muscles chapter 12

muscle relaxation

-calcium concentration in the cytosol must decrease. -calcium unbinds from troponin. -troponin allow tropomyosin to return to off position. the filaments of sarcomere slide back to original position with aid of titian and elastic connective tissue.

the contraction cycle

1) ATP binds and myosin detaches 2) ATP hydrolysis provides energy for the myosin yea to rotate and reattach to actin 3) power stroke 4) myosin releases ADP

excitation contraction coupling

1) acetylcholine is released 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 initiate contraction.

3 types of muscle tissues

1) cardiac 2) skeletal 3) smooth

the diversity of motor units in the muscle allows to vary contraction by

1) chaining the types of motor units that are active 2) chaining the number of motor units that are responding at any one time.

contractile cycle - calcium signal initiates contraction

1) troponin-C binds reversibly to calcium. 2) this complex pulls tropomyosin away from actin's myosin binding sites. 3) on position enables myosin heads to form strong high force cross bridges and carry out power strokes 4). moving the actin filament 5)

myoglobin

A globular protein found in muscle tissue that has the ability to bind oxygen. Myoglobin helps to store oxygen in the muscle for use in aerobic respiration (it does not move, just stays there). Muscles that participate in endurance activities (including cardiac muscle) have abundant supplies of myoglobin.

troponin

a calcium binding complex of three proteins, troponin controls the positioning of an elongated protein polymer, tropomyosin.

events of neuromuscular junction

convert an acetylcholine signal from a somatic motor neuron into an electrical signal in the muscle fiber.

according to the convention for naming enzymes what does the name creatine kinase tell you about this enzyme's function?

creatine is the substrate and kinase tells you that this enzyme phosphorylates the substance.

each myosin molecule has binding sites for what molecules?

ATP and actin

Myosin hydrolyzes ATP to ADP and phosphate. Enzymes that hydrolyze ATP are collectively known as

ATPase

sarcoplasm

cytoplasm of muscle fiber

I band

Appears Light; Thin filaments only, actin only, Z disk runs right in the middle of it.

A band

Band of sarcomere that extends full length of the thick filament. A band includes regions of thick & thin filament overlap, & a region of thick filament only. A bands alternate with I bands to give skeletal and cardiac muscle a striated appearance. A band doesn't shorten during muscle contraction.

sarcolemma

Cell membrane of a muscle fiber

Titin

Connects the Z line and the M disc. Large skeletal muscle protein. aids recoil. more than 25000 amino acids. 1) stabiles the position of the contractile filaments and 2) its elasticity returns stretched muscles to their resting length

myosin atpase

Enzyme in the head of myosin that hydrolyzes the ATP

what is the difference between f actin and g actin

F actin is the polymer filament of actin made of the globular g actin molecules

muscle tension

Force exerted on an object by contracting muscle

power stroke

Myosin heads, which are hinged at their base, then toggle in a mechanism similar to a light switch. This action causes thin myofilaments to slide toward the center of the sarcomere which shortens the overall length of the muscle fiber. We have contraction!

end plate potential

The depolarzation of the motor end plate on a muscle cell.

H zone

The region at the center of an A band of a sarcomere that is made up of myosin only. The H zone gets shorter (and may disappear) during muscle contraction. M line passes right in the middle of H zone.

L type calcium channel called a dihydropyridine DHP receptor

The t tube membrane voltage sensing. transduction of the electrical signal into a calcium signal requires two key membrane proteins. these specialized ion channels are mechanically linked to calcium release channels in the adjacent sarcoplasmic reticulum.

sarcoplasmic reticulum

a form of modified endoplasmic reticulumn that warps around each myofibril like a peace of lace. it concentrates and sequesters Ca2+ with the help of a calcium ion ATPase in the SR membrane. Calcium release from the SR creates calcium signals that play a key role in contraction in all types of muscle.

a skeletal muscle is a collection off muscle cells or muscle fibers just as

a nerve is a collection of neurons.

