Histology: Muscular Tissue

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Questions and Answers

What distinguishes smooth muscle from striated muscle?

Smooth muscle fibers are spindle-shaped and uninucleate. (correct)

Smooth muscle is under voluntary control.

Striated muscle fibers respond to autonomic stimulation.

Striated muscle is composed of uninucleate cells.

Which statement accurately describes the role of striated muscle?

It controls involuntary movements in the digestive tract.

It is primarily found in the walls of glands.

It is responsible for locomotion and voluntary movements. (correct)

It regulates blood vessel caliber under autonomic control.

Which type of muscle is characterized by multinucleate syncytia?

Striated muscle fibers (correct)

Smooth muscle fibers

Fibrous muscle

Cardiac muscle

Which part of the nervous system innervates smooth muscle?

Autonomic nervous system Signup and view all the answers

What is the average length of smooth muscle fibers in the wall of the intestine?

0.2 mm Signup and view all the answers

Which of the following is NOT a type of muscle distinguished in vertebrates?

Skeletal muscle Signup and view all the answers

What is the primary function of smooth muscle in blood vessels?

To regulate blood vessel diameter Signup and view all the answers

How do smooth muscle fibers respond to stimulation?

They respond through the autonomic nervous system. Signup and view all the answers

What happens to the I-bands during muscle contraction?

They become very short. Signup and view all the answers

What remains constant during the cycle of contraction and relaxation?

Length of A-bands Signup and view all the answers

Which structural unit is defined by segments of myofibrils between successive Z-lines?

Sarcomere Signup and view all the answers

What is the H-band in skeletal muscle?

A slightly paler zone traversing the center of each A-band Signup and view all the answers

What characterizes the Z-line in relation to the I-bands?

It bisects each I-band. Signup and view all the answers

What structural feature of skeletal muscle fibers is primarily visible under a light microscope?

A-bands, I-bands, and Z-discs Signup and view all the answers

How do the lengths of the I-bands compare during relaxation and passive stretching?

Both are longer than during contraction. Signup and view all the answers

What is the primary requirement for each skeletal muscle fiber to activate?

Stimulation by its own neuromuscular junction Signup and view all the answers

How do visceral smooth muscles generate contraction in unison?

By autorhythmicity through gap junctions Signup and view all the answers

Which statement is true about the morphological changes during contraction?

They are described with reference to the sarcomere structure. Signup and view all the answers

What term describes the smooth muscle found in large arteries?

Multiunit smooth muscle Signup and view all the answers

What physiological state does smooth muscle in blood vessels usually maintain?

State of partial contraction (muscle tonus) Signup and view all the answers

Which substance, when released, results in vasoconstriction of smooth muscle?

Norepinephrine Signup and view all the answers

What can result in loss of smooth muscle tone leading to vasodilation?

Local production of bradykinin and prostaglandins Signup and view all the answers

What type of muscle fibers are significantly larger than smooth muscle fibers?

Skeletal muscle fibers Signup and view all the answers

What phenomenon helps in the coordinated contraction of visceral smooth muscle?

Autorhythmicity through gap junctions Signup and view all the answers

What characteristic is associated with red muscle fibers?

Greater content of myoglobin Signup and view all the answers

Which type of muscle fibers is most resistant to fatigue?

Red fibers Signup and view all the answers

What is a distinguishing feature of white muscle fibers?

Few mitochondria Signup and view all the answers

How do the Z-bands of red fibers compare to those of other fiber types?

They are wider than others Signup and view all the answers

Which type of muscle fibers is primarily involved in quick, powerful movements?

White fibers Signup and view all the answers

What type of motor units are red muscle fibers typically part of?

Units with small axons Signup and view all the answers

Which statement best describes intermediate fibers?

They possess characteristics of both red and white fibers Signup and view all the answers

What contributes to the dark color of red fibers?

Greater myoglobin content Signup and view all the answers

What is the diameter of a myosin filament?

2-3 nm Signup and view all the answers

How many myosin molecules are approximately found in one thick filament after dissociation?

350 myosin molecules Signup and view all the answers

What structural feature permits the flexibility of the myosin molecule?

The junction of the head and tail Signup and view all the answers

Which part of the myosin filament corresponds to one of the cross-bridges?

The globular heads Signup and view all the answers

What is the spacing between the lateral projections on the ends of the thick filament?

14 nm apart Signup and view all the answers

Which procedure enhances the examination of myofilaments at high magnification?

Negative-staining procedures Signup and view all the answers

What happens to the myosin molecule during enzymatic proteolysis?

It is cleaved into two fragments Signup and view all the answers

What is the appearance of isolated thick filaments at the center?

Smooth Signup and view all the answers

What is the primary function of the pacemaker myocytes in the heart?

Initiate spontaneous rhythmic depolarization Signup and view all the answers

How does the arrangement of myofibrils in cardiac muscle differ from skeletal muscle?

