Microscopic Anatomy of Skeletal Muscle

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Questions and Answers

What are the three types of muscle tissue?

Smooth, cardiac, and skeletal.

Describe the structural characteristics that differentiate skeletal muscle fibers from other types of muscle.

Skeletal muscle fibers are striated, multi-nucleated, cylindrical, and under voluntary control.

What is the role of the sarcolemma in skeletal muscle fibers?

The sarcolemma serves as the cell membrane that surrounds muscle fibers, containing the nuclei and myofibrils.

Define sarcomere and its significance in muscle contraction.

A sarcomere is the functional contractile unit of a muscle cell, composed of actin and myosin, crucial for muscle contraction. Signup and view all the answers

Differentiate between the A band, H zone, and I band in a sarcomere.

The A band contains overlapping actin and myosin, the H zone has only myosin, and the I band consists of only actin. Signup and view all the answers

What is the function of tendons in the muscular system?

Tendons connect muscles to bones and provide pathways for nerves and blood vessels. Signup and view all the answers

Explain the process leading to muscle fiber contraction at the neuromuscular junction.

An action potential triggers the release of acetylcholine, which binds to the sarcolemma, causing depolarization and muscle contraction. Signup and view all the answers

What comprises a motor unit and its significance in muscle function?

A motor unit consists of a motor neuron and all muscle fibers it innervates, allowing for coordinated muscle contraction. Signup and view all the answers

What is the role of calcium and troponin in muscle contraction?

They move tropomyosin away from the active site, allowing myosin heads to attach. Signup and view all the answers

Describe the principle of all or none in muscle fiber contraction.

A muscle fiber either contracts fully or does not contract at all. Signup and view all the answers

How does multiple motor unit summation enhance muscle contraction strength?

It increases contractile strength by activating more muscle cells through greater stimulation intensity. Signup and view all the answers

What occurs during the latent phase of a muscle twitch?

It is the initial phase where no visible contraction occurs despite stimulus application. Signup and view all the answers

Explain what is meant by 'treppe' in muscle contraction.

Treppe refers to the staircase effect where successive contractions increase in strength due to heat and calcium buildup. Signup and view all the answers

What characterizes tetanus in muscle activity?

Tetanus is characterized by sustained contraction with no relaxation due to rapid stimulation. Signup and view all the answers

What is muscle fatigue and what causes it?

Muscle fatigue is the inability of a muscle cell to contract due to ATP depletion and lactic acid buildup. Signup and view all the answers

Differentiate between isometric and isotonic contractions.

Isometric contractions involve no change in muscle length, while isotonic contractions involve a change in muscle length. Signup and view all the answers

How does calcium influence muscle contraction at the sarcomere level?

Calcium binds to Troponin, leading to a shift in Tropomyosin, which exposes the active sites on actin filaments for myosin binding. Signup and view all the answers

What are the characteristics of a muscle named 'Longus'?

A muscle named 'Longus' is typically elongated in shape and is often associated with larger muscle groups. Signup and view all the answers

Identify the primary role of agonist muscles in movement.

Agonist muscles, or prime movers, are primarily responsible for generating the main force during a specific movement. Signup and view all the answers

What occurs during the Absolute Refractory Period in muscle cells?

During the Absolute Refractory Period, sodium gates are open but inactivated, preventing any new action potentials from being generated. Signup and view all the answers

Explain the relationship between sodium and potassium ions during action potential.

During action potential, sodium gates open causing depolarization, and subsequently, potassium gates open for repolarization, restoring resting potential. Signup and view all the answers

What is the function of fixator muscles?

Fixator muscles immobilize the origin of a prime mover, stabilizing the joint and allowing the prime mover to exert more force at the insertion. Signup and view all the answers

How does the direction of muscle fibers affect muscle naming?

Muscles can be named based on the direction of their fibers, such as Transverse (horizontal) or Rectus (vertical), indicating their orientation in the body. Signup and view all the answers

What happens after calcium binds to Troponin?

