أسئلة المحاضرة 11 فسيولوجي

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Questions and Answers

What initiates cross bridge cycling during muscle contraction?

Release of myosin from the actin filaments

Binding of cross-bridges of myosin with actin (correct)

Increased levels of ATP in the muscle cells

Decreased calcium levels in the bloodstream

Which of the following changes occurs in the sarcomere during muscle contraction?

Separation of Z lines

Lengthening of the A band

Widening of the H zone

Shortening of the I band (correct)

What is required for the detachment of cross bridges from actin?

Increased calcium concentration

Low levels of troponin

Release of phosphates from actin

Hydrolysis of ATP (correct)

What is the role of Ca++ during muscle contraction?

To enable troponin to expose binding sites on actin Signup and view all the answers

Which mechanism is responsible for muscle relaxation?

Active Ca++ uptake by the terminal cisternae of the sarcoplasmic reticulum Signup and view all the answers

What is the primary component of thick filaments in muscle contraction?

Myosin protein molecules Signup and view all the answers

What structure connects thin filaments from one sarcomere to another?

Z-lines Signup and view all the answers

Which part of the myosin molecule serves as a binding site for actin?

Head Signup and view all the answers

What role does calcium (Ca++) play in muscle contraction?

It combines with troponin to expose actin binding sites. Signup and view all the answers

What is the A band of the sarcomere primarily composed of?

Thick filaments Signup and view all the answers

Which component covers the binding sites of actin during muscle relaxation?

Tropomyosin Signup and view all the answers

How is the muscle action potential propagated along the muscle fiber?

Through T-tubules Signup and view all the answers

What is the function of the cross bridges during muscle contraction?

To facilitate the movement of actin filaments Signup and view all the answers

What is the primary characteristic that differentiates skeletal muscle from other types of muscles?

Skeletal muscle is striated. Signup and view all the answers

Which part of the sarcomere is located at the center of the A-band?

M-line Signup and view all the answers

What role do transverse tubules (T-tubules) play in skeletal muscle fibers?

They allow electrical impulses to penetrate deep into the muscle fiber. Signup and view all the answers

Which component is NOT a part of the myofibers in skeletal muscle?

Cardiac cells Signup and view all the answers

What is the functional unit of skeletal muscle called?

Sarcomere Signup and view all the answers

How do skeletal muscles primarily contribute to body posture?

By providing voluntary movement for compensation. Signup and view all the answers

What percentage of body weight is constituted by skeletal muscles?

40% Signup and view all the answers

What happens at the Z-line within a sarcomere?

It anchors the myofilaments. Signup and view all the answers

What occurs during the bending of cross-bridges in muscle contraction?

Actin is pulled toward the center of the sarcomere. Signup and view all the answers

Which change occurs to the Z lines during muscle contraction?

They approximate or come closer together. Signup and view all the answers

What is required for the return of cross-bridges to their original position after muscle contraction?

Hydrolysis of ATP. Signup and view all the answers

What initiates muscle relaxation after contraction?

Decrease in calcium binding to troponin. Signup and view all the answers

Which statement accurately describes the A band during muscle contraction?

It remains constant despite changes in filament lengths. Signup and view all the answers

What binds to troponin to initiate the exposure of binding sites on actin molecules?

Ca++ ions Signup and view all the answers

Which part of the myosin molecule combines with ATP?

The head Signup and view all the answers

What structural feature connects thick filaments in the middle of the sarcomere?

M-line Signup and view all the answers

Which protein molecule is responsible for covering the binding sites on actin during muscle relaxation?

Tropomyosin Signup and view all the answers

Which process must occur for the release of Ca++ ions into the cytoplasm?

Muscle action potential propagation Signup and view all the answers

What type of structure do thin filaments extend from in the sarcomere?

Z-line Signup and view all the answers

What configuration do actin molecules have in thin filaments?

Twisted chains forming a helix Signup and view all the answers

Which muscle structure is directly responsible for connecting the ends of sarcomeres?