Myofibrils in cardiac muscle branch and interconnect Signup and view all the answers

What is the significance of the area ratio between the sarcolemma and the cross-sectional area of myofibrils in cardiac muscle?

It reduces stress and enhances force transmission Signup and view all the answers

What types of collagen are associated with the lamina densa in cardiac muscle?

Type-IV and Type-II collagen Signup and view all the answers

What is the architectural arrangement of organelles in cardiac muscle myocytes?

Organelles outline a fusiform axial region around the nucleus Signup and view all the answers

Study Notes

Muscle Tissue Overview

Contractility converts chemical energy into mechanical work, fundamental for muscle tissue's functions.
Muscle types specialized for locomotion, heartbeats, and internal organ movements.

Types of Muscle Tissue

Three muscle categories in vertebrates:
- Smooth Muscle: Involuntary, controlled by the autonomic nervous system; found in walls of digestive tract, respiratory passages, and blood vessels.
- Striated Muscle (Skeletal Muscle): Voluntary, innervated by the cerebrospinal nervous system; responsible for locomotion and exerting movements.
- Cardiac Muscle: Specific to the heart, with unique properties separating it from smooth and striated muscle.

Smooth Muscle Fibers

Comprised of fusiform, uninucleate cells; exhibit involuntary control.
Variations in smooth muscle include:
- Visceral Smooth Muscle: Autorhythmic capability, contracts in unison due to gap junctions; e.g., found in gut.
- Multiunit Smooth Muscle: Requires individual innervation for contraction, involved in blood vessel walls and iris of the eye.

Contraction Mechanism

Smooth muscle maintains partial contraction (muscle tonus), modulated by hormones.
Contraction is influenced by norepinephrine and other local substances leading to vasoconstriction or vasodilation.

Striated Muscle Structure

Muscle Fibers: Long, cylindrical, multinucleated cells, larger than smooth muscle fibers, involved in voluntary movements.
Structural components: Sarcomeres, A-bands, I-bands, and Z-discs; crucial for muscle contraction dynamics.
Contraction alters the I-bands (shorter during contraction) while A-bands remain constant.

Types of Striated Muscle Fibers

Traditionally categorized as red (slow-twitch), white (fast-twitch), and intermediate fibers based on metabolic and histological properties.
Red Fibers: Smaller, richer in myoglobin, and mitochondria, characterized by resistance to fatigue due to oxidative capability.
White Fibers: Larger with fewer mitochondria; quicker to fatigue.

Muscle Filament Composition

Thick filaments composed of myosin molecules; structure includes two a-helical polypeptide chains.
Myosin interacts with actin through cross-bridges during contraction; enzymatic actions impact myosin and actin properties.

Muscular Tissue Overview

Cardiac muscle exhibits myogenic contraction, meaning it can contract independently of nervous stimulation.
Cardiac myocytes, around 80 µm long and 15 µm in diameter, form intercalated discs, enabling rhythmical contraction and coordination.

Membrane and Mechanical Properties

Sarcolemma has a high surface area due to longitudinal processes, enhancing force transmission.
The stress-to-force ratio in cardiac muscle varies from 10:1 to 14:1, indicating effective force distribution.

Histology of Cardiac Muscle

Under light microscopy, cardiac muscle shows striations similar to skeletal muscle but features branching fibers.
Myofibrils surround a central nucleus and are separated by rows of mitochondria and organelles.

Unique Features of Cardiac Muscle

Transverse intercalated discs create junctional connections between myocytes, promoting a syncytial function despite being cellular units.
Cardiac muscle lacks triads (terminal cisternae and T-tubules), with simpler sarcoplasmic reticulum arrangements.

Intercalated Discs and Cell Junctions

Intercalated discs consist of desmosomes and gap junctions, important for cell connectivity and signal propagation.
Structural specialization includes ridges and grooves facilitating intercellular communication and mechanical strength.

Myoendocrine Cells

Myocyte types in the atrium synthesize and secrete biologically active polypeptides known as cardiodilatins or atrial natriuretic peptides (ANP).
Secretory granules found in myoendocrine cells are responsible for the release of these hormones, influencing cardiovascular function.

Conducting System of the Heart

Specialized conduction pathways include the sinoatrial node and atrioventricular node, regulating heartbeat initiation and propagation.
Impairments in the conduction system can lead to uncoordinated ventricular contractions and reduced heart efficiency.

Innervation of the Myocardium

The heart is innervated by autonomic fibers from the vagus nerve (parasympathetic) and sympathetic trunk, creating modulating effects on heart rate.
Interaction with the autonomic nervous system ensures adaptability to physiological demands, affecting cardiac rhythm and strength.

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Description

Explore the fundamental properties and functions of muscular tissue in this 10th class quiz. Delve into the characteristics of smooth muscle and its role in digestion and bodily movements. Test your knowledge on the various types of muscular tissue and their physiological significance.