Chapter 8: The Muscular System Study Guide

Flashcard study set covering muscle tissue types, skeletal muscle structure, mechanism of contraction, metabolic energy sources, muscular responses, smooth and cardiac muscle comparison, lever systems, and major skeletal muscle identification.

What are the primary outcomes generated by muscular actions in the body?

Muscles generate force to cause body movements including walking, breathing, pumping blood, and moving food through the digestive tract.

What are the three types of muscle tissue found in the body?

Skeletal muscle, smooth muscle, and cardiac muscle.

How do fascia, tendons, and aponeuroses differ in structure and function?

Fascia consists of layers of dense connective tissue that surround and separate muscles; tendons are cord-like extensions that fuse to bone periosteum; aponeuroses are broad sheets of connective tissue connecting muscles to each other.

How are epimysium, perimysium, and endomysium organized in a skeletal muscle?

Epimysium directly surrounds each skeletal muscle; perimysium extends inward to surround bundles of fibers called fascicles; endomysium covers each individual muscle cell (fiber).

What are fascicles?

Bundles of skeletal muscle fibers.

What are the functions of the sarcolemma and sarcoplasm in a skeletal muscle fiber?

The sarcolemma acts as the cell membrane of the muscle fiber, while the sarcoplasm is the cytoplasm containing mitochondria, nuclei, and myofibrils.

What protein filaments compose myofibrils?

Thick filaments composed of myosin, and thin filaments composed primarily of actin along with troponin and tropomyosin.

What is a sarcomere?

The structural and functional unit of myofibrils joined end-to-end, extending from one Z line to the next.

What defines the I Bands, A Bands, H Zone, and M Line in skeletal muscle striations?

I Bands are light actin bands anchored to Z lines; A Bands are dark overlapping thick and thin filaments; H Zone is the central region of the A band with myosin only; M Line is the center of the H zone holding myosin filaments in place.

What are the roles of the sarcoplasmic reticulum (SR) and Transverse (T) tubules?

The SR stores and releases calcium ions to activate muscle contraction; T tubules are sarcolemma invaginations that conduct muscle impulses deep into the fiber between SR cisternae.

What structures compose the Neuromuscular Junction (NMJ)?

The motor neuron axon terminal, synaptic vesicles storing acetylcholine (ACh), synaptic cleft, and the motor end plate of the sarcolemma with deep folds and neurotransmitter receptors.

How does the Sliding Filament Model explain muscle contraction?

Myosin heads attach to actin binding sites to form cross-bridges, perform a power stroke to pull thin filaments toward the sarcomere center, and release to reattach to the next site, shortening the sarcomere.

What are the five steps of the skeletal muscle contraction sequence?

1. Action potential releases ACh into synaptic cleft. 2. ACh binds motor end plate receptors, spreading an impulse across sarcolemma and T tubules. 3. SR releases $\text{Ca}^{2+}$ into cytosol. 4. $\text{Ca}^{2+}$ binds troponin, shifting tropomyosin to expose actin sites. 5. Myosin heads bind actin cross-bridges and pull thin filaments inward.

What four events occur during skeletal muscle relaxation?

1. Acetylcholinesterase decomposes ACh in synaptic cleft. 2. $\text{Ca}^{2+}$ is actively transported back into SR using ATP. 3. ATP breaks cross-bridges and cocks myosin heads. 4. Troponin-tropomyosin complex re-covers actin binding sites.

What causes rigor mortis after death?

Increased calcium permeability, cross-bridge formation, and a lack of ATP to break cross-bridge linkages, causing partial contraction and rigidity.

How is creatine phosphate used during muscle contraction?

Creatine phosphate acts as a high-energy store that rapidly regenerates ATP from ADP via the enzyme creatine phosphokinase.

What is oxygen debt (EPOC)?

The amount of oxygen required by liver cells to convert accumulated lactate back into glucose, plus the oxygen needed by muscle cells to restore original ATP and creatine phosphate levels.

What causes muscle fatigue and muscle cramps?

