Ch10 Muscle tissue Study Question

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

Skeletal muscle, cardiac muscle, smooth muscle.

Which type of muscle tissue composes 40–50% of an adult's body weight?

Skeletal muscle.

List the six major functions of skeletal muscle.

Move the body; Maintain posture; Protect and support; Regulate elimination of materials; Produce heat; Venous return.

Define excitability in skeletal muscle.

Ability to respond to internal/external stimuli by changing electrical resting membrane potential (RMP).

Define conductivity in skeletal muscle.

Sending an electrical change down the cell membrane.

Define contractility in skeletal muscle.

Filaments slide past each other, causing the muscle to shorten.

Define elasticity in skeletal muscle.

Ability to return to its original shape.

Define extensibility in skeletal muscle.

Ability to be stretched.

What is the role of the sarcolemma in muscle contraction?

Contains voltage-gated ion channels for action potentials.

What is the role of T-tubules in muscle contraction?

Allow electrical signals to travel deep into the cell and contain voltage-sensitive calcium channels.

What are fascicles?

Bundles of many muscle fibers found within the whole muscle.

Describe the epimysium of the skeletal muscle.

Dense irregular connective tissue around the whole muscle.

Describe the perimysium of the skeletal muscle.

Dense irregular connective tissue around fascicles with blood vessels.

Describe the endomysium of the skeletal muscle.

Areolar connective tissue around individual fibers for electrical insulation, capillary support, and binding cells.

What is the function of tendons?

Attach muscle to bone via dense regular connective tissue.

What is the function of aponeuroses?

Flat sheet-like dense regular connective tissue attachment.

Differentiate between deep fascia and superficial fascia.

Deep fascia wraps individual muscles and binds similar function muscles, contains nerves/blood vessels/lymph. Superficial fascia separates muscle from skin and is composed of areolar and adipose connective tissue.

What are satellite cells?

Myoblasts that remain after development; they assist in muscle repair.

Describe the structure and function of the sarcoplasmic reticulum.

Similar to smooth endoplasmic reticulum; it stores calcium and releases it when triggered by electrical signals.

What is a triad in skeletal muscle?

One T-tubule and two terminal cisternae.

Explain the role of calcium in muscle contraction.

Calcium is stored in the sarcoplasmic reticulum, released into the sarcoplasm, binds to troponin, shifts tropomyosin, and exposes myosin binding sites, enabling crossbridge cycling.

What proteins make up thick filaments?

Thick filaments are made of myosin (including heads, H zone, M line, A band, connectin).

What proteins make up thin filaments?

Thin filaments are made of actin (F-actin, G-actin), tropomyosin, and troponin.

Describe the sliding filament theory.

Thick and thin filaments do not shorten; they slide past each other, causing Z-discs to move closer, the H-zone to disappear, and the I-band to narrow.

What happens to the H band, I band, and Z lines during contraction?

H-zone disappears; I-band narrows or disappears; Z-discs move closer together.

What is the function of troponin and tropomyosin?

Tropomyosin covers actin binding sites at rest; troponin binds Ca2+ and moves tropomyosin to expose binding sites.

What is the role of dystrophin in muscle fibers?

Anchors myofibrils to the sarcolemma; deficiency causes Duchenne muscular dystrophy.

List the three ways skeletal muscle fibers generate ATP.

Creatine phosphate (anaerobic, 10 seconds, phosphate transfer), glycolysis (anaerobic, produces 2 ATP, generates lactic acid when O2 low), aerobic respiration (requires O2, ~30 ATP, uses glucose, triglycerides, amino acids).

What is the role of creatine phosphate in muscle contraction?

Quickly donates phosphate to ADP to form ATP via creatine kinase.

Compare glycolysis and aerobic respiration in terms of ATP yield and oxygen requirement.

Glycolysis produces 2 ATP without oxygen and generates lactate when O2 is low. Aerobic respiration requires oxygen and produces ~30 ATP.

