Muscular Tissue Overview

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Questions and Answers

Which type of muscle tissue is characterized by long cylindrical striated fibers?

Cardiac muscle tissue

Connective muscle tissue

Skeletal muscle tissue (correct)

Smooth muscle tissue

What is the primary function of skeletal muscle tissue?

Heat production and motion (correct)

Hormonal secretion

Nutrient absorption

Regulating blood flow

Which feature is true regarding the nuclei of skeletal muscle tissue?

Nuclei are absent

Nuclei are centrally located

Nuclei are located on the surface

Nuclei are peripherally located (correct)

Which of the following statements best describes isometric contraction?

Muscle tension increases during contraction without changing length Signup and view all the answers

What defines a motor unit?

A single motor neuron and all the skeletal muscle fibers it innervates Signup and view all the answers

What type of muscle tissue has involuntary control and is responsible for propulsion of food in the gastrointestinal tract?

Smooth muscle tissue Signup and view all the answers

Which property of muscular tissue refers to its ability to respond to stimuli?

Electrical excitability Signup and view all the answers

What is the role of the epimysium in muscular tissue?

It encircles the entire muscle Signup and view all the answers

Which type of muscle tissue contains striated fibers and is under involuntary control?

Cardiac muscle tissue Signup and view all the answers

What is a key feature of fascia in relation to muscles?

It supports and surrounds muscles and organs Signup and view all the answers

Which connective tissue component separates muscle fibers into bundles called fascicles?

Perimysium Signup and view all the answers

Which of the following statements about smooth muscle tissue is false?

It has striated fibers Signup and view all the answers

Elasticity in muscular tissue refers to which of the following abilities?

To return to its original shape after contraction Signup and view all the answers

What is the primary function of a tendon?

Attaches a muscle to the periosteum of a bone Signup and view all the answers

Which characteristic is not associated with cardiac muscle tissue?

Multiple nuclei Signup and view all the answers

What is the primary role of acetylcholine (ACh) at the neuromuscular junction?

To bind to receptors and initiate muscle contraction Signup and view all the answers

Which event occurs first in the neuromuscular junction process?

Release of acetylcholine from synaptic vesicles Signup and view all the answers

What causes muscle action potential to be triggered?

Inflow of sodium ions that depolarizes the muscle fiber Signup and view all the answers

Which enzyme is responsible for the breakdown of acetylcholine?

Acetylcholinesterase Signup and view all the answers

What is a defining characteristic of a motor unit?

It consists of a single motor neuron and all muscle fibers it innervates Signup and view all the answers

How does creatine phosphate aid in muscle metabolism?

It serves as a fast energy source for short bursts of activity Signup and view all the answers

What occurs during anaerobic cellular respiration in muscle fibers?

Glucose is catabolized to produce a net gain of 2 ATP Signup and view all the answers

What is a major consequence of muscle fatigue?

Inability to maintain force of contraction Signup and view all the answers

Which muscle fiber source provides oxygen for activities lasting more than 10 minutes?

Oxygen released from myoglobin Signup and view all the answers

What is indicated by the term 'oxygen debt' after exercise?

The extra oxygen required to restore metabolic conditions post-exercise Signup and view all the answers

Which statement is true regarding the contraction cycle?

Calcium ions bind to troponin to trigger muscle contractions Signup and view all the answers

What type of muscles are characterized as fusiform?

Thick in the middle and tapered at both ends Signup and view all the answers

What is the primary function of the synovial fluid found between the visceral and parietal layers of tendon sheaths?

To reduce friction as tendons slide back and forth Signup and view all the answers

What is the characteristic structure of skeletal muscle fibers?

Multinucleated and striated Signup and view all the answers

Which component of the sarcotubular system transmits action potentials?

T-tubules Signup and view all the answers

What do the H zone and M line indicate in the sarcomere structure?

Regions of thick filaments only Signup and view all the answers

What happens to tropomyosin during muscle contraction?

It shifts to expose myosin-binding sites on actin Signup and view all the answers

What role do the contractile proteins myosin and actin play in muscle function?

Generate force during contraction Signup and view all the answers

Which term describes the portion of the myofibril between two adjacent Z discs?

Sarcomere Signup and view all the answers

What is the primary role of acetylcholine in the neuromuscular junction?

To stimulate muscle contraction Signup and view all the answers

What structural feature differentiates thick filaments from thin filaments in skeletal muscle?

Thick filaments are composed primarily of myosin molecules Signup and view all the answers

During muscle relaxation, what role does tropomyosin play?

It blocks myosin-binding sites on actin Signup and view all the answers

What structure connects the outer layer of the tendon sheath to the bone?

Parietal layer Signup and view all the answers

How does the sarcotubular system contribute to muscle contraction?

By facilitating calcium release Signup and view all the answers

What is the primary characteristic of the I bands in the sarcomere?

Contain only actin filaments Signup and view all the answers

What property of skeletal muscles is essential for the rapid generation of force during contraction?

Extensive myofibrils Signup and view all the answers

What type of muscle is characterized by fascicles arranged in a parallel fashion?

Parallel muscles Signup and view all the answers

Which muscle type is responsible for producing the most force during a joint action?

