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What is the basic repeating unit of muscle called?
What is the basic repeating unit of muscle called?
Which structure surrounds each myofibril and is responsible for calcium storage?
Which structure surrounds each myofibril and is responsible for calcium storage?
Which bands in the myofibrils are identified as isotropic and anisotropic?
Which bands in the myofibrils are identified as isotropic and anisotropic?
What is the primary function of the transverse tubules (T-tubules)?
What is the primary function of the transverse tubules (T-tubules)?
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The sliding filament theory primarily describes the interaction between which two proteins?
The sliding filament theory primarily describes the interaction between which two proteins?
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What component provides energy for muscle contraction and is found in abundance in the sarcoplasm?
What component provides energy for muscle contraction and is found in abundance in the sarcoplasm?
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What structure can be described as membranous folds extending from the plasma membrane?
What structure can be described as membranous folds extending from the plasma membrane?
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Which component is NOT a part of the muscle's ultrastructure as defined in muscle anatomy?
Which component is NOT a part of the muscle's ultrastructure as defined in muscle anatomy?
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What initiates the muscle contraction process described in the sliding filament theory?
What initiates the muscle contraction process described in the sliding filament theory?
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What happens to the myosin heads after they bind to the actin binding sites?
What happens to the myosin heads after they bind to the actin binding sites?
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Which statement describes the role of ATP in muscle contraction?
Which statement describes the role of ATP in muscle contraction?
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What role does tropomyosin play in the contraction process?
What role does tropomyosin play in the contraction process?
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What occurs during the power stroke in muscle contraction?
What occurs during the power stroke in muscle contraction?
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What effect does the reabsorption of calcium have on muscle contraction?
What effect does the reabsorption of calcium have on muscle contraction?
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What is the primary function of the myosin heads during contraction?
What is the primary function of the myosin heads during contraction?
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How does ADP relate to the energy utilization during muscle contraction?
How does ADP relate to the energy utilization during muscle contraction?
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What happens to the I-band during muscle contraction?
What happens to the I-band during muscle contraction?
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What is the outcome when actin and myosin filaments increase their overlap?
What is the outcome when actin and myosin filaments increase their overlap?
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Which of the following correctly describes the powerstroke?
Which of the following correctly describes the powerstroke?
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Which biochemical reaction describes the energy transformation during muscle contraction?
Which biochemical reaction describes the energy transformation during muscle contraction?
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Which component inhibits the myosin binding site on actin in resting muscle?
Which component inhibits the myosin binding site on actin in resting muscle?
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What triggers the exposure of the myosin binding site on actin?
What triggers the exposure of the myosin binding site on actin?
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How many ATP molecules are used per myosin head for each powerstroke?
How many ATP molecules are used per myosin head for each powerstroke?
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What occurs during the breaking of the actin/myosin interaction?
What occurs during the breaking of the actin/myosin interaction?
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What gives skeletal muscle its striated appearance?
What gives skeletal muscle its striated appearance?
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What role do tropomyosin and troponin play in muscle contraction?
What role do tropomyosin and troponin play in muscle contraction?
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What triggers the movement of tropomyosin away from the myosin binding sites?
What triggers the movement of tropomyosin away from the myosin binding sites?
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Which components make up the thin filament of muscle fibers?
Which components make up the thin filament of muscle fibers?
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How is the thick filament of myosin structured?
How is the thick filament of myosin structured?
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What is the function of myosin heads during muscle contraction?
What is the function of myosin heads during muscle contraction?
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What type of proteins are TnC, TnI, and TnT?
What type of proteins are TnC, TnI, and TnT?
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Where are myosin filaments primarily found in the muscle sarcomere?
Where are myosin filaments primarily found in the muscle sarcomere?
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Which component of myosin is responsible for forming cross bridges with actin?
Which component of myosin is responsible for forming cross bridges with actin?
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What is the primary role of calcium ions in muscle contraction?
What is the primary role of calcium ions in muscle contraction?
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What replaces ADP in the myosin head to form the A-M-ATP complex?
What replaces ADP in the myosin head to form the A-M-ATP complex?
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What initiates the muscle contraction process at the neuromuscular junction?
What initiates the muscle contraction process at the neuromuscular junction?
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Which ion is released from the sarcoplasmic reticulum to facilitate muscle contraction?
Which ion is released from the sarcoplasmic reticulum to facilitate muscle contraction?
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What change occurs in troponin when Ca2+ binds to Troponin-C?
What change occurs in troponin when Ca2+ binds to Troponin-C?
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What is the function of non-depolarizing muscle relaxants in anaesthesia?
What is the function of non-depolarizing muscle relaxants in anaesthesia?
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After muscle contraction, what happens to Ca2+ ions?
After muscle contraction, what happens to Ca2+ ions?
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The wave of depolarization during muscle excitation travels via which structure?
The wave of depolarization during muscle excitation travels via which structure?
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What is the role of tropomyosin in muscle contraction?
What is the role of tropomyosin in muscle contraction?
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Study Notes
Muscle Ultrastructure
- The sarcomere is the basic repeating unit of muscle. It's a complex arrangement of many protein-protein interactions.
- Each muscle fibre is enclosed by a specialized cell membrane called the sarcolemma.
- Muscle fibres contain smaller myofibrils embedded in the cytoplasm, known as sarcoplasm.
- Sarcoplasm is rich in glycogen, ATP, Creatine Phosphate, and glycolytic enzymes.
- Transverse tubules (T-tubules) are membrane folds extending from the plasma membrane. They transmit electrical signals.
- The Sarcoplasmic Reticulum (SR) surrounds myofibrils and stores calcium.
