Muscle Tissue Overview

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Questions and Answers

What initiates the contraction process in skeletal muscle fibers?

Activation of phosphocreatine stores

Release of acetylcholine from motor neurons

Increase in blood flow to muscles

Release of calcium from the sarcoplasmic reticulum (correct)

Which type of muscle contraction occurs when the muscle length changes resulting in movement?

Concentric contraction

Eccentric contraction

Isotonic contraction (correct)

Isometric contraction

What happens during rigor mortis after death?

Calcium accumulates in the sarcoplasm (correct)

Ca2+ levels decrease in the sarcoplasm

ATP production ceases completely

Ion pumps continue functioning properly

What characterizes complete tetanus?

Sustained contraction without relaxation Signup and view all the answers

Which statement accurately describes muscle tone?

It represents the firmness of a muscle at rest. Signup and view all the answers

Which of the following best describes a motor unit?

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

During which contraction does the muscle develop tension but does not change length?

Isometric contraction Signup and view all the answers

What is the effect of repetitive stimulation at a low frequency on muscle contraction?

Leads to incomplete tetanus with periodic relaxation Signup and view all the answers

What initiates the release of calcium ions from the sarcoplasmic reticulum during muscle contraction?

Action potential reaching the T tubule Signup and view all the answers

What role do calcium ions play in the process of muscle contraction?

Calcium ions bind to troponin, revealing binding sites on actin Signup and view all the answers

What occurs after the sarcoplasmic reticulum reabsorbs calcium ions?

Active sites on actin become covered again by tropomyosin Signup and view all the answers

What triggers the breakdown of acetylcholine (ACh) during muscle contraction?

Action of acetylcholinesterase (AChE) Signup and view all the answers

What is the result of decreased calcium concentration in the cytosol?

Contraction ends and muscle relaxes Signup and view all the answers

What sequence occurs immediately after cross-bridge formation between myosin and actin?

Myosin heads pivot, pulling actin filaments Signup and view all the answers

What is the final step that occurs after muscle contraction has ended?

The muscle passively returns to its resting length Signup and view all the answers

During the muscle contraction cycle, which step occurs immediately after the binding of myosin heads to active sites?

Pivoting of myosin heads Signup and view all the answers

What is hypertrophy primarily caused by?

Heavy training Signup and view all the answers

What type of muscle fibers are primarily involved in endurance activities?

Slow-twitch fibers Signup and view all the answers

Which hormone is responsible for increasing the duration and force of muscle contraction?

Epinephrine Signup and view all the answers

What leads to muscle atrophy?

Lack of muscle activity Signup and view all the answers

Which characteristic is NOT typical of cardiac muscle tissue?

Multinucleated Signup and view all the answers

Which function is associated with intercalated discs in cardiac muscle cells?

Structural integrity and electrical conduction Signup and view all the answers

What type of muscle is responsible for regulating blood flow in blood vessels?

Smooth muscle Signup and view all the answers

Which of the following statements about smooth muscle is accurate?

It is mononucleated. Signup and view all the answers

What physiological characteristic is NOT associated with cardiac tissue?

Tetany Signup and view all the answers

What impact does prolonged inactivity have on muscles?

Causes fibrous tissue to replace muscle fibers Signup and view all the answers

Which type of skeletal muscle fibers is more prevalent in strength training?

Fast-twitch fibers Signup and view all the answers

What is a characteristic of smooth muscle cells?

They are fusiform in shape. Signup and view all the answers

Which of the following statements about skeletal muscle performance is accurate?

Power and endurance both depend on physical condition and muscle fiber types. Signup and view all the answers

What happens to muscle tone during inactivity?

It decreases and muscles become flaccid. Signup and view all the answers

What is the primary cause of tetanus?

Toxin of Clostridium tetani bacteria Signup and view all the answers

During peak exertion, why do muscles rely on glycolysis for ATP production?

Muscles lack oxygen to support aerobic metabolism Signup and view all the answers

What is a result of muscle fatigue?

Accumulation of lactic acid Signup and view all the answers

What is the primary function of creatine kinase (CK) in muscles?

To restore ATP from ADP and creatine phosphate Signup and view all the answers

What is the role of glycolysis in muscle metabolism?

To break down glucose and generate ATP anaerobically Signup and view all the answers

Which of the following statements about the recovery period is true?

Oxygen availability increases during this time Signup and view all the answers

What percentage of muscle energy can be converted into heat during contraction?

Up to 70% Signup and view all the answers

What happens to pyruvic acid during sustained muscle exertion?

It is converted to lactic acid Signup and view all the answers

Which pathway generates the most ATP per glucose molecule?

Krebs cycle Signup and view all the answers

What is the primary energy source during moderate exercise?

Glucose Signup and view all the answers

Which condition is NOT associated with muscle fatigue?

