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Flashcards in Muscle Tissue Part 1 Deck (74):
1

Most important characteristics of muscles tissue

Contractility and Conductivity

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What gives muscle tissue it's ability to contract?

Actin, myosin, ATP

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3 major types of muscle cells

Skeletal, smooth, cardiac

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Characteristics of skeletal muscle

Attached to the skeleton, voluntary, *cross-striations*, used for locomotion/respirations. Quick acting but tire fast. Multi-nucleated.

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Characteristics of Smooth muscle

Primarily in walls of internal organs. No striations. Involuntary

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Characteristics of Cardiac muscle

Branching striated tissue. Found only in the heart. Involuntary.

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Sarcolemma

Specialized plasma membranes of muscle tissue

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Sarcoplasm

Cytoplasm of the muscle cell

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Sarcoplasmic Reticulum

Specialized endoplasmic reticulum of muscle cells

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Origin of skeletal muscles

Myoblasts of the embryonic mesenchymal cells

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Skeletal muscle fiber

Each fiber is a cell. Multinucleated syncytium

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T-tubules

Long processes formed by the sarcolemma that carry the action potential deep into the sarcoplasm

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Where are the nuclei of skeletal muscles found?

Peripheral and immediately deep to the sarcolemma

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What does the sarcoplasm of skeletal muscle contain?

Myofibrils, filamentous mitochondria, myoglobin, sarcoplasmic reticulum

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Myofibrils

Contractile filaments are in the myofibrils that gives the striated appearance

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Filamentous mitochondria

Lie between the myofibrils and close to the sarcolemma. Are the the source of ATP for myofibrils

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Myoglobin

Oxygen-binding protein in skeletal muscle cells

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Sarcoplasmic reticulum

Specialized form of SER. Used for deposit of Ca. Releases Ca into the cytoplasm initiating muscle contraction

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Thin filaments of muscle fiber

F-Actin, Tropomyosin, Troponin Complex

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How are muscle fibers arranged?

Hexagonal array

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F-Actin

Forms the double-stranded helical filament (is the polymerization of G-actin)

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Tropomyosin

Forms filaments that lie in the groove between 2 actin monomers. Masks the myosin-binding sites on actin filament.

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Troponin Complex

Attached to tropomyosin. Has Troponin T, I, C subunits

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Troponin T

Binds to tropomyosin, anchoring the complex

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Troponin I

Binds to actin

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Troponin C

Binds to Ca (essential part of muscle contraction). Smallest subunit.

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Thick filaments of muscle fiber

Myosin II

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What does Myosin II consist of?

2 heavy chains: α-helices
2 globular heads: ATPase and motor activity
2 light chains: attach to heads

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Where are the binding sites for ATP and actin?

Thick filament myosin II globular heads

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What are the dark bands of myofibril made of ?

A-bands

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What are the light bands of myofibril made of?

I-bands

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What are the areas of A-bands?

H-zone and M-line

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H-zone

Part of A-bands that contains ONLY thick filaments

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M-line

Dense line that bisects the H-zone. Formed by accessory protein (myomesin). Holds thick filaments in register

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I-band

Pale area formed primarily by thin filaments. Is bisected by Z-disk

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Z-disk

Composed of accessory proteins (α-actinin). Provides anchoring points for thin filaments. Supports architecture of myofibrils

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Sarcomere

Portion of the myofibril between 2 adjacent Z-disks. Basic contractile unit of skeletal muscle.

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In what muscle fiber unit does muscle contraction take place?

Sarcomere (shortens)

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What bands change during muscle contraction?

I-band, H-zone shrink

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What band(s) do NOT change during muscle contraction?

A-band

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What maintains precise alignment of thick and thin filaments of muscle fibers?

Accessory proteins, make up less than 25% of total muscle fiber protein

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8 types of accessory proteins

α-actinin. Nebula. Tropomodulin. Titin. Myomesin. C-protein. Desmin. Dystrophin.

