Physiology & Anatomy of Smooth Muscle

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Questions and Answers

What is the role of 'Ca2+ sensitisation' in smooth muscle contraction?

It inhibits contraction by activating myosin phosphatase.

It enhances contraction by increasing F-Actin stability.

It promotes contraction by activating rho kinase. (correct)

It promotes relaxation by decreasing ATP requirement.

Which of the following correctly describes 'Ca2+ desensitisation'?

It leads to increased ATP consumption during contraction.

It promotes contraction in smooth muscle.

It reduces the sensitivity of smooth muscle to calcium. (correct)

It activates rho kinase to enhance tension development.

What is the significance of the latch bridge mechanism in smooth muscle?

It allows for rapid cross-bridge cycling.

It decreases the resting tone of the muscle.

It increases ATP hydrolysis rates.

It enables sustained contraction without fatigue. (correct)

What effect does nitric oxide (NO) have on smooth muscle contraction?

It causes 'Ca2+ desensitisation' and promotes relaxation. Signup and view all the answers

How does the cross-bridge cycle in smooth muscle differ from that in skeletal muscle?

Smooth muscle can generate force indefinitely without fatigue. Signup and view all the answers

Which factor is NOT associated with the process of smooth muscle contraction?

Increased ATP levels during relaxation. Signup and view all the answers

What is the primary consequence of prolonged activation of rho kinase in smooth muscle?

Sustained contraction due to increased myosin activity. Signup and view all the answers

During smooth muscle contraction, what role does adenosine diphosphate (ADP) play?

It is involved in the activation of myosin light chain. Signup and view all the answers

Which organ is primarily involved in the regulation of urine storage and micturition?

Bladder Signup and view all the answers

What is a key characteristic that differentiates smooth muscle cells from striated muscle cells?

Worm-shaped morphology Signup and view all the answers

What initiates rhythmic contractions in the gastrointestinal (GI) tract?

Pacemaker cells Signup and view all the answers

Which receptor type is primarily activated in smooth muscle contraction through G q-coupled pathways?

Gq-coupled receptors Signup and view all the answers

How do smooth muscle cells relax in response to nitric oxide?

By activating Gs-coupled receptors Signup and view all the answers

What structural feature is common in both arteries and veins?

Endothelium Signup and view all the answers

What role do smooth muscle cells play in the respiratory system?

Controlling diameter of airways Signup and view all the answers

Which hormone primarily influences the contraction of smooth muscle in blood vessels?

Epinephrine Signup and view all the answers

What type of muscle tissue is primarily responsible for mediating the movement of eggs from the ovaries to the uterus?

Smooth muscle Signup and view all the answers

In what way does membrane depolarization influence smooth muscle contractility?

It can promote contractility or relaxation depending on muscle type Signup and view all the answers

What primarily anchors actin filaments in smooth muscle?

Dense bodies Signup and view all the answers

Which mechanism primarily regulates smooth muscle contraction due to external stimuli?

Autacoids and hormones Signup and view all the answers

Which type of muscle has a higher actin-to-myosin ratio?

Smooth muscle Signup and view all the answers

What is the role of calmodulin in smooth muscle contraction?

Activates myosin light chain kinase Signup and view all the answers

What type of channels are primarily opened by membrane depolarization in smooth muscle?

Voltage-gated Ca2+ channels Signup and view all the answers

How does nitric oxide affect smooth muscle contraction?

It promotes vasorelaxation Signup and view all the answers

Which of the following increases cytoplasmic Ca2+ in smooth muscle?

Release from the sarcoplasmic reticulum via RyR Signup and view all the answers

What is the primary effect of adrenaline on smooth muscle?

Primarily acts on specific receptors Signup and view all the answers

Which statements are true about vascular smooth muscle contraction regulation?

Tissue metabolites can influence contraction Signup and view all the answers

Which process is responsible for the slower cross-bridge cycling seen in smooth muscle?

Regulation by myosin light chain kinase Signup and view all the answers

Study Notes

Smooth Muscle Overview

Found in walls of hollow organs, including blood vessels but not capillaries.
Functions as conduits for transporting gases, liquids, and solids.
Cells appear non-striated and are elongated in shape.

