Muscular System: Organization, Contraction Physiology, and Functional Mechanics

Comprehensive practice flashcards covering muscle tissue types, organization, sarcomere anatomy, neuromuscular junction physiology, steps of contraction, energy systems, and muscle mechanics for A&P 1 Exam 3.

What are the distinguishing structural and functional features of skeletal muscle tissue?

It is voluntary, striated, multinucleated, and attached to bones.

What are the key characteristics and location of cardiac muscle tissue?

It is involuntary, striated, and composed of branched cells; it is found in the heart.

What are the primary characteristics and locations of smooth muscle tissue?

It is involuntary and nonstriated; it is found in hollow organs and blood vessels.

What are the five primary functions of skeletal muscles listed in the notes?

Movement, posture, joint stability, heat production, and support of soft tissues.

Which connective tissue sheath surrounds an entire muscle organ?

Epimysium.

What is a muscle fascicle, and which connective tissue layer envelops it?

A fascicle is a bundle of muscle fibers surrounded by perimysium.

What is an individual muscle fiber, and which layer of connective tissue covers it?

It is an individual muscle cell surrounded by endomysium.

What is the functional contractile unit of skeletal muscle?

Sarcomere.

What are the two major myofilaments found within myofibrils?

Actin (thin filament) and myosin (thick filament).

What are the sarcolemma and the sarcoplasm?

The sarcolemma is the muscle cell membrane, and the sarcoplasm is the cytoplasm of a muscle cell.

What is the function of the sarcoplasmic reticulum (SR)?

It stores and releases calcium.

What role do T-tubules play in muscle fibers?

They carry electrical signals deep into muscle fibers.

What structures compose a muscle triad?

One T-tubule and two terminal cisternae.

What is the difference between a tendon and an aponeurosis?

A tendon connects muscle to bone, whereas an aponeurosis is a broad, flat tendon.

What structure forms the boundaries of an individual sarcomere?

Z Disc.

What is the M line of a sarcomere?

The middle of the sarcomere.

What does the A band represent, and how does its length change during contraction?

It represents the entire length of thick filaments and remains constant (stays the same) during contraction.

What does the I band contain, and what happens to it during muscle contraction?

It contains only thin filaments and shortens during contraction.

What does the H zone contain, and what happens to it during muscle contraction?

It contains only thick filaments; it shortens or disappears during contraction.

What roles do troponin and tropomyosin play in muscle contraction?

Troponin binds calcium to initiate contraction, while tropomyosin blocks myosin-binding sites on actin at rest.

What is the function of the protein titin?

It is an elastic protein that helps stabilize thick filaments.

What happens to the Z discs and the sarcomere during muscle contraction?

The Z discs move closer together, and the sarcomere shortens.

How do actin and myosin behave during contraction according to the sliding filament model?

They slide past each other without shortening.

What is the motor end plate?

A specialized muscle membrane containing acetylcholine (ACh) receptors.

What is the function of acetylcholinesterase at the neuromuscular junction?

It is the enzyme that breaks down acetylcholine (ACh).

What are the first three steps of muscle contraction at the neuromuscular junction?

1. Nerve impulse reaches the axon terminal. 2. Calcium enters the axon terminal. 3. Acetylcholine is released into the synaptic cleft.

What occurs after acetylcholine binds to receptors on the motor end plate?

A muscle action potential travels along the sarcolemma and T-tubules, prompting the sarcoplasmic reticulum to release $Ca^{2+}$.

How does calcium release lead to the power stroke during muscle contraction?

Calcium binds troponin, moving tropomyosin to expose binding sites; myosin then binds actin and performs power strokes.

What allows myosin to detach from actin during the cross-bridge cycle?

ATP binding to myosin.

What final step allows a muscle fiber to relax?

Calcium returns to the sarcoplasmic reticulum (SR).

What is the specific role of ATP hydrolysis in cross-bridge cycling?

It energizes the myosin head.

Why does rigor mortis cause muscles to become stiff after death?

Muscles become stiff because ATP is unavailable for cross-bridge detachment.

How does creatine phosphate function in muscle energy metabolism?

It rapidly regenerates ATP.

How do anaerobic glycolysis and aerobic respiration differ in ATP yield and oxygen requirement?

Anaerobic glycolysis produces ATP without directly requiring oxygen, whereas aerobic respiration produces large amounts of ATP using oxygen.

What is the difference between isometric and isotonic contractions?

In isometric contractions, the muscle produces tension without changing overall length; in isotonic contractions, the muscle changes length while moving a load.

How do concentric and eccentric contractions differ?

Concentric contraction occurs when muscle shortens while contracting; eccentric contraction occurs when muscle lengthens while producing tension.

What is a muscle twitch?

A single contraction-relaxation cycle.

What are the three distinct periods of a muscle twitch?

Latent period (time between stimulation and contraction), contraction period (tension increases), and relaxation period (tension decreases).

What is wave summation?

Repeated stimulation that increases muscle tension.

What distinguishes incomplete tetanus from complete tetanus?

Incomplete tetanus is sustained contraction with partial relaxation, while complete tetanus is sustained contraction without relaxation.

What is motor unit recruitment?

Activating additional motor units to increase force.

What is muscle tone?

Continuous low-level muscle tension.

What are the properties and typical functions of Slow Oxidative (Type I) muscle fibers?

They are fatigue-resistant and utilized for endurance activities.

What are the properties of Fast Oxidative-Glycolytic (Type IIa) muscle fibers?

They exhibit intermediate fatigue resistance and are used in mixed activities.

What are the properties of Fast Glycolytic (Type IIx) muscle fibers?

They produce powerful, rapid contractions and fatigue quickly.

How are muscle origin and insertion defined?

Origin is generally the less movable attachment; insertion is generally the more movable attachment.

How do agonist and antagonist muscles differ?

An agonist is the prime mover producing an action, whereas an antagonist opposes or reverses an action.

What are the roles of synergist and fixator muscles?

A synergist assists the prime mover, while a fixator stabilizes a bone or joint.

What is the definition of a motor unit?

One motor neuron and all muscle fibers it controls.