Muscle Physiology: Skeletal Muscle Lecture 3

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Questions and Answers

The muscle is a contractile muscle tissue and accomplishes diverse functions. What is NOT an example of muscle functions?

Digestion

Initiate electrical impulses (correct)

Supporting locomotion

Generating body heat

What is contractility in muscles?

The ability to shorten (correct)

The ability to generate body heat

The ability to stretch

The ability to circulate blood and lymph

Which of the following is NOT a function of muscle?

Respiration

Parturition

Digestion

Photosynthesis (correct)

What is the correct order of orginization of skeletal muscle?

Epimysium, fasicle, perimysium, endomysium, myofibril, myofilament Signup and view all the answers

What are the types of muscles as discussed in the lecture?

Skeletal, smooth and cardiac Signup and view all the answers

Which of the following statements is true?

All statements are true Signup and view all the answers

Which of the following is synonymous to the cell membrane of a muscle fiber?

Sarcolemma Signup and view all the answers

What is the contractile unit of skeletal muscle?

Sarcomere Signup and view all the answers

Which of the following is a muscular property?

More than one above Signup and view all the answers

What are the two types of muscle fibers, respectively?

Type 1 (slow twitch red fibers), Type 2 (Fast twitch white fibers) Signup and view all the answers

What is the term for the ability to return to its original shape after being stretched?

Elasticity Signup and view all the answers

What is the thick myofilament, and what describes the properties/composition best?

Myosin, it contains a tail of intertwined helices with two globular heads that can bind to ATP and Actin as it functions as an ATPase Signup and view all the answers

What are the types of myofilaments?

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

What is the function of the epimysium?

To surround the entire muscle Signup and view all the answers

Which of the following describes the thin myofilaments and their function or composition, respectively?

Actin and tropomyosin form a large helical complex; the end of these actin filaments are attached to a Z disc Signup and view all the answers

What is the function of type 1 muscle fibers?

To provide slow, prolonged activity Signup and view all the answers

What is the characteristic of type 2B muscle fibers?

Fast-contracting and fast-fatiguing glycolytic fibers Signup and view all the answers

What is the term for the ability to receive and respond to a stimulus?

Excitability Signup and view all the answers

What is the term for the small bundle or cluster of muscle fibers?

Fascicle Signup and view all the answers

What is the function of the perimysium?

To surround each fascicle Signup and view all the answers

What is the function of myosin heads in muscle contraction?

To bind to actin, forming these cross-bridges, and shorten the sarcomere Signup and view all the answers

What type of muscle fibers contain more type 2B fibers?

Muscles designed for sprinting Signup and view all the answers

What is the function of titin filamentous molecules?

To keep the myosin and actin filaments in place Signup and view all the answers

What is the purpose of the sarcoplasmic reticulum in muscle cells?

To regulate calcium storage, release, and reuptake Signup and view all the answers

What is the function of myoglobin in muscle cells?

To temporarily store oxygen for intense muscular activity Signup and view all the answers

What is the composition of thin filaments?

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

What is the function of the T-tubules?

To carry the depolarization of the action potential to the interior of the fiber Signup and view all the answers

What is the composition of thick filaments?

Myosin only Signup and view all the answers

What is the purpose of the M-line?

To form the middle of the sarcomere Signup and view all the answers

What is the function of troponin in thin filaments?

To bind to calcium ions and regulate muscle contraction Signup and view all the answers

Myoglobin is found exclusively in _ and

skeletal and cardiac muscle cells Signup and view all the answers

Mitochondria supply contracting myofibrils with large amounts of energy in the form of ATP

True Signup and view all the answers

Mitochondria are more numerous in Type 2 fibers (red)

False Signup and view all the answers

The sarcoplasmic reticulum is bigger in fast contracting fibers (type 2-white)

True Signup and view all the answers

What is the primary function of the thick filaments in the sarcomere?

Generation of muscle contraction Signup and view all the answers

What is the region within the A-band where thick filaments overlap?

H-Zone Signup and view all the answers

What is the boundary between the A-band and I-band where thin filaments are anchored?

Z-Line Signup and view all the answers

What is the mechanism by which muscle contraction occurs, where thick and thin filaments slide past each other to shorten the sarcomere length?

Sliding Filament Theory Signup and view all the answers

Which of the following is incorrect about myofilament organization?

