Exercise Physiology Knowledge checks (Muscle)

What is a sarcomere?

The functional contractile unit of skeletal muscle.

What separates one sarcomere from another?

Z-lines.

What are thick filaments made of?

Myosin.

What are thin filaments made of?

Actin, troponin, and tropomyosin.

What is the A band?

The region containing thick filaments and overlapping thin filaments.

What is the H-zone?

The center region containing ONLY thick filaments.

What is the I-band?

The region containing ONLY thin filaments.

What happens to the sarcomere during contraction?

It shortens as thick and thin filaments slide past each other.

What happens to the A-band during contraction?

It stays the same length.

What is the sliding filament theory?

Muscles shorten because thick and thin filaments slide past each other without changing their individual lengths.

What chemical signal is released from a stimulated neuron?

Acetylcholine (ACh).

What happens when ACh binds to muscle receptors?

It allows an action potential to propagate across the muscle cell membrane.

Where is calcium stored in skeletal muscle?

The sarcoplasmic reticulum (SR).

What triggers calcium release from the SR?

An action potential.

What does calcium bind to during muscle contraction?

Troponin C (TnC).

What happens when calcium binds to TnC?

A conformational change moves the inhibitory component, exposing actin's binding sites.

What is the role of tropomyosin?

It covers the active binding sites on actin during rest.

What is the role of Troponin I (TnI)?

It inhibits contraction by blocking the active binding sites during rest.

What is the role of Troponin T (TnT)?

It connects troponin to tropomyosin and helps move TnI when calcium binds.

What is the sarcoplasmic reticulum?

A tubular network that stores calcium and helps distribute the action potential.

What is a muscle fascicle?

A bundle of muscle fibers.

What is a muscle fiber?

An individual muscle cell.

What are myofilaments?

The actin and myosin filaments that make up muscle contractile structures.

What is ATP's role in muscle contraction?

It provides stored energy used for the myosin power stroke.

What is myosin ATPase?

An enzyme on the myosin head that breaks down ATP to release energy.

What are the three main skeletal muscle fiber types?

Fast Twitch (FT), Slow Oxidative (SO), and Fast Oxidative Glycolytic (FOG).

What are Fast Twitch (FT) fibers used for?

High-power, high-force activities.

What are Slow Oxidative (SO) fibers used for?

Long, sustained contractions with low power and low force.

What are Fast Oxidative Glycolytic (FOG) fibers?

Fibers with the potential for fast or oxidative characteristics depending on training.

What determines muscle fiber distribution and performance?

The activity requirements and training stimulus.

What is a motor unit?

An alpha motor neuron and all the muscle fibers it innervates.

What is the all-or-none principle?

A motor unit's fibers either all contract or none contract when adequately stimulated.

What is the size principle?

Muscle fibers are recruited from small, slow fibers first to large, fast fibers last.

What determines which muscle fibers are recruited?

The type of activity and the amount of power or force required.

What do muscle spindles detect?

Changes in muscle length and tension.

What is the role of the Golgi tendon organ?

It senses excessive muscle tension and sends an inhibitory signal to help prevent injury.

How do muscle spindles and Golgi tendon organs differ?

Muscle spindles provide feedback about muscle length; Golgi tendon organs detect excessive tension.

Sarcomere anatomy

Know the A-band, I-band, H-zone, Z-lines, thick filaments, and thin filaments

Muscle contraction sequence

ACh → action potential → calcium release → troponin → exposed binding sites → contraction