Muscle Tissue Characteristics and Functions

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Questions and Answers

Which characteristic of muscle tissue refers to its ability to return to resting length after contraction?

Elasticity (correct)

Excitability

Contractility

Extensibility

What is the primary function of skeletal muscle tissue related to posture?

Body movement

Temperature regulation

Maintenance of posture (correct)

Storage and movement of materials

Which type of muscle tissue is typically striated and under voluntary control?

All muscle types

Skeletal muscle (correct)

Cardiac muscle

Smooth muscle

What unique characteristic of muscle tissue describes its responsiveness to stimuli?

Excitability Signup and view all the answers

How many types of muscle tissue are recognized in the body?

Three Signup and view all the answers

What are the bundles called that muscle fibers are organized into?

Fascicles Signup and view all the answers

What is the function of the connective tissue layers surrounding skeletal muscle?

Provide protection and sites for blood vessel distribution Signup and view all the answers

Which of the following best describes the perimysium?

Connective tissue surrounding fascicles Signup and view all the answers

What is the name of the less moveable point of attachment of a muscle during contraction?

Origin Signup and view all the answers

What unique structure acts as the plasma membrane in muscle fibers?

Sarcolemma Signup and view all the answers

During muscle contraction, what happens to the articulating bones?

One bone moves while the other does not Signup and view all the answers

What type of connective tissue is the endomysium composed of?

Areolar connective tissue Signup and view all the answers

What forms from the merging of connective tissue at the ends of a muscle?

Tendon Signup and view all the answers

What is the main function of transverse tubules (T-tubules) in muscle fibers?

Enable muscle impulses to spread quickly internally Signup and view all the answers

What defines a triad in skeletal muscle fiber anatomy?

Two terminal cisternae and one T-tubule Signup and view all the answers

Which of the following describes the characteristics of thick filaments?

They consist of bundled myosin molecules Signup and view all the answers

What type of proteins are involved in the structure of thin filaments?

Actin, tropomyosin, and troponin Signup and view all the answers

What is the diameter of thick filaments?

11 nm Signup and view all the answers

Which band in skeletal muscle is described as containing the entire myosin molecule and overlapping actin?

A band Signup and view all the answers

What is the role of the protein titin in the structure of muscle fibers?

Maintaining the structure of thick filaments Signup and view all the answers

Which of the following statements is accurate regarding myofibrils?

They are composed of myofilaments arranged in repeating units Signup and view all the answers

What occurs within the H zone during muscle contraction?

It disappears. Signup and view all the answers

What is the role of the M line within the sarcomere?

To align the thick filaments. Signup and view all the answers

Which statement accurately describes the sarcomere?

It is the functional contractile unit of a muscle fiber. Signup and view all the answers

What changes occur to the I bands during muscle contraction according to the sliding filament theory?

They narrow. Signup and view all the answers

What is a primary component of the neuromuscular junction?

Synaptic vesicles. Signup and view all the answers

Which of the following describes the relationship between thick and thin filaments during a muscle contraction?

Thick and thin filaments slide past each other without changing length. Signup and view all the answers

How does the Z disc function within the sarcomere?

It serves as an attachment site for thin filaments. Signup and view all the answers

What initiates muscle contraction in skeletal muscle fibers?

A motor neuron impulse. Signup and view all the answers

What role does acetylcholinesterase (AChE) play in the synaptic cleft?

It breaks down ACh to terminate the muscle impulse. Signup and view all the answers

Which statement about motor units is accurate?

All muscle fibers within a motor unit will contract simultaneously when stimulated. Signup and view all the answers

What occurs first when a nerve impulse reaches the synaptic knob?

Acetylcholine (ACh) is released into the synaptic cleft. Signup and view all the answers

In muscle contraction, what role does calcium play?

It triggers the binding of troponin, allowing uncovering of active sites. Signup and view all the answers

Which type of muscle contraction occurs when the muscle length changes while maintaining constant tension?

Isotonic contraction Signup and view all the answers

What is a significant characteristic of the all-or-none principle in muscle fibers?

A muscle fiber contracts fully or not at all when stimulated. Signup and view all the answers

During muscle relaxation, which process is essential?

Degradation of ACh to stop its signal. Signup and view all the answers

What function does the synaptic cleft serve in the neuromuscular junction?

