Cardiac vs Skeletal Muscle Study Guide

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Questions and Answers

How do cardiac muscles differ from skeletal muscle cells?

Cardiac muscle is voluntary and found in the limbs.

Cardiac muscle is striated but connected at irregular angles. (correct)

Skeletal muscle has intercalated discs.

Skeletal muscle is primarily involuntary.

What are intercalated discs?

Microscopic identifying features of cardiac muscle that support synchronized contraction.

Why do cardiac muscle fibers have gap junctions?

They allow direct transmission of the depolarizing current from cell to cell.

Why is cardiac muscle highly oxidative?

Cardiac muscle cells generate most ATP from the β-oxidation of fatty acids. Signup and view all the answers

Explain why cardiac muscle has a relatively long action potential.

It has a sustained depolarization 'plateau' that provides for a longer contraction. Signup and view all the answers

Why doesn't cardiac muscle have wave summation?

Cardiac muscle cells have a long refractory period. Signup and view all the answers

What is meant by Ca2+-induced Ca2+ release in cardiac muscle?

Initial depolarization triggers Ca2+ influx opening voltage-gated Ca2+ channels. Signup and view all the answers

How does smooth muscle differ from skeletal muscle?

Smooth muscle is not striated and is involuntary. Signup and view all the answers

Where is smooth muscle found?

In the walls of hollow organs like the intestines and stomach. Signup and view all the answers

What are dense bodies in smooth muscle?

Actin filaments of contractile units are attached to dense bodies. Signup and view all the answers

Why does Ca2+ for the contraction of smooth muscle come from extracellular fluid?

Calcium enters the cell from extracellular sources and diffuses into the cytoplasm. Signup and view all the answers

How is most smooth muscle innervated?

Primarily by the sympathetic nervous system using norepinephrine and acetylcholine. Signup and view all the answers

What is single-unit (or visceral) smooth muscle?

Found in the uterus and gastrointestinal tract. Signup and view all the answers

What is multi-unit smooth muscle?

Composed of cells that rarely possess gap junctions and are not electrically coupled. Signup and view all the answers

Briefly list local factors that regulate smooth muscle contraction.

Graded membrane response can be stimulated by local humoral factors, hormones, or mechanical stimulation. Signup and view all the answers

What is excitation-contraction coupling in smooth muscle?

Calmodulin activates myosin light chain kinase. Signup and view all the answers

What role does caldesmon play in smooth muscle contraction?

Caldesmon inhibits ATPase activity of myosin. Signup and view all the answers

What is myosin light-chain kinase?

A calcium/calmodulin-dependent kinase that facilitates myosin binding to actin. Signup and view all the answers

Where is skeletal muscle found?

Between bones, connected by tendons. Signup and view all the answers

Study Notes

Cardiac Muscle

Involuntary muscle located solely in the heart, distinguishing it from skeletal muscle.
Striated appearance due to regular arrangements of fibers and sarcomeres.
Features intercalated discs for structural integrity and synchronized contraction.

Intercalated Discs

Microscopic structures unique to cardiac muscle.
Essential for supporting the simultaneous contraction of cardiac tissue.

Gap Junctions in Cardiac Muscle

Composed of protein-lined tunnels facilitating direct electrical signaling.
Allow rapid transmission of depolarization across heart cells for coordinated contraction.

Oxidative Nature of Cardiac Muscle

Relies heavily on aerobic respiration for ATP production, primarily through β-oxidation of fatty acids.
Sensitive to oxygen supply; function declines if coronary blood flow is insufficient.

Action Potential Duration in Cardiac Muscle

Characterized by a prolonged plateau phase during depolarization.
Longer action potential translates to extended contraction duration.

Lack of Wave Summation in Cardiac Muscle

Long refractory period prevents wave summation and tetanus.
Ensures rhythmic, effective heart contractions without fatigue.

Calcium-Induced Calcium Release

Initial sarcolemma depolarization opens voltage-gated Ca2+ channels.
Leads to a cascade of calcium influx, crucial for muscle contraction.

Smooth Muscle Characteristics

Non-striated, involuntary muscle not under conscious control.
Found in walls of hollow organs, enabling various physiological functions.

Locations of Smooth Muscle

Present in structures such as intestines, stomach, and blood vessels.

Dense Bodies in Smooth Muscle

Structures where actin filaments of contractile units attach.
Play a role in maintaining structural organization during contraction.

Calcium Source for Smooth Muscle Contraction

Calcium required for contraction originates from extracellular fluid.
Diffuses into the cytoplasm, initiating and sustaining contraction.

Innervation of Smooth Muscle

Primarily innervated by sympathetic nervous system via adrenergic receptors.
Utilizes neurotransmitters like norepinephrine (NE) and acetylcholine (ACh).

Single-Unit Smooth Muscle

Known as visceral smooth muscle, located in areas like the uterus and gastrointestinal tract.
Exhibits fatigue resistance, rapid contraction onset, and cannot undergo tetanus.

Multi-Unit Smooth Muscle

Composed of cells with rare gap junctions, preventing electrical coupling.
Located in airways leading to the lungs and in large blood vessels.

Regulation of Smooth Muscle Contraction

Membrane potential influences contraction initiation and modulation.
Local factors include hormones, humoral factors, and mechanical stimuli such as cell stretching.

Excitation-Contraction Coupling in Smooth Muscle

Calmodulin binds to calcium ions, initiating the activation of myosin light-chain kinase.
Caldesmon, a calcium-binding protein, inhibits myosin's ATPase activity, regulating contraction.
Myosin light-chain kinase enhances interaction between myosin and actin, promoting contractility.

Skeletal Muscle Characteristics

Found between bones, connected to bone via tendons and epimysium.
Distinctly striated, comprised of parallel bundles, and under voluntary control.

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Description

This quiz compares cardiac and skeletal muscle cells, focusing on their structural differences and unique features such as intercalated discs. Test your understanding of muscle types with this study guide. Perfect for students studying anatomy and physiology.