Muscle Chapter 10: Skeletal and Smooth Muscle

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Questions and Answers

Which property of muscle allows it to respond to a stimulus?

Elasticity

Excitability (correct)

Extensibility

Contractility

What distinguishes skeletal muscle tissue from cardiac muscle tissue?

Cardiac muscle is striated and voluntary.

Skeletal muscle is voluntary and striated. (correct)

Skeletal muscle is involuntary and striated.

Cardiac muscle is voluntary and nonstriated.

During the sliding filament mechanism, which concept describes the muscle's ability to generate pulling force?

Extensibility

Elasticity

Contractility (correct)

Excitability

What is the primary role of titin filaments in muscle function?

Keeping thick and thin filaments in proper alignment Signup and view all the answers

Which type of muscle tissue is primarily involved in the constriction of blood vessels?

Smooth muscle tissue Signup and view all the answers

What do the Z lines indicate in the structure of myofibrils?

They represent the ends of a sarcomere. Signup and view all the answers

What best describes the relationship between muscle length and tension?

There is an optimal length where tension is maximized. Signup and view all the answers

Which characteristic of muscle allows it to return to its resting length after being stretched?

Elasticity Signup and view all the answers

Which proteins are primarily classified as contractile proteins?

Actin and Myosin Signup and view all the answers

How do the thick and thin filaments behave during muscle contraction?

Thick filaments slide over thin filaments without changing length. Signup and view all the answers

What type of contraction occurs when the muscle length changes and moves a load?

Isotonic contraction Signup and view all the answers

What action do myosin cross bridges perform in the contraction cycle?

They pull on thin filaments to shorten the muscle. Signup and view all the answers

Which of the following statements about muscle metabolism is accurate?

Muscle metabolism includes both anaerobic and aerobic pathways. Signup and view all the answers

What occurs to tropomyosin during a muscle contraction?

It exposes the myosin-binding site on actin. Signup and view all the answers

What primarily distinguishes the contraction of cardiac muscle from skeletal muscle?

Increased calcium delivery from the sarcoplasmic reticulum and extracellular fluid Signup and view all the answers

Which feature is characteristic of visceral smooth muscle?

Autorhythmic with gap junctions facilitating synchronized contraction Signup and view all the answers

What is the role of calmodulin in smooth muscle contraction?

Activates myosin light chain kinase for myosin-actin binding Signup and view all the answers

How does the energy generation mechanism in cardiac muscle differ from that in skeletal muscle?

Larger mitochondria in cardiac muscle generate ATP aerobically Signup and view all the answers

What factor contributes to the prolonged contraction of cardiac muscle?

Prolonged opening of calcium channels allowing slow influx Signup and view all the answers

Which type of smooth muscle is primarily responsible for synchronized contractions across an entire tissue?

Visceral smooth muscle due to autorhythmic fibers Signup and view all the answers

What is the primary determinant of the total strength of a muscle contraction?

The number and size of activated motor units Signup and view all the answers

During the latent period of a twitch contraction, which of the following occurs?

Calcium ions are released from the sarcoplasmic reticulum Signup and view all the answers

Which period occurs when the muscle fiber cannot respond to a new stimulus?

Refractory Period Signup and view all the answers

Wave summation leads to increased strength of contraction when?

A second stimulus is applied before complete relaxation Signup and view all the answers

What characterizes fast glycolytic (fast-twitch B) fibers?

Few mitochondria and blood vessels, low myoglobin Signup and view all the answers

In cardiac muscle, what feature connects adjacent fibers?

Intercalated discs Signup and view all the answers

How long does the relaxation period of a twitch contraction last?

10 to 100 msec Signup and view all the answers

Which type of skeletal muscle fiber is primarily used for maintaining posture?

Slow oxidative fibers Signup and view all the answers

What is the primary function of acetylcholinesterase (AChE) at the neuromuscular junction?

To break down acetylcholine in the synaptic cleft Signup and view all the answers

Which factor is NOT a contributor to muscle fatigue?

