Ultra-structural Organization of Myofibrils

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Questions and Answers

What is the primary function of actin in muscle fibers?

Structural support

Energy storage

Forming thick filaments

Forming thin filaments (correct)

Dystrophin links actin to the extracellular matrix (ECM).

True

What term describes the polymerized form of globular actin?

F actin

The thick filament in muscle fibers is primarily composed of __________.

myosin Signup and view all the answers

Match the following proteins to their descriptions:

Actin = Forms thin filaments Myosin = Forms thick filaments Tropomyosin = Regulates muscle contraction Dystrophin = Links actin to the ECM Signup and view all the answers

Which components make up the thick filament?

2 heavy chains and 4 light chains Signup and view all the answers

ATP-binding sites are located on actin molecules.

False Signup and view all the answers

Which structure remains constant during muscle contraction according to the sliding filament theory?

A band Signup and view all the answers

Name the disease associated with mutations of the dystrophin gene.

Duchenne muscular dystrophy Signup and view all the answers

Myosin consists of __________ polypeptide chains.

6 Signup and view all the answers

During muscle contraction, the I band becomes more prominent.

False Signup and view all the answers

What is the role of tropomyosin in muscle contraction?

It regulates the interaction between actin and myosin. Signup and view all the answers

What is released into the synaptic cleft to initiate muscle contraction?

acetylcholine Signup and view all the answers

The space between the nerve ending and the sarcolemma is called the ______.

synaptic cleft Signup and view all the answers

Match the following components with their functions in muscle contraction:

Axon terminals = Release acetylcholine Sarcolemma = Receives acetylcholine T-tubule system = Transmits action potential Sarcoplasmic reticulum = Stores calcium ions Signup and view all the answers

In which disorder do antibodies interfere with the activation of acetylcholine receptors?

Myasthenia gravis Signup and view all the answers

The myelin sheath remains intact at the myoneural junction.

False Signup and view all the answers

What happens to junctional folds of the sarcolemma in patients with myasthenia gravis?

They are internalized and digested. Signup and view all the answers

The muscle fibers become ______ and broader during contraction.

shorter Signup and view all the answers

Match the muscle fiber types to their characteristics:

Type I = Slow twitch, endurance Type II = Fast twitch, power Type III = Intermediate, versatile Type IV = Fast twitch, fatigue easily Signup and view all the answers

Study Notes

Ultra-structural Organization of Myofibrils

Myofibrils are composed of repeating units called sarcomeres.
Sarcomeres are the functional units of muscle contraction.
Thick filaments are composed of myosin, which has a tail and two globular heads.
Thin filaments are composed of actin, tropomyosin, and troponin.
Actin is a globular protein that polymerizes to form a double helical filament.
Tropomyosin is a rod-shaped protein that lies along the groove of the actin filament.
Troponin is a complex of three proteins that binds to both actin and tropomyosin.

Mechanism of Muscle Contraction

Sliding filament theory describes the interaction between thick and thin filaments during contraction.
Myosin heads bind to actin and pull the thin filaments towards the center of the sarcomere.
ATP is required for muscle contraction.
Calcium is released from the sarcoplasmic reticulum and binds to troponin, causing a conformational change that allows myosin to bind to actin.

Neuromuscular Junction

Neuromuscular junction is the site where a motor neuron connects to a muscle fiber.
Motor neuron releases acetylcholine into the synaptic cleft.
Acetylcholine binds to receptors on the muscle fiber membrane, triggering an action potential.
The action potential travels along the muscle fiber membrane and into the T-tubule system, initiating contraction.

Dystrophin

Dystrophin is a protein that links the actin cytoskeleton to the extracellular matrix.
Mutations in the dystrophin gene can lead to Duchenne muscular dystrophy.
Duchenne muscular dystrophy is characterized by muscle weakness and atrophy.

Medical Application

Myasthenia gravis is an autoimmune disorder that affects the neuromuscular junction.
Antibodies against acetylcholine receptors interfere with neuromuscular transmission.
Symptoms of myasthenia gravis include muscle weakness and fatigue.

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Description

Explore the fascinating structure and function of myofibrils and sarcomeres in this quiz. Learn about the components of thick and thin filaments, the sliding filament theory, and the role of ATP and calcium in muscle contraction. Test your understanding of muscle physiology!