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anatomy CH10
| Question | Answer |
|---|---|
| What are the four properties shared by all muscle tissue types? | 1. Excitability: ability to receive and respond to a stimulus 2. Extensibility: ability to stretch 3. Contractility: ability of a muscle cell to shorten when stimulated 4. Elasticity: ability to recoil |
| What are the primary functions of skeletal muscle? | Produce movement, maintain posture and balance, support soft tissues, guard entrances and exits, generate heat, and store/release nutrients |
| Why are skeletal muscles considered voluntary muscles? | They only activate when instructed by the nervous system |
| What is a muscle fiber? | A single skeletal muscle cell |
| What is a muscle fascicle? | A bundle of muscle fibers |
| What is the epimysium? | The outer collagen fiber layer surrounding the whole muscle; connected to deep fascia |
| What is the perimysium? | A connective tissue layer containing collagen and elastic fibers that surrounds fascicles and contains blood vessels and nerves |
| What is the endomysium? | A connective tissue layer surrounding individual muscle fibers that contains capillaries, myosatellite cells, and nerve fibers |
| How is a tendon formed? | Collagen fibers from the epimysium, perimysium, and endomysium combine to form a tendon that attaches to bone |
| Why are skeletal muscle fibers multinucleated? | Multiple nuclei help control production of enzymes and structural proteins |
| How are skeletal muscle fibers formed? | By fusion of embryonic myoblasts |
| What are myosatellite cells? | Myoblasts that do not fuse and remain available for muscle repair |
| Why does skeletal muscle appear striated? | Due to the arrangement of actin and myosin filaments in myofibrils |
| What is the sarcolemma? | The plasma membrane of a muscle fiber |
| What role does a change in sarcolemma membrane potential play? | It initiates contraction |
| What are T-tubules? | Invaginations of the sarcolemma filled with extracellular fluid that carry action potentials deep into the muscle fiber |
| What is the function of T-tubules? | They transmit action potentials throughout the fiber |
| What is the sarcoplasmic reticulum (SR)? | A specialized smooth ER surrounding myofibrils that stores calcium ions |
| What are terminal cisternae? | Enlarged regions of the SR that store calcium ions |
| What forms a triad? | One T-tubule and two terminal cisternae |
| What is the function of calsequestrin? | It reversibly binds calcium ions inside terminal cisternae |
| What are myofibrils? | Contractile structures within muscle fibers that extend the length of the cell |
| What structures make up myofibrils? | Actin filaments, myosin filaments, and titin |
| What is a sarcomere? | The smallest contractile unit of skeletal muscle |
| Which filaments produce contraction? | Thick myosin filaments and thin actin filaments |
| What is the I band? | The light region containing only thin filaments |
| What is the A band? | The dark region containing thick filaments |
| What is the H band? | The region in the middle of the A band containing only thick filaments |
| What is the M line? | The line in the center of the H band that stabilizes thick filaments |
| What protein helps stabilize neighboring thick filaments? | M-line proteins |
| Why is the H band light in a resting sarcomere? | It contains only thick filaments and no thin filaments |
| What is the zone of overlap? | The area where thick and thin filaments overlap |
| Where are triads located? | At the edges of the A band in the zone of overlap |
| How many thick filaments surround each thin filament in the overlap zone? | Three |
| How many thin filaments surround each thick filament in the overlap zone? | Six |
| What are Z lines? | Structures made of alpha-actinin that mark sarcomere boundaries and anchor thin filaments |
| What is titin? | An elastic protein that helps maintain filament alignment and restore sarcomere length after contraction |
| What are the four proteins of thin filaments? | Actin, nebulin, tropomyosin, and troponin |
| What is F-actin? | A twisted strand composed of two rows of G-actin molecules |
| How many G-actin monomers are present in F-actin? | Approximately 300-400 monomers |
| What is nebulin? | A protein running along actin that helps hold the filament together |
| What is G-actin? | The protein monomer containing active sites for myosin binding |
| What is the function of tropomyosin? | Covers active sites on actin |
| How many active sites does one tropomyosin molecule cover? | Seven active sites |
| What are the three subunits of troponin responsible for? | Binding tropomyosin, binding actin, and binding calcium ions |
| How many calcium ions bind to troponin? | Two calcium ions |
| Why can't contraction occur when calcium levels are low? | Tropomyosin blocks the active sites on actin |
| What happens when calcium binds troponin? | The troponin-tropomyosin complex shifts, exposing actin active sites |
| What are thick filaments composed of? | Myosin molecules |
| Approximately how many myosin molecules form one thick filament? | About 200 |
| What is the diameter of thick filaments? | 10-12 nm |
