Unit 2 Test: Chapter 9

Muscle

Involuntary muscle tissues whose actions are not consciously controlled.

Cardiac and smooth muscle tissues

Muscle tissue that works under voluntary control and is composed of bundles of muscle fibers.

Skeletal muscle

Long cylindrical cells containing several nuclei that make up skeletal muscle.

Muscle fibers

The site of signal exchange where the synaptic bulb of an axon terminal and muscle fiber connect.

Neuromuscular Junction

A component of muscle fibers that contains repeating contractile units called sarcomeres; extend from one end of the muscle fiber to the other

Myofibril

Which structure is responsible for the skeletal muscle’s striated appearance?

Myofibrils

Contractile units that run adjacent to one another down the length of a myofibril, composed of alternating thick and thin protein filaments.

Sarcomeres

The thick protein filaments anchored at the center of the sarcomere, known as the M line.

Myosin

The center of the sarcomere where thick myosin filaments are anchored.

M line

The thin protein filaments anchored to the Z lines on the outer edges of the sarcomere.

Actin

Which protein binds Ca2+ and helps initiate muscle contraction?

Actin

Structures located on the outer edges of the sarcomere to which thin actin filaments are anchored.

Z lines

Which two successive lines define one sarcomere?

Z-Lines

The action of muscle contraction where myosin cross bridges attach to actin filaments and exert force to pull them, causing the sarcomere to shorten without the filaments changing length.

Sliding filament mechanism

An action triggered during contraction where myosin pulls the actin filament toward the M line while ADP and inorganic phosphate are released.

Power stroke

A regulatory protein associated with actin that blocks crossbridge binding sites when the muscle is relaxed.

Tropomyosin

A regulatory protein associated with actin that binds calcium ions, causing tropomyosin to displace and expose myosin binding sites.

Troponin

A specialized membrane system surrounding each myofibril.

Sarcoplasmic reticulum

Function of the sarcoplasmic reticulum

Stores and releases Ca2+

Tubular extensions of the sarcolemma that carry action potentials from the surface deep into the muscle fiber

T tubules

A group of muscle fibers bound together by connective tissue that produces movement by generating force

Skeletal Muscle

Undifferentiated stem cells located between the plasma membrane and basement membrane.

Satellite cells

When are satellite cells active?

After strain or injury and help repair damaged muscle fibers or contribute to hypertrophy

Which structure has the function of binding muscle fibers together and helping transmit force generated by the muscle?

Connective Tissue

A bundle of collagen-containing connective tissue that attaches skeletal muscle to bone and transmits force from muscle to bone

Tendon

Which structure is the globular myosin heads that extend from thick filaments and bind to actin and exert the force during contractions?

Cross-Bridges

Which is the wide, dark band containing the thick filaments

A Band

Enlarged regions of the SR that store large amounts of Ca2+

Terminal Cisternae

A Ca2+ binding protein in the terminal cisternae that allows large quantities of calcium stored

Calsequestrin

Do thick and thin filaments change length?

No

One motor neuron and all the muscle fibers it controls; all muscle fibers in a single ____ are of the same fiber type.

Motor Unit

Muscle cells that act together as a single unit.

Single unit smooth muscle

Muscle cells that act independently of one another

Multiunit smooth muscle

How are cells in single-unit smooth muscle connected, and what do gap junctions do?

They are connected by gap junctions, which allow action potentials to spread from one cell to another.

What are pacemaker cells in single-unit smooth muscle?

Cells that spontaneously generate action potentials.

What can cause single-unit smooth muscle to contract?

Stretching

Where is single-unit smooth muscle found?

In the walls of hollow organs, such as the stomach.

How are cells in multiunit smooth muscle connected and innervated?

They have few or no gap junctions and are richly innervated by the autonomic nervous system.

What determines the strength of multiunit smooth muscle contraction?

How many muscle cells are activated and the frequency of nerve stimulation.

Do most multiunit smooth muscle cells produce action potentials?

No. Most do not produce action potentials.

Does stretching induce contraction in multiunit smooth muscle?

No

Where is multiunit smooth muscle found?

Large airways, large arteries, and muscles attached to hairs in the skin.

How is skeletal muscle controlled?

By the somatic nervous system

How does a motor neuron communicate with a skeletal muscle fiber?

Through a specialized motor end-plate region

How does a motor neuron stimulate skeletal muscle fibers?

releases acetylcholine (ACh) at the neuromuscular junction, which stimulates an action potential in the muscle fiber and causes contraction.

How is smooth muscle controlled?

By the autonomic nervous system and is not normally under direct voluntary control.

Does smooth muscle have a specialized motor endplate?

No

Autonomic neuron axons branch and contain regions which release neurotransmitters.

Varicosities

How can one autonomic neuron affect smooth muscle?

A single neuron can influence multiple smooth muscle cells.

Can a single smooth muscle cell be influenced by more than one neuron?

Yes

Besides nerves, what else can influence smooth muscle contraction?

Hormones and local factors can also influence contraction.

What protein does smooth muscle use instead of troponin to help regulate contraction?

Caldesmon

What role does Ca²⁺ play in muscle contraction?

Ca²⁺ controls cross-bridge activity and therefore controls muscle contraction.

What happens when Ca²⁺ levels increase in a muscle fiber?

Ca²⁺ binds to troponin, causing tropomyosin to move away from the myosin-binding sites on actin.

