Chapter 10 STUDY FOR TEST

What are the three types of muscle tissue?

Skeletal, cardiac, and smooth muscle.

What is the basic function of all muscle tissue?

Generating force, also known as muscle tension.

List four functions of muscle tissue besides generating movement.

Maintain posture, stabilize joints, generate heat, and regulate flow through hollow organs.

What is skeletal muscle tissue composed of?

Long, multinucleated muscle cells arranged parallel to one another.

Why are skeletal muscle cells called fibers?

Because they are long and resemble fibers.

Are skeletal muscle contractions voluntary or involuntary?

Voluntary.

What attaches skeletal muscle to bones?

Connective tissue.

Where is cardiac muscle tissue found?

Only in the heart.

What do cardiac muscle cells look like?

Short, thick, branched cells with one or two nuclei.

What are intercalated discs?

Specialized structures containing gap junctions and desmosomes that link cardiac muscle cells.

Are cardiac contractions voluntary or involuntary?

Involuntary.

Where is smooth muscle found?

Walls of hollow organs, eyes, skin, and certain ducts.

What do smooth muscle cells look like?

Long, flattened, spindle-shaped cells with a single nucleus.

Do smooth muscle cells have striations?

No, they are non-striated.

Are smooth muscle contractions voluntary or involuntary?

Involuntary.

What property allows smooth muscle to contract as a unit?

Gap junctions linking cells electrically.

What is contractility?

The ability of a muscle cell to contract and generate tension.

What is excitability?

The ability of a muscle cell to respond to stimuli.

What is conductivity?

The ability to conduct electrical changes across the entire membrane.

What is extensibility?

The ability to stretch up to three times resting length without damage.

What is elasticity?

The ability of a muscle cell to return to its original length after stretching.

What is the sarcoplasm?

The cytoplasm of a muscle cell.

What is the sarcolemma?

The plasma membrane of a muscle cell.

What is the sarcoplasmic reticulum (SR)?

A modified smooth ER that stores and releases calcium ions.

What are myofibrils?

Long cylindrical protein bundles essential for muscle contraction.

How much of the muscle cell volume do myofibrils make up?

Approximately 50–80%.

What organelle is in high quantity inside muscle cells and why?

Mitochondria, because muscles require high amounts of ATP.

What is different about smooth muscle myofibrils?

They are arranged differently compared to skeletal and cardiac muscle.

What tissue surrounds each individual muscle fiber?

The endomysium.

How long can skeletal muscle fibers be?

As long as the entire muscle, up to 30 centimeters.

How thick can skeletal muscle fibers be?

Up to 100 micrometers.

Why do skeletal muscle fibers have multiple nuclei?

Because they form from the fusion of many myoblast cells.

What is the primary organelle within skeletal muscle fibers?

Myofibrils.

What is the function of the sarcoplasmic reticulum?

It stores and releases calcium required for contraction.

What are T-tubules?

Invaginations of the sarcolemma that conduct electrical signals deeper into the cell.

What are terminal cisternae?

Enlarged SR sacs that store calcium and flank T-tubules.

What forms a triad inside a muscle fiber?

One T-tubule and two terminal cisternae.

What are the three categories of myofilament proteins?

Contractile, regulatory, and structural proteins.

What do contractile proteins do?

Generate tension during contraction.

What do regulatory proteins do?

Control when muscle fibers can contract.

What do structural proteins do?

Maintain structural integrity and proper alignment.

What are thick filaments composed of?

Myosin.

What are thin filaments composed of?

Actin, tropomyosin, and troponin.

What protein forms elastic filaments?

Titin.

What is the function of titin?

Provides elasticity and resists excessive stretching.

What part of myosin binds to actin?

The myosin head.

What allows the myosin head to pivot during contraction?

A flexible hinge-like neck.

What does tropomyosin do?

Covers actin’s active sites to prevent crossbridge formation.

What does troponin do?

Binds calcium and moves tropomyosin off actin’s binding sites.

What is a sarcomere?

The functional unit of contraction in skeletal muscle.

What is found in the I band?

Only thin filaments.

What structure defines the boundaries of a sarcomere?

Z-discs.

What is found in the A band?

Thick filaments and the zone of overlap.

What is the H zone?

The center of the A band containing thick filaments only.

What is the M line?

The supporting protein structure in the middle of the A band.

What forms a fascicle?

A bundle of muscle fibers.

What connective tissue surrounds each fascicle?

Perimysium.

What connective tissue surrounds the whole muscle?

Epimysium.

What happens to sarcomeres during contraction?

They shorten as filaments slide past one another.

Do thick and thin filaments shorten during contraction?

No, they slide over each other.

What happens to the I band during contraction?

It narrows.

What happens to the H zone during contraction?

It narrows.

What happens to the A band during contraction?

It remains unchanged.

What causes the sarcomere to shorten?

Myosin heads pull thin filaments toward the M line.

What creates the polarized resting state of a muscle cell?

Unequal distribution of ions across the membrane.

Where are negative ions concentrated at rest?

Inside the cytosol.

Where are positive ions concentrated at rest?

Outside the cell.

What happens when ion barriers are removed?

Ions follow their gradients, creating electrical flow.

What is an electrical gradient?

A separation of charges that stores potential energy.

Is the intracellular fluid electrically neutral away from the membrane?

Yes.

Is the extracellular fluid electrically neutral away from the membrane?

Yes.

What is the resting membrane potential of a muscle fiber?

–85 mV.

What does a negative membrane potential mean?

The inside is more negative than the outside.

What is voltage?

Difference in electrical charge between two points.

Why can’t ions diffuse through the plasma membrane?

Because the phospholipid bilayer is hydrophobic.

What are leak channels?

Channels that are always open.

What are gated channels?

Channels that open only when stimulated.

What opens ligand-gated channels?

Binding of a chemical (ligand).

What opens voltage-gated channels?

Changes in membrane voltage.

What opens mechanically-gated channels?

Mechanical pressure or stretch.

What two ions rely on channels to cross the membrane?

Na⁺ and K⁺.

When will ions diffuse across the membrane?

Only when a gradient exists.

How many Na⁺ ions does the pump move out per cycle?

Three.

How many K⁺ ions does the pump move into the cell per cycle?

Two.

Why does the Na⁺/K⁺ pump require ATP?

It moves ions against their gradients.

What maintains steep Na⁺ and K⁺ gradients?

Millions of Na⁺/K⁺ pumps in the sarcolemma.

What determines movement of uncharged molecules?

Concentration gradient alone.

What determines movement of ions?

Both concentration and electrical gradients.

What is the combined force acting on ions called?

Electrochemical gradient.

Which gradient favors K⁺ leaving the cell?

Concentration gradient.

Which gradient favors K⁺ entering the cell?

Electrical gradient.

What is the net driving force for K⁺ at rest?

Slight outward movement.

Which gradients favor Na⁺ entering the cell?

Both concentration and electrical gradients.

Is Na⁺’s electrochemical gradient strong or weak?

Very strong.

Which ion must leave more to create resting membrane potential?

K⁺.

Which ion enters the cell due to its gradient?

Na⁺.

Why does more K⁺ exit the cell than Na⁺ enters?

There are more K⁺ leak channels.

What is the initial condition before membrane potential forms?

Equal distribution of charges inside and outside the cell.

Which ion diffuses first to create negativity inside?

K⁺ diffuses out.

What happens as many K⁺ ions leave the cell?

The inside becomes progressively more negative.