32.2 Muscular system

When a motor neuron is stimulated, its axon terminals release a neurotransmitter called _________ (ACh), which diffuses across the synapse, producing an impulse (action potential) in the cell membrane of the muscle fiber.

Acetylcholine

What causes the release of calcium ions (Ca2+), which affect regulatory proteins that allow myosin cross-bridges to bind to actin filaments?

An impulse in the cell membrane of the muscle fiber.

Skeletal muscles are usually attached to what?

Bones

What muscle is striated like skeletal muscle, although its cells are smaller and usually have just one or two nuclei?

Cardiac

Tendons

Connect muscle to bone

How do muscles contract?

During a muscle contraction, myosin filaments form cross-bridges with actin filaments. The cross-bridges then change shape, pulling the actin filaments toward the center of the sarcomere.

Red muscle is useful for___.

Endurance activities

What is the fixed point around which the lever moves?

Fulcrum

The cells in smooth muscle tissue are connected to one another by what?

Gap junctions

What allow electrical impulses to travel directly from one muscle cell to a neighboring muscle cell?

Gap junctions

What control the contraction of muscle fibers?

Impulses from motor neurons

Tendons pull on the bones and make them work like _____.

Levers

Red muscle contains many ______.

Mitochondria

Because skeletal muscle cells are long and slender, they are often called what?

Muscle fibers

What is muscle tone responsible for?

Muscle tone is responsible for keeping the back and legs straight and the head upright, even when you are relaxed.

Each myofibril contains thick filaments of a protein called ____ and thin filaments of a protein called _______.

Myosin, actin

Is the cardiac muscle under direct control under the nervous system?

No

What are the two principal types of skeletal fibers?

Red and white

Skeletal muscles remain in a state of partial contraction called what?

Resting muscle tone

Two Z lines and the filaments between them make up a unit called a _________.

Sarcomere

What muscle cells are large, have many nuclei, and vary in length?

Skeletal muscle cells

How do muscle contractions produce movement?

Skeletal muscles generate force and produce movement by pulling on body parts as they contract.

What muscle cells don't have striations and are spindle-shaped and usually have a single nucleus?

Smooth muscle cells

When viewed under a microscope, skeletal muscle appears to have alternating light and dark bands called what?

Striations

When one muscle contracts,

The other relaxes

What are the principal types of muscle tissue?

There are three different types of muscle tissue: skeletal, smooth, and cardiac.

Which muscle contracts more rapidly and generates more force than red muscle, but its cells contain few mitochondria and tire quickly?

White muscle

fast-twitch muscle

White muscles

Is the skeletal muscle under the direct control of the central nervous system?

Yes

Is the smooth muscle under the direct control of the central nervous system?

Yes

What are areas where the actin filaments are bound together?

Z lines

White fibers are useful for __________.

activities that require great strength or quick bursts of speed like sprinting.

Where is cardiac muscle found?

heart

Are smooth muscles voluntary or involuntary?

involuntary

Skeletal muscle cells, or fibers, are filled with tightly-packed filament bundles called _____.

myofibrils

What happens during a muscle contraction?

myosin filaments form cross-bridges with actin filaments. The cross-bridges then change shape, pulling the actin filaments toward the center of the sarcomere. Then the cross-bridge detaches from actin, and repeats the cycle by binding to another site on the actin filament. As thick and thin filaments slide past each other, the length of the fiber shortens, hence the name "sliding-filament model" of muscle contraction.

What is the point of contact between a motor neuron and a skeletal muscle cell known as?

neuromuscular junction

slow twitch muscle

red muscle

The dark color of red muscle comes from ________.

small blood vessels that deliver blood and from an oxygen- storing protein called myoglobin.

A muscle cell contracts until _______.

the release of ACh stops and an enzyme destroys any remaining ACh.

Are skeletal muscles involuntary or voluntary?

voluntary