| What is the length of thick filaments? | 1.6 µm |
| What is the structure of myosin? | Two twisted protein chains with globular heads |
| What is the function of a myosin head? | It binds actin and produces force |
| What forms the core of the thick filament? | Titin |
| What role does titin serve within thick filaments? | Acts as a molecular spring |
| What happens to the H band during contraction? | It narrows |
| What happens to the I band during contraction? | It narrows |
| What happens to the zone of overlap during contraction? | It widens |
| What happens to the Z lines during contraction? | They move closer together |
| What happens to the A band during contraction? | Its width remains constant |
| What is the sliding filament theory? | Thin filaments slide toward the center of the sarcomere along thick filaments |
| What happens during extremely strong contraction? | I bands disappear and Z lines contact the ends of thick filaments |
| What is the primary role of ATP in muscle cells? | Transport energy rather than store it |
| What are the three methods of ATP production in muscle fibers? | Phosphorylation of ADP, glycolysis, and aerobic metabolism |
| What is phosphocreatine? | A high-energy molecule formed when ATP transfers energy to creatine |
| What enzyme catalyzes the phosphocreatine reaction? | Creatine kinase |
| What reaction forms phosphocreatine? | ATP + creatine → ADP + phosphocreatine |
| What is glycolysis? | Anaerobic breakdown of glucose into pyruvate |
| What are the products of glycolysis per glucose molecule? | 2 ATP and 2 pyruvate |
| Where does muscle glucose commonly come from? | Glycogen reserves |
| Where are glycogen reserves commonly stored? | Close to the I band |
| When is glycolysis especially useful? | When mitochondria cannot keep up with ATP demand |
| What substances enter mitochondria for aerobic metabolism? | Oxygen, ADP, phosphate ions, and organic substrates |
| What cycle breaks down organic molecules in mitochondria? | Citric acid (Krebs) cycle |
| What waste product is released during aerobic metabolism? | Carbon dioxide |
| How much ATP can be produced from one pyruvate? | Approximately 15 ATP |
| What happens to excess pyruvate? | It is converted into lactate |
| What causes lactic acidosis? | Lactate accumulation and hydrogen ion buildup |
| What effect does lactic acidosis have on muscle? | Lowers intracellular pH and eventually stops contraction |
| What is muscle force? | Maximum tension produced by a muscle |
| What is muscular endurance? | How long a particular activity can be sustained |
| What are the three skeletal muscle fiber types? | Fast, slow, and intermediate fibers |
| What are characteristics of fast fibers? | Large diameter, many myofibrils, large glycogen reserves, few mitochondria, strong contractions, fatigue quickly |
| Why are fast fibers powerful? | They contain many myofibrils |
| What type of metabolism primarily supports fast fibers? | Anaerobic metabolism |
| What are slow fibers specialized for? | Endurance |
| Why are slow fibers highly aerobic? | They contain many mitochondria |
| Why do slow fibers receive abundant oxygen? | They are surrounded by many capillaries |
| What is myoglobin? | A red pigment that stores oxygen |
| Why do slow fibers require less ATP? | Cross-bridges cycle more slowly |
| Why do slow fibers have smaller glycogen reserves? | They can use stored lipids for energy |
| What are characteristics of intermediate fibers? | Little myoglobin, intermediate capillary supply, intermediate mitochondrial supply, more fatigue-resistant |
| What is hypertrophy? | Enlargement of muscle following repeated stimulation |
| What cellular changes occur during hypertrophy? | More mitochondria, glycolytic enzymes, glycogen reserves, myofilaments, and myofibrils |
| Does hypertrophy increase the number of muscle fibers? | No |
| What are the four requirements for normal muscle fiber activity? | Energy reserves, normal circulation, normal blood oxygen, and normal blood pH |
| What can excess lactate become when oxygen is available? | Pyruvate |
| What is the recovery period? | Period during which lactate is converted back to pyruvate and energy reserves are restored |
| What are two possible fates of pyruvate during recovery? | ATP production or glucose synthesis |
| What happens to lactate during exercise? | It diffuses into the bloodstream |
| What organ absorbs circulating lactate? | The liver |
| What is EPOC (oxygen debt)? | The oxygen required to restore pre-exercise conditions |
| What effect does growth hormone have on skeletal muscle? | Stimulates synthesis of contractile proteins and enlargement |
| What effect does testosterone have on skeletal muscle? | Stimulates synthesis of contractile proteins and enlargement |
| What effect do thyroid hormones have on skeletal muscle? | Increase energy consumption |
| What effect does epinephrine have on muscle? | Stimulates metabolism and increases force of contraction |
| What happens in resting muscle when ATP supply exceeds demand? | Glucose is converted to glycogen and creatine is converted to phosphocreatine |
| What energy reserves accumulate in resting muscle? | Glycogen and phosphocreatine |