Prime mover (agonist) Signup and view all the answers

What is the main function of synergist muscles?

To stabilize joints and assist the prime mover Signup and view all the answers

What characteristic is NOT associated with slow oxidative muscle fibers?

High glycogen stores Signup and view all the answers

Which type of muscle fiber has a high rate of fatigue?

Fast glycolytic fibers Signup and view all the answers

What role do fixator muscles play in the body?

They prevent a bone from moving. Signup and view all the answers

Which type of muscle is known for being fan-shaped and converging to a narrower insertion?

Triangular (convergent) muscle Signup and view all the answers

Which of the following is a characteristic of white muscle fibers?

Low mitochondria Signup and view all the answers

What type of muscle fibers are primarily used for endurance-type activities?

Slow oxidative fibers Signup and view all the answers

What distinguishes multipennate muscles from other types of pennate muscles?

They consist of multiple muscle bellies with fascicles in various directions. Signup and view all the answers

Which of the following best describes the action of antagonistic muscles?

They oppose the action of the prime mover. Signup and view all the answers

What is the key defining feature of circular muscles?

They form rings around body openings. Signup and view all the answers

Which type of muscle fiber is characterized by the recruitment order where it is used last?

Fast glycolytic fibers Signup and view all the answers

What type of muscle is known for having a quadrilateral shape?

Parallel muscles Signup and view all the answers

Study Notes

Muscular Tissue

Muscle tissue consists of long cylindrical fibers that allow for motion, posture, heat production, and protection.
Skeletal muscle tissue is attached to bones by tendons and is under voluntary control.
Cardiac muscle tissue is located in the heart wall and is responsible for pumping blood throughout the body. It is involuntarily controlled.
Smooth muscle tissue is located in various parts of the body, like the walls of blood vessels and airways, and is responsible for motion, constriction, and propulsion. It is involuntarily controlled.

Properties of Muscular Tissue

Electrical excitability: The ability of muscular tissue to respond to stimuli and trigger an action potential.
Contractility: The ability of muscular tissue to contract forcefully when stimulated.
Extensibility: The ability of muscular tissue to stretch without being damaged.
Elasticity: The ability of muscular tissue to return to its original length and shape after contraction.

Connective Tissue Components

Fascia: A dense sheet or band of irregular connective tissue that supports and surrounds muscles and other organs.
Epimysium: The outermost layer of connective tissue surrounding the entire muscle, made of dense irregular connective tissue.
Perimysium: Dense irregular connective tissue surrounding groups of muscle fibers, separating them into bundles called fascicles.
Endomysium: Thin sheath of areolar connective tissue that penetrates each fascicle, separating individual muscle fibers.
Tendon: Extension of all three connective tissue layers that attaches a muscle to the periosteum of a bone. Composed of parallel bundles of collagen fibers, e.g. Calcaneal (Achilles) tendon.
Aponeurosis: A broad, flat layer of tendon, e.g. Epicranial aponeurosis.
Synovial Sheaths: Tubules of fibrous connective tissue that enclose tendons of the wrist and ankle.
- Visceral layer: The inner layer attached to the surface of the tendon.
- Parietal layer: The outer layer attached to bone.
  - The cavity between these layers contains synovial fluid, reducing friction during tendon movement.

Structure of Skeletal Muscle

Muscles are attached to bones by tendons.

Structure of Muscle Fiber

Muscle fibers: Long, thin, cylindrical cells that form skeletal muscle.
- Sarcolemma: Membrane surrounding each muscle fiber.
- Sarcoplasm: Cytoplasm within the muscle fiber.
- Myofibrils: Bundles of protein filaments within each muscle fiber responsible for contraction.
- Mitochondria: Extensive presence of mitochondria provides energy for muscle contraction.
- Sarcotubular System: Elaborate endoplasmic reticulum vital for muscle excitation and contraction.

Sarcotubular System

T-tubule: Inward extension of the sarcolemma, open to the exterior and containing extracellular fluid. It runs transversely to myofibrils and transmits action potentials.
Sarcoplasmic reticulum: Runs parallel to myofibrils and terminates in terminal cisternae which store calcium ions.
Triads: Two terminal cisternae abutting a t-tubule.

Myofibrils

Thick filaments: Composed primarily of myosin, 16nm in diameter, 1-2µm long.
Thin filaments: Composed primarily of actin, 8nm in diameter, 1-2µm long.
Myofibrils exhibit light and dark bands.

Components of the Sarcomere

Sarcomere: The functional unit of contraction, the portion of a myofibril between two adjacent Z discs.
- I bands: Light bands containing only actin filaments.
- A bands: Dark bands containing myosin filaments and the ends of actin filaments.
- Z discs: The ends of actin filaments are anchored in Z discs.
- H zone: Narrow region in the center of each A band containing only thick filaments.
- M line: Region in the center of the H zone that holds thick filaments together.