What is oxygen debt?

The additional O2 needed to restore pre-exercise conditions, including replacing O2 on hemoglobin/myoglobin, replenishing glycogen, ATP, creatine phosphate, and converting lactic acid to glucose.

Compare slow-twitch and fast-twitch muscle fibers in terms of structure and function.

Slow-twitch fibers (SO) are slow, less powerful, high endurance, aerobic, red, and contain many mitochondria/myoglobin. Fast-twitch fibers (FO/FG) are fast, powerful, brief, anaerobic (FG), white, and have large glycogen reserves.

What are oxidative and glycolytic fibers?

Oxidative fibers are aerobic, fatigue-resistant, and contain many mitochondria/myoglobin. Glycolytic fibers are anaerobic, fatigable, and have fewer mitochondria/myoglobin and large glycogen reserves.

Which muscle fiber type is the most fatigue-resistant?

Slow oxidative (SO) fibers.

How does training affect muscle fiber composition?

Endurance training increases mitochondria; resistance training increases hypertrophy; sprinters have more fast-twitch (FG) fibers; marathon runners have more slow-twitch (SO) fibers.

What are the three components of a neuromuscular junction?

Synaptic knob, synaptic cleft, motor end plate.

Describe the sequence of events that occur at the NMJ leading to muscle contraction.

Action potential reaches synaptic knob → voltage-gated Ca2+ channels open → Ca2+ enters → ACh released → ACh binds receptors → Na+ enters, K+ exits → end-plate potential → AChE breaks down ACh.

What is the role of acetylcholinesterase?

Breaks down ACh to prevent continuous firing.

Explain the process of excitation–contraction coupling.

End-plate potential reaches threshold (–65 mV) → action potential propagates along sarcolemma → depolarization (Na+ in to +30 mV) → repolarization (K+ out to –90 mV) → refractory period → action potential reaches triad → voltage-sensitive channels open → Ca2+ released from the sarcoplasmic reticulum.

Outline the steps of the crossbridge cycle.

Crossbridge formation (myosin binds actin) → Power stroke (pulls actin; releases ADP + P) → Release (ATP binds, myosin detaches) → Reset (ATPase splits ATP; myosin resets).

Why is ATP necessary for muscle contraction and relaxation?

Needed for myosin release; needed for myosin reset; needed for Ca2+ pumps returning Ca2+ to the sarcoplasmic reticulum.

Differentiate between isotonic and isometric contractions.

Isotonic: tension overcomes resistance; movement occurs; length changes. Isometric: tension increases but does not overcome resistance; length stays the same.

What is the difference between concentric and eccentric contractions?

Concentric: muscle shortens. Eccentric: muscle lengthens while contracting.

How does load affect the speed of muscle contraction?

Heavier loads slow contraction speed.

What is a muscle twitch and what are its three phases?

Single brief contraction with three phases: Latent period (no tension), Contraction period (tension increases), Relaxation period (Ca2+ returned to SR; tension decreases).

Define motor unit recruitment.

Increasing voltage recruits more motor units, resulting in increased force.

What is wave summation and how does it lead to tetanus?

Stimuli added over time causing muscle twitches to overlap; incomplete tetany occurs, leading to complete tetany (40–50 stimuli/sec) resulting in smooth sustained contraction.

What factors contribute to muscle fatigue?

Decreased glycogen; ACh exhaustion; impaired action potential conduction (Na+, K+, Ca2+ imbalance); phosphate accumulation impairing Ca2+/troponin and myosin function.

What is hypertrophy and how is it achieved?

Increase in muscle size due to increased proteins, mitochondria, and glycogen.

What is atrophy and what causes it?

Decrease in muscle mass due to lack of use; occurs quickly.

List the effects of aging on skeletal muscle.

Decreased size, power, endurance; decreased fiber number/diameter; decreased oxygen storage; decreased circulation; decreased satellite cells; fibrosis; decreased flexibility.

