Module 3 Chapter 9

What are the major types of muscle tissue?

Skeletal, cardiac, and smooth muscle.

What is the primary function of skeletal muscle?

Controls body movement.

What is unique about cardiac muscle in terms of cell connections?

Cardiac muscle cells are connected by intercalated disks.

What is the significance of striations in muscle tissue?

Striations indicate the presence of organized fiber arrangements, seen in skeletal and cardiac muscles.

How does smooth muscle differ from skeletal and cardiac muscle in terms of control?

Smooth muscle is involuntary, while skeletal muscle is voluntary and cardiac muscle is also involuntary.

What role does excitability play in muscle function?

It allows muscles to respond to electrical stimuli.

Define contractibility in the context of muscle tissue.

The ability of a muscle to shorten or contract.

Explain the importance of elasticity in muscles.

Elasticity allows muscles to return to their original length after being stretched.

How does extensibility benefit muscle function?

It allows muscles to stretch beyond their normal length while still being able to contract.

What is the epimysium?

The outermost layer of connective tissue surrounding each skeletal muscle, made of dense irregular connective tissue.

Define perimysium.

Connective tissue that divides the whole muscle into bundles of muscle fibers called fascicles.

What is the function of endomysium?

A delicate layer of connective tissue that separates individual muscle fibers within each fascicle.

How do the three layers of connective tissue in muscles relate to tendons?

They blend into the ends of muscles to form tendons, which attach muscles to bones.

What role do motor neurons play in skeletal muscle?

Motor neurons stimulate muscle contractions.

Describe the blood supply to skeletal muscles.

Skeletal muscles have a rich supply of blood vessels that deliver oxygen and nutrients, aided by numerous branches of arteries.

What are myoblasts?

Embryonic cells that fuse to form skeletal muscle cells.

Explain muscle hypertrophy.

Hypertrophy is the enlargement of muscle fibers, leading to increased muscle size without an increase in the number of muscle fibers.

What is the significance of striation in muscle fibers?

Striations indicate the organized arrangement of muscle fibers, characteristic of skeletal and cardiac muscles.

What are the two main parts of a muscle contraction?

Electrical and mechanical components.

Define sarcolemma.

The plasma membrane of muscle fibers.

What is the function of transverse tubules in muscle fibers?

They carry electrical impulses into the center of the muscle fiber for contraction.

Describe the role of the sarcoplasmic reticulum.

A specialized smooth endoplasmic reticulum that stores high levels of Ca2+.

What are myofibrils?

Bundles of protein filaments that shorten during a muscle contraction.

Identify the two types of myofilaments involved in muscle contraction.

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

What is a sarcomere?

The smallest unit of a muscle that can contract, formed by myofibrils.

What are Z disks in a sarcomere?

Filamentous network of proteins that anchor actin myofilaments.

Explain the difference between I bands and A band in sarcomeres.

I bands are light regions, while A bands are darker stained regions containing both actin and myosin.

What is the H zone in a sarcomere?

The area where only myosin filaments are present.

What does the M line do in a sarcomere?

It holds myosin myofilaments in place.

What are G-actin molecules?

Globular subunits that form fibrous actin strands, with each having an active site for myosin binding during contraction.

Describe the role of tropomyosin in muscle contraction.

A fibrous protein that lies in the grooves of actin strands and must uncover active sites for muscle contraction to occur.

What is the function of troponin in muscle fibers?

Regulates muscle contraction by anchoring to actin, preventing tropomyosin from covering active sites, and binding calcium ions (Ca2+).

What is the structure of myosin filaments?

Composed of elongated myosin molecules, consisting of two heavy chains and two myosin heads.

Explain the function of myosin heads in muscle contraction.

They bind to active sites on actin to form cross-bridges and contain ATPase activity to release energy from ATP.

What is the resting membrane potential?

The charge difference across the plasma membrane of an unstimulated cell.

How do ion channels contribute to an action potential?

They create electrical properties in resting and stimulated cells, allowing ions to enter or exit the cell.

What are ligand-gated ion channels?

Ion channels that open when a specific ligand binds, allowing ions like Na+ to enter the cell.

Explain voltage-gated ion channels.

Channels that open and close in response to specific membrane potentials, allowing ions such as K+ and Ca2+ to cross.

What happens during depolarization?

The inside of the plasma membrane becomes more positive, triggering action potential once the threshold is reached.

What occurs during repolarization?

The membrane potential returns to its resting value after depolarization.

Describe the all-or-none principle in relation to action potential.

Action potential occurs fully or not at all, meaning it either reaches a sufficient threshold or does not occur.

What is the function of the neuromuscular junction?

It's the synapse between a motor neuron and a skeletal muscle fiber where acetylcholine is released.

How is an action potential transmitted across the neuromuscular junction?

Action potential causes Ca2+ influx, releasing acetylcholine which opens Na+ channels in the muscle fiber, leading to depolarization.

What is excitation-contraction coupling?

The link between the action potential on the sarcolemma and the shortening of a sarcomere.

Summarize the events of cross-bridge movement.

Myosin heads bind to actin, pivot to pull actin inward, release with new ATP binding, and re-cock for another cycle.

