Skeletal Muscles Flashcards by Jessica Taylor

Each muscle fiber is served by one __, one __, and one or more veins.

artery, nerve

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Where do all innervations enter/exit in the muscle?

The central part, and branch through connective tissue sheaths

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Every skeletal muscle fiber is supplied by a __ ___ that controls its activity.

Nerve ending

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Skeletal muscles have a huge nutrient and oxygen need; generates large amount of __ __

Metabolic waste

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What are the connective tissue sheaths of skeletal muscle, external to internal?

Epimysium
Perimysium
Endomysium

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What do the connective tissue sheaths of skeletal muscles do?

Support cells; reinforce whole muscle

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Dense irregular connective tissue surrounding entire muscle; may blend with fascia

Epimysium

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Fibrous connective tissue surrounding fascicles (groups of muscle fibers)

Perimysium

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Fine areolar connective tissue surrounding each muscle fiber

Endomysium

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Skeletal muscle attach in at least 2 places. What is the insertion?

Moveable bone, farthest point

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What is the origin?

Immoveable bone, closest point of attachment

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Epimysium fused to periosteum of bone or perichondrium of cartilage

Direct attachment

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Connective tissue wrappings extend beyond muscle as ropelike tendon or sheetlike aponeurosis

Indirect attachment

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A muscle consists of hundreds of thousands of muscle cells, plus connective tissue wrappings, blood vessels, and nerve fibers. It is covered externally by the ___.

Epimysium

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A fascicle is a discrete bundle of muscle cells, segregated from the rest of the muscle by a connective tissue sheath. The fascicle is surrounded by

Perimysium

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A muscle fiber is an elongated multinucleated cell; it has a banded (striated) appearance. The muscle fiber is surrounded by

Endomysium

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Myofibrils are rodlike contractile elements that occupy most of the muscle cell volume. Composed of sarcomeres arranged end to end, they appear banded, and bands of adjacent myfibrils are aligned. What are myofibrils composed of?

Composed of bundles of myofilaments = sarcomeres

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A sarcomere is the __ __, composed of myofilaments made up of contractile proteins.

Contractile unit

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Contractile myofilaments are of two types: __ and __.

Thick and thin

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Thick filaments contain bundled ___ molecules.

myosin

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The sliding of the thin filaments past the thick filaments produces muscle ___.

Shortening

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Plasma membrane is called

Sarcolemma

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Cytoplasm of the skeletal muscle fiber

Sarcoplasm

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What is the sarcoplasm made of?

Glycosomes for glycogen storage

Myoglobin for O2 storage

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What are the modified structures of skeletal muscle fibers?

Myofibrils, sarcoplasmic reticulum, and T tubules

What are myofibrils?

- Densely packed, rodlike elements - ~80% of cell volume - Contain sarcomeres (contracile units) - Exhibit striations

Sarcomeres are the __ __ of myofibrils and contain ___

Contractile units | Myofilaments

Perfectly aligned repeating series of dark A bands and light I bands

Striations

Color of A bands?

Dark

Color of I bands?

Light

What is the connective tissue of epimysium?

Dense irregular connective tissue

What is the connective tissue of perimysium?

Fibrous connective tissue

What is the connective tissue of endomysium?

Fine areolar connective tissue

Myofibrils contain...?

Sarcomeres

Sarcomeres contain...?

Myofilaments

Lighter region in midsection of dark A band where filaments do not overlap

H zone

What does the H in H zone stand for?

"helle" ; bright | lighter region in midsection of A band where filaments do not overlap

Line of protein myomesin bisects H zone

M line

What does the M in M line stand for?

M for middle

Coin-shaped sheet of proteins on midline of light I band that anchors thin filaments and connects myofibrils to one another

Z disc

What does the Z in Z disc stand for?

Represents the zig zag appearance of the Z disc

Thick filaments ...

Run entire length of an A band

Thin filaments ...

Run length of I band and partway into A band

Region between two successive Z discs.

Sarcomere

What does the word sarcomere literally translate into?

Muscle segment

What is the smallest contractile unit (functional unit) of muscle fiber?

Sarcomere

Sarcomeres align along ___ like boxcars of train, extending from one Z disc to another and to another.

myofibril

Sarcomeres contains A band with 1/2 ____ at each end.

I band

Sarcomeres are composed of thick and thin myofilaments made of __ __.

Contractile proteins

Each bright H zone is bisected vertically by a dark line called the M line formed by molecules of the protein ...?

Myomesin

Each light I band (where only thin filaments are) has a midline darker interruption called the

Z disc

Region of a sarcomere with thick filaments only

H zone

Region of a sarcomere with thin filaments only

I band

Region of a sarcomere with thick filaments linked by accessory proteins

M line

Thick and thin filaments overlap

A band

Which filament containing myosin (red) extends the entire length of the A band?

Thick

Thick filaments are connected in the middle of the sarcomere at the ___.

M line

Which filament containing actin (blue), located more laterally, extends across the I band and partway into the A band?

Thin

What anchors the thin filaments?

