Muscle Physiology Quiz

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Questions and Answers

What is the primary function of skeletal muscles?

Heat production

Movement (correct)

Storage of glucose

Protection of nerves

Which of the following characteristics allows muscle cells to respond to stimuli?

Extensibility

Excitability (correct)

Contractility

Elasticity

What is the innermost connective tissue layer surrounding a muscle fiber called?

Perimysium

Endomysium (correct)

Epimysium

Myofilament

Which muscle type is characterized by voluntary control and striation?

Skeletal muscle Signup and view all the answers

What are the smallest contractile elements of a muscle unit?

Myofilaments Signup and view all the answers

Which connective tissue layer surrounds a muscle fascicle?

Perimysium Signup and view all the answers

What is the functional unit of a muscle cell called?

Sarcomere Signup and view all the answers

Which muscle type is involuntary and has a single centrally located nucleus?

Smooth muscle Signup and view all the answers

What initiates the power stroke during muscle contraction?

The separation of phosphate from the myosin head Signup and view all the answers

What role does ATP play in the muscle contraction cycle?

It aids in the reuptake of calcium ions after contraction Signup and view all the answers

Which sequence of events correctly describes the process immediately after muscle contraction?

Troponin-tropomyosin returns to resting position, and calcium reuptake occurs Signup and view all the answers

What happens to myosin heads after the power stroke is completed?

They release ADP and bind to a new ATP molecule Signup and view all the answers

What is the function of acetylcholinesterase (AChE) in muscle contraction?

To degrade acetylcholine and stop muscle contraction Signup and view all the answers

When does the muscle relaxation process begin?

When acetylcholine is degraded in the synaptic cleft Signup and view all the answers

What is the primary function of the SERCA channel during muscle relaxation?

To pump calcium ions back into the sarcoplasmic reticulum Signup and view all the answers

What is the role of tropomyosin in muscle contraction?

To block myosin head binding sites on actin at rest Signup and view all the answers

What is the primary role of tropomyosin in muscle contraction?

To cover the active points of actin Signup and view all the answers

What protein connects myosin to the Z line in the muscle fiber structure?

Titin Signup and view all the answers

Which of the following structures exclusively contains thick filaments?

H zone Signup and view all the answers

What is the significance of the dystrophin-glycoprotein complex in muscle cells?

It provides stability and integrity to muscle fibers Signup and view all the answers

What type of channels open in the terminal cisternae when an action potential arrives?

Calcium channels Signup and view all the answers

How many myosin filaments are typically present in a single myofibril?

1500 Signup and view all the answers

Which protein is responsible for producing F-actin from G-actins?

Nebulin Signup and view all the answers

What structure is formed by one T tubule and two terminal cisternae?

Triad Signup and view all the answers

What is the initial energy source used during muscle contraction?

ATP stored in muscle fibers Signup and view all the answers

Which process follows the use of creatine phosphate in muscle energy production?

Aerobic glycolysis Signup and view all the answers

What is the role of the motor neuron in muscle contraction?

To innervate muscle fibers for contraction Signup and view all the answers

What is meant by recruitment in muscle contraction?

Activation of additional motor units for stronger contraction Signup and view all the answers

The size of a motor unit is determined by what?

The number of muscle fibers innervated Signup and view all the answers

What results from repeated stimulation of skeletal muscle fibers?

Muscle fatigue and decreased tension Signup and view all the answers

Which factor is NOT a determinant of muscle contraction strength?

Duration of aerobic metabolism Signup and view all the answers

What characteristic differentiates small motor units from large ones?

Number of muscle fibers they innervate Signup and view all the answers

Study Notes

Skeletal Muscle Contraction

Skeletal muscles are responsible for movement, posture maintenance, and heat production. They protect bones and internal organs.
Muscle cells, the fundamental units, exhibit excitability, responding to stimuli by producing action potentials.
Excitability allows cells to shorten and thicken, generating force.
Extensibility means muscles can extend without damage.
Elasticity allows muscles to return to their original shape.

Muscle Cell Types

Skeletal muscle: multinucleated, striated fibers, voluntary control; found attached to the skeleton.
Smooth muscle: uninucleated, spindle-shaped fibers, involuntary control; found in internal organs.
Cardiac muscle: uninucleated, branched fibers, involuntary control; found only in the heart.

Skeletal Muscle Structure

Organized into hierarchical structures: myofilaments, myofibrils, muscle fibers, fascicles, and the entire skeletal muscle itself.
Myofilaments are the smallest contractile elements; actin (thin) and myosin (thick) are the primary components.
Myofibrils are bundles of myofilaments.
Muscle fibers are bundles of myofibrils.
Fascicles are bundles of muscle fibers.
Skeletal muscle is the outermost layer surrounding the fascicles.
Endomysium, perimysium, and epimysium are the connective tissue layers surrounding muscle units in order from innermost to outermost.

Sarcomere Structure

Sarcomere is the functional unit of muscle.
I band: contains only thin filaments (actin).
H zone: contains only thick filaments (myosin).
A band: contains both thick and thin filaments.
M line: in the middle of the H zone, connecting thick filaments.
Z line: boundaries of the sarcomere.

Muscle Proteins

Dystrophin, titin, actinin, and desmin are important intracellular skeletal proteins for structural integrity.
Titin connects myosin to the Z line.
Nebulin produces F-actin from G-actin.
α-actinin connects actin to the Z line.
These proteins contribute stability and prevent excessive stretching of the sarcomere.

Sarcotubular System

Sarcolemma: surrounds muscle fiber.
Sarcoplasm: cytoplasm within the muscle cell.
Sarcoplasmic reticulum (SR): calcium storage within the muscle fiber.
T tubules: inward folds of sarcolemma allowing action potentials to reach the SR.
Triad: T tubule and 2 terminal cisternae.
Action potentials traveling through T tubules trigger release of Ca2+ in muscle cell.

Neuromuscular Junction

Neuromuscular junction is the connection between a motor neuron and muscle fiber.
Acetylcholine (ACh) is released from the motor neuron.
Ligand-gated sodium channels open causing local muscle depolarization.
Muscle action potential is generated causing contraction of the muscle.

Contraction Mechanism

ATP powers muscle contraction. Muscle contraction occurs via the sliding filament theory.
Calcium (Ca2+) released from SR binds to troponin and exposes myosin-binding sites on actin.
Myosin heads bind to actin, and ATP is hydrolyzed, causing the myosin heads to pivot and pull the actin filaments.

Muscle Fatigue

Skeletal muscle fatigue occurs with repeated stimulation.
Reduced tension and slow rate of relaxation are associated with muscle fatigue.

Muscle Fiber Types

Slow-twitch (Type I): endurance activities, contain substantial amount of mitochondria and capillaries.
Fast-twitch (Type II): strength or speed-based activities, have low amounts of mitochondria and capillaries.
Fast-oxidative-glycolytic (Type IIa): intermediate properties.
Fast-glycolytic (Type IIx): rapid strength or bursts of activity, contain almost no myoglobin.

Muscle Metabolism

ATP is the primary energy molecule used for muscle contraction.
Creatine phosphate is immediately available to regenerate ATP.
Aerobic respiration is used to generate ATP when adequate oxygen is present.
Anaerobic respiration is employed when oxygen is limited..

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Description

Test your knowledge on muscle physiology with this quiz focusing on skeletal muscle functions, characteristics, and contraction mechanisms. Explore topics such as muscle types, tissue layers, and the roles of ATP and acetylcholinesterase. Perfect for students in anatomy and physiology courses.