twitch

a single contraction relaxation cycle in a skeletal muscle fiber.

what is the chemical signal at a neuromuscular junction?

acetylcholine

t tubules

allow action potentials to move rapidly from the cell surface into the interior of the fiber so that they reach the terminal cistrae nearly simultaneously. W/O it, slower and less direct process that would delay the response time of the muscle fiber.

what is the function of t tubules?

allow action potentials to travel from the surface of the muscle fiber to its interior.

isotonic contraction

any contraction that creates force and moves a load. sarcomeres shorten more but because elastic elements are already stretched the muscles shorten

lenghtening eccentric contraction

are thought to contribute most to cellular damage after exercise and to lead to delayed muscle soreness

sarcomere shortens during contraction

as contraction takes place, actin and myosin do not change length but instead slide past one another. H zone and I band both shorten while A band remains constant.

fatigue submaxiaml exertion

associated with depletion of muscle glycogen storage. leads to alterations in the release of calcium from the sarcoplasmic reticulum

why are the ends of the A band the darkest region of the sarcomere when viewed under the light microscope?

because they are where thick and thin filaments overlap.

movement of what ions in what directions creates a) the neuronal action potential? b) the muscle action potential?

both neuronal and muscle action potentials are due to Na+ entering fiber during depolarization & K+ leaving during depolarization. neuronal channel for Na+ entry is a voltage gated Na+ channel, but muscle channel for Na+ entry is acetylcholine gated monovalent cation channel.

universal second messenger

calcium - signal for muscle contraction

contraction relaxation cycle

can be explained by the sliding filament theory of contraction. In intact muscles one contraction relaxation cycle is called a muscle twitch.

cytosol between myofibrils

contains many glycogen granules and mitochondria. glycogen, the storage form of glucose found in animals is a reserve source of energy. mitochondria provide much of the ATP of muscle contraction through oxidative phosphorylation of glucose and other biomolecules.

if potassium concentration increases in the ECF surrounding a cell but does no change significantly in the cell's cytoplasm, the cell membrane --- and becomes --- negative

depolarizes, less

fascicles

each skeletal muscle fiber is sheathed in connective tissue with groups of adjacent muscle fibers bundled together into units called fascicles. collagen, elastic fibers, nerves & blood vessels are found between fascicles. Entire muscle is enclosed in a connective tissue sheath, continuous with connective tissue around muscle fibers & fascicles & with the tendons holding muscle to underlying bones.

rigor state

end of power stroke, myosin tightly binds to actin. it is brief bc ATP binds to myosin again once ADP is released. Rigor mortis after death muscle freezes no ATP. tight binding of actin and myosin persists for a day.

muscle contraction summary

events of neuromuscular junction - excitation contraction coupling - Ca2+ signal - contraction relaxation cycle - 1) muscle twitch 2) sliding filament theory.

antagonistic muscle groups

flexor-extensor pairs. they exert opposite effects. e.g. biceps brachia which acts as flexor and the triceps brachia which acts as the extensor, hamstring, flexor and quadriceps, extensor in the upper legg. tibialis anterior, flexor, gastrocnemius, extensor for foot movement at the ankle.

muscles have two common functions

generate motion and to generate force. skeletal muscles generate heat as well and contribute significantly to the homeostasis of body temperature. the brain direct our muscles to shiver, creating additional heat.

myosin ATPase

hydrolyzes ATP to ADP and inorganic phosphate. an enzyme found on the globular heads of the myosin crossbridges, which breaks down ATP to release energy needed for muscle contraction crossbridge motion.

fatigue short duration maximal exertion

increased level of inorganic phosphate produced from the use of ATP and phosphocreatine

what is the response of a muscle fiber to a increase in the firing rate of the somatic motor neuron?

increased motor neuron firing rate causes summation in a muscle fiber, which increases the force of contraction.

crossbridge

when myosin heads attach to actin during contraction

elevated level of blood creatine kinase enzyme

indicates damage to skeletal or cardiac muscles. This is because both muscles contain different isozymes.