Structure of Thick and Thin Filaments

Thick filaments: Contain approximately 300 myosin molecules with tails forming the shaft and heads projecting toward thin filaments. The heads have both actin-binding sites and ATP-binding sites.
Thin filaments: Contain actin, troponin, and tropomyosin.
- Actin: Two intertwined helical chains form its structure, with myosin-binding sites.
- Tropomyosin: Covers the myosin-binding sites on actin in relaxed muscles, preventing myosin from binding.
- Troponin: During muscle contraction, Ca2+ binds to troponin, causing conformational changes that move tropomyosin away from the myosin-binding sites on actin allowing contraction.

Neuromuscular Junction

Somatic motor neurons stimulate muscle fibers to contract.
Neuromuscular junction (NMJ): Synapse between a somatic motor neuron and a skeletal muscle fiber.
- Synaptic vesicle: Contain the neurotransmitter acetylcholine.
- Motor end plate: Region of the sarcolemma opposite the synaptic end bulbs. Contains acetylcholine receptors.
A nerve impulse (nerve action potential) triggers a muscle action potential.

Neuromuscular junction

The nerve impulse causes release of acetylcholine (ACh) from synaptic vesicles.
ACh diffuses across the synaptic cleft and binds to receptors on the motor end plate.
ACh binding opens Na+ channels, causing depolarization and triggering a muscle action potential.
AChE breaks down ACh, terminating its activity.

Contraction Cycle

Action potential travels along the sarcolemma and into the T tubule system.
Stored Ca2+ is released from the sarcoplasmic reticulum into the sarcoplasm.
Ca2+ binds to troponin, causing tropomyosin to move away from myosin binding sites on actin.
ATPase hydrolyzes ATP on the myosin head, allowing it to bind to actin, forming a crossbridge.
Actin and myosin filaments slide past each other, causing muscle fiber contraction.
The power stroke continues until another ATP molecule binds to the myosin head, causing it to detach from actin.

Excitation-Contraction Coupling

The sequence of events from a nerve impulse to muscle contraction is called excitation-contraction coupling.

Myasthenia Gravis

An autoimmune disease that causes damage to the neuromuscular junction (NMJ).
The immune system produces antibodies that block ACh receptors.
Symptoms include weakness of eye muscles, causing double vision, and weakness of throat muscles, leading to difficulties with swallowing, chewing, and talking.

Motor Units

A motor unit consists of a somatic motor neuron and all the skeletal muscle fibers it stimulates.
A single motor neuron typically contacts around 150 muscle fibers.
Muscle fibers in a motor unit contract together.

Muscle Metabolism and Exercise

Muscle fibers can produce ATP in three ways: creatine phosphate, anaerobic respiration, and aerobic respiration.
Creatine phosphate provides ATP for short bursts of activity (e.g., 100-meter dash).
Anaerobic respiration provides ATP for moderate activity (e.g., 400-meter race).
Aerobic respiration provides ATP for long-term activity (e.g., running a marathon).

Muscle Fatigue

Muscle fatigue occurs when the muscle can no longer maintain force of contraction.
Causes include depletion of energy stores, reduced neurotransmitter levels, and buildup of metabolic byproducts.

Oxygen Consumption After Exercise

Oxygen debt is the increased oxygen intake required after exercise to restore metabolic conditions.
Extra oxygen is used to convert lactic acid back to glycogen, resynthesize creatine phosphate and ATP, and replace oxygen in myoglobin.

Fascicles and Muscle Shapes

Muscle fibers are bundled into fascicles.
Muscle shape is determined by the arrangement of fascicles:
- Fusiform: thick in the middle, tapered at the ends.
- Parallel: uniform width.
- Triangular: fan-shaped, broad origin, narrow insertion.
- Pennate: feather-shaped.
- Circular: ring-shaped.

Functional Groups of Muscles

Muscles work together in groups to produce coordinated movements.
Muscle groups are classified into four categories:
- Prime mover (agonist): produces most of the force.
- Synergist: aids the prime mover.
- Antagonist: opposes the prime mover.
- Fixator: stabilizes a bone to prevent movement.

Types of Skeletal Muscle Fibers

Muscle fibers can be classified based on structure and function:
- Slow oxidative (SO) fibers: high myoglobin, many mitochondria, red in color, slow contraction speed, fatigue resistant.
- Fast oxidative-glycolytic (FOG) fibers: intermediate myoglobin, many mitochondria, red to pink, fast contraction speed, moderately fatigue resistant.
- Fast glycolytic (FG) fibers: low myoglobin, few mitochondria, white in color, fastest contraction speed, fatigue quickly.

Naming of Skeletal Muscles

Skeletal muscles are named based on criteria such as:
- Muscle location: indicates the bone or body region associated with the muscle.
- Muscle shape: describes the shape of the muscle.
- Muscle size: indicates the relative size of the muscle.
- Muscle direction: identifies the direction of muscle fibers.
- Muscle origin and insertion: refers to the points where the muscle attaches to bones.
- Muscle action: indicates the main function of the muscle.
- Number of origins: describes the number of attachment points.

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Description

Explore the key properties and types of muscular tissue, including skeletal, cardiac, and smooth muscles. This quiz will test your knowledge on the characteristics that enable muscle fibers to facilitate movement, posture, and more. Get ready to enhance your understanding of this vital body system!