cp 9

What is excitability in muscle tissue?

The ability of muscle cells to detect and respond to a stimulus by generating an electrical signal.

What is contractility?

The ability of muscle fibers to shorten forcibly when stimulated.

What is extensibility?

The ability of muscle tissue to stretch without being damaged.

What is elasticity?

The ability of muscle fibers to return to their original length after stretching.

What is the sarcolemma?

The plasma membrane of a muscle fiber.

What is the sarcoplasm?

The cytoplasm of a muscle fiber; contains myoglobin and organelles.

What are myofibrils?

Rod-like structures inside muscle fibers that contain sarcomeres; make up ~80% of cell volume.

What is a sarcomere?

The smallest contractile unit of muscle; extends from Z-disc to Z-disc.

What protein makes up the thick filament?

Myosin.

What protein makes up the thin filament?

Actin (plus tropomyosin and troponin).

What does tropomyosin do?

Blocks actin’s active sites when Ca²⁺ is low.

What does troponin do?

Binds Ca²⁺ and moves tropomyosin off actin’s active sites.

What is the function of the sarcoplasmic reticulum?

Stores and releases Ca²⁺ for contraction.

What are T-tubules?

Invaginations of the sarcolemma that carry action potentials deep into the muscle fiber.

What is a triad?

One T-tubule + two terminal cisternae of the SR.

What does the sliding filament theory state?

Myosin pulls actin toward the M-line, shortening sarcomeres without shortening filaments.

What is a motor unit?

A motor neuron and all the muscle fibers it innervates.

What is recruitment?

Increasing the number of active motor units to increase force.

What is the neuromuscular junction?

The synapse between a motor neuron and a muscle fiber; uses ACh.

What does acetylcholinesterase do?

Breaks down ACh to stop muscle contraction.

What is an end plate potential?

Local depolarization caused by Na⁺ entering through ACh receptor channels.

What is excitation–contraction coupling?

The process linking an action potential to Ca²⁺ release and sarcomere shortening.

What is cross-bridge formation?

Myosin head attaches to actin when Ca²⁺ exposes binding sites.

What is the power stroke?

Myosin head pivots and pulls actin toward the M-line.

What causes cross-bridge detachment?

ATP binding to myosin.

What “cocks” the myosin head?

ATP hydrolysis.

What is the latent period?

Time between AP arrival and contraction; E–C coupling occurs here.

What is the origin of a muscle?

The immovable bone.

What is the insertion of a muscle?

The movable bone.

What is the epimysium?

Dense irregular connective tissue around the entire muscle.

What is the perimysium?

Dense irregular connective tissue around fascicles.

What is the endomysium?

Areolar connective tissue around each muscle fiber.