Histology Quiz 3 (p 13-18)

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Questions and Answers

Which one of the following is NOT a component of a myofibril?

Thick and thin myofilaments

Myosin and F-actin

Tropomyosin and troponin

End to end chainlike arrangement of sarcomere (correct)

Which protein forms a head at one end of each heavy chain of myosin?

Myosin light chains (correct)

Tropomyosin

Troponin

Actin

What is the function of tropomyosin in muscle contraction?

To regulate actin-myosin interaction (correct)

To bind to Ca2+

To attach to myosin

To shift filaments during muscle contraction

Which type of muscle fiber is best suited for brief bursts of intense muscle activity?

Fast-twitch fibers Signup and view all the answers

What is the main structural basis for myofibrillar elasticity?

Titin Signup and view all the answers

What is the primary source of ATP generation in muscle contraction?

Glycolysis Signup and view all the answers

Which of the following is NOT a characteristic of a sarcomere in skeletal muscle?

Contains mitochondria and glycogen granules Signup and view all the answers

What is the role of the A band in a sarcomere?

Transverse alignment of links creating M-line Signup and view all the answers

What is the main component of the I band in a sarcomere?

Actin filament Signup and view all the answers

What is the function of the Z disc in a sarcomere?

Marks one end of the sarcomere Signup and view all the answers

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

Transverse alignment of links creating the H-band Signup and view all the answers

What is the function of the H zone in a sarcomere?

Elastic connection between thick filaments and Z line Signup and view all the answers

Smooth muscle cells are arranged in layers or bundles in the walls of which of the following large hollow organs?

Intestine Signup and view all the answers

What is the direction of the smooth muscle fibers in each layer?

Same in each layer Signup and view all the answers

Which staining methods can be used to visualize the reticular fibers in smooth muscle cells?

Mallory's aniline blue Signup and view all the answers

What is the role of elastic fibers in smooth muscle?

Provide structural support Signup and view all the answers

What happens to smooth muscle cells during contraction?

They shorten and become thicker Signup and view all the answers

What is the pathway of smooth muscle contraction?

Influx of calcium ions, binding to myosin light chain kinase, phosphorylation of myosin light chain, interaction with actin Signup and view all the answers

Which of the following is true about cardiac muscle cells?

Transitional myocytes contribute to the atrioventricular delay. Signup and view all the answers

What is the role of the Purkinje myocytes in the heart?

Increase in cell to cell contact Signup and view all the answers

How is the heart rate modulated by the autonomic nervous system?

Vagus nerve stimulation slows down the heart rate. Signup and view all the answers

Where are smooth muscles found in the body?

In the walls of blood vessels Signup and view all the answers

What is the shape of smooth muscle cells?

Fusiform Signup and view all the answers

What is the process of contraction in smooth muscles?

Influx of calcium ion via calmodulin Signup and view all the answers

Which of the following is true about the sliding filament mechanism of skeletal muscle contraction?

The initiation and release of Ca2+ into the sarcoplasm results in the shortening and contraction of actin filaments Signup and view all the answers

Which of the following is true about the innervation of skeletal muscle?

Acetylcholine release at the myoneural junction leads to the depolarization of the sarcolemma Signup and view all the answers

Which of the following is true about cardiac muscles?

They consist of separate cellular units joined end to end at junctional complexes Signup and view all the answers

Which of the following is true about the contraction of cardiac muscles?

The increase in calcium concentration leads to the depolarization of the sarcolemma and T-tubules Signup and view all the answers

Which of the following is true about the conduction system of the heart?

The atrioventricular node is located between the right ventricle and atrium Signup and view all the answers

Which of the following is true about the histology of cardiac muscle cells?

Cardiac muscle cells are joined end to end at junctional complexes called intercalated discs Signup and view all the answers

Study Notes

Muscle Structure and Function

Myofibrils are composed of thick and thin filaments, which include myosin and actin respectively.
Myosin protein has heads that interact with actin filaments during muscle contraction.
Tropomyosin regulates muscle contraction by blocking the binding sites on actin for myosin in a relaxed state.

Muscle Fiber Types

Fast-twitch muscle fibers are optimal for brief, intense activities, offering strength but fatigue rapidly.

Myofibrillar Characteristics

Myofibrillar elasticity primarily arises from titin, a large protein that acts as a molecular spring.
ATP generation during muscle contraction is primarily provided by aerobic respiration in muscles.
Sarcomeres lack certain characteristics commonly found in other muscle tissues, such as a prominent nuclei.

Sarcomere Structure

The A band in a sarcomere contains thick filaments (myosin) and is responsible for muscle striations.
The I band comprises only thin filaments (actin) and appears lighter.
Z discs define the boundaries of sarcomeres, anchoring the thin filaments.
The M-line serves as an anchor for thick filaments, helping stabilize myosin during contraction.
The H zone within the A band is the area where only thick filaments are present, reducing during contraction.

Smooth Muscle

Smooth muscle cells are organized in layers or bundles in large hollow organs like the intestines and blood vessels.
The arrangement of smooth muscle fibers alternates in direction across layers to facilitate movement.
Reticular fibers in smooth muscle can be visualized using specific staining methods, such as silver staining.
Elastic fibers provide flexibility and resilience in smooth muscle, allowing it to stretch and return to shape.
During contraction, smooth muscle cells shorten and constrict the surrounding structures.

Cardiac Muscle

Cardiac muscle cells possess unique structural and functional characteristics, including intercalated discs for strong adhesion and communication.
Purkinje myocytes facilitate rapid conduction of electrical impulses across the heart, maintaining its rhythmic contraction.
Autonomic nervous system modulates heart rate, with sympathetic stimulation increasing and parasympathetic decreasing the rate.
Smooth muscles are found in various locations, including the digestive tract, blood vessels, and respiratory passages.
Smooth muscle cells exhibit a spindle shape with a single nucleus.

Contraction Mechanisms

The sliding filament mechanism describes how overlapping thick and thin filaments contract to shorten muscle fibers.
Skeletal muscle requires innervation from somatic motor neurons to initiate contraction, unlike cardiac muscle which can contract autonomously.
Cardiac muscles contract rhythmically and are involuntary, regulated by intrinsic conduction systems.
Histologically, cardiac muscle cells show striations and branched morphology, differentiating them from skeletal muscle fibers.

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Description

Test your knowledge on the activation of skeletal muscle contraction and the sliding filament mechanism. Explore topics such as AP generation, Ca2+ release, and the binding of myosin and actin filaments. Challenge yourself with this quiz and enhance your understanding of muscle physiology.