Skeletal Muscles Flashcards
Each muscle fiber is served by one __, one __, and one or more veins.
artery, nerve
Where do all innervations enter/exit in the muscle?
The central part, and branch through connective tissue sheaths
Every skeletal muscle fiber is supplied by a __ ___ that controls its activity.
Nerve ending
Skeletal muscles have a huge nutrient and oxygen need; generates large amount of __ __
Metabolic waste
What are the connective tissue sheaths of skeletal muscle, external to internal?
Epimysium
Perimysium
Endomysium
What do the connective tissue sheaths of skeletal muscles do?
Support cells; reinforce whole muscle
Dense irregular connective tissue surrounding entire muscle; may blend with fascia
Epimysium
Fibrous connective tissue surrounding fascicles (groups of muscle fibers)
Perimysium
Fine areolar connective tissue surrounding each muscle fiber
Endomysium
Skeletal muscle attach in at least 2 places. What is the insertion?
Moveable bone, farthest point
What is the origin?
Immoveable bone, closest point of attachment
Epimysium fused to periosteum of bone or perichondrium of cartilage
Direct attachment
Connective tissue wrappings extend beyond muscle as ropelike tendon or sheetlike aponeurosis
Indirect attachment
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
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
A muscle fiber is an elongated multinucleated cell; it has a banded (striated) appearance. The muscle fiber is surrounded by
Endomysium
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
A sarcomere is the __ __, composed of myofilaments made up of contractile proteins.
Contractile unit
Contractile myofilaments are of two types: __ and __.
Thick and thin
Thick filaments contain bundled ___ molecules.
myosin
The sliding of the thin filaments past the thick filaments produces muscle ___.
Shortening
Plasma membrane is called
Sarcolemma
Cytoplasm of the skeletal muscle fiber
Sarcoplasm
What is the sarcoplasm made of?
Glycosomes for glycogen storage
Myoglobin for O2 storage
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+.
SR
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