Z-lines Signup and view all the answers

What type of muscle constitutes the largest percentage of body weight?

Skeletal muscle Signup and view all the answers

Which of the following statements accurately describes skeletal muscle fibers?

They are elongated and multinucleated. Signup and view all the answers

What is the significance of the sarcomere in skeletal muscle contraction?

It is the functional unit of muscles. Signup and view all the answers

Which structure in skeletal muscle fibers contains transverse tubules?

Cell membrane Signup and view all the answers

What role do the A-band and I-band play in the structure of myofibrils?

They give skeletal muscle its transverse striations. Signup and view all the answers

What is the main characteristic that distinguishes skeletal muscle from cardiac and smooth muscle?

Skeletal muscle fibers are striated. Signup and view all the answers

What is the Z-line's function within the sarcomere?

It connects adjacent sarcomeres. Signup and view all the answers

How does skeletal muscle contribute to maintaining body temperature?

Through contraction, which generates heat. Signup and view all the answers

Describe the process of cross bridge cycling in muscle contraction.

Cross bridge cycling involves the binding of myosin to actin, the bending and pulling of actin towards the sarcomere center, ATP-hydrolysis for detachment, and resetting the cross bridges for another cycle. Signup and view all the answers

What are the changes that occur in the sarcomere during muscle contraction?

During contraction, the Z lines move closer together, the I band shortens, the H zone narrows, while the A band remains constant. Signup and view all the answers

How does calcium influence muscle contraction and relaxation?

Calcium binds to troponin to initiate muscle contraction and is actively taken up by the sarcoplasmic reticulum to promote relaxation by covering actin's binding sites. Signup and view all the answers

What role does ATP play in cross bridge cycling?

ATP is essential for the detachment of myosin cross bridges from actin and for resetting the cross bridges to their original position for another cycling. Signup and view all the answers

Explain the relationship between cross bridge cycling and the presence of calcium ions.

Cross bridge cycling occurs continuously as long as calcium ions are bound to troponin, allowing actin and myosin interaction. Signup and view all the answers

What are the primary types of muscle in the human body and their respective percentages of body weight?

Skeletal muscle constitutes 40%, cardiac muscle 10%, and smooth muscle is the remainder. Signup and view all the answers

Explain the significance of the sarcomere in skeletal muscle contraction.

The sarcomere is the functional unit of muscle that enables contraction through its organized arrangement of myofilaments. Signup and view all the answers

Describe the structure and role of transverse tubules (T-tubules) in muscle fibers.

T-tubules are tubular extensions of the cell membrane that penetrate deep into the muscle fibers, facilitating impulse transmission. Signup and view all the answers

What distinguishes skeletal muscle fibers from other types of muscle fibers?

Skeletal muscle fibers are striated, multinucleated, and under voluntary control. Signup and view all the answers

What is the arrangement of light and dark bands in a myofibril, and what do they represent?

The alternating light (I) and dark (A) bands represent the arrangement of thin and thick myofilaments, respectively. Signup and view all the answers

What is the role of the M-line and Z-line in a sarcomere?

The M-line anchors the thick filaments, while the Z-line marks the borders of each sarcomere. Signup and view all the answers

How do skeletal muscles aid in thermoregulation?

Skeletal muscles generate heat as a byproduct of contractions, helping to maintain body temperature. Signup and view all the answers

What components are found in the cytoplasm (sarcoplasm) of muscle fibers?

The sarcoplasm contains organelles such as the sarcoplasmic reticulum, mitochondria, glycogen, and ribosomes. Signup and view all the answers

Describe the role of tropomyosin in muscle contraction.

Tropomyosin covers the binding sites on actin during muscle relaxation, preventing interaction with myosin until calcium binds to troponin and moves tropomyosin away. Signup and view all the answers

What is the structural significance of the M-line in relation to myofilaments?

