Muscle Tissue Structure and Function Quiz

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Questions and Answers

What is the organization of myofilaments in smooth muscle?

Thin and thick filaments are present with no visible striations.

The ratio of thin to thick filaments is the same as in skeletal muscle.

Thick and thin filaments are arranged diagonally. (correct)

Thick filaments have heads along their entire length.

What is the key difference between smooth muscle and skeletal muscle in terms of myofilament arrangement?

Skeletal muscle has no intermediate filament bundles unlike smooth muscle.

Smooth muscle has a higher density of troponin complex than skeletal muscle.

Skeletal muscle has a more diagonal arrangement of thick and thin filaments.

Thick filaments in smooth muscle have heads along their entire length, unlike in skeletal muscle. (correct)

Which statement accurately describes the myofilaments in smooth muscle?

Smooth muscle has sarcomeres similar to skeletal muscle.

The ratio of thin to thick filaments is lower than in skeletal muscle. (correct)

The arrangement of thick and thin filaments is the same as in cardiac muscle.

There are no thick filaments present.

What is a characteristic feature of the arrangement of thick filaments in smooth muscle?

Thick filaments lack heads along their length. Signup and view all the answers

How do the thin and thick filaments in smooth muscle contribute to its contraction?

Thin filaments dominate the organization with the ratio being higher than in skeletal muscle. Signup and view all the answers

What distinguishes the myofilament organization in smooth muscle from skeletal muscle?

Thick filaments have heads distributed along their entire length in smooth muscle. Signup and view all the answers

What is the main reason for the shortening of sarcomeres during muscle contraction?

The interaction between actin and myosin molecules Signup and view all the answers

What is the role of T-tubules in muscle fibers?

Conducting impulses to the deepest regions of the muscle Signup and view all the answers

Which structure regulates intracellular calcium levels in muscle cells?

Sarcoplasmic reticulum Signup and view all the answers

What is the function of smooth endoplasmic reticulum (SR) in muscle cells?

Regulation of intracellular calcium levels Signup and view all the answers

What component pairs form perpendicular cross channels within muscle cells?

Terminal cisternae of the sarcoplasmic reticulum Signup and view all the answers

Which protein molecule hydrolyzes ATP during muscle contraction?

Myosin ATPase Signup and view all the answers

What gives muscle cells their striated appearance?

Alternating light (I) and dark (A) bands Signup and view all the answers

Which region contains tiny protein rods that hold adjacent thick filaments together in a sarcomere?

H-zone/bare zone Signup and view all the answers

What is the chief protein component of thin filaments?

Actin Signup and view all the answers

Which myofilament extends the entire length of dark A-bands?

Myosin filaments Signup and view all the answers

What are the two smaller, light polypeptide chains on each myosin molecule called?

Cross bridges Signup and view all the answers

What are the two regulatory subunits bound to actin in thin filaments?

Tropomyosin and troponin Signup and view all the answers

Study Notes

Intercalated Discs

Appear as dark, transverse lines that occur at irregular intervals in LM
Exhibits two regions: transverse and lateral portions in EM

Skeletal Muscle

Multinucleate with oval nuclei beneath the sarcolemma
Nuclei are pushed aside by long, ribbon-like organelles called myofibrils
Displays birefringence in polarized light
Striated appearance due to alternating light (I) and dark (A) bands

Sarcomeres

Structural and functional units of skeletal muscle
Responsible for the striations of skeletal muscle
Consist of light I-bands with a midline interruption called Z-disc and dark A-bands with a lighter central area called the H-zone

Myofilaments

Thick (myosin) filaments extend the entire length of dark A-bands
Thin (actin) filaments are present in the light I-bands
Thick filaments composed of myosin molecules with rod-like tails and globular heads
Thin filaments composed of actin, tropomyosin, and troponin

Sarcomere Arrangement

Thick and thin filaments slide past each other, causing sarcomere shortening during muscle contraction
Sliding filament theory explains muscle contraction

Muscle Contraction

Motor units consist of a motor neuron and all the muscle fibers it activates
Myosin ATPase hydrolyzes ATP, activating the myosin head and "cocking" it in an extended position
Myosin head binds to an active site on actin, enabling muscle contraction

Smooth Muscle

Non-striated, uninucleate, and fusiform in shape
Thin and thick filaments are present, but with a higher ratio of thin to thick filaments compared to skeletal muscle
Thick filaments have heads along their entire length, and there is no troponin complex
Filaments are arranged diagonally, causing contraction in a corkscrew manner
Non-contractile intermediate filament bundles attach to dense bodies at regular intervals
Exhibits slow, synchronized contractions due to electrical coupling with gap junctions
Some smooth muscle cells act as pacemakers, setting the contractile pace for the whole sheet of muscles

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Description

Test your knowledge on the arrangement of filaments in a sarcomere, myofilaments banding pattern, and the structure of the sarcoplasmic reticulum. Explore topics such as transverse tubules, excitation of muscle fibers, and the role of T-tubules in muscle function.