Neuromuscular Junction and Muscle Functions

Somatic motor neurons stimulate skeletal muscle fibers to contract by transmitting action potentials.

The synaptic cleft is a small gap that separates the somatic motor neuron from the muscle fiber, preventing direct electrical communication.

The primary functions of muscles include movement, stability, control of body openings, heat production, and glycemic control.

<p>Muscles maintain posture by resisting gravitational forces and stabilizing joints through tension on tendons and bones.</p> Signup and view all the answers

<p>Skeletal muscles produce about 85% of body heat, which is vital for enzyme functioning and metabolism.</p> Signup and view all the answers

<p>Muscles help regulate blood glucose concentration within its normal range through their metabolic actions.</p> Signup and view all the answers

<p>Myofibrils are structures within muscle fibers that enable contraction and are responsible for muscle force generation.</p> Signup and view all the answers

<p>Muscles facilitate the movement of bodily contents through actions like breathing, digestion, and circulation.</p> Signup and view all the answers

<p>Troponin I binds to the myosin binding site on actin, partially covering it and preventing myosin-actin interaction.</p> Signup and view all the answers

<p>ATP binds to the myosin head, breaking the actin-myosin interaction and allowing muscle relaxation.</p> Signup and view all the answers

<p>Calcium is not pumped back into the sarcoplasmic reticulum due to the absence of ATP, and calcium ions diffuse from the extracellular fluid into the cytoplasm.</p> Signup and view all the answers

<p>The troponin-tropomyosin complex acts as a relaxing protein that inhibits the interaction between myosin and actin, preventing contraction.</p> Signup and view all the answers

<p>Myofibrils are surrounded by sarcoplasmic reticulum and invaginated by transverse tubules (T tubules).</p> Signup and view all the answers

<p>The muscle fibers become stiff due to the inability of myosin heads to detach from actin, caused by the lack of ATP.</p> Signup and view all the answers

<p>The inactive muscle membrane cannot maintain the calcium ion gradient, leading to increased intracellular calcium concentration.</p> Signup and view all the answers

<p>Thick filaments are primarily composed of myosin, which consists of six polypeptide chains forming heavy and light chains, with heavy chains coiling to form a tail and globular heads on the ends.</p> Signup and view all the answers

<p>Tropomyosin blocks the myosin-binding sites on actin when the muscle is at rest, preventing interaction between actin and myosin.</p> Signup and view all the answers

<p>The sliding filament model explains how muscle contraction occurs through the sliding of actin and myosin filaments past each other, shortening the sarcomere.</p> Signup and view all the answers

<p>Calcium ions bind to troponin, causing a conformational change that moves tropomyosin away from the myosin binding sites on actin, allowing cross-bridge formation.</p> Signup and view all the answers

<p>The binding of Ca2+ to troponin C initiates the conformational change, moving tropomyosin and exposing the myosin-binding sites on actin.</p> Signup and view all the answers

<p>Thin filaments are composed of actin, tropomyosin, and troponin, where actin provides the binding sites for myosin, and tropomyosin and troponin regulate the interaction between actin and myosin.</p> Signup and view all the answers

<p>Actin exists as G-actin in a globular form and polymerizes into F-actin, which forms two twisted strands to create the filamentous structure.</p> Signup and view all the answers

<p>Myosin ATPase hydrolyzes ATP, providing the energy required for the cross-bridge cycle during muscle contraction.</p> Signup and view all the answers

<p>The interdigitating arrangement of thick and thin filaments in sarcomeres creates a distinct banding pattern, which is visually apparent in striated muscle.</p> Signup and view all the answers

<p>Slow-twitch fibers contract slowly and primarily produce ATP through oxidative phosphorylation, while fast-twitch fibers contract quickly and mainly generate ATP through glycolysis.</p> Signup and view all the answers

<p>The phosphagen system provides nearly all the energy for short bursts of intense activity, such as during weight lifting or sprinting.</p> Signup and view all the answers

