Muscular System

What are the three types of muscle tissue?

• Cardiac muscle

• smooth muscle

• skeletal muscle.

Where is cardiac muscle found?

In the heart.

Is cardiac muscle voluntary or involuntary?

Involuntary.

What does cardiac muscle look like?

Branched striated fibers with a single nucleus.

What special structures connect cardiac muscle cells?

Intercalated discs.

Why do cardiac muscles look striated?

Due to its presence of sarcomeres

• the basic functional unit of muscle fibers

Where is smooth muscle found?

In organs such as digestive tract blood vessels bladder and eyes.

Is smooth muscle voluntary or involuntary?

Involuntary.

What does smooth muscle look like?

Non‑striated spindle‑shaped cells with a single nucleus.

Where is skeletal muscle found?

Attached to bones and skin.

Is skeletal muscle voluntary or involuntary?

Voluntary.

What does skeletal muscle look like?

Long cylindrical striated fibers with multiple nuclei.

What is extensibility?

The ability of muscle to stretch.

What is elasticity?

The ability of muscle to return to its original shape after stretching.

What is excitability?

The ability of muscle cells to respond to stimuli and generate electrical signals.

What is contractility?

The ability of muscle to shorten and produce force.

What are muscle fibers?

Muscle cells.

The myosin attaches to the?

M line

What are myofibrils?

Long cylindrical structures inside muscle fibers.

• segmented into repeating units known as sarcomeres

What are sarcomeres?

Repeating contractile units inside myofibrils.

What gives skeletal muscle its striated appearance?

The arrangement of sarcomeres.

Sarcomeres span from?

From one Z disc to the next

Where does actin attach too?

Z discs

What protein forms the thin filament?

Actin.

What protein forms the thick filament?

Myosin.

What part of myosin binds to actin?

The myosin head.

Do actin and myosin shorten during contraction?

No they slide past each other.

What happens to the sarcomere during contraction?

It shortens.

What happens to Z‑lines during contraction?

They move closer together.

What must bind to myosin first?

ATP.

What is tropomysosin?

Long thin protein that hides the binding site on actin

What is Troponin

Attaches tropomyosin to actin and contains binding sites for calcium

What happens to ATP on the myosin head?

It is hydrolyzed into ADP and phosphate.

What does hydrolysis of ATP allow?

Myosin to bind to actin (cross‑bridge formation).

What is the power stroke?

The bending motion of myosin pulling actin toward the center.

What causes the power stroke?

Release of ADP and phosphate.

What causes myosin to detach from actin?

Binding of a new ATP molecule.

Why does rigor mortis occur?

No ATP is available to detach myosin from actin.

Do thick and thin filaments shorten?

No they only slide.

What causes muscle contraction?

Repeated cross‑bridge cycles of myosin pulling actin.

What ensures filaments don’t slip backward?

Many myosin heads are always attached during contraction.