What is a motor unit?

A single motor neuron and all the muscle fibers it innervates.

How do motor unit numbers affect muscle control?

Muscles with small motor unit numbers allow for delicate and precise control, while a few large motor units provide only coarse control.

What is graded response in muscles?

Muscles respond to stimuli with contractions that vary in strength based on frequency of stimulation, muscle fiber diameter, and fiber length during contraction.

How can the force of muscle contraction be increased?

The force can be increased with larger muscle size and more motor unit recruitment.

What occurs in the phenomenon of treppe?

In treppe, muscle fibers contract with greater force with each successive stimulus after a resting period.

What is multiple motor unit recruitment?

The process of increasing muscle force by activating more motor units, leading to a stronger muscle contraction.

What is wave summation?

Wave summation occurs when a muscle is stimulated before it has completely relaxed, causing a stronger subsequent contraction due to Ca2+ ion buildup.

How does initial muscle length affect tension production?

Initial muscle length influences tension; optimal length increases active tension, while excessive stretching decreases it.

Distinguish between isometric and isotonic contractions.

Isometric contractions maintain muscle length while increasing tension; isotonic contractions change muscle length while maintaining tension.

How is muscle tone maintained?

Muscle tone is maintained through prolonged contraction of muscles.

Distinguish between slow-twitch and fast-twitch muscle fibers.

Slow-twitch fibers are resistant to fatigue, use aerobic respiration, and have a higher myoglobin content; fast-twitch fibers contract quickly, fatigue faster, and primarily use anaerobic respiration.

What adaptations are fast-twitch fibers best suited for?

Fast-twitch fibers are best suited for short bursts of high-intensity activities, such as sprinting or weightlifting.

What adaptations are slow-twitch fibers best suited for?

Slow-twitch fibers are best suited for endurance activities, such as long-distance running or cycling.

How does training influence muscle fibers?

Training can increase the size and efficiency of both muscle fiber types, with strength training enlarging fast-twitch fibers and endurance training enhancing slow-twitch fibers.

What is the effect of intense exercise on fast-twitch muscle fibers?

Intense exercise enhances muscular strength and mass, leading to more significant enlargement of fast-twitch fibers.

How does aerobic exercise affect slow-twitch muscle fibers?

Aerobic exercise increases the vascularity and size of slow-twitch fibers, enhancing their endurance capabilities.

What role does muscle metabolism play in regulating body temperature?

Muscle metabolism generates heat as a byproduct of chemical reactions, helping to maintain normal body temperature.

How do muscles respond to an increase in body temperature?

When body temperature rises, muscles trigger sweating and vasodilation to enhance heat loss.

How do muscles respond to a decrease in body temperature?

If body temperature drops, the nervous system induces shivering to generate heat and restore normal temperature.

What are four sources of energy for ATP production in muscles?

1. Conversion of two ADP to one ATP and one AMP by adenylate kinase. 2. Transfer of phosphate from creatine phosphate by creatine kinase. 3. Anaerobic production of ATP during high-intensity short-term exercise. 4. Aerobic production of ATP during most exercises.

What is oxygen deficiency during exercise?

Oxygen deficiency refers to the lag time before increased breathing rates following the onset of exercise.

What is excess postexercise oxygen consumption (EPOC)?

EPOC is the additional oxygen consumed after exercise to restore the body to its pre-exercise state.

What are the mechanisms of muscle fatigue?

Muscle fatigue can result from acidosis, ATP depletion, oxidative stress, and inflammation.

How does acidosis contribute to muscle fatigue?

Acidosis results from the breakdown of glucose to lactate and protons, lowering pH and interfering with Ca2+ binding to troponin.

What is oxidative stress in muscle fatigue?

Oxidative stress refers to the buildup of excess reactive oxygen species (ROS or free radicals) that can impair muscle function.

How does inflammation affect muscle fatigue?

Inflammation involves T-lymphocytes migrating to muscles, increasing perception of pain and likely protecting tissues from damage.

Contrast physiological contracture and rigor mortis.

Physiological contracture occurs with low ATP, preventing muscle relaxation; rigor mortis occurs after death, leading to muscle rigidity.

What are the structural features of smooth muscle cells?

Smooth muscle cells are spindle-shaped, smaller than skeletal muscle fibers, have a single nucleus, and more actin than myosin.

How does smooth muscle contraction differ from skeletal muscle contraction?

Smooth muscle contracts slower, initiates from both extracellular Ca2+ and the sarcoplasmic reticulum, and can sustain tension longer.

What is visceral smooth muscle?

Visceral smooth muscle is the most common type, found in sheets in digestive and reproductive tracts, has numerous gap junctions, and is autorhythmic.

What is multiunit smooth muscle?

Multiunit smooth muscle consists of small bundles and single cells, has fewer gap junctions, and contracts only when stimulated by nerves or hormones.

What are the electrical properties of smooth muscle?

Smooth muscle has a less negative resting membrane potential, action potentials that plateau, and does not follow an all-or-nothing response.

How is smooth muscle contraction regulated?

Smooth muscle is regulated by neurotransmitters like acetylcholine and norepinephrine, and hormones like epinephrine and oxytocin.