The M line is the light zone in the center made from thick filaments Signup and view all the answers

Myofilaments contain the basic contractile unit, the sarcomere

False Signup and view all the answers

Study Notes

Muscle Functions

Muscle is a contractile tissue that accomplishes diverse functions, including:
- Locomotion
- Respiration
- Digestion
- Parturition
- Blood and lymph circulation
- Swallowing
- Generation of body heat

Muscular Properties

Muscle has four specific properties:
- Contractility: the ability to contract or shorten
- Excitability: the capacity to receive and respond to a stimulus
- Extensibility: the ability to be stretched
- Elasticity: the ability to return to its original shape after being stretched

Types of Muscle

There are three types of muscle:
- Skeletal muscle (40% of body mass)
- Smooth muscle (10% of body mass)
- Cardiac muscle
Each type of muscle has distinct characteristics, including:
- Contractions: fast, slow, or fast
- Location: trunk, extremities, head, and neck; viscera, blood vessels; heart
- Control: voluntary, involuntary, or involuntary

Skeletal Muscle

Skeletal muscle is crucial for body movement and is attached to bones, usually by tendons
It is stimulated by a motor nerve and is under voluntary (conscious) control
Body movement is the result of the contraction of skeletal muscle across a movable joint
Most joints have one or more muscles on both sides to increase or decrease their angle

Organization of Skeletal Muscle

Skeletal muscle has a hierarchical organization:
- Epimysium: a sheath of connective tissue surrounding the muscle
- Fascicle: a small bundle or cluster of muscle fibers (cells)
- Perimysium: connective tissue extensions from the epimysium that surrounds each fascicle
- Endomysium: connective tissue extensions from the perimysium that surrounds the individual muscle fibers and is attached to the sarcolemma
Muscle fibers are long, cylindrical, and multinucleated, containing the basic contractile units (sarcomeres)

Types of Muscle Fibers

Mammalian muscles are composed of muscle fibers with different contractile properties:
- Type 1 (red fibers): slow-contracting and fatigue-resistant, rich in mitochondria, myoglobin, and capillaries
- Type 2 (white fibers): fast-contracting and more easily fatigable, with fewer mitochondria, relying on glycolytic metabolism
- Type 2a: mixed oxidative-glycolytic, fast-contracting, and fatigue-resistant (intermediate between type 1 and type 2b)
- Type 2b: fast-contracting, fast-fatiguing, and glycolytic, relying on glycogen for energy supply

Myofilaments

Myofilaments are responsible for actual muscle contraction:
- Thin filaments: composed of actin, troponin, and tropomyosin
- Thick filaments: composed of myosin, with multiple myosin molecules, each containing a tail and two globular heads that can bind both ATP and actin
- Myosin heads flex and relax, forming cross-bridges that interact with actin to shorten the sarcomere

Organization of Myofilaments

Myofilaments are organized into sarcomeres, the basic contractile units of striated muscle fibers:
- Sarcomeres are found between Z lines or Z disks and contain protein myofilaments (thin and thick)
- Thin filaments are composed of actin, tropomyosin, and troponin, and are responsible for interacting with myosin heads
- Thick filaments are composed of myosin and are responsible for generating force

Organelles of the Muscle Cell

Organelles of the muscle cell include:
- Sarcoplasmic reticulum: specialized endoplasmic reticulum that regulates calcium storage, release, and reuptake
- Mitochondria: present in large numbers, lying in parallel to the myofibrils, supplying contracting myofibrils with energy in the form of ATP
- T-tubules: tubules arranged transversely to the myofibril, allowing the plasma membrane of the muscle fiber to carry the depolarization of the action potential to the interior of the fiber
- Myoglobin: a protein located primarily in the striated muscles of vertebrates, serving as a local oxygen reservoir and temporarily providing oxygen during periods of intense muscular activity

Sarcomere Structure

Functional unit of muscle contraction, composed of organized myofilaments

Myofilament Organization

Thick filaments composed of myosin, responsible for contraction
Thin filaments composed of actin, tropomyosin, and troponin, regulating contraction

Sarcomere Regions

A-Band: region with thick filaments, including
- H-Zone: region of thick filament overlap
- M-Line: region of thick filament anchoring
I-Band: region with thin filaments, including
- Z-Disk: region of thin filament anchoring
Z-Line: boundary between A-Band and I-Band, with thin filament anchoring

Important Features

Sarcomere length: 2.5-3.5 μm, varying by muscle type
Myofilament overlap: necessary for contraction, between thick and thin filaments
Sliding Filament Theory: mechanism of muscle contraction, where filaments slide past each other to shorten sarcomere length

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Description

This quiz covers the fundamentals of muscle physiology, including muscle function, properties, and types of muscle fibers. Learn about the levels of organization in skeletal muscle and more.