Histology: Smooth Muscle Tissue Flashcards

Questions and Answers

What is smooth muscle tissue primarily found in?

Skeletal muscles

Blood vessels

Walls of internal organs (correct)

Heart

What are the characteristics of smooth muscle tissue?

Single nucleus per cell, no branches, no cross striations, slow rhythmic prolonged contractions, involuntary movement.

Describe the structure of smooth muscle cells.

Fusiform cells (spindle shaped with tapered ends)

Where are the nuclei of smooth muscle cells located?

Centrally placed, long with tapered ends Signup and view all the answers

What does the sarcoplasm of smooth muscle cells contain?

Myofilaments and organelles, numerous mitochondria. Signup and view all the answers

Describe the arrangement of myofilaments in smooth muscle cells.

Randomly distributed throughout the cytoplasm and poorly organized. Signup and view all the answers

What are dense bodies in smooth muscle cells analogous to?

Z-line of skeletal muscle fibers. Signup and view all the answers

What is the function of cavolae in smooth muscle cells?

Deliver Ca++ to the cytoplasm Signup and view all the answers

What is the role of gap junctions in smooth muscle cells?

Allow movement of molecules and ions for contraction regulation. Signup and view all the answers

What surrounds smooth muscle cells?

External lamina and reticular fibers Signup and view all the answers

Thin filaments of smooth muscle cells contain troponin complex.

False Signup and view all the answers

What are the three major proteins of thin filaments?

G-actin, Tropomyosin, Caldesmon Signup and view all the answers

What is G-actin?

Globular protein existing as a free monomer. Signup and view all the answers

What is the function of tropomyosin in smooth muscle?

Masks the myosin binding sites on G-actin monomers in resting muscle. Signup and view all the answers

What does caldesmon do in smooth muscle?

Masks the myosin-binding site on the actin filament. Signup and view all the answers

Describe the structure of thick filaments in smooth muscle cells.

Myosin II composed of 2 heavy polypeptide chains and 4 light chains. Signup and view all the answers

How is smooth muscle stimulated neurally?

Through postganglionic fibers of the autonomic nervous system. Signup and view all the answers

What kind of hormones can stimulate smooth muscle contraction?

Angiotensin II, vasopressin, and other agents. Signup and view all the answers

What causes mechanical stimulation of smooth muscle fibers?

Passive stretching of the organ. Signup and view all the answers

What are the steps in smooth muscle contraction?

Release of Ca++, binding to calmodulin, activates MLCK, phosphorylates myosin, binding to actin. Signup and view all the answers

What happens during smooth muscle relaxation?

Ca++ is pumped back, calmodulin dissociates, myosin is dephosphorylated. Signup and view all the answers

What is the latch state of smooth muscle cells?

Allows for long term contractions with minimum energy spent. Signup and view all the answers

Study Notes

Smooth Muscle Tissue Overview

Located in the walls of internal organs
Characterized by the absence of cross striations

Characteristics of Smooth Muscle Tissue

Each cell contains a single nucleus, centrally placed
Lacks branches and sarcomeres
Exhibits slow, rhythmic, and prolonged contractions
Functions involuntarily

Smooth Muscle Cell Structure

Fusiform in shape, tapering at both ends
Sarcoplasm contains myofilaments and numerous mitochondria along the tapered ends of nuclei

Myofilaments in Smooth Muscle Cells

Randomly distributed and poorly organized
Thin filaments anchored to dense bodies, while thick filaments are dispersed within the sarcoplasm

Dense Bodies

Composed of α-Actinin
Serve a similar function as Z-lines in skeletal muscle, anchoring intermediate filaments (desmin)

Sarcolemma Structure

Sarcolemma has multiple invaginations forming cavolae
Close proximity of sarcolemmal vesicles and smooth endoplasmic reticulum, functioning similar to skeletal muscle’s membrane triad for calcium delivery

Intercellular Communication

Gap junctions provide connections between smooth muscle cells, facilitating movement of molecules and ions for coordinated contractions

Connective Tissue Surrounding Smooth Muscle

Smooth muscle cells are enclosed by external lamina and reticular fibers

Thin Filaments

Resemble skeletal muscle thin filaments but lack troponin
Composed of G-actin, F-actin, tropomyosin, and caldesmon

Actin Dynamics

G-actin (globular) polymerizes into F-actin (filamentous), forming a double-stranded helical structure
Tropomyosin covers myosin-binding sites on G-actin during rest

Caldesmon Function

A unique smooth muscle actin-binding protein that masks myosin-binding sites on actin

Thick Filaments Composition

Made of Myosin II, which consists of heavy and light polypeptide chains
Myosin only binds to actin when phosphorylated, remaining inactive (folded) when dephosphorylated

Smooth Muscle Fiber Stimulation

Neural stimulation occurs via postganglionic fibers of the autonomic nervous system
Chemical stimulation is triggered by hormones like angiotensin II or vasopressin
Mechanical stimulation (e.g., passive stretching) can also induce contractions

Smooth Muscle Contraction Mechanism

Calcium ions are released into the sarcoplasm and bind to calmodulin
The calcium-calmodulin complex activates myosin light chain kinase (MLCK), leading to myosin phosphorylation and actin binding
Filaments slide, resulting in cell shortening and a corkscrew appearance of the nucleus

Smooth Muscle Relaxation Process

Calcium is sequestered back into the sarcoplasmic reticulum
Calmodulin releases from myosin light chain kinase, leading to myosin dephosphorylation
Caldesmon rebinds to the myosin-binding site on actin, facilitating relaxation

Latch State of Smooth Muscle Cells

Enables sustained contractions with minimal energy expenditure, allowing for prolonged muscle tone

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Description

This quiz consists of flashcards detailing smooth muscle tissue, its characteristics, and cell structure. It's designed to enhance your understanding of histology and the unique features of smooth muscle. Ideal for students studying anatomy and physiology.