| What is the primary ATP source during moderate activity? | Aerobic metabolism |
| What fuel can muscle use when glucose becomes limited? | Fatty acids |
| Why is glycolysis important during peak activity? | Mitochondria cannot meet ATP demand |
| Why does pyruvate accumulate during peak activity? | It is generated faster than mitochondria can utilize it |
| What causes increased cytosolic acidity during peak activity? | Hydrogen ion accumulation |
| How does acidity affect muscle performance? | It inhibits contraction and causes fatigue |
| What are the dimensions of cardiac muscle cells? | Approximately 10-20 µm diameter and 50-100 µm length |
| How many nuclei do cardiac muscle cells usually contain? | One |
| Are cardiac muscle cells branched or unbranched? | Branched |
| Do cardiac muscle cells contain triads? | No |
| How are cardiac T-tubules different from skeletal muscle T-tubules? | They are shorter, branched, and located at Z lines |
| Does cardiac SR contain terminal cisternae? | No |
| Does cardiac SR store more or less calcium than skeletal muscle SR? | Less calcium |
| What energy source is preferred by cardiac muscle? | Aerobic metabolism |
| What energy reserves exist in cardiac muscle? | Glycogen and lipid inclusions |
| Why does cardiac muscle contain abundant myoglobin? | To store oxygen |
| What are intercalated discs? | Specialized connections between adjacent cardiac muscle cells |
| What structures are found within intercalated discs? | Gap junctions and desmosomes |
| What is the function of desmosomes? | Stabilize adjacent cells and maintain tissue structure |
| What is the function of gap junctions? | Allow ions to pass between neighboring cells |
| What is a functional syncytium? | A group of cells functioning together as one unit |
| What is automaticity? | Ability of cardiac muscle to contract without neural stimulation |
| What determines the basic cardiac contraction rate? | Pacemaker cells |
| Can the nervous system influence cardiac muscle? | Yes, it can alter contraction rate and force |
| How do cardiac contractions compare in duration to skeletal muscle contractions? | They last about ten times longer |
| Why can't cardiac muscle undergo tetanus? | Long refractory periods prevent wave summation |
| What happens during a cardiac action potential? | Increased permeability to extracellular calcium |
| What would happen if cardiac muscle entered tetanus? | The heart could not pump blood |
| What is the general function of smooth muscle? | Move substances through organs and regulate organ functions |
| Where is smooth muscle found? | In sheets, bundles, or sheaths surrounding organs and passageways |
| How does smooth muscle regulate the skin? | Controls blood flow and operates arrector pili muscles |
| How does smooth muscle influence blood vessels? | Controls blood flow and blood pressure |
| How does smooth muscle affect airways? | Regulates airway diameter and airflow resistance |
| How does smooth muscle aid digestion? | Moves food and injects bile into the digestive tract |
| How does smooth muscle affect the urinary system? | Alters kidney filtration, transports urine, and expels urine |
| How does smooth muscle aid reproduction? | Moves sperm, transports oocytes, and expels a fetus |
| What is the shape of smooth muscle cells? | Spindle-shaped with tapered ends |
| How many nuclei do smooth muscle cells contain? | One central nucleus |
| Do smooth muscle cells contain T-tubules? | No |
| How is the smooth muscle SR organized? | As a loose network throughout the cell |
| Why is smooth muscle nonstriated? | It lacks myofibrils and sarcomeres |
| What structures anchor thin filaments in smooth muscle? | Dense bodies |
| What protein network connects dense bodies? | Desmin filaments |
| How does smooth muscle shorten during contraction? | Twists in a corkscrew-like manner |
| Do smooth muscle cells form tendons or aponeuroses? | No |
| What triggers smooth muscle contraction? | Increased free calcium in the cytoplasm |
| Where does smooth muscle obtain calcium? | Extracellular fluid and sarcoplasmic reticulum |
| What protein binds calcium in smooth muscle? | Calmodulin |
| What enzyme is activated by calmodulin? | Myosin light-chain kinase |
| What does myosin light-chain kinase allow? | Myosin heads to bind actin |
| What is smooth muscle plasticity? | Ability to function over a wide range of lengths |
| Can smooth muscle maintain prolonged contractions? | Yes |
| Is smooth muscle under voluntary control? | No |
| What are sphincters? | Rings of smooth muscle that control passage through openings |
| What are the two major types of smooth muscle? | Multiunit and visceral smooth muscle |
| What characterizes multiunit smooth muscle? | Cells operate independently and lack direct cell-to-cell contact |
| Where is multiunit smooth muscle found? | Iris, large arteries, arrector pili muscles, and male reproductive tract |
| What characterizes visceral smooth muscle? | Cells are linked by gap junctions and contract in coordinated waves |
| Where is visceral smooth muscle found? | Digestive tract, gallbladder, and bladder |
| Besides neural stimulation, what can activate visceral smooth muscle? | Stretching, hormones, CO2 levels, O2 levels, and irritation |