Increased calcium release Signup and view all the answers

What is the effect of curare on muscle function?

It blocks ACh receptors, causing muscle paralysis Signup and view all the answers

What defines the optimal resting length of a muscle in relation to sarcomeres?

Length where thick and thin filaments overlap maximally Signup and view all the answers

When does the calcium-binding protein calsequestrin play a critical role?

During the relaxation phase to store calcium Signup and view all the answers

What is the best description of a motor unit?

One somatic motor neuron and all skeletal muscle fibers it stimulates Signup and view all the answers

Which process generates ATP primarily during high-intensity exercise?

Anaerobic cellular respiration Signup and view all the answers

What happens when a muscle is stretched beyond its optimal length?

It decreases the muscle's ability to generate force Signup and view all the answers

Study Notes

Microscopic Anatomy of Skeletal Muscle

Skeletal muscle fibers exhibit a striated appearance and are voluntary in nature.
Each muscle is a separate organ composed of fibers that serve as attachments for actin myofilaments.
Proteins in muscle include contractile (myosin, actin), regulatory (troponin, tropomyosin), and structural proteins (titin, myomesin).

Muscle Function

Primary functions include movement, thermogenesis, protection, posture maintenance, and joint stabilization.
Functionality varies based on muscle tissue type and its location in the body.

Characteristics of Muscle Tissue

Muscle tissues possess excitable, contractile, elastic, and extensible properties.
Excitability allows response to stimuli; contractility enables force generation; extensibility facilitates stretching; elasticity ensures muscles return to original length.

Contraction Mechanism

Neuromuscular junction (NMJ) initiates muscle contraction when acetylcholine (ACh) binds to receptors on the muscle fiber.
Myosin cross bridges pull thin filaments inward, leading to muscle fiber shortening without changing filament length.

Length-Tension Relationship

Muscle contraction strength depends on initial sarcomere length; optimal overlap between thick and thin filaments produces maximum tension.
Resting muscle length is typically maintained between 80-120% of optimal for force production.

Muscle Metabolism

ATP is generated through creatine phosphate, anaerobic respiration, and aerobic respiration.
Muscle action requires a high rate of ATP, with reserves lasting only seconds.

Muscle Fatigue

Fatigue occurs from prolonged activity due to factors like central fatigue, depleted creatine phosphate, decreased Ca2+, insufficient oxygen or glycogen, and lactic acid accumulation.

Control of Muscle Tension

Motor units consist of a motor neuron and the muscle fibers it stimulates; size and recruitment of these units determine contraction strength.
Twitch contraction phases include latent (Ca2+ release), contraction (filament sliding), relaxation (active Ca2+ transport), and refractory (unresponsive period).

Types of Skeletal Muscle Fibers

Slow oxidative fibers (red, high endurance) are suited for postural maintenance.
Fast oxidative-glycolytic fibers (red, quick energy) support walking and sprinting.
Fast glycolytic fibers (white, low endurance) are for anaerobic activities like weight lifting.

Cardiac Muscle Characteristics

Cardiac muscle fibers are striated, form intercalated discs, and have autorhythmic contractions.
Longer contraction duration is facilitated by slow-dependent Ca2+ influx, requiring high oxygen and larger mitochondria for aerobic ATP production.

Smooth Muscle Physiology

Visceral smooth muscle contracts as a unit due to gap junctions and exhibits autorhythmic qualities.
Multiunit smooth muscle contains individual fibers with distinct motor neuron endings, found in various structures like blood vessels and eyes.
Contraction mechanisms in smooth muscle are slower and rely on extracellular Ca2+, with calmodulin activating myosin light chain kinase for contraction.

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Description

This quiz covers the microscopic anatomy of skeletal muscle fibers and the mechanisms of muscle contraction. Topics include excitation-contraction coupling, muscle metabolism, and the control of muscle tension. Additionally, it explores various types of skeletal muscle fibers and smooth muscle physiology.