Physiology of Smooth Muscle

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Questions and Answers

What primarily initiates a slow wave potential in smooth muscle cells?

Calcium influx from the ECF

Intrinsic rhythmic activity of the muscle itself (correct)

Action potentials from neighboring cells

Extrinsic neural stimulation

How does calcium primarily enter smooth muscle cells to trigger contraction?

Endocytosis processes that engulf calcium ions

Through specialized channels unique to smooth muscle

Via diffusion through the membrane due to small size (correct)

Transport proteins that require ATP

What is the result of a slow wave reaching -35 mV in smooth muscle cells?

Causes complete muscle relaxation

Initiates a full action potential that spreads across the muscle (correct)

Leads to the generation of a local potential only

Triggers calcium release from the sarcoplasmic reticulum

What characterizes caveoli in smooth muscle cells?

They are small invaginations of the membrane acting as a rudimentary analog of t-tubules. Signup and view all the answers

What effect does stretching visceral smooth muscle have on its activity?

It typically leads to spontaneous action potentials. Signup and view all the answers

What type of muscle contraction is characterized by a prolonged, tonic contraction lasting for hours or days?

Smooth muscle contraction Signup and view all the answers

Which component of smooth muscle plays a role similar to Z discs in skeletal muscle?

Dense bodies Signup and view all the answers

What is a key feature of the cross-bridge cycling in smooth muscle compared to skeletal muscle?

Slower cycling of cross-bridges Signup and view all the answers

What primarily characterizes the energy requirement of smooth muscle?

Very low energy requirement Signup and view all the answers

Which of the following types of smooth muscle is known for its unitary contraction?

Single-unit smooth muscle Signup and view all the answers

What is the primary function of the protein bridges linking dense bodies in smooth muscle?

Providing structural support Signup and view all the answers

Which of the following best describes the sustained duration of smooth muscle contraction?

Prolonged and sustained Signup and view all the answers

How does the abundance of actin and myosin in smooth muscle compare to skeletal muscle?

More actin and less myosin Signup and view all the answers

Which neurotransmitter is primarily responsible for stimulating contraction in smooth muscle?

Norepinephrine Signup and view all the answers

What allows smooth muscle to maintain a full force of contraction with minimal energy consumption?

Latch mechanism Signup and view all the answers

What determines whether smooth muscle will be excited or inhibited by a neurotransmitter?

Type of receptor present Signup and view all the answers

Which characteristic distinguishes multi-unit smooth muscle from single-unit smooth muscle?

Each fiber contracts independently Signup and view all the answers

Which of the following correctly describes the action potential of visceral smooth muscle?

Action potentials in smooth muscle include a plateau phase. Signup and view all the answers

How does smooth muscle compare to skeletal muscle in terms of contraction force?

Smooth muscle contracts with greater strength Signup and view all the answers

What role do calcium channels play in smooth muscle action potentials?

They are more numerous than sodium channels. Signup and view all the answers

What structural feature of single-unit smooth muscle contributes to synchronized contraction?

Adherent cell membranes at multiple points Signup and view all the answers

Which statement about hormones affecting smooth muscle contraction is accurate?

A hormone can inhibit contraction if inhibitory receptors are present. Signup and view all the answers

What determines the flexibility of smooth muscle in shortening its length?

Percentage of length shortened Signup and view all the answers

Which of the following examples best represents multi-unit smooth muscle?

Ciliary muscles of the eye Signup and view all the answers

What contributes to the reduced need for excitatory signals in smooth muscle contraction?

Prolonged attachment of cross-bridges Signup and view all the answers

What structure allows ions to flow freely between smooth muscle cells?

Gap junctions Signup and view all the answers

What is a key feature of the latch phenomenon in smooth muscle physiology?

Sustained contraction with minimal activation Signup and view all the answers

Which component does NOT play a role in the contraction of smooth muscle?

Troponin Signup and view all the answers

What initiates the phosphorylation of the myosin light chain in smooth muscle contraction?

Calcium binding to calmodulin Signup and view all the answers

How does smooth muscle respond to being elongated or shortened?

It maintains the same pressure regardless of length. Signup and view all the answers

What role does calcium play in smooth muscle contraction?

It helps remove inhibition by exposing binding sites. Signup and view all the answers

In which type of muscle is troponin absent?

Smooth muscle Signup and view all the answers

Which statement about the action potential in smooth muscle is true?

It involves a slower depolarization process. Signup and view all the answers

What happens during the power stroke of smooth muscle contraction?

Phosphorylated light chains bind to actin. Signup and view all the answers

Study Notes

Smooth Muscle Physiology

Smooth muscle cells are connected via dense bodies that serve a role similar to Z discs in skeletal muscle.
Contains a higher proportion of actin and much less myosin compared to skeletal muscle.
Two main types of smooth muscle:
- Multi-unit: Fibers function independently, each innervated by a single nerve ending (e.g., iris and ciliary muscles).
- Single-unit (syncytial): Fibers contract in unison due to many gap junctions, found in walls of viscera like the gut and blood vessels.

Smooth Muscle Contraction Characteristics

Exhibits prolonged, tonic contraction lasting hours or days compared to the rapid contractions of skeletal muscle.
Slow cycling of cross-bridges results in longer attachment times between actin and myosin.
Very low energy requirement makes smooth muscle economical.
Capable of sustaining contraction force greater than that of skeletal muscle.
High flexibility in shortening, able to maintain force while shortening a significant percentage of its length.
The latch mechanism allows maintenance of contraction strength with minimal energy expenditure.

Regulation of Contraction

Contraction triggered by calcium ions (Ca++), binding to calmodulin, an essential regulatory process.
Calcium influx through slower-opening calcium channels contributes to unique action potentials in smooth muscle.
Stress-relaxation allows smooth muscle to adapt its contraction force after being stretched or shortened.

Action Potentials and Calcium Role

Two types of action potentials exist:
- Spike potential: resembles skeletal action potentials; duration of 10-50 ms; can be induced by various stimuli.
- Action potential with plateau: includes a prolonged depolarization phase, lasting several hundred milliseconds.
The primary source of Ca++ for contraction is extracellular fluid, facilitated by rudimentary structures like caveoli.

Hormonal Influence and Neural Control

Hormones can initiate contractions through specific receptors on muscle fibers; some hormones may induce inhibition depending on receptor type.
Neurotransmitters such as acetylcholine and norepinephrine modulate muscle contraction through diffuse junctions and varicosities.
The resting membrane potential of smooth muscle is between -50 mV to -60 mV, influencing excitability.

Summary of Key Mechanisms

Calcium channels in smooth muscle membranes play a vital role in generating action potentials, more so than sodium channels.
The overall contraction mechanism relies on the synchronized activity among muscle fibers and the regulatory effects of calcium and hormones.

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Description

This quiz covers the fundamental concepts of smooth muscle physiology as outlined in the first bimonthly assessment. Participants will explore the structure, function, and importance of smooth muscle in the human body. Enhance your understanding of how smooth muscle contributes to various physiological processes.