After calcium binds to Troponin, Tropomyosin moves away from the actin sites, allowing myosin heads to attach and initiate contraction. Signup and view all the answers

Study Notes

Microscopic Anatomy of Skeletal Muscle

Three types of muscle: smooth, cardiac, and skeletal
Skeletal muscle characteristics: voluntary control, striated, multi-nucleated, cylindrical, found in bundles
Sarcolemma: cell membrane of a skeletal muscle fiber
Myofibrils: bundles of filaments within muscle fibers
Sarcomeres: functional contractile units of myofibrils
Myosin and Actin: thick and thin filaments within sarcomeres
A band: zone of overlap of actin and myosin filaments
H zone: contains only myosin filaments
I band: contains only actin filaments
Muscle fiber: a muscle cell, formed by bundles of myofibrils and sarcolemma
Endomysium: areolar connective tissue surrounding individual muscle fibers
Fascicles: bundles of muscle fibers
Perimysium: connective tissue surrounding fascicles
Epimysium: Connective tissue surrounding bundles of fascicles (muscles)
Tendons/Aponeuroses: strong connective tissue that connects muscles to bones, providing a path for nerves and blood vessels
Neuromuscular Junction: junction between a motor neuron and a muscle fiber
Axon Terminal: end of the motor neuron that approaches the muscle fiber
Motor Unit: a motor neuron and all the muscle fibers it innervates
Synaptic Cleft: space between the axon terminal and the sarcolemma of the muscle fiber
Muscle Contraction: Action Potential/Nerve Impulse travels down the axon to the axon terminal, releasing Acetylcholine, triggering depolarization and contraction. Calcium enters the sarcomere triggering events.

Naming Skeletal Muscles

Muscles named by direction (transverse, oblique, rectus)
Muscles named by size (maximus, minimus, longus, brevis)
Muscles named by location (e.g., Extensor carpi ulnaris)
Muscles named by origin and insertion (e.g., Sternocleidomastoid)
Muscles named by shape (e.g., deltoid)
Muscles named by action (e.g., adductors)

Types of Muscles

Prime Movers/Agonists: primarily responsible for a particular movement
Antagonists: oppose or reverse the movement of a prime mover
Synergists: aid actions of agonists by reducing undesirable movements
Fixators: specialized synergists that immobilize the origin of a prime mover

Muscle Activity

Resting Potential: -60 to -90mV (-90 for skeletal muscle) due to potassium and sodium concentration difference and pumps
Action Potential: sodium gates open, depolarization occurs, polarity increases to +35, sodium gates close, potassium gates open, repolarization.
Absolute Refractory Period: time when sodium gates are open and inactivated, no other action potential.
Relative Refractory Period: time when the sodium gates close and potassium gates open, but another action potential may be possible.
Muscle Contraction: After calcium enters the sarcomere causing a series of events resulting in a Power Stroke and contraction.
Muscle Twitch: a single muscle contraction, 3 phases (latent, contraction, relaxation). Subthreshold stimulus does not lead to contraction.
Maximal Stimulus: causes all muscle fibers in a muscle to contract
Multiple Motor Unit Summation/Recruitment: increasing contraction strength by stimulating more muscle cells.
Treppe: staircase effect, progressive increase in contractile strength with same stimulus. Wave summation: stimuli with increased rate, increasing contractile strength, tetanus: sustained contraction with no relaxation, and muscle fatigue: loss of contractile ability due to ATP depletion, and oxygen debt, lactic acid buildup.
Isometric Contractions: muscle length stays the same, force generated can changes
Isotonic Contractions: muscle length changes, forces generated stays the same.
Tonus: constant state of slight muscle tension
Electromyography: detecting, amplifying, and recording skin voltage due to skeletal muscle contraction (electromyograph/ electromyogram).
Work is the application of muscle force needed to move an object.
Dynamometry is the study of power. A Dynogram is the recording obtained.

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Description

Test your knowledge on the microscopic anatomy of skeletal muscle, including the characteristics of skeletal, cardiac, and smooth muscle types. Explore the structure and function of muscle fibers, myofibrils, and sarcomeres, along with their associated connective tissues and filaments.