The M-line is the center of the sarcomere, serving as an attachment point for thick filaments and helping maintain the structure of the A-band. Signup and view all the answers

Explain the sequence of events that occurs when calcium ions are released into the cytoplasm.

Calcium ions bind to troponin, causing tropomyosin to shift and exposing the binding sites on actin, allowing myosin cross bridges to attach. Signup and view all the answers

Identify the main components of the thick filaments and their functionalities.

Thick filaments are primarily composed of myosin, which has a head for binding with actin and an ATP binding site, facilitating muscle contraction. Signup and view all the answers

How do cross bridges facilitate muscle contraction?

Cross bridges form when myosin heads bind to exposed sites on actin, pulling the filaments past each other to shorten the muscle fiber. Signup and view all the answers

Discuss the role of the sarcoplasmic reticulum in muscle contraction.

The sarcoplasmic reticulum stores calcium ions and releases them into the cytoplasm, initiating the process of muscle contraction. Signup and view all the answers

What structural feature connects thin filaments from one sarcomere to another?

Z-lines connect the ends of thin filaments from adjacent sarcomeres, helping to organize the skeletal muscle structure. Signup and view all the answers

What triggers the cessation of cross bridge cycling during muscle relaxation?

The cessation of cross bridge cycling is triggered by the release of Ca++ from troponin, which allows tropomyosin to cover the binding sites on actin. Signup and view all the answers

Describe the significance of ATP hydrolysis in the muscle contraction cycle.

ATP hydrolysis is crucial for the detachment of cross bridges from actin and for reloading myosin heads back into their original position. Signup and view all the answers

How does the change in the sarcomere's I band and H zone reflect muscle contraction?

During muscle contraction, the I band shortens and the H zone narrows, indicating the sliding action of thin filaments over thick filaments. Signup and view all the answers

What continuous cycle ensures muscle contraction as long as Ca++ is present?

The cross bridge cycling continues as long as Ca++ binds with troponin, facilitating the sequential binding and releasing of myosin to actin. Signup and view all the answers

Explain the role of the sarcoplasmic reticulum in muscle relaxation.

The sarcoplasmic reticulum actively pumps Ca++ back into its terminal cisternae, reducing cytosolic calcium levels and allowing tropomyosin to block actin binding sites. Signup and view all the answers

What distinguishes skeletal muscle fibers from smooth and cardiac muscle fibers?

Skeletal muscle fibers are voluntary, striated, and multinucleated. Signup and view all the answers

What is the role of the Z-line within the sarcomere?

The Z-line anchors the thin filaments and defines the boundaries of each sarcomere. Signup and view all the answers

How do transverse tubules (T-tubules) contribute to muscle contraction?

T-tubules facilitate the rapid transmission of action potentials into the interior of the muscle fibers. Signup and view all the answers

What is the structural relationship between the A-band and I-band in myofibrils?

The A-band contains thick filaments, while the I-band contains only thin filaments. Signup and view all the answers

What cellular organelle is primarily responsible for storing calcium ions in muscle fibers?

The sarcoplasmic reticulum stores calcium ions in muscle fibers. Signup and view all the answers

What is the primary function of skeletal muscle beyond movement?

Skeletal muscle also plays a key role in maintaining body posture and regulating body temperature. Signup and view all the answers

What is the role of tropomyosin in skeletal muscle contraction?

Tropomyosin covers the binding sites on actin, preventing cross bridge formation during muscle relaxation. Signup and view all the answers

Describe the relationship between myosin head binding and ATP.

The myosin head has a binding site for ATP, which is necessary for its detachment from actin after power stroke. Signup and view all the answers

What structural feature allows thick filaments to attach to the M-line?

Thick filaments, composed of myosin, are anchored to the M-line, providing stability within the sarcomere. Signup and view all the answers

Explain the significance of calcium ions in activating actin during contraction.

Calcium ions bind to troponin, causing a conformational change that moves tropomyosin, exposing actin's binding sites. Signup and view all the answers

What is meant by the term 'cross bridges' in muscle contraction?