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α-Actinin

Short, bipolar, rod-shaped protein. Actin-binding. bundles thin filaments into parallel arrays and anchors them at the Z-line

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Nebulin

Elongated, inelastic proteins. Attached to Z-lines and runs parallel to thin filaments. Helps α-actinin anchor thin filaments. Regulates length of thin filaments during muscle development

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Tropomodulin

Small, actin-binding protein (actin-capping). Attached to the free portion of the thin filament. Maintains/regulates length of sarcomeric actin filament.

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Titin

Large protein. Forms elastic lattice that anchors filaments in the Z-line. 2 "springs" off of the protein help stabilize the centering of the myosin-containing thick filament. Prevents excessive stretching of the sarcomere.

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Myomesin

Myosin-binding protein. Holds thick filaments in line at the M-line

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C protein

Myosin-binding protein. Holds thick filaments in line at the M-line. Forms several distinct transverse stripes on either side of the M-line.

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Desmin

Type of intermediate filament. Forms lattice that surrounds the sarcomere at the level of the Z-lines, attaching them to one another/plasma membrane. Forms stabilizing cross-links between neighboring myofibrils

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Dystrophin

Large protein. Links laminin in external lamina of the muscle cell to the actin filaments

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Muscular dystrophy

Mutations in the structural proteins of skeletal muscle. Results in severe muscle weakness, muscle atrophy, and destruction of muscle fibers.

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Duchenne's muscular dystrophy

Absence of dystrophin protein

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Membrane Triad components

Formed by scarcoplasmic reticulum. One T-tubule and 2 cisternae

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T-tubular system

Formed by deep invaginations of the sarcolemma. Allows impulse to travel down the cell and excite terminal cisternae. Run at junction of A and I bands

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Terminal Cisternae

Formed by the sarcoplasmic reticulum. Run parallel to T-tubules on both sides (triad formed). Contain high [Ca++]. Run near the boundary of A and I bands.

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What does an action potential cause in the sarcolemma/sarcoplasmic reticulum?

Descends down along the T-tubules, causing the release of Ca++ into the sarcoplasm.

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What ion's influx causes muscle contraction?

Ca++

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What does Ca++ bind to in the sarcoplasm and what does it do?

Troponin C, causing the spatial configuration of troponin to change, moving it away from the myosin-binding sites on the actin

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What does myosin use to move along the actin filament?

ATP

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Stage 1 of contraction cycle

Attachment: rigor configuration

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Rigor configuration

Myosin head is tightly bound to the actin molecule of the thin filament (ATP is absent)

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Rigor Mortis

Lack of ATP causes myosin to remain bound to actin

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Stage 2 of contraction cycle

Release: ATP induces conformational changes to the myosin head, so myosin is released from actin

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Stage 3 of contraction cycle

Bending: ATP is broken into ADP and Pi (inorganic phosphate). Myosin head bends

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Stage 4 of contraction cycle

Force generation: Myosin head binds to actin again. Power stroke happens. Forces actin filament along the thick filament

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Power stroke

Release of Pi from myosin head causes head to generate a force and returns to its initial position

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Stage 5 of contraction cycle

Reattachment: myosin head is attached to new actin and is ready for a new cycle

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Relaxation of skeletal muscle

Ca++ activated ATPase pumps transport Ca to the sarcoplasmic reticulum. Ca disassociates from troponin C. Troponin returns to initial configuration blocking the actin/myosin interaction.

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Which cells cause regeneration of skeletal muscle?

Satellite cells

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What are the actions of satellite cells?

Activated after injury, proliferate, give rise to mew myoblasts. Myoblasts fuse to form new fiber

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How do muscles respond to aging?

Increase in diameter

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How do muscles respond to exercising?

hypertrophy

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How do muscles respond to disuse?

Atrophy

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Layers of connective tissue sheaths?

Endomysium: most internal layer, around each muscle fiber
Perimysium: Thicker layer, surrounds groups of muscle fibers
Epimysium: most external layer, surrounds groups of fascicles (makes the muscle)