Ultra-structural Organization of Myofibrils

What is the primary function of actin in muscle fibers?

Dystrophin links actin to the extracellular matrix (ECM).

What term describes the polymerized form of globular actin?

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

Match the following proteins to their descriptions:

Which components make up the thick filament?

ATP-binding sites are located on actin molecules.

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

Name the disease associated with mutations of the dystrophin gene.

Myosin consists of __________ polypeptide chains.

During muscle contraction, the I band becomes more prominent.

What is the role of tropomyosin in muscle contraction?

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

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

Match the following components with their functions in muscle contraction:

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

The myelin sheath remains intact at the myoneural junction.

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

The muscle fibers become ______ and broader during contraction.

Match the muscle fiber types to their characteristics:

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.

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 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 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.

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.