Smooth Muscle Physiology Quiz

Smooth Muscle Physiology

• Smooth muscle lacks the striations of skeletal muscle
• Smooth muscle cells are spindle-shaped, with a single nucleus centrally located.
• They are found in various locations throughout the body, including blood vessels, digestive tract, urinary tract, respiratory system, and reproductive system.
• Smooth muscle regulation of contraction/relaxation is primarily contrasted to skeletal muscle function.
• Smooth muscle is innervated by the autonomic nervous system, not the somatic nervous system.
• Contraction and relaxation are slower than in skeletal muscle.
• Smooth muscle can maintain tension for prolonged periods.
• Smooth muscle can be activated by stretch

Overview of Muscle Types

• Skeletal muscles are attached to bones.
• They control movement.
• Cardiac muscle is found in the heart, and is responsible for pumping blood.
• Smooth muscle is found in various internal organs, and performs a variety of critical functions.

Smooth Muscle: General Characteristics

• Smooth muscle cells are not arranged in sarcomeres.
• They contain actin and myosin, but lack the organized arrangement of these proteins seen in skeletal muscle.
• Smooth muscle cells are spindle-shaped with a centrally placed nucleus.
• Found in clusters of cells.
• Innervated by the autonomic nervous system.
• Under involuntary control.
• Can be inhibited and excited.

Differences between Skeletal and Smooth Muscle

• Skeletal muscle contracts and relaxes faster than smooth muscle.
• Smooth muscle can change contractile activity without changing membrane potential.
• Smooth muscle can maintain tension for extended periods.
• Smooth muscle can be activated by stretching.
• Smooth muscle develops active tension over a wider range of muscle lengths.

Manipulating Smooth Muscle Contraction and Relaxation

• Smooth muscle contraction and relaxation are crucial for many physiological processes.
• Smooth muscle regulation is important in the management of various conditions like hypertension.
• Smooth muscles control processes like blood vessel diameter and organ motility.
• The course discussed various pathologies regulated by smooth muscle.

Location of Major Types of Smooth Muscle

• Smooth muscle is found in vascular (blood vessel) walls.
• It is found in the walls of the digestive tract.
• It lines the urinary tract(bladder & ureters).
• It is found in the respiratory system's airways.
• It is found in the female reproductive system (uterus).
• It is found in the eye (ciliary and iris muscle).
• Smooth muscle is typically organized in sheets.

Two Types of Smooth Muscle

• Multi-unit smooth muscle exhibits finer control of contraction.
• Single-unit smooth muscle demonstrates coordinated contraction via gap junctions

Differences between Skeletal and Smooth Muscle

• Skeletal muscle SR is highly developed, whereas smooth muscle SR is less developed.
• Most of the Calcium needed to initiate smooth muscle contraction comes from the extracellular fluid.
• Smooth muscle utilize vesicles near the cell surface that allow for Calcium entry.

Differences between Skeletal and Smooth Muscle Myosin ATPase

• Myosin ATPase activity is lower in smooth muscle than in skeletal muscle, resulting in slower contraction rates and extended contraction durations.
• Myosin in smooth muscle forms a continuous chain of heads, enabling smooth muscle to stretch and lengthen.
• The bladder and other visceral organs change drastically in size due to smooth muscle properties.

Differences between Skeletal and Smooth Muscle Signals

• Smooth muscle contraction can be initiated by autonomic nervous system, hormones, and local chemical conditions.
• Skeletal muscle contraction is primarily triggered by somatic nervous system signals.

Differences between Skeletal and Smooth Muscle NMJ

• Smooth muscles lack neuromuscular junctions (NMJ).
• Depolarization for smooth muscle contraction is primarily caused by a change in intracellular Calcium, not Sodium, in contrast to skeletal muscle.
• Smooth muscle action potentials exhibit variable types.

Smooth Muscle Contraction

• Increase in cytosolic Ca++ levels from extracellular fluid and sarcoplasmic reticulum (SR).
• Ca++ binds to calmodulin.
• Calcium-calmodulin complex activates myosin light chain kinase (MLCK).
• MLCK phosphorylates light chains in myosin heads, enhancing myosin ATPase activity, initiating cross-bridge formation, and driving contraction.
• Then cross-bridge and power stroke.

Mechanisms of Smooth Muscle Contraction

• Hormone/neurotransmitter binding.
• IP3 - gated Ca++ channel opening.
• Voltage-gated Ca++ channel opening.

How Smooth Muscle Relaxes

• Decrease in intracellular Calcium
• Dephosphorylation of myosin.
• Myosin releases from actin.
• Myosin remains loosely attached to actin (Latch bridges) maintaining tonic tension with low ATP cost.

Regulation of Smooth Muscle Contraction Force

• Regulation of smooth muscle force is dependent on the relative balance of myosin light chain phosphorylation and dephosphorylation.
• A secondary level of control can be achieved by regulating Ca++ sensitivity in regulatory protein.

Pathologies of Smooth Muscle

• Various pathologies arise from smooth muscle dysfunction in vascular, gastrointestinal, urinary, respiratory, reproductive, and ocular systems.
• Pathologies can affect the walls of blood vessels, digestive tract, bladder, ureters, airways, uterus, and eye muscles.

Smooth Muscle and Exercise

• Nitric oxide (NO) signaling is critical for smooth muscle relaxation associated with blood vessel dilation, and is enhanced with exercise training.
• Exercise training impacts smooth muscle health affecting processes like vascular function and elasticity.

Test your knowledge on the unique characteristics and functions of smooth muscle. Learn about its structure, innervation, and comparison with skeletal and cardiac muscle types. This quiz covers key aspects of smooth muscle found in various systems throughout the body.