It is the space where neurotransmitters travel to reach muscle receptors. Signup and view all the answers

What type of muscle fiber is primarily responsible for endurance and sustained contractions?

Slow oxidative fibers Signup and view all the answers

Which muscle fiber type would be present in muscles that require quick but powerful contractions?

Fast glycolytic fibers Signup and view all the answers

What is the primary reason for muscle atrophy?

Lack of stimulation Signup and view all the answers

Which classification of lever is exemplified by the action of a seesaw?

First-class lever Signup and view all the answers

Which term describes a muscle that assists the agonist in performing its action?

Synergist Signup and view all the answers

What distinguishes fast oxidative fibers from slow oxidative fibers?

They have a larger diameter Signup and view all the answers

Which fascicle arrangement allows for the greatest range of motion in the muscle?

Parallel Signup and view all the answers

What happens to mitochondria in muscle fibers as they undergo hypertrophy?

They increase in number Signup and view all the answers

In which muscle region would you expect to find a higher density of slow oxidative fibers?

Back muscles Signup and view all the answers

What characteristic differentiates fast glycolytic fibers from fast oxidative fibers?

Greater anaerobic capacity Signup and view all the answers

Study Notes

Introduction to Muscle Tissue

Three types of muscle tissue exist in the body: skeletal, cardiac, and smooth
Over 700 skeletal muscles form the muscular system

Properties of Muscle Tissue

Four unique characteristics:
- Excitability: Muscle cells respond to stimuli
- Contractility: Stimulation leads to muscle fiber contraction and shortening
- Elasticity: A contracted muscle returns to resting length when tension is released
- Extensibility: The ability of a muscle fiber to be stretched beyond its resting length

Characteristics of Skeletal Muscle Tissue

Each skeletal muscle is an organ, containing all four tissue types
Skeletal muscle is striated
Generally attached to bones
Skeletal muscle is under voluntary control

Functions of Skeletal Muscle Tissue

Skeletal muscle tissue is responsible for:
- Body movement
- Maintaining posture
- Temperature regulation
- Storage and movement of materials
- Support

Anatomy of Skeletal Muscle

Muscles are comprised of muscle fibers organized into bundles called fascicles
Muscle fibers contain myofibrils
Myofibrils are made up of myofilaments

Organization of Skeletal Muscle

Organized into layers of connective tissue: epimysium, perimysium, and endomysium
Layers of connective tissue surround and separate different components of muscle
They provide protection, as well as sites for blood vessel and nerve distribution

Muscle Attachments

At each end of the muscle, connective tissue merges to form a tendon
Tendons attach muscle to bone, skin, or another muscle
A tendon is usually cord-like, but some can appear as a flat sheet called an aponeurosis
The less movable attachment point is the origin
The more movable attachment point is the insertion

Muscle Origin and Insertion

Most muscles extend over a joint and attach to both articulating bones
Upon contraction, one bone moves, and the other remains fixed

Microscopic Anatomy of Skeletal Muscle

Skeletal muscle fibers have the same components as typical cells, but some are named differently
Examples include sarcolemma (plasma membrane), sarcoplasm (cytoplasm), and sarcoplasmic reticulum (smooth ER)
Two unique structures are transverse tubules (T-tubules) and terminal cisternae

Myofibrils and Myofilaments

Myofibrils are cylindrical structures running the entire length of the muscle cell
This cellular component facilitates shortening and thus contraction
Myofilaments are bundles of proteins within each myofibril, they do not run the entire length of the fiber.
Myofilaments are categorized as either thick or thin

Myofilaments: Thick Filaments

Thick filaments are 11 nm in diameter and twice as thick as thin filaments
Myosin molecules comprise thick filaments, composed of a head and an elongated tail
The heads of myosin act as crossbridges during contraction

Myofilaments: Thin Filaments

Thin filaments have a diameter of 5-6 nm
They consist of two F-actin strands woven together, with each containing G-actin monomers
The filaments also contain two regulatory proteins: tropomyosin and troponin

Molecular Structure of Thick and Thin Filaments

The organization of the thick and thin filaments results in striated appearance in skeletal muscle
Dark bands (A bands) include the entire myosin molecule and an overlapping portion of actin
Light bands (I bands) consist only of thin filaments