| Can visceral smooth muscle contract without neural stimulation? | Yes, through rhythmic cycles of activity |
| What is smooth muscle tone? | A normal background level of smooth muscle activity |
| What factors can change smooth muscle tone? | Neural, chemical, and hormonal factors |
| How does low oxygen affect smooth muscle? | Causes relaxation and increased blood flow |
| What is a twitch? | A single contraction-relaxation cycle lasting about 7-100 ms |
| What are the three phases of a twitch? | Latent period, contraction phase, and relaxation phase |
| What occurs during the latent period? | Action potential spreads and calcium is released with no tension yet produced |
| What occurs during the contraction phase? | Calcium binds troponin, active sites are exposed, cross-bridges form, and tension rises |
| What occurs during the relaxation phase? | Calcium is pumped back into the SR and tension decreases |
| What happens if a muscle fiber is stimulated immediately after relaxation? | The next contraction has slightly greater tension |
| What is treppe? | Progressive increase in contraction strength with repeated stimuli |
| Why does treppe occur? | Calcium pumps cannot fully recapture calcium between stimuli |
| What is wave summation? | Increased tension when a second stimulus arrives before complete relaxation |
| What is stimulus frequency? | Number of stimuli delivered per unit time |
| What is tetanus? | Sustained contraction in which relaxation is incomplete or absent |
| What causes complete tetanus? | Continuous stimulation maintains high cytosolic calcium |
| Why is no relaxation seen in complete tetanus? | The SR has insufficient time to recapture calcium |
| What is a motor unit? | A motor neuron and all muscle fibers it controls |
| Why doesn't changing the number of active motor units alter pull direction? | Motor unit fibers are intermingled with fibers from other motor units |
| What is a fasciculation? | A visible muscle twitch involving a motor unit |
| What is recruitment? | Activation of increasing numbers of motor units to increase force |
| What is asynchronous motor unit summation? | Different motor units alternate activity to maintain force while reducing fatigue |
| What is muscle tone in skeletal muscle? | Continuous low-level activity of some motor units |
| How does muscle tone help recruitment? | Some motor units are already active |
| What happens when tension exceeds the load? | The muscle shortens |
| What happens when the load exceeds tension? | The muscle does not shorten |
| What is excitation-contraction coupling? | The link between an action potential and muscle contraction |
| Where does excitation-contraction coupling occur? | At the triads |
| What event causes calcium release from terminal cisternae? | Arrival of an action potential |
| What starts the contraction cycle? | Calcium exposure of active sites on actin |
| What is the first step of the contraction cycle? | Myosin binds actin to form a cross-bridge |
| What is the second step of the contraction cycle? | ATP hydrolysis powers the myosin power stroke |
| What determines how long contraction lasts? | Duration of stimulation, calcium availability, and ATP availability |
| What is the first event in relaxation? | Acetylcholine is broken down by acetylcholinesterase |
| How is calcium removed from the cytosol during relaxation? | Active transport into the SR and out through the sarcolemma |
| What happens after calcium levels fall? | Troponin returns to its original position |
| What is the final event in relaxation? | Tropomyosin covers active sites on actin |
| What is the resting membrane potential range of neurons and skeletal muscle fibers? | Approximately -70 to -85 mV |
| Why is the inside of a resting cell negatively charged? | Negatively charged proteins remain inside the cell |
| What does sodium influx cause? | Depolarization |
| What does potassium influx cause? | Hyperpolarization |
| What are excitable membranes capable of? | Rapid communication throughout a cell |
| What happens when voltage-gated sodium channels open? | Sodium enters and depolarizes the membrane |
| What restores ion gradients after an action potential? | Sodium-potassium pumps |
| What prevents action potentials from traveling backward? | The refractory period |
| What is the neuromuscular junction (NMJ)? | The synapse between a motor neuron and skeletal muscle fiber |
| What neurotransmitter is released at the NMJ? | Acetylcholine |
| What receptor does acetylcholine bind on muscle fibers? | Acetylcholine receptor on the motor end plate |
| What type of channel is the acetylcholine receptor? | A chemically gated sodium channel |
| What happens after acetylcholine binds its receptor? | Sodium enters the muscle fiber |
| What does sodium entry generate? | Depolarization and an action potential |
| Why is calcium release nearly instantaneous after excitation? | Terminal cisternae are positioned beside zones of overlap |
| How does calcium exposure affect the troponin-tropomyosin complex? | Tropomyosin moves away from actin active sites |
| What immediately marks the beginning of contraction? | Exposure of actin active sites |
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