nebulin

inelastic giant protein that lies alongside thin filaments and attaches to the Z disk. Helps align the actin filaments of the sarcomere.

cardiac muscles

involuntary, not so true - found in heart, moves blood through the circulatory system. 1) smaller Striated 2) branched 3) uninucleate 4) cells joined in series by junctions called intercalated disks

smooth muscles

involuntary, not so true - primary muscle of internal organs and tubes such as the stomach, urinary bladder and blood vessels. primary function, influence the movement of material into, out of and within the body. 1) small 2) lack striations - less organized arrangement of contractile fibers within the muscle cells

myosin

is a motor protein with the ability to create movement. determine muscle's speed of contraction. consisted of protein chains are intertwined to form a long tail and a pari of tadpole like heads.

actin

is a protein that makes up the thin filaments of the muscle fiber. A globular protein that links into chains, two of which twist helically about each other, forming microfilaments in muscle and other contractile elements in cells.

the signal to initiate muscle contraction

is an intracellular calcium signal and movement is created when a motor pertain called myosin uses energy from ATP to change its conformation. vary with different muscle types.

recruitment

is controlled by the nervous system and proceeds in a standardized sequence.

origin of a skeletal muscle

is the end of the muscle that is attached closeted to the trunk pr to the more stationary bone

insertion of the skeletal muscle

is the more distal or more mobile attachment.

excitation contraction coupling

is the process in which muscle action potentials initiate calcium signals that in turn activate a contraction relaxation cycle.

relaxation

is the release of tension created by a contraction

what are the three anatomical elements of a neuromuscular junction?

it consists of 1) axon terminals from one somatic motor neuron, 2) synaptic cleft 3) the motor and plate on the muscle fiber.

satellite cells

lie just outside the muscle fiber membrane. satellite cells activate and differentiate into muscle when needed for muscle growth and repair.

asynchronous recruitment

when recruiting, the nervous system modulates the firing rates of the motor neurons so that different motor units take turns maintaining muscle tension. Alternating active motor units allows rest between contractions and avoiding fatigue in maximal contraction

myofibrils

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

extensor

moves bones away from each other - the muscle is called an extensor if the bones move away from each other when the muscle contracts and the movement is called extension.

flexor

moves bones closer to each other - when the bond attached to a muscle are connected by a flexible joint, contraction of the muscle moves the skeleton. the muscle is called a flexor if the centers of the connected bones are brought closer together when the muscle contracts and the movement is called flexion.

phosphocreatine

muscle at rest store energy from ATP metabolism + creatine kinase to ADP and phosphocreatine. when muscles become active such as during exercise the high energy phosphate group of phosphocreatine is transferred to ADP, creating more ATP to power the muscles.

thick filament

myosin heads are clustered at each end of the filament and the central region of the filament is a bundle of myosin tails.

M line

myosin linked with accessory proteins.

sliding filament theory of contraction

overlapping acton and myosin filaments of fixed length slide past one another in an energy requiring process that results in contraction.

in the presence of adequate oxygen,

pyruvate goes into citric acid cycle producing 30 ATP for each molecule of glucose.

fast twitch oxidative glycolytic fiber type2A

red muscle fibers that contract rapidly, but sustain shorter contractions; rely mostly on aerobic respiration to generate ATP, playing piano, twitches last 7.5 msec. walking and standing

slow twitch fiber type 1

red muscle. slow to fatigue and have a high level of aerobic endurance, used for long-term, low to moderate intensity activities ranging from maintaining proper posture to long-distance running,

oxidative fivers

red muscle. smaller diameter, more mitochondria, more myoglobin and more capillaries, maintain a abetter supply of oxygen and are able to use oxidative phosphorylation for ATP production

Sarcoplasmic reticulum calcium release channels are known as

ryanodine receptors or RyR.