Increased oxygen consumption Signup and view all the answers

Which factor does NOT influence muscle performance?

Color of muscle fibers Signup and view all the answers

What is the primary function of an electromyogram (EMG)?

To measure electrical activity of muscle fibers Signup and view all the answers

What type of muscle tissue is primarily responsible for voluntary movement?

Skeletal muscle tissue Signup and view all the answers

What is the main function of the connective tissue covering of skeletal muscles?

To provide structure and support to the muscles Signup and view all the answers

What is the function of the endomysium in skeletal muscle?

Surrounds individual muscle fibers Signup and view all the answers

Which of the following describes the sarcomere?

It is the functional unit of muscle contraction. Signup and view all the answers

The influx of which ion is critical for initiating muscle action potential?

Sodium (Na+) Signup and view all the answers

Which structure is primarily responsible for calcium ion storage within skeletal muscle cells?

Sarcoplasmic reticulum Signup and view all the answers

What role does acetylcholine (ACh) play in muscle contraction?

It acts as a neurotransmitter to initiate muscle action potential. Signup and view all the answers

What is the primary protein found in thick muscle filaments?

Myosin Signup and view all the answers

Which statement best describes the sliding filament theory?

Thin filaments slide past thick filaments during contraction. Signup and view all the answers

The area where the synaptic terminal of a neuron meets the motor end plate of a muscle fiber is known as the:

Neuromuscular junction Signup and view all the answers

What primarily causes the Z lines to move closer during muscle contraction?

Sliding of thin filaments towards the M line Signup and view all the answers

The primary role of T tubules in muscle fibers is to:

Transmit action potentials to the muscle surface Signup and view all the answers

When a muscle contracts, what happens to the A band?

It remains the same length. Signup and view all the answers

What is the function of the perimysium?

Surrounds muscle fascicles Signup and view all the answers

Study Notes

Muscle Tissue

Three types of muscle tissue: skeletal, cardiac, and smooth
Skeletal muscles are attached to the skeletal system and allow body movement
The muscular system includes only skeletal muscles
Cardiac muscle is found in the heart
Smooth muscle is found in the walls of hollow organs

Functions of Skeletal Muscles

Produce movement
Maintain body position
Support soft tissues (like organs)
Guard body openings, such as the mouth and anus
Maintain body temperature by generating heat

Skeletal Muscle Structure

Muscle cells (fibers) are composed of elongated, multinucleated cells
Connective tissue surrounds the fibers
Blood vessels supply oxygen and nutrients
Lymphatics dispose of waste
Nerves stimulate muscle contraction

Levels of Organization of Muscle Tissues

Skeletal muscle is the organ
Muscle fascicles are groups of muscle fibers
Muscle fibers are individual muscle cells
Myofibrils are long, cylindrical structures within muscle fibers
Sarcomeres are the basic contractile units of muscle fibers

Connective Tissue Covering of Skeletal Muscles

Three layers: epimysium, perimysium, and endomysium
Epimysium surrounds the entire muscle
Perimysium surrounds muscle fascicles
Endomysium surrounds individual muscle fibers

Muscle Attachments

Connective tissues from the epimysium, perimysium, and endomysium converge at muscle ends
They attach to bone matrix through tendons (bundles) or aponeuroses (sheets)

Innervations & Blood Supply

Skeletal muscles are controlled by somatic nerves
Blood vessels supply oxygen and nutrients, and remove waste

Skeletal Muscle Cells (fibers)

Very long, multinucleated cells
Develop through the fusion of myoblasts

Structure of Skeletal Muscle Fibers

Sarcolemma is the cell membrane
Sarcoplasm is the cytoplasm
Sarcosome is the mitochondrion
Sarcoplasmic reticulum is the smooth endoplasmic reticulum
Transverse (T) tubules are deep invaginations of the sarcolemma

Sarcolemma

The cell membrane of a muscle cell
Surrounds the sarcoplasm
Changes in transmembrane potential initiate muscle contraction

Transverse (T) Tubules

Deep invaginations of the sarcolemma
Transmit action potentials across the myofibrils
Allow the entire muscle fiber to contract simultaneously

Sarcoplasmic Reticulum (SR)

Stores and releases calcium ions (Ca2+)
Surrounds each myofibril
Helps to transmit action potentials to myofibrils
Forms cisternae, which store Ca2+ for muscle contraction

Triad

Formed by two terminal cisternae and one T tubule
Essential for excitation-contraction coupling

Myofibrils

Long, cylindrical structures within muscle fibers
Divided into sarcomeres
Made up of bundles of protein filaments called myofilaments

Myofilaments

Part of the cytoskeleton, responsible for muscle contraction
Composed of proteins
Thin filaments consist of actin, nebulin, tropomyosin, and troponin
Thick filaments consist of myosin and titin

