Muscle Physiology Quiz

Questions and Answers

What characterizes an isometric contraction?

The load is moved without any muscle contraction.

The muscle generates force but does not change length. (correct)

The tension in the muscle decreases over time.

The muscle shortens while contracting.

During isotonic contractions, which statement is true?

The load cannot be moved irrespective of muscle stimulation.

Muscle cannot generate enough force to move the load.

The muscle stays at a constant length while contracting.

The muscle produces force and shortens to move the load. (correct)

What occurs when a muscle relaxes during an isotonic contraction?

The muscle will shorten further to increase movement.

Muscle tension remains constant regardless of length change.

The load continues to move without any muscle activity. (correct)

The force required to maintain tension decreases.

What is the role of the force in an isometric contraction?

It is less than the resistance of the load. Signup and view all the answers

In the context of muscle contractions, what does 'stimulated muscle' refer to?

A muscle that is actively generating tension. Signup and view all the answers

Which statement best describes the relationship between load and muscle contraction?

A heavier load requires greater muscle tension to move it. Signup and view all the answers

What typically happens to muscle tension during a prolonged isometric contraction?

Tension eventually decreases as fatigue sets in. Signup and view all the answers

Which of the following best differentiates isotonic from isometric contractions?

Isotonic contractions result in movement, while isometric do not. Signup and view all the answers

What is the main characteristic of isometric contractions?

They create force without moving a load. Signup and view all the answers

What happens to sarcomeres during isometric contractions?

They do not change in length but cause elastic elements to stretch. Signup and view all the answers

What typically causes muscle cramps?

Sustained painful contraction. Signup and view all the answers

Which inherited disorder is characterized by a loss of dystrophin?

Duchenne muscular dystrophy. Signup and view all the answers

What is a significant risk associated with Duchenne muscular dystrophy?

Progressive muscle weakness leading to respiratory failure. Signup and view all the answers

How do cardiac muscle fibers differ from skeletal muscle fibers?

Cardiac fibers are striated and smaller with intercalated disks. Signup and view all the answers

What contributes to muscle atrophy?

Disuse of the muscle. Signup and view all the answers

What is the appearance of skeletal muscle fibers under a microscope?

Striated and multinucleate. Signup and view all the answers

What role does myosin light chain kinase (MLCK) play in muscle contraction?

It phosphorylates myosin light chains, increasing ATPase activity. Signup and view all the answers

What type of contraction results in movement of a load?

Isotonic contraction. Signup and view all the answers

What is the effect of increased myosin phosphatase activity on muscle tension?

It decreases muscle tension by removing phosphate from myosin light chains. Signup and view all the answers

How does ATP influence the activity of myosin ATPase?

ATP is required for the activation of myosin ATPase. Signup and view all the answers

What is the consequence of decreased myosin ATPase activity?

Decreased muscle contraction and tension. Signup and view all the answers

What initiates the activation of myosin light chain kinase (MLCK)?

Binding of calcium ions to calmodulin (CaM). Signup and view all the answers

What characteristic of smooth muscle allows it to sustain contractions for extended periods without fatiguing?

Slow contraction and relaxation Signup and view all the answers

How do smooth muscle myosin molecules differ from skeletal muscle myosin?

Smooth muscle myosin has hinged heads along its length Signup and view all the answers

What is a key difference in calcium source during contraction between smooth muscle and skeletal muscle?

Calcium for smooth muscle comes from both extracellular fluid and the sarcoplasmic reticulum Signup and view all the answers

Which of the following statements about smooth muscle is false?

Smooth muscle operates within a limited length range Signup and view all the answers

What initiates contraction in smooth muscle cells?

Phosphorylation of myosin light chains Signup and view all the answers

What is a significant feature of smooth muscle cell arrangement?

Layers of cells may run in several directions Signup and view all the answers

What triggers contraction in smooth muscle cells?

Increased cytosolic calcium Signup and view all the answers

Which process is involved in the relaxation of smooth muscle?

Dephosphorylation of myosin light chains Signup and view all the answers

What energy characteristic distinguishes smooth muscle from other muscle types?

Uses less energy overall Signup and view all the answers

What is the first step in the relaxation of smooth muscle?

Removal of Ca2+ from the cytosol Signup and view all the answers

What type of muscle has smaller, spindle-shaped cells with a single nucleus?

Smooth Muscle Signup and view all the answers

What happens to cytosolic calcium levels when smooth muscle relaxes?

They decrease Signup and view all the answers

Which of the following features does not describe smooth muscle?

Organized in a parallel arrangement Signup and view all the answers

What role does calmodulin (CaM) play in smooth muscle contraction?

It forms a complex with Ca2+ that activates MLCK Signup and view all the answers

What triggers the release of Ca2+ from the sarcoplasmic reticulum?

Increased cytosolic calcium Signup and view all the answers

What is the effect of calcium unbinding from calmodulin (CaM)?

MLCK activity decreases Signup and view all the answers

How is Ca2+ returned to the sarcoplasmic reticulum?

By active transport using ATP Signup and view all the answers

What effect does an increase in extracellular calcium (ECF) have on smooth muscle contraction?

It promotes the influx of calcium into the cell Signup and view all the answers

Which component is involved in the signaling pathway for smooth muscle contraction?

Calcium-calmodulin complex Signup and view all the answers

Which ion's levels must decrease for smooth muscle to relax?

Calcium (Ca2+) Signup and view all the answers

Study Notes

Muscle Contractions

Isometric Contraction: Muscle contracts without shortening; force created does not move the load.
Isotonic Contraction: Muscle shortens while contracting, resulting in movement of the load.
Series Elastic Elements: Sarcomeres shorten while elastic elements stretch; minimal change in overall muscle length.

Muscle Disorders

Muscle Cramps: Sustained, painful contractions often due to overuse or disuse, leading to atrophy.
Duchenne Muscular Dystrophy: Inherited disorder caused by absence of dystrophin, leading to progressive muscle weakness; often fatal by age 30 due to respiratory failure.

Muscle Cell Types

Skeletal Muscle: Large, multinucleate fibers appear striated under a microscope; responsible for voluntary movements.
Cardiac Muscle: Smaller, branched, uninucleate fibers connected by intercalated disks; striated and involuntary, found in the heart.
Smooth Muscle: Small, spindle-shaped cells with one nucleus; contracts and relaxes slowly, sustaining long-term contractions without fatiguing.

Smooth Muscle Mechanics

Contraction Initiation: Calcium ions (Ca2+) from extracellular fluid (ECF) and sarcoplasmic reticulum; does not require an action potential.
Troponin Absence: Ca2+ triggers contraction through a cascade effect, involving phosphorylation of myosin light chains.
Relaxation Process: Involves dephosphorylation of myosin light chains; removal of Ca2+ from the cytosol initiates relaxation.

Muscle Fiber Structure

Smooth Muscle Structure: Actin filaments attach to dense bodies; myosin molecules have hinged heads along their length, facilitating contraction.
Intermediate Filaments: Form a cytoskeleton within smooth muscle, providing structural support during contraction.

Calcium Dynamics in Smooth Muscle

Calcium Role: Increased cytosolic Ca2+ signals contraction; its removal is essential for relaxation.
Calmodulin (CaM): Binds to Ca2+ to activate myosin light chain kinase (MLCK), promoting contraction.
Myosin Phosphatase: Dephosphorylates myosin light chains, reducing myosin ATPase activity and muscle tension.

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Description

Test your knowledge on muscle tension and relaxation. This quiz covers key concepts related to the development of muscle tension in various conditions. Ideal for students studying exercise physiology or related fields.