How does cardiac muscle differ from skeletal muscle in structure and function?

Cardiac muscle is striated, involuntary, has intercalated discs, and pumps blood. Skeletal muscle is voluntary, multinucleated, and attached to bones.

What are intercalated discs and what is their function?

Specialized junctions in cardiac muscle for rapid electrical conduction.

What is automaticity in cardiac muscle?

Ability to generate its own rhythm without nervous stimulation.

How does smooth muscle differ from skeletal muscle in structure?

Smooth muscle has no striations, is involuntary, and is found in organs and blood vessels.

What is plasticity in smooth muscle?

Ability to stretch and maintain contractility.

Compare multiunit and visceral smooth muscle.

Multiunit: independent fibers with precise control. Visceral: sheets of muscle with coordinated contraction.

What is the resting membrane potential (RMP) of skeletal muscle fibers and what is the threshold?

RMP = –90 mV; threshold = –65 mV.

What clinical condition results from ACh receptor destruction?

Myasthenia gravis.

What toxins cause spastic paralysis and flaccid paralysis?

Tetanus (Clostridium tetani) causes spastic paralysis; Botulism (Clostridium botulinum) causes flaccid paralysis.

What happens during muscle relaxation?

Nerve signal stops → ACh stops → AChE breaks down ACh → Ca2+ pumped into SR → troponin changes → tropomyosin covers binding sites → muscle returns to resting length.

What fuels can aerobic respiration use besides glucose?

Triglycerides and amino acids.

What determines whether pyruvate becomes lactate?

Low O2 results in lactate; sufficient O2 leads to aerobic respiration.

What is fermentation and what does it produce?

Anaerobic continuation after glycolysis; produces CO2, alcohol, and lactic acid.

What is the length-tension relationship?

Shortened length equals weak force; resting length equals max force; extended length equals weak force.

What is muscle tone?

Resting tension from involuntary nervous stimulation; decreases during sleep.

What is the function of a sarcomere?

Contractile unit producing muscle shortening.

What causes muscle contraction?

Ca2+ binding to troponin causes tropomyosin to shift, exposing myosin binding sites for crossbridge cycling.

What is released at the neuromuscular junction?

Acetylcholine (ACh).

Why is calcium important in muscle contraction?

Calcium binds to troponin, exposing myosin binding sites.

Describe the organization of skeletal muscle.

Muscle → fascicles → muscle fibers → myofibrils → myofilaments.

What is a sarcomere?

A repeating unit of filaments in skeletal muscle that shortens during contraction.

Describe the structure and function of thin and thick filaments.

Thin filaments consist of actin, tropomyosin, and troponin; thick filaments consist of myosin heads for binding, pulling, and releasing.

What proteins regulate the binding of actin and myosin?

Troponin and tropomyosin.

Explain the steps of excitation at the NMJ.

Action potential → Ca2+ enters → ACh released → ACh binds to receptors → Na+ enters, K+ exits → end-plate potential.

What is the role of ACh?

Binds to receptors at the NMJ to initiate end-plate potential and muscle excitation.

Describe excitation–contraction coupling.

End-plate potential → action potential → depolarization → repolarization → calcium release from the sarcoplasmic reticulum.

Explain the steps in crossbridge cycling.

Bind → Pull → Release → Reset.

What is the role of ATP in muscle contraction and relaxation?

ATP is needed for myosin release, resetting, and calcium pump function.

What is a motor unit?

A motor neuron and all muscle fibers it controls.

Compare small and large motor units.

Small motor units provide precise control; large motor units produce strong force.

Describe the three ways muscles generate ATP.

Creatine phosphate, glycolysis, aerobic respiration.

What is muscle fatigue?

Reduced ability to produce tension due to fuel depletion, ion imbalance, and ACh exhaustion.

Compare isotonic and isometric contractions.

Isotonic contractions involve movement; isometric contractions involve no movement.