Muscle Sarcomere
- The sarcomere is the basic contractile unit of a muscle fiber.
- It is composed of two main protein filaments: actin (thin filaments) and myosin (thick filaments).
- The arrangement of these filaments is responsible for the striated appearance of skeletal muscle under a microscope.
- Key components include:
- Z-line: The boundary of the sarcomere.
- I-band: The light band, which contains only thin filaments.
- A-band: The dark band, containing both thick and thin filaments.
- H-zone: The central region of the A-band, containing only thick filaments.
- M-line: The center of the sarcomere, where thick filaments are linked.
Molecular Structure of Thin Filament (Actin)
- Composed of three components:
- F-actin (filamentous-actin): A double-stranded protein molecule wound into a double helix.
- Tropomyosin: A double-stranded α-helical protein molecule lying in the groove of the F-actin helix.
- Troponin: A complex of three globular proteins (TnC, TnI, TnT) attached periodically to the tropomyosin strand.
Thin Filament Arrangement
- Tropomyosin and troponin regulate actin.
- Tropomyosin covers the myosin binding sites on actin in the resting state.
- Troponin subunits have specific functions:
- TnT binds to tropomyosin.
- TnI binds to F-actin.
- TnC binds to calcium ions (Ca2+).
- When Ca2+ is released, it binds to TnC, causing tropomyosin to move away from the myosin binding site, allowing myosin to bind to actin.
Myosin Filaments (Thick Filaments)
- Composed of approximately 400 myosin polypeptides, with 200 on each side of the M-line.
- Each myosin molecule consists of:
- A compact head region.
- A long tail region formed by two α-helices.
- The tails pack together to form the thick central portion of the myosin filament.
- The heads extend outwards, forming "cross bridges" with actin filaments.
- Most of the tail is called light meromyosin.
- The head and a portion of the tail are composed of heavy meromyosin.
Molecular Structure Of Myosin
- Myosin molecules consist of two heavy chains and four light chains.
- The C-terminal parts of the myosin heavy chains (MHC) twist together to form the coiled-coil α-helical rod-shaped tail domain.
- The N-terminal parts of the heavy chains form the two myosin heads.
- Each head acts as an enzyme, binding to ATP and hydrolyzing it.
- The myosin head stores energy in the form of ADP and inorganic phosphate (Pi).
Sliding Filament Theory
- Proposed by A.F. Huxley and H.E. Huxley in 1950 to explain muscle contraction.
- Myosin filaments use ATP energy to "walk" along actin filaments using their cross bridges.
- Contraction is due to the sliding of actin and myosin filaments past each other.
- The movement of cross bridges generates the force of contraction.
- This pulls actin filaments closer together.
Sliding Filament Theory Steps
- Nerve signals stimulate calcium release from the sarcoplasmic reticulum.
- Calcium binds to troponin C, causing tropomyosin to shift position, exposing the actin binding sites.
- Myosin heads bind to exposed actin binding sites, forming cross bridges.
- ADP is released, initiating the "power stroke" where the thin filament is pulled towards the sarcomere midline.
- New ATP binds to the myosin head, separating the actin-myosin cross bridge. ATP is then hydrolyzed to ADP and Pi, transferring energy to the myosin head.
- This cycle continues until the nerve signal stops and calcium is reabsorbed.
Muscle Sarcomere Ultrastructure During Contraction
- The A-band remains the same length.
- The I-band shortens.
- The H-zone is reduced or disappears.
Ratchet Mechanism of Contraction
- Describes the biochemical and biophysical events during contraction.
- Converts ATP energy into the physical work of actin and myosin filament displacement.
- Involves the formation of cross bridges between the myosin head and actin binding sites.
Powerstroke and Cross-bridge Action
- Myosin head binds to actin.
- The myosin head "contracts" due to a conformational change, pulling the actin filament.
- The actin-myosin interaction breaks.
- The myosin head re-attaches further along the actin filament.
Ratchet Mechanism Steps
- Actin is uncovered when Ca2+ binds to troponin. The Myosin-ADP-Pi complex binds to actin.
- Pi is released, triggering the powerstroke. The myosin head changes conformation.
- ATP replaces ADP, binding to the actomyosin complex, leading to actin release. The myosin head returns to its resting conformation.
- ATP is hydrolyzed to ADP-Pi, returning to the resting state.
Excitation-Contraction Coupling (ECC)
- Describes the rapid communication between electrical events in the muscle fiber's plasma membrane and calcium release from the sarcoplasmic reticulum, resulting in contraction.
- A nerve impulse triggers acetylcholine (ACh) release at the neuromuscular junction (NMJ).
- ACh binds to receptors, depolarizing the sarcolemma, and the depolarization propagates through the T-tubule system.
- This triggers Ca2+ release from the sarcoplasmic reticulum, leading to muscle contraction.
- Ca2+ is pumped back into the sarcoplasmic reticulum, ending contraction.
Muscle Relaxants
- Two types of muscle relaxants used in anesthesia:
- Depolarizing muscle relaxants: Cause initial muscle contraction, but prevent further contractions.
- Example: Suxamethonium.
- Non-depolarizing muscle relaxants: Prevent muscle contraction.
- Example: Not specified in the text.
- Depolarizing muscle relaxants: Cause initial muscle contraction, but prevent further contractions.
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Description
Test your knowledge on the ultrastructure of muscle and the specifics of the sarcomere. This quiz covers critical elements like myofibrils, sarcoplasm, and the role of filaments in muscle contraction. Dive deep into the anatomy of muscle fibers and discover their fascinating details!
