation demands

myosin

motor protein with the ability to create movement -determines the muscle speed of contraction -composed of protein chains that intertwine to form a long tail and a pair of tadpole-like heads -rod-like tail is stiff but the protruding myosin heads have an elastic hinge region where the heads join the rods -hinge region allows the head to swivel around their point of attachment

skeletal muscle is a collection of..

muscle cells or muscle fibers -fiber: long cylindrical cell with up several hundred nuclei near the surface of the fiber -largest cell in the body

rigor mortis

muscles are unable to bind more ATP, so they remain in the tightly bound rigor state -freeze owing to inmovable corssbridges

phasic smooth muscle

muscles that undergo periodic contraction and relaxation cycles ex: wall of the lower esophagus which contracts only when food passes through it -other smooth muscles (intestine): cycle rhythmically through contractions alternating with relaxation

insertion

of the muscle is the more distal or more mobile attachment

single twitches

repeated action potentials are seperated by long intervals of time, muscle fiber has time to relax completely betweent stimuli

fatigue

reversible condition in which and exercising muscle is no longer able to generate or sustain the expected power output

terminal cisternae

sacroplasmic reticulum consist of longitudinal tubules with enlarged end regions

The arm amplifies speed of movement of the load

small movement of the forearm at the point where the muscle inserts becomes a much larger movement at the hand -speed of contraction amplified at the hand, distae of the load is moved and the speed at which this movement takes place

paracrine signals alter

smooth muscle contraction ex: asthma in smooth muscle of the airways constricts in response to histamine release -reversed: administration of epinephrine, neurohormone that relaxes smooth muscle and dilated the airway

cell membrane

store independent Ca2+ entry from the extracellular fluid takes place with the help of membrane channels that are voltage-gated, ligand-gated or mechanically gated

Do muscles run out of ATP?

studies show that intense exercise uses only 30% of the ATP in a muscle fiber

transverse tubules

terminal cisternae are adjacent to and closely associated with a branching network -t tubules -triad: t tubule and two flanking terminal cisternae -makes the lumen of t tubules continuous with the extracellular fluid -allow action potentials to move rapidly from the cell surface into the interior of the fiber, reach the terminal cisternae simultaneously

ryanodine receptor (RyR)

the calcium release channel of the sarcoplasmic reticulum

tonic smooth muscle

continuously contracted, always maintain some level of muscle tone ex. esophageal and urinary bladder sphincters

isotonic contraction

creates force and moves a load

contraction

creating of tension in a muscle is an active process that requires energy input from ATP

sarcoplasm

cytoplasm

Botulinum toxin

decrease acetylcholine release from somatic motor neuron -treatment for writers cramp: disabling cramp of the hand that apparently arises as a result of hyperexcitability in the distal portion of the somatic motor neuron -botox: injected under the skin temporarily paralyzes facial muscles that pull the skin into wrinkles

latch state

dephosphorylated myosin may remain in an isometric contraction

muscles require energy constantly

during contraction for crossbridge movement and release, during relaxation to pumps Ca2+ back into the sarcoplasm reticulum, after E-C couping restore Na+ and K+ to the extracellular and intracellular compartments

creatine kinase (CK)

enzyme that transfers the phosphate group from phosphocreatine to ADP -creatine phosphokinase (CPK) -elevated blood level of creatine causes muscle damage in cardiac and skeletal

antagonistic muscle groups

flexor-extensor pairs, exert opposite effects -biceps brachii act as the flexor and triceps brachii which act as the extensor

muscle tension

force created by a contracting muscle

mechanics

how muscles move load and how the anatomical relationship between muscles and bones maximizes the work the muscles can do

Titin

huge elastic molecule and the largest known protein, composed of more than 2500 amino acids -molecules streches from one Z disk to the neighboring M line

complete or fused tetanus

the stimulation rate is fast enough that the muscle fiber does not have time to relax. Instead, it reaches maximum tension and remains there

Incomplete or unfused tetanus

the stimulation rate of the muscle fiber is not at a maximum value, and consequently the fiber relaxes slightly between stimuli.

smooth muscle

primary muscle of internal organs and tubes -stomach, urinary bladder and blood vessels -primary function: influence the movement of material into, out of, and within the body -ex: passage of food through the gastrointestinal tract -lacks cross bands of striated muscles: contains an organized arrangement of contractile fibers within the muscle cells -involuntary -extrensic control: autonomic innervation -modulated by endocrine system

endurance athletes

prodominance of slow-twitch fibers, sprinters or hockey players and weight lifters larger percentage of fast twitch fibers -aerobic capacity of some fast-twitch fibers can be enhanced until they are almost as fatigue-resistant as slow-twitch fibers -increases numbers of capillaries and mitochondria in muscle tissue