Muscle fatigue is caused by electrolyte imbalances, decreased ATP, and decreased pH from lactic acid; muscle cramps are sustained involuntary contractions caused by extracellular fluid changes around fibers.

How do slow-twitch and fast-twitch muscle fibers differ?

Slow-twitch fibers are smaller, fatigue-resistant, rich in mitochondria/capillaries, and use aerobic metabolism; fast-twitch fibers are larger, contract rapidly, fatigue quickly, contain fewer mitochondria, and store glycogen for short-term anaerobic power.

What is the structural difference between hypertrophy and atrophy?

Hypertrophy is muscle enlargement from forceful exercise that increases actin and myosin filaments (cell size increases, not fiber count); atrophy is a decrease in muscle size and strength due to disuse.

What is a threshold stimulus, a twitch, and the latent period?

Threshold stimulus is the minimum strength needed to generate an impulse; a twitch is a single contraction-relaxation cycle of a single fiber; latent period is the brief delay between stimulation and contraction onset.

What is the difference between summation, partial tetany, and complete tetanic contraction?

Summation combines individual twitch forces when high-frequency stimuli arrive before relaxation; partial tetany has very short relaxation periods; complete tetanic contraction lacks any relaxation.

What is a motor unit and how does recruitment work?

A motor unit is a single motor neuron and all the muscle fibers it controls; recruitment is the increase in activated motor units as stimulus intensity increases to build total force.

What is muscle tone?

A continuous state of sustained, partial contraction of a few motor units at rest, essential for maintaining posture.

How do isotonic and isometric contractions differ?

Isotonic contractions shorten the muscle to move a load while tension stays constant; isometric contractions develop force without changing muscle length.

How do multiunit smooth muscle and visceral smooth muscle differ?

Multiunit smooth muscle fibers occur separately in blood vessel walls and iris, stimulated independently; visceral smooth muscle fibers form sheets with gap junctions in hollow organ walls, exhibiting self-exciting rhythmic contractions and peristalsis.

How does smooth muscle contraction differ from skeletal muscle contraction?

Smooth muscle uses both acetylcholine and norepinephrine (plus hormones), contracts/relaxes slower, holds contractions longer with less ATP, and changes length without altering tension.

What function do intercalated discs serve in cardiac muscle?

Intercalated discs are specialized cell junctions that join cardiac cells and transmit force across the 3D cell network.

What is the difference between a muscle's origin and insertion?

Origin is the immovable or less movable end of attachment; insertion is the movable end pulled toward the origin during contraction.

What are the four components of a lever system in skeletal movement?

Rigid Bar (bones), Fulcrum (joint pivot point), Force (contracting muscle pulling on insertion), and Resistance (object or weight moved).

What are the roles of agonist, synergist, and antagonist muscles?

Agonist (prime mover) is primarily responsible for producing a movement; synergists assist the prime mover; antagonists oppose a specific movement.

What are the actions of the Masseter and Temporalis muscles?

Masseter elevates and protracts the mandible; Temporalis elevates and retracts the mandible.

What is the action of the Sternocleidomastoid muscle?

Flexes head/neck forward, rotates head to opposite side, and elevates sternum/ribs.

Which muscles make up the Rotator Cuff group and what is their combined function?

Supraspinatus, Infraspinatus, Teres Minor, and Subscapularis; they abduct, laterally/medially rotate the arm, and stabilize the shoulder joint.

Which muscles form the Hamstring Group and what are their actions?

Biceps Femoris, Semitendinosus, and Semimembranosus; they flex the leg at the knee and extend the thigh at the hip.

Which muscles form the Quadriceps Femoris Group and what are their actions?

Rectus Femoris, Vastus Lateralis, Vastus Medialis, and Vastus Intermedius; they extend the leg at the knee (rectus femoris also flexes thigh at hip).

What are the actions of the Tibialis Anterior, Gastrocnemius, and Soleus muscles?

Tibialis Anterior performs dorsiflexion and inversion of the foot; Gastrocnemius and Soleus perform plantar flexion of the foot (gastrocnemius also flexes leg at knee).