Z disc, the coin shaped sheet

What filament extends from the Z disc and connects each myofibril to the next throughout the width of the muscle cell?

Intermediate filaments

Myosin myofilaments are thick or thin?

Thick

Actin myofilaments are thick or thin?

Thin

Actin/thin myofilaments are anchored to ?

Z discs

Myosin/thick myofilaments are connected at ?

M line

Thick filament is composed of the protein...?

Myosin

Each myosin molecule consists of __ heavy and __ light polypeptide chains

2, 4

Myosin __contain 2 interwoven, heavy polypeptide chains

Tails

Myosin __contain 2 smaller, light polypeptide chains that act as __ __ during contraction.

Heads, Cross bridges

The globular myosin heads are the business end of myosin. Three actions of myosin heads are:

- Binding sites for actin of thin filaments - Binding sites for ATP - ATPase enzymes

Actin/thin myofilaments are composed of the protein...?

Actin

Twisted double strand of fibrous protein is called

F actin

F actin consists of ...?

G actin subunits

G actin bears __ __for myosin head attachment during contraction

active sites

What are the regulatory proteins bound to actin?

Tropomyosin and troponin

In the center of the sarcomere, the thick filaments lack myosin heads. Myosin heads are present only in areas of __ __ __.

Myosin-actin overlap

What thin filament (which is shaped like a kidney) bears active sites for myosin head attachment during contraction?

G actin of thin filaments Named for its GLOBULAR shape - "G"

A __ filament consists of 2 strands of actin subunits twisted into a helix plus two types of regulatory proteins.

thin

__ filaments bear the active sites for myosin head attachment.

Thin

Each __ filament consists of many myosin molecules whose heads protrude at opposite ends of the filament.

thick

Red filament:

Thick

Blue filament:

Thin

Where is the ATP binding site on the myosin head?

At the base of the myosin head

Where are the actin-binding sites on the myosin head?

At the top surface of the head.

Actin is associated with

Thin filaments

Myosin is associated with

Thick filaments

In the thin filaments, G actin subunits are polymerized into long actin filaments called filamentous or ___.

F actin

Actin-binding site of the myosin head binds to ...?

Active sites for myosin attachment in the G actin subunit

Troponin and tropomyosin help control the myosin-actin interactions involved in .

contraction

Which 2 regulatory proteins help form the structure of the myofibril?

Elastic filament | Dystrophin

Elastic filaments maintain the organization of the A band and provide __ __when muscle contraction ends.

elastic recoil

Elastic filament is composed of the protein

Titin

Dystrophin links thin filaments to proteins of the

Sarcolemma

Nebulin, myomesin, C proteins bind filaments or sarcomeres together; also to __ __.

Maintain alignment

Skeletal muscles contain two sets of intracellular tubules that help regulate muscle contraction. What are they?

- The sarcoplasmic reticulum | - T tubles

Which of the two sets of intracellular tubules are a network of smooth endoplasmic reticulum surrounding each myofibril?

Sarcoplasmic reticulum

The __ __ has interconnecting tubules that surround each myofibril the way the sleeve of a loosely crocheted sweater surrounds your arm.

sarcoplasmic reticulum

Most sarcoplamic reticulum run _____. along the myofibril, communicating with each other at the __ __.

Longitudinally (east to west) H zone

Pairs of terminal cisterae form ___ __ __.

perpendicular cross channels

Other sarcoplasmic reticula form larger, perpendicular cross channels at the A band-I band junctions, and always occur in pairs. These are called?

Terminal cisterns

Terminal cisterns literally mean

End sacs

Where do terminal cisterns form?

At the A band - I band junctions

Terminal cisterns always run ____ and always form in ___.

Perpendicularly, pairs

What does the SR do?

- Regulates intracellular levels of calcium | - Stores and releases calcium upon muscle's stimulation to contract

At each A band- I band junction, the sarcolemma of the muscle cell protrudes deep into the cell interior, forming an elongated tube called the __ __.

T tubule

The T tubule is a continuation of the

Sarcolemma

T tubule lumen are continuous with the

extracellular space

T tubules act to

Increase muscle fiber's surface area

Where do T tubules penetrate?

Penetrate cell's interior at each A band–I band junction

T tubules associate with paired terminal cisterns to form ___, which encircles each sarcomere

triads

A triad, in order, looks like

Terminal cistern, T tubule, Terminal cistern

T tubules conduct ___ deep into muscle fiber; every sarcomere.

impulses

The roles of the T tubules and SR in providing signals for ___ are tightly linked.

contraction

At the triads, ___ ___ (some from the T tubule and some from the SR) protrude into the intermembrane spaces.

integral proteins

The protruding integral proteins of the T tubule act as ___ ___.

voltage sensors

The voltage sensors of the __ form gated channels through which the teminal cisterns release Ca2+.

The voltage sensors of the Sr form __ ___ through which the terminal cisterns release Ca2+.

gated channels

The voltage sensors of the SR form gated channels through which the __ __ release Ca2+.

terminal cisterns