Molecular Structure of Thick and Thin Filaments: Additional Features

Within the A band, the H zone is the central, light region where there are no thin filaments
The M line is a protein structure within the H zone that holds the thick filaments in alignment
The Z discs are protein structures in the middle of the I band and serve as an anchoring point for the thin filaments

Organization of a Sarcomere

The sarcomere is the functional contractile unit of a muscle fiber
It's defined by the area between two adjacent Z lines
Myofibrils contain multiple, repeating sarcomeres

Contraction of Skeletal Muscle Fibers

Muscle fibers shorten due to the interaction between thin and thick filaments within each sarcomere
Sliding filament theory explains contraction mechanism

The Sliding Filament Theory

During contraction, thin and thick filaments interact and slide past each other
The width of the A band remains constant but the H zone and I bands narrow
The length of the thick and thin filaments don't change, but their positions do

Neuromuscular Junctions

Muscle contraction is initiated when a motor neuron impulse stimulates a muscle fiber
The neuromuscular junction is the region where the motor neuron is in close proximity to the muscle fiber

Components of the Neuromuscular Junction

Synaptic knob (expanded end of axon)
Synaptic vesicles (contain acetylcholine)
Motor end plate (region of sarcolemma)
Synaptic cleft (space between knob and plate)
ACh receptors (on motor end plate)
Acetylcholinesterase (breaks down ACh)

Physiology of Muscle Contraction

A nerve impulse releases ACh into the synaptic cleft
ACh binds. to receptors, initiating a muscle impulse along the sarcolemma and T-tubules
Spread of impulse causes calcium release from terminal cisternae into the sarcoplasm
Calcium binding to troponin causes tropomyosin to reveal G-actin active sites
Myosin heads bind, form crossbridges as ATP is hydrolyzed (pivoting)
Thick and thin filaments detach and cycle repeats; requires ATP

Motor Units

A motor unit consists of a single motor neuron and the muscle fibers it controls
Control is inversely related to motor unit size.
Smaller units provide the most precise control

Muscle Tone

Muscle tone is the constant tension in a resting muscle
Motor units stimulate randomly to avoid fatigue
Two main types of muscle contraction:
- Isometric: Length is constant; tension changes
- Isotonic: Tension is constant; length changes

Types of Skeletal Muscle Fibers

Skeletal muscles are a mixture of three fiber types:
- Slow oxidative (SO) fibers
- Fast oxidative (FO) fibers
- Fast glycolytic (FG) fibers
The ratio of fiber types determines the speed and sustainability of contraction

Exercise and Skeletal Muscle

Muscle atrophy is a wasting of tissue due to reduced muscle size, tone, and power due to lack of stimulation
Muscle hypertrophy is an increase in muscle fiber size caused by repetitive stimulation

Levers and Joint Biomechanics

A lever is an elongated, rigid object that rotates around a fixed point (fulcrum)
Rotation occurs when effort exceeds resistance
Three classes of levers operate in the human body: first, second, and third class

Actions of Skeletal Muscles

Agonist: Prime mover producing a specific movement
Antagonist: Muscle opposing the agonist's action
Synergist: Muscle assisting the agonist

The Naming of Skeletal Muscles

Muscle names provide clues to their identification and are based on several criteria, including:
- Muscle action
- Specific body regions
- Muscle attachments
- Orientation of muscle fibers
- Muscle shape and size
- Muscle heads/tendons of origin

Characteristics of Cardiac and Smooth Muscle

Three types of muscle in the human body: skeletal, cardiac, smooth
Similarities and differences among the three types

Cardiac Muscle

Found in the heart wall
Striated
One or two nuclei
Form Y-shaped branches, joined by intercalated discs with gap junctions
Autorhythmic: Generates muscle impulse without nervous stimulation
Under involuntary control

Smooth Muscle

Found in the walls of visceral organs and blood vessels
Short, fusiform cells
One centrally located nucleus
No striations
Thin filaments attached to dense bodies
Under involuntary control

Development of Skeletal Muscle

Embryonic development of skeletal muscle

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Description

This quiz explores the fundamental characteristics and functions of different types of muscle tissues, including skeletal muscle. It covers key concepts such as muscle contraction, connective tissue roles, and muscle organization. Test your understanding of muscle physiology with these essential questions.