<p>As the phosphagen system is exhausted, the muscles switch to anaerobic fermentation to temporarily meet the energy demand.</p> Signup and view all the answers

<p>Muscular hypertrophy is the enlargement of existing muscle fibers caused by increased production of myofibrils and organelles due to forceful, repetitive muscular activity.</p> Signup and view all the answers

<p>Aerobic respiration delivers sufficient oxygen to meet the ATP demand of muscles after about 40 seconds of exercise, enabling sustained activity.</p> Signup and view all the answers

<p>Fast glycolytic fibers primarily produce ATP through glycolysis, while fast oxidative fibers use both glycolysis and oxidative phosphorylation for ATP production.</p> Signup and view all the answers

<p>The soleus muscle contains mostly slow-twitch fibers, which have a high oxidative capacity and contract slowly.</p> Signup and view all the answers

<p>Myosin ATPase activity helps classify muscle fibers by their contraction speed; fast oxidative fibers have an intermediate activity compared to slow and fast glycolytic fibers.</p> Signup and view all the answers

<p>Unitary smooth muscle cells are linked by gap junctions, allowing for coordinated contraction, while multiunit smooth muscle cells have few or no gap junctions and function independently.</p> Signup and view all the answers

<p>Gap junctions in unitary smooth muscle allow for the rapid transmission of electrical impulses between cells, leading to coordinated contractions.</p> Signup and view all the answers

<p>Spontaneous pacemaker activity in unitary smooth muscle leads to rhythmic contractions, essential for the functioning of the gastrointestinal tract and similar organs.</p> Signup and view all the answers

<p>Action potentials in smooth muscle cells have a prolonged upstroke due to slower opening of Ca2+ channels compared to Na+ channels in striated muscle cells.</p> Signup and view all the answers

<p>The depolarization phase is initiated by the influx of Ca2+ ions through voltage-gated calcium channels in the sarcolemmal membrane.</p> Signup and view all the answers

<p>Visceral smooth muscle can contract in response to action potentials, while multiunit smooth muscle typically does not generate action potentials and contracts independently under neural control.</p> Signup and view all the answers

<p>In multiunit smooth muscle, individual cells receive signals for contraction primarily through autonomic nerve innervation and may respond to hormonal or local chemical stimuli.</p> Signup and view all the answers

<p>Potassium channels contribute to repolarization by opening slowly, allowing K+ ions to exit the cell, which helps return the membrane potential to its resting state.</p> Signup and view all the answers

<p>Junctional potential is a local depolarization that spreads along the muscle fiber, leading to calcium influx through voltage-gated Ca++ channels, which ultimately causes muscle contraction.</p> Signup and view all the answers

<p>In visceral smooth muscle, pacemaker potentials do not originate from a fixed location but can shift between multiple sites, while in cardiac muscle, they are generated at predetermined locations.</p> Signup and view all the answers

<p>The two additional mechanisms are ligand-gated Ca2+ channels and IP3-gated Ca2+ release channels, both of which permit the entry or release of calcium into the cell.</p> Signup and view all the answers

<p>Calmodulin binds to calcium ions, forming a Ca2+-calmodulin complex that activates myosin-light-chain kinase, which is essential for initiating contraction.</p> Signup and view all the answers

<p>When calcium concentration decreases, myosin is dephosphorylated by myosin-light-chain phosphatase, leading to the formation of latch-bridges instead of cross-bridges.</p> Signup and view all the answers

<p>The influx of Ca2+ increases intracellular calcium concentrations, which triggers contraction processes in the smooth muscle cells.</p> Signup and view all the answers

<p>Latch-bridges are stable attachments between actin and dephosphorylated myosin that allow smooth muscle to maintain tension with minimal energy use.</p> Signup and view all the answers

<p>Action potentials in the smooth muscle cell membrane trigger the opening of voltage-gated Ca2+ channels.</p> Signup and view all the answers