Cross bridges refer to the connections formed between the myosin heads and the actin binding sites during contraction. Signup and view all the answers

How does the sarcoplasmic reticulum contribute to muscle contraction?

The sarcoplasmic reticulum releases Ca++ ions into the cytoplasm, triggering muscle contraction. Signup and view all the answers

What occurs at the Z-line when muscle contraction takes place?

During contraction, the Z-lines move closer together as the sarcomere shortens. Signup and view all the answers

Describe the process by which myosin heads interact with actin during contraction.

Myosin heads attach to the exposed binding sites on actin, pull during the power stroke, and then detach after ATP binding. Signup and view all the answers

Study Notes

Skeletal Muscle Contraction

Muscles are machines converting chemical energy to mechanical energy (work) and heat.
Muscle tissue constitutes 50% of body weight.
Muscle Types:
- Skeletal: 40%
- Cardiac: 10%
- Smooth: 10%
Skeletal Muscle:
- Attached to skeleton
- Somatic (body)
- Voluntary control
- Striated under a microscope
- Functions:
  - Movement of body parts (limbs)
  - Maintaining posture
  - Regulating body temperature

Functional Histology of Skeletal Muscles

Skeletal muscles are made of thousands of muscle fibers (myofibers).
Muscle fibers are elongated, multinucleated cells (10-100µm in diameter).
Sarcoplasm (cytoplasm) contains typical organelles (sarcoplasmic reticulum, Golgi, ribosomes, mitochondria, glycogen).
Cell membrane has transverse tubules (T-tubules) extending deep into muscle fibers.
Myofibrils (1µm diameter):
- Extend from one end of muscle to the other, creating longitudinal striations.
- Alternating light (I) and dark (A) bands due to myofilament arrangement.
- Bands form transverse striations in skeletal muscle.
- I band center has a Z-line.
- A band center has an H-zone, and M-line within it.
- Sarcomere: Area between two Z-lines.

Sarcomere

Functional unit of muscle tissue.
Composed of A-band and half of the I-bands on each side.
Myofilaments (contractile filaments):
- Thick filaments:
  - Located in the center of the sarcomere.
  - Composed of myosin protein molecules with heads, bodies/arms, and tails.
  - Produce the A-band and are attached by M-line.
- Thin filaments:
  - Located on both sides of the sarcomere.
  - Composed of actin, tropomyosin, and troponin.
  - Attached to Z-lines, connecting sarcomeres.
- Space between thick and thin filaments bridged by cross bridges (thick filament projections).

Thick Filaments

Composed of myosin protein molecules.
Each myosin molecule has:
- A head with actin binding site and ATP binding site.
- A body/arm extending from the head.
- A tail extending from the body/arm.

Thin Filaments

Composed of:
- Actin: Two intertwined strands, forming spiral structure with myosin binding sites.
- Tropomyosin: Thin filamentous protein covering actin's binding sites in relaxed state.
- Troponin: Complex of proteins bound to tropomyosin regulating the interaction between actin and myosin.

Excitation-Contraction Coupling

Muscle action potential propagation and release of Ca2+ ions initiating contraction.
Ca2+ activates actin by causing tropomyosin movement on actin, exposing binding sites for myosin.
Cross-bridge cycling: Binding of myosin to actin, bending of cross bridges pulls actin towards center of sarcomere, detachment with ATP hydrolysis, and return to original position.
Cycle repeats as long as Ca2+ present on troponin.

Muscle Relaxation

Ca2+ uptake by sarcoplasmic reticulum, removing the Ca2+ stimulus from the actin.
Tropomyosin covers the binding sites, preventing further cross-bridge formation.
Muscle fiber relaxes.

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Description

This quiz explores the mechanics and functional histology of skeletal muscles. Learn about the different muscle types, the structure of muscle fibers, and the key functions of skeletal muscle in the human body. Test your understanding of how muscles convert energy and contribute to movement.

أسئلة المحاضرة 11 فسيولوجي - دمياط

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