each myofibril is composed of

several types of proteins: the contractile proteins myosin and actin, the regulatory proteins tropomyosin and troponin and the giant accessory proteins titian and nebulin.

latent period

short delay - between the muscle action potential and the beginning of muscle tension development. this delay represents the time required for calcium release and binding to troponin.

striated muscles

skeletal and cardiac muscles are classified as striated muscles because of their alternating lint and dark bands seen under the light microscope.

tendons

skeletal muscles are usually attached to bones by tendons made of collagen.

who has more slow and who has more fast twitch fibers?

sprinter fast marathoner slow

tetanus

state of maximal contraction achieved by short intervals of muscle fiber stimulation at high frequency until the relaxation in between diminishes. there are two types unfused, short relaxation, complete, no relaxation more likely followed by fatigue.

temporal summation in neurons means that the ---- of the neuron increases when two depolarizing stimuli occur close together in time.

strength of the graded potential

summation in muscle fibers means that the --- of the fiber increases with repeated action potentials.

tension

transverese tubules

terminal cistrae are adjacent & closely associated with a branching network of transverse tubules. 1 t-tubule & its two flanking terminal cistrae r called a triad. membrane of t-tubules r a continuation of muscle fiber membrane, which makes lumen of t-tubules continuous with ECF.

why are skeletal muscles described as striated?

the banding pattern of organized filaments in the sarcomere forms striations in the muscle.

motor neuron

the basic unit of contraction in an intact skeletal muscle, composed of a group of muscle fibers that function together and the somatic motor neuron that controls them.

contraction

the creation of tension in a muscle is an active process that requires energy input from ATP.

in the sliding filament theory of contraction, what prevents the filaments from sliding back to their original position each time a myosin head releases to bind to the next actin binding site?

the cross bridges do not all unlink at one time, so while some myosin heads are free and swiveling, others are still tightly bound.

what events are taking place during the latent period before contraction begins?

the events of the latent period include creation of the muscle action potential, release of calcium from the sarcoplasmic reticulum, and different of calcium to the contractile filaments

skeletal muscles fibers are

the largest cells in the body, created by the infusion of many individual muscle cells.

how does the nervous system increase the force of contraction in a muscle composed of many motor units?

the nervous system increases the rate of contraction by recruiting additional motor units.

which part of contraction requires ATP? does relaxation require ATP?

the release of myosin heads from actin requires ATP binding. Energy from ATP is required of the power stroke. relaxation does not directly require ATP, but relaxation cannot occur unless Ca2+ is pumped back into the sarcoplasmic reticulum using a Ca2+ ATPase.

terminal cisternae

the sarcoplasmic reticulum consist of longitudinal tubules with enlarged end regions called the terminal cistern.

calcium ATPase

the sarcoplasmic reticulum pumps calcium back into its lumen using a calcium ATPase. As the free cytosolic calcium concentration decreases, the equilibrium between bound and unbound calcium is disrupted.

name an elastic fiber in the sarcomere that aids relaxation

titin is an elastic fiber in sarcomere.

skeletal muscles

voluntary - attached to bones, control body movements 1) large 2) multinucleate cells 3) contrat in response to signal from somatic motor neuron, cannot initiate their own contraction, 4) not directly influenced by hormones. 40% of body weight

fast twitch glycolytic fiber type 2B

white Muscle fibers that can produce a large amount of tension in a very short period of time but fatigue quickly. rely on oxidative phosphorylation to produce ATP, have more mitochondria and blood vessels, jumping, quick fine movements.

glycolytic fibers

white muscle. large diameter, lower myoglobin, fear blood vessels, more likely to run out of oxygen after repeated contractions. rely on anaerobic glycolysis for ATP synthesis and fatigue most rapidly.

tropomyosin

wraps around actin filaments & partially covers actin's myosin binding sites. This is tropomyosin's in off position. myosin is blocked from completing its power stroke. Before contraction can occur, tropomyosin must be shifted to an on position that uncovers remainder of actin's myosin binding site.