What happens when tropomyosin moves away from actin's myosin-binding sites?

Myosin can attach to actin and form cross-bridges.

Where does the Ca²⁺ that initiates skeletal muscle contraction come from?

The sarcoplasmic reticulum, which releases Ca²⁺ into the sarcoplasm in response to a nervous system signal.

Does Ca²⁺ provide the energy for muscle contraction?

No. ATP provides the energy for the myosin cross-bridge cycle.

What happens to troponin when Ca²⁺ is absent?

Ca²⁺ cannot bind to troponin C, so troponin does not cause tropomyosin to move.

What happens to tropomyosin when Ca²⁺ is absent?

Tropomyosin stays in place and blocks the myosin-binding sites on actin.

What happens to muscle contraction when Ca²⁺ is absent?

Myosin cannot effectively bind to actin, so cross-bridge cycling stops, causing contraction to stop and the muscle to relax.

The muscle is actively producing force while lengthening

Eccentric contractions

When do eccentric contractions happen?

When the load is greater than the force produced by the muscle

Which type of contraction causes the muscle to change length while the tension/load remains relatively constant

Isotonic Contraction

Which contractions both concentric(shortening) and eccentric(lengthening) contractions?

Isotonic contractions

Which twitch fibers contain myosin with ATPase activity that about 4 times higher?

Fast twitch fiber (Type 2)

Which twitch fibers Contain myosin with low ATPase activity?

Slow Twitch Fiber (Type 1)

How are skeletal muscle fibers classified?

Their maximal velocity of shortening

Their major pathway they use to form ATP-oxidative or glycolytic.

Which type of skeletal muscle fiber combine low myosin ATPase activity with high oxidative capacity.

Slow-oxidative Fibers (Type 1)

Which type of skeletal muscle fiber combine high myosin-ATPase activity with high oxidative capacity and intermediate glycolytic capacity

Fast-oxidative-glycolytic Fibers (Type 2A)

Which type of skeletal muscle fiber combine high myosin-ATPase activity with high glycolytic capacity 

Fast-glycolytic Fibers (Type 2X)

What is controlled by the recruitment of motor units; increasing the number of active motor units increases___?

Muscle Tension

According to what are motor units recruited?

To their neuron size with the smaller ones being recruited first.

In which order are the muscle fibers recruited?

Slow-oxidative, fast-oxidative-glycolytic, and fast-glycolytic

Does smooth muscle have troponin?

No

What does Ca²⁺ bind to in smooth muscle?

Calmodulin

What happens when Ca²⁺ binds to calmodulin?

The Ca²⁺–calmodulin complex activates myosin light-chain kinase (MLCK).

What does MLCK do?

MLCK uses ATP to phosphorylate myosin light chains.

What happens when myosin light chains are phosphorylated?

Myosin can bind to actin and begin cross-bridge cycling, producing contraction.

Why does smooth muscle contract more slowly and use energy more slowly than skeletal muscle?

Smooth muscle myosin has lower ATPase activity, so cross-bridge cycling is slower, and energy is used more slowly.

Which two proteins are primarily responsible for the sliding mechanism in muscle contraction?

Actin and Myosin

What role does calcium play in muscle contraction?

It binds to troponin causing tropomyosin to shift

What happens during the power stroke of muscle contraction?

Myosin heads pivot and pull actin filaments inward

Which molecule is required for myosin to detach from actin after a contraction?

ATP

What is the correct sequence of events in the sliding filament theory?

Calcium release → Tropomyosin shift → Cross-bridge formation → Power stroke → ATP detachment → Reset

Which organ is primarily responsible for the excretion of hormones from the body?

Kidneys

How are steroid hormones typically excreted from the body?

After being metabolized by the liver and excreted in bile or urine

“Some neurons release neurotransmitters that prevent muscle contraction” is an example that

neuronal stimulation of muscles can be inhibitory

Which of the following best describes how hormones influence the secretion of other hormones?

Hormones can regulate other hormones through hierarchical signaling and feedback loops

What occurs in skeletal muscle during isotonic contraction?

The muscle shortens or lengthens while maintaining constant tension

During isotonic contraction, what happens to the sarcomere according to the sliding filament theory?

The sarcomere shortens as actin and myosin filaments slide past each other

What distinguishes isotonic contraction from isometric contraction in terms of filament behavior?

Filaments slide past each other in isotonic contraction, changing muscle length

What is the primary difference between osteoblasts and osteoclasts?

Osteoblasts build bone tissue, while osteoclasts break it down

What is the primary mechanism responsible for the growth in length of long bones during childhood and adolescence?

Activity at the epiphyseal (growth) plates

Which of the following is an endocrine function performed by the liver?

Conversion of thyroxine (T₄) to triiodothyronine (T₃)

Which hormone-like protein produced by the liver plays a key role in stimulating cell growth and development?

Insulin-like Growth Factor 1 (IGF-1)

Which of the following best describes single-unit smooth muscle cells?

They contract together due to electrical coupling via gap junctions.

Which hormone lowers blood glucose levels by promoting glucose uptake into cells?

Insulin

Which hormone increases blood glucose levels by stimulating gluconeogenesis and reducing glucose uptake in tissues?

Cortisol

Which of the following is a primary role of cortisol in the human body?

Regulating stress response and metabolism