Muscular System ni maam karra baro

8/11/2019 Muscular System ni maam karra baro

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Animal Movement Most animal movement depends on a single

fundamental mechanism:

contractile proteins - can change their form to allowrelaxation and contraction

Contractile machinery is always composed of ultrafinefibrils arranged to contract when powered byATP.

By far the most important protein contractile system:actomyosin system = composed of two proteins,actin and myosin


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3 kinds of animal movement: ameboid

ciliary and flagellar

muscular


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Ameboid movement a form of movement especially characteristic of

amebas and other unicellular forms

move by extension and withdrawal of pseudopodia

(false feet)

the outer layer of nongranular, gel-like ectoplasm

surrounds a more fluid core of endoplasm


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Ciliary and Flagellar movement

Cilia are minute, hair-like, motile processes thatextend from surfaces of cells of many animals.

Flagellum is a whiplike structure longer than a ciliumand usually present singly or in small numbers at one

end of a cell.


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Ciliary Movement


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Flagellar Movement


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Muscular movement Contractile tissue that is highly developed is called a

fiber

fibers are arranged in so many different configurationsand combinations that permits any movement


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Types of Vertebrate MuscleClassified according to the appearance of muscle cells

(fibers):

1. Skeletal striated, multinucleated

2. Cardiac striated, uninucleated

3. Smooth not stritated, uninucleated


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Skeletal Muscle typically organized into

sturdy, compact bundles orbands

attached to skeletal elementsand is responsible for

movements of body parts


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packed into bundles called fascicles

which

areenclosed by tough connective tissue

fascicles are in turn grouped into a discrete musclesurroundedby a thick connective tissue layer

Skeletal muscle is calledvoluntary muscle because it

is stimulated by motor neurons under consciouscontrol


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Smooth Muscle lacks the striations typical of

skeletal muscle

each cell contains a single,central nucleus

has involuntary contractions


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Cardiac Muscle muscle of the vertebrate heart

combines certain characteristicsof both skeletal and smooth

muscle an involuntary muscle

the heartbeat originates withinspecialized cardiac muscle

has intercalated discs thatconnect muscle fibers


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Muscle structure Each cell / fiber, contains numerous myofibrils,

packedtogether by a plasma membrane, thesarcolemma.

The myofibril contains two types of filaments:

myosin, andactin.

Theseare the contractile proteins of the muscle. Actin

filaments are held together by a dense structure calledthe Z line. The functional unit of the myofibril, thesarcomere, extends between successive Z lines.


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Myosin Filament Each myosin filament is composed of many myosin

molecules packed in a bundle.

Each myosin molecule contains two polypeptidechains, each having a club-shaped head.

They are lined up in two bundles to form a myosinfilament.

The myosin heads act as binding sites for high-energy

ATP and during muscle contraction they formmolecular cross bridges that interact with the actinfilaments.


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Actin Filament composed of a backbone of a double strand of the protein

actin, twisted into a double helix.

two actin-binding proteins, tropomyosin and troponin,form part of the actin filament complex.

Two thin strands of tropomyosin lie near the groovesbetween the actin strands. Troponinis located at intervalsalong the actin filament.

Troponin acts as a calcium-dependent switch that controlsthe contraction process.

The actin filament complexes extend outward from bothsides of the Z line and overlap with myosin bundles towardthe center of each sarcomere


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Sliding Filament Hypothesis the actin and myosin filaments become linked together by

molecular cross bridges, which act as levers to pull thefilaments past each other.

during contraction, the club-shaped heads on the myosinfilaments form cross bridges, alternately attaching to andreleasing from receptor sites on the actin filaments.

as contraction continues, the Z lines are pulled closertogether. Thus the sarcomere shortens. Because allsarcomere units shorten together, the whole musclecontracts.


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Relaxation is a passive process.

When cross bridges between the actin and myosinfilaments release, the sarcomeres are free to lengthen.

This requires some force, which is supplied by recoil ofelastic fibers within the connective tissue layers of the

muscle.


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Control of contraction Muscle contracts in response to nerve stimulation.

Skeletal muscle fibers are innervated by motorneurons whose cell bodies are located in the centralnervous system

If the nerve supply to a muscle is severed, the muscleatrophies, or wastesaway.

Amotor neuron and all muscle fibers it innervates iscalled a motor unit.

The motor unit is the functional unit of skeletal musclecontrol.


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Neuromascular Junction The place where a motor axon terminates on a muscle fiber is

called the neuromuscular ( or myoneural) junction.

AT THE JUNCTION YOU WILL FIND THE FF:

1. Synaptic cleft - thinly separates a nerve terminal and musclefiber

2. Synaptic vesicles stores acetylcholine, released into thesynaptic cleft when a nerve signal or action potential reaches a

synapse.3.Acetylcholineis a neurotransmitter that diffuses across the

synaptic cleft and acts on the sarcolemma, by binding toreceptor sites and generating an electrical depolarization


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Excitation-Contraction coupling

1. When muscle is stimulated and the action potential istransmitted down the T-tubules, the electricaldepolarization stimulates the sarcoplasmic reticulumsurrounding the fbrils to release calcium ions.

2. The calcium binds to the actin-binding protein, troponin.

3. Troponin immediately undergoes changes in shape that

causes tropomyosin to move out of its blocking position,exposing active sites on the actin filaments.


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4. Myosin heads then bind to these sites, forming cross bridgesbetween adjacent myosin and actin filaments.

5. This sets in motion an attach-pull-release cycle, or cross-bridge cycling, that occurs in a series of steps.

6. ATP hydrolysis activates the myosin head, which swings 45degrees, at the same time releasing a molecule of ADP. Thisis the power stroke that pulls the actin filament.

7. End when phosphate is released and another ATP moleculebinds to the myosin head, freeing it from the active site.


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Energy for contraction Muscle contraction requires large amounts of energy

and ATP is the immediate source of energy.

ATP can be obtained from 3 sources.

Glucose is transported to muscle in the blood where itis catabolized during aerobic metabolism to produceATP.

Glycogen store within muscle can also supply glucose

molecules for ATP production. Muscles have an energy reserve in the form of

creatine phosphate.


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Glycogen a polysaccharide chain of glucose molecules stored in

both liver and muscle. But muscles have more; three-fourths of all glycogen in the body is stored in muscle.

3 advantages of glycogen: it is relatively abundant

it can be mobilized quickly

it can provide energy under anoxic conditions

Enzymes convert glycogen to glucose-6-phosphatemolecules, the first stage of glycolysis


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Creatine Phosphate a high-energy phosphate compound that stores bond

energy during periods of rest

as ADP is produced from ATP during contraction,creatine phosphate releases its stored bond energy toconvert ADP to ATP.

This reaction can be summarized as:

Creatine Phosphate + ADPATP + Creatine


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Oxygen debt

muscles rely heavily on glucose and oxygen suppliestransported to muscle via the circulatory system

if activity is not too vigorous glucose can be completelyoxidized to CO2 and H2O by aerobic metabolism.

during prolonged activities blood flow to the muscles,cannot supply oxygen to the mitochondria rapidly enoughto complete oxidation of glucose.

muscles result eventually to obtaining energy fromanaerobic glycolysis which results to formation of lacticacid

build up of lactic acid causes muscle fatigue and oxygendebt

Muscular System ni maam karra baro

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