Muscle Biology and Contraction

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Questions and Answers

What is the primary function of skeletal muscles?

Protection of internal organs

Storing nutrients

Production of blood cells

Facilitating movement (correct)

Which characteristic allows muscle cells to respond to stimuli?

Elasticity

Contractility

Extensibility

Excitability (correct)

Which connective tissue layer surrounds an entire skeletal muscle?

Endomysium

Epimysium (correct)

Perimysium

Fascia

What is the smallest contractile unit of muscle called?

Sarcomere Signup and view all the answers

Which type of muscle is under voluntary control?

Skeletal muscle Signup and view all the answers

What is found between muscle fibers and serves as an electrical insulator?

Endomysium Signup and view all the answers

Which of the following structures consists of actin and myosin?

Myofibrils Signup and view all the answers

What is the role of mitochondria in muscle cells?

Energy production Signup and view all the answers

What initiates the power stroke during muscle contraction?

Phosphate separation from the myosin head Signup and view all the answers

Which process is NOT directly involved in the muscle contraction cycle?

Degradation of acetylcholine by acetylcholinesterase Signup and view all the answers

What is the role of tropomyosin in thin myofilaments?

It covers the active points of actin Signup and view all the answers

What role does ATP play in muscle contraction?

It provides energy for myosin head movement Signup and view all the answers

When muscle relaxation begins, what happens to Ca+2 ions?

They are pumped back into the sarcoplasmic reticulum Signup and view all the answers

What comprises a triad in skeletal muscle?

1 T tubule and 2 terminal cisternae Signup and view all the answers

During the resting state of muscle, what covers the active sites of actin?

Tropomyosin Signup and view all the answers

Which protein is primarily responsible for connecting actin to the Z line?

α-ACTININ Signup and view all the answers

What happens to the troponin-tropomyosin complex when Ca+2 binds to troponin?

It changes confirmation to expose actin sites Signup and view all the answers

What is the primary component of thick myofilaments?

Myosin Signup and view all the answers

Which component is responsible for reestablishing the sodium-potassium gradient in a muscle cell after contraction?

Sodium-potassium ATPase Signup and view all the answers

What region of the sarcomere consists only of thick filaments?

H zone Signup and view all the answers

What is the main function of dystrophin in skeletal muscle fibers?

It links actin to the dystroglycan in the outer cell membrane Signup and view all the answers

What is primarily stored in muscle cells to provide quick energy for contraction?

Creatine phosphate Signup and view all the answers

What happens when an action potential reaches the triad?

Calcium channels in the terminal cisternae open Signup and view all the answers

Which of the following proteins prevents excessive stretching of the sarcomere?

Titin Signup and view all the answers

What is the main energy source used by muscles for contraction during the first 1-2 seconds?

Stored ATP Signup and view all the answers

What process occurs after the depletion of creatine phosphate stores during muscle contraction?

Aerobic glycolysis Signup and view all the answers

Which term describes the stimulation of additional motor units to increase muscle contraction strength?

Recruitment Signup and view all the answers

What factor does NOT influence the strength of muscle contraction?

Duration of muscle activity Signup and view all the answers

What primarily results in muscle fatigue during repeated stimulation?

Decreased tension in the muscle fiber Signup and view all the answers

What is the relationship between motor unit size and precision of movement?

Larger motor units provide less precise control Signup and view all the answers

Which of the following is true about motor neurons?

A motor neuron can innervate multiple muscle fibers. Signup and view all the answers

What occurs in the muscle fibers when they are stimulated repeatedly?

Diminished tension over time Signup and view all the answers

Study Notes

Skeletal Muscle Contraction

Skeletal muscles are responsible for movement, posture maintenance, heat production, and protection of internal organs.
Muscle cells exhibit excitability (respond to stimuli), contractility (shorten to generate force), extensibility (extend without damage), and elasticity (return to original shape).

Muscle Types

Skeletal muscle: Striated, voluntary, multi-nucleated, and attached to bones.
Smooth muscle: Non-striated, involuntary, uni-nucleated, and found in internal organs.
Cardiac muscle: Striated, involuntary, uni-nucleated, and found only in the heart.

Skeletal Muscle Structure

Organized into: myofilaments (actin and myosin), myofibrils, muscle fibers, muscle fascicles, and skeletal muscle.
Connective tissue layers: endomysium (surrounds individual muscle fibers), perimysium (surrounds muscle fascicles), and epimysium (surrounds the entire muscle).
Tendons connect muscles to bones.

Sarcomere Structure

The functional unit of the muscle.
Contains repeating units of actin and myosin filaments.
I band: thin actin filaments
H zone: thick myosin filaments.
A band: both thick and thin filaments
M line: connects the thick filaments, and Z lines: connect thin filaments.

Muscle Proteins

Important intracellular proteins: Dystrophin, titin, actinin, desmin, and nebulin.
Dystrophin-glycoprotein complex: maintains muscle integrity.
Titin: prevents overstretching of sarcomeres.

Sarcotubular System

T tubules: invaginations of the sarcolemma to transmit action potentials.
Sarcoplasmic reticulum (SR): stores calcium ions that trigger muscle contraction.
Terminal cisternae: portions of SR that surround T tubules (triad).

Neuromuscular Junction

The junction between a motor neuron and muscle fibers.
Acetylcholine (ACh): neurotransmitter released to initiate muscle contraction.
Acetylcholinesterase (AChE): enzyme that degrades ACh, stopping the signal.

Molecular Mechanisms of Muscle Contraction

Steps involved in muscle contraction, including the roles of ATP, calcium, actin, troponin, and tropomyosin.
Sliding filament theory: Myosin filaments pull on actin filaments, causing muscle fibers to shorten.
Phosphate separation initiates the power stroke and also moves the filaments in opposite directions.
ATP hydrolysis and its role in the cross-bridge cycle are essential for muscle contraction.

Muscle Fatigue

Reduced muscle tension resulting from repeated stimulation.
Decreased rate of shortening and slower rate of relaxation.
Factors contributing to muscle fatigue include decreased ATP, metabolites, and ion imbalances.

Skeletal Muscle Fiber Types

Type 1 (slow-twitch): slow contraction speed, high endurance, and oxidative metabolism.
Type IIa (fast-oxidative-glycolytic): fast contraction speed, moderate endurance, and both oxidative and glycolytic metabolism.
Type IIx (fast-glycolytic): fastest contraction speed, low endurance, and substantial glycolytic metabolism.

Muscle Energy Metabolism

ATP stores: immediate energy source.
Creatine phosphate: short-term energy reserve.
Glycolysis: anaerobic ATP production from glucose.
Oxidative phosphorylation; aerobic ATP production in the mitochondria..

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Description

Explore the fascinating world of skeletal muscle contraction, including the types of muscle tissues and their structures. This quiz covers the key features of skeletal, smooth, and cardiac muscles, and provides insights into their organization and function. Test your knowledge on the essential components and roles of muscles in the human body.