Sarcomere

Contractile unit of muscle
Structural unit of myofibrils
Contains thin and thick myofilaments
Alternating dark and light bands give muscle tissue a striped appearance

Sarcomere Lines & Zones

A band: myosin filaments, with actin at both ends
M line: center of the A band, holds myosin thick filaments together
I band: actin filaments only, light region
Z line: center of the I band, holds thin filaments together
Sarcomere extends between two Z lines
H zone: area around the M line, myosin filaments only
Zone of overlap: dark region where thick and thin filaments overlap

Neuromuscular Junction (NMJ)

The connection between a motor neuron and a muscle fiber
Synaptic terminal of a neuron and motor end plate of a muscle fiber

Nerve Action Potential

Travels along the nerve axon and reaches the synaptic terminal
The synaptic terminal releases the neurotransmitter acetylcholine (ACh) into the synaptic cleft

Acetylcholine (ACh)

A neurotransmitter essential for muscle contraction
Stored in synaptic vesicles
Binds to receptors on the sarcolemma at the motor end plate
Triggers sodium influx into the sarcoplasm
Initiates a muscle action potential

Muscle Action Potential

Electrical signal generated by sodium influx
Travels along the T tubules
Initiates excitation-contraction coupling

Excitation-Contraction Coupling

Muscle action potential reaches a triad
Ca2+ is released from the SR
Ca2+ triggers muscle contraction

Muscle Contraction

Caused by interactions between thin and thick filaments
Triggered by Ca2+ ions
Explained by the sliding filament theory

Sliding Filament Theory

Thin filaments slide between thick filaments towards the M line during muscle contraction
Z lines move closer together, shortening the sarcomere
Zone of overlap gets thicker
H zone gets narrower
A band does not change in length

Muscle Relaxation

Ca2+ is reabsorbed by the SR
Tropomyosin returns to its normal position, blocking the active sites on actin
Cross-bridge formation ends, and the sarcomere returns to its resting length

Rigor Mortis

State of muscle stiffness after death
Occurs due to a lack of ATP, which prevents the detachment of myosin heads from actin

Definitions & Concepts

Motor unit: a single motor neuron and the muscle fibers it innervates
Motor end plate: a pocket formed around a motor neuron by the sarcolemma
Muscle tone: normal tension and firmness of a muscle at rest
Muscle twitch: a fine movement of a small area of muscle

Muscle Tension

Force exerted on connective tissues when a muscle fiber shortens
Two types:
- Isotonic contraction: muscle length changes, producing movement
- Isometric contraction: muscle develops tension but does not change length

Tetany

Sustained muscle contraction without relaxation
Caused by repetitive stimulation of muscle fibers
Incomplete tetany: less frequent stimulation, brief periods of relaxation
Complete tetany: high frequency stimulation, no relaxation, continuous contraction

Tetanus

An acute infectious disease caused by Clostridium tetani bacteria
Affects the central nervous system, leading to continuous muscle contractions
Can be fatal

Electromyogram (EMG)

Measurement of the electrical activity of muscle fibers

Energy Storage in Muscle Fibers

ATP is the primary energy source for muscle contraction
Creatine phosphate (CP) is a high-energy phosphate molecule used to regenerate ATP
Glycogen is a stored form of glucose that can be broken down to provide energy

ATP Generation

ATP can be generated via aerobic and anaerobic pathways
Anaerobic pathways occur in the cytosol and are independent of oxygen
Aerobic pathways occur in the mitochondria and require oxygen

Energy Use & Muscle Activity

At rest and mild exertion, muscles use aerobic metabolism
During peak exertion, muscles rely on anaerobic glycolysis
Lactic acid builds up during anaerobic metabolism, leading to muscle fatigue

Muscle Fatigue

The inability of a muscle to sustain contraction
Caused by depletion of metabolic reserves, accumulation of lactic acid, and muscle damage

Recovery Period

Time required for muscles to return to normal after exertion
Oxygen is restored, and mitochondria resume aerobic metabolism

Muscles & Heat Production

Muscle contraction generates heat
Shivering is a mechanism for generating heat by the body

Muscle Contraction & Sliding Filament Theory

Thin filaments slide along thick filaments, shortening the sarcomere
The H zone decreases in size, while the A band remains the same
The sliding of filaments is driven by the connection of myosin heads to actin

Muscle Relaxation & Ca2+ Reabsorption

Calcium ions are reabsorbed by the sarcoplasmic reticulum
Tropomyosin recoves its blocking position
Active sites on actin are covered.
Myosin detaches from actin.
Muscle returns to its resting length.

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Description

Explore the different types of muscle tissue including skeletal, cardiac, and smooth. This quiz covers their structure, functions, and organization levels. Test your knowledge on how these muscles support movement and bodily functions.