Histology of Muscle Tissue

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Questions and Answers

What is the characteristic nuclear location unique to skeletal muscle fibers?

Throughout the sarcoplasm

Just under the sarcolemma (correct)

In the center of the fiber

Near the perimysium

What is the function of the epimysium?

To provide a pathway for lymphatics

To surround each bundle of muscle fibers

To surround the entire muscle and carry larger nerves and blood vessels (correct)

To supply each fascicle with nerves and blood vessels

What proportion of the total protein in striated muscle is represented by myosin and actin together?

Over one quarter

Over one third

Over three quarters

Over half (correct)

What is the primary function of the sarcoplasmic reticulum in skeletal muscle fibers?

Ca2+ sequestration Signup and view all the answers

What is the name of the reserve progenitor cells found adjacent to most fibers of differentiated skeletal muscle?

Satellite cells Signup and view all the answers

What is the primary function of the collagen in the connective tissue layers of muscle?

To transmit mechanical forces generated by contracting muscle cells Signup and view all the answers

What is the term for the cross-striations found in skeletal muscle fibers?

Myofibrillar striations Signup and view all the answers

What is the name of the complex formed by a T-tubule and two terminal cisternae of sarcoplasmic reticulum?

Triad Signup and view all the answers

What is the primary function of the T-tubules in skeletal muscle fibers?

Transmission of electrical signals Signup and view all the answers

What type of connective tissue forms a rich network in the endomysium, bringing oxygen to the muscle fibers?

Capillaries Signup and view all the answers

What is the name of the thin connective tissue layer that surrounds each bundle of muscle fibers?

Perimysium Signup and view all the answers

What is the pattern of structures observed in TEM cross-sections of sarcomeres?

Hexagonal Signup and view all the answers

What is the characteristic shape of skeletal muscle fibers?

Cylindrical Signup and view all the answers

What is the characteristic pattern of transverse striations in muscle fibers due to?

The lateral registration of sarcomeres in adjacent myofibrils Signup and view all the answers

What is the primary component of the A bands in sarcomeres?

Myosin filaments Signup and view all the answers

What is the term for the muscle cell membrane and its external lamina?

Sarcolemma Signup and view all the answers

What is the primary event that triggers contraction of sarcomeres?

Release of Ca2+ ions Signup and view all the answers

What is the structure that contains the myofibrils and runs parallel to the long axis of the muscle fiber?

Myofibril Signup and view all the answers

What is the term for the cytoplasm of muscle cells?

Sarcoplasm Signup and view all the answers

What is the structure that joins the muscle to bone, skin, or another muscle?

Myotendinous junction Signup and view all the answers

What is the composition of the thick myosin filaments in sarcomeres?

Two identical heavy chains and two pairs of light chains Signup and view all the answers

What is the function of the sarcoplasmic reticulum in muscle fibers?

To regulate muscle contraction and relaxation Signup and view all the answers

What is the shape of the motor proteins that make up myosin heavy chains?

Thin, rodlike Signup and view all the answers

What is the function of the myosin heads?

Binding to ATP and catalyzing energy release Signup and view all the answers

What is the purpose of the M line in the A band?

To hold the thick filaments in place Signup and view all the answers

What is the function of the protein α-actinin?

To anchor the thin filaments to the Z disc Signup and view all the answers

What is the function of the protein nebulin?

To specify the length of the actin polymers during myogenesis Signup and view all the answers

What is the characteristic of the I bands?

They are lightly stained Signup and view all the answers

What is the function of the protein titin?

To support the thick myofilaments and connect them to the Z disc Signup and view all the answers

What is the characteristic of the H zone?

It is a region with only the rodlike portions of the myosin molecule and no thin filaments Signup and view all the answers

Study Notes

Muscle Tissue

Muscle tissue is composed of cells that optimize the universal cell property of contractility.
There are three types of muscle tissue: skeletal muscle, cardiac muscle, and smooth muscle.

Skeletal Muscle

Skeletal muscle consists of long, cylindrical, multinucleated cells with diameters of 10-100 μm and cross-striations.
Contraction is quick, forceful, and usually under voluntary control.
Elongated nuclei are found peripherally just under the sarcolemma, a characteristic nuclear location unique to skeletal muscle fibers.
Muscle satellite cells are a small population of reserve progenitor cells that remain adjacent to most fibers of differentiated skeletal muscle.

Organization of Skeletal Muscle

The entire muscle is surrounded by the epimysium, an external sheath of dense irregular connective tissue.
The perimysium is a thin connective tissue layer that surrounds each bundle of muscle fibers (fascicle).
The endomysium is a very thin, delicate layer of reticular fibers and scattered fibroblasts that surrounds the external lamina of individual muscle fibers.
Collagens in these connective tissue layers serve to transmit the mechanical forces generated by the contracting muscle cells.

Ultrastructure of Skeletal Muscle Fibers

Longitudinally sectioned skeletal muscle fibers show striations of alternating light and dark bands.
The sarcoplasm is highly organized, containing primarily long cylindrical filament bundles (myofibrils) that run parallel to the long axis of the fiber.
Myofibrils consist of an end-to-end repetitive arrangement of sarcomeres.
The dark bands on the myofibrils are called A bands, and the light bands are called I bands.
Mitochondria and sarcoplasmic reticulum are found between the myofibrils.

Sarcomeres

The A and I banding pattern in sarcomeres is due mainly to the regular arrangement of thick and thin myofilaments, composed of myosin and F-actin, respectively.
The thick myosin filaments occupy the A band at the middle region of the sarcomere.
Myosin is a large complex with two identical heavy chains and two pairs of light chains.
The myosin heads bind both actin, forming transient crossbridges between the thick and thin filaments, and ATP, catalyzing energy release (actomyosin ATPase activity).
The thin, helical actin filaments are each 1.0-μm long and 8-nm wide and run between the thick filaments.

Sarcoplasmic Reticulum and Transverse Tubule System

The membranous smooth ER, called sarcoplasmic reticulum, contains pumps and other proteins for Ca2+ sequestration and surrounds the myofibrils.
The sarcolemma has tubular infoldings called transverse or T-tubules.
The triad complex (T-tubule with two terminal cisternae of sarcoplasmic reticulum) allows depolarization of the sarcolemma in a T-tubule to affect the sarcoplasmic reticulum and trigger release of Ca2+ ions into the cytoplasm around the thick and thin filaments, which initiates contraction of sarcomeres.

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Description

This quiz covers the ultrastructure of skeletal, smooth, and cardiac muscles, including their morphologic and functional characteristics.