M line

proteins that form the attachment site for thick filaments -divides the A band in half -mittel

fast-twitch glycolytic fibers type 2x

-anaerobic glycosis to produce ATP -H+ from ATP hydrolysis: acidosis, fatigue more easily -white muscle: lower myoglobin -large in diamater -run out of oxygen after repeated contractions -rely on anerobic glycolysis for ATP and fatigue rapidly -fastest -jumping, quick, fine movements

pheripheral fatigue

-arise from neuromuscular junction and the contractile elements of the muscle -excitation-contraction failure in the muscle fiber -depletion of muscle glycogen stores: release of Ca2+ from sarcoplasmic reticulum

skeletal muscle

-attached to the bones of the skeleton, enabling these muscles to control body movement -striated muscles: alternating light and dark bands seen under the light microscope -voluntary -contract only in response to a signal from a somatic motor neuron

Force calculations

-biceps hold the forearm stationary and flexed at 90 angle,the muscle must exert enough upward rotational force to exactly oppose the downward rotational force exerted by gravity on the forarm -calculations: the downward rotational force on the forearm is proportional to the weight of the forearm (F2) times the distance from the fulcrum to the forearm's center of gravity

stretch activated channels

-blood vessels -contains stretch activated channels that open when pressure or other force distorts the cell membrane -cell depolarizing: opens calcium channels -adapt is the cells are stretch for longer times: Ca2+ channels begin to close in a time-dependent fashion -muscles relaxes

smooth muscles must act as integrating centers

-blood vessels receive contradictory messages from two sources: one message signal for contraction and the other for relaxation -execute appropriate response

relaxation

-calcium must be removed from the cytosol -SR pumps Ca2+ back into its lumen using a Ca2+-ATPase -calcium releases troponin and tropomyosin block actin's myosin binding site

smooth muscle functions

1. must operate over a large range of lengths -found in the walls of hollow organs and tubes 2. Within an organ, the layers of smooth muscle may run in several directions 3. contract and relax much more slowly than skeletal or cardiac muscle 4. uses less energy to generate and maintain a given amount of force -slow down they myosin ATPase, crossbridges cycle slow -fewer mithochondria, relies on glcolysis for ATP production 5. smooth muscle can sustain contraction for extended periods without fatiguing (tonically active) 6. have small, spindle-shaped cells with a single nucleus 7. the contractile fibers are not arranged in sarcomeres -lack the distinct banding patterns 8. contraction may be initiated by electrical or chemical signals or both 9. controlled by autonomic system 10. lacks specialized receptor regions -found in cell surface 11. Ca2+ for contraction comes from the extracellular fluid as well as from the sarcoplasmic reticulum 12. Ca2+ signal initates a cascade that end with phosphorylation of myosin light chains and activation of myosin ATPase

other ways to stored energy

1.metabolism of biomolecules to transfer energy from covalent bonds to ATP 2. carbohydrates, glucose most rapid and efficient source of energy for ATP production -glucose metabolized through glycolysis to pyruvate: citric acid and oxygen produces 30 ATP for each molecule of glucose 3. oxygen concentration fall: anaerobic glycolysis, glucose metabolized to lactate that yields 2 ATP per glucose 4.fatty acids: requires oxygen, fatty acids converted to acetyl CoA is slow and cannot produce ATP rapidly 5. proteins not a source for muscle contraction: amino acids for synthesizing proteins than ATP

relaxation in smooth muscle

6. free Ca2+ removed from the cytosol when Ca2+-ATPase pumps it back into the SR -some Ca2+ is pumped out of the cell with the help of Ca2+-ATPase and the Na+-Ca2+ exchanger (NCX) 7. decrease in free cytosolic Ca2+ causes Ca2+ to unbind from calmodulin 8. absense of Ca2+-calmodulin, myosin light chain kinase becomes inactive. MLCK becomes less active, myosin light chain phosphotase deposphorylates myosin 9. Myosin ATPase activity decreases, and the muscle relaxes

isometric contractions

Muscle contracts but there is no movement, muscle stays the same length

single unit smooth muscle

Smooth muscle with gap junctions linking the cells together so they function as a unit

multiunit smooth muscle

cells are not linked electrically and each muscle cell functions independently

sarcomeres

myofibril composed of several proteins organized into repeating contractile structures

rigor state

myosin heads are tightly bound to G-actin molecules -no nucleotide (ATP or ADP) is bound to myosin -very brief

pacemaker potentials

oscillating membrane potentials have regular depolarizations that always reach threshold and fire an action potential. they create regular rhythms of contraction. Pacemaker potentials are found in some cardiac muscles as well as in smooth muscle. Both slow wave and pacemaker potentials are due to ion channels in the cell membrane that spontaneously open and close.

muscle disorders arise from..

overuse -severe trauma: muscle fibers, the connective tissue sheath or the union of muscle and tendon may tear