Smooth Muscle Location and Purpose

Iris and ciliary body: Control pupil diameter and lens focusing.
Fallopian tube: Facilitates egg movement from ovaries to uterus.
Uterus (myometrium): Involved in labor and childbirth.
Vas deferens: Assists in sperm delivery during ejaculation.
Bladder, ureters, urethra: Manage urine storage and expulsion.
Gastrointestinal tract: Responsible for mixing and moving contents.
Respiratory system: Controls airway diameter.

Structural Characteristics

Smooth muscle cells lack striations and have a higher actin-to-myosin ratio than striated muscles.
Dense bodies anchor actin filaments, functioning like Z-lines in cardiac muscle.
Contains intermediate filaments and sarcoplasmic reticulum, which stores calcium.

Smooth Muscle Contraction Regulation

Regulated by the autonomic nervous system (ANS), hormones, and local substances.
In the GI tract, rhythmic contractions initiated by specific pacemaker cells.
Different stimuli can lead to contraction, including neurotransmitters and hormones.

Mechanisms of Smooth Muscle Activation

Gq-coupled receptor activation leads to contraction through phospholipase C signaling, resulting in calcium release from the sarcoplasmic reticulum.
Nitric oxide (NO) and Gs-coupled receptor activation promote relaxation via cyclic GMP pathways.

Membrane Depolarization

Depolarization influences contractility through a steady modulation of membrane potential or action potential firing, depending on muscle type.

Comparison to Striated Muscle

Smooth muscle regulation is more complex than that of striated muscles, involving various hormonal and local factors.
Striated muscle contraction typically initiated by acetylcholine release from motor neurons, leading to action potentials.

Vascular Smooth Muscle Dynamics

Blood vessels are balanced by constricting (e.g., noradrenaline, angiotensin II) and dilating influences (e.g., NO).
Stretch and pressure also modulate vascular smooth muscle contraction significantly.

Key Terminology

Autacoids: Local hormones acting in an autocrine or paracrine manner.
Calcium Sensitization: Mechanisms enhancing contractile response independent of calcium levels.
Vasorelaxation: The process of relaxing blood vessels, often mediated by NO or cyclic AMP.

Summary of Contraction and Relaxation Mechanisms

Contraction involves myosin light chain kinase activation and actin-myosin interactions, slower than in striated muscle.
Relaxation via NO promotes hyperpolarization and decreased intracellular calcium through various signaling pathways.

Additional Notes

Understanding these mechanisms is vital for comprehending numerous physiological processes including blood flow regulation and digestive functions.### Calcium Regulation in Smooth Muscle
Calcium Ions (Ca2+): The concentration of Ca2+ affects muscular contraction levels; an increase enhances contraction while a decrease reduces it.
ATP Dependency: Smooth muscle can contract for extended periods with reduced ATP requirements due to unique mechanisms.
Myosin Light Chain (MLC20): Activation of MLC20 forms an active complex with F-Actin and myosin, allowing for muscle contraction.

Contraction Mechanisms

Agonist Inhibition: Smooth muscle contraction can be inhibited by certain agonists that activate Rho kinase, promoting 'Ca2+ sensitization'.
Cross-Bridge Cycle: The interaction between myosin and actin is crucial - this cycle is fast and contributes to force generation and muscle shortening.

Relaxation Mechanisms

Nitric Oxide (NO) Activation: NO promotes relaxation through cGMP, which leads to 'Ca2+ desensitization' and reduced contractility.
Pro-contractile vs Pro-relaxant Agents: Blue indicates agents that promote contraction, while red indicates those promoting relaxation, highlighting the dual regulation of smooth muscle.

Latch Bridge Mechanism

Indefinite Contraction: Smooth muscle can maintain contraction without fatigue, allowing it to function in prolonged states.
Tension Development: The latch bridge mechanism is essential for maintaining tension and avoiding fatigue in smooth muscle fibers.

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Description

Explore the fundamentals of smooth muscle function in various organs. This quiz will cover the structure of smooth muscle-containing tissues and their roles within different systems of the body. Perfect for students in the Physiology & Pharmacology block.