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muscle tissue

Mind map of histology and embryology knowledge points on muscle tissue. Muscle tissue is mainly composed of muscle cells with contractile function. There are a small amount of connective tissue, blood vessels, lymphatic vessels and nerves between these muscle cells. For study and review!

Edited at 2024-04-17 23:21:04

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Outline

muscle tissue

Overview

Classification

skeletal muscle

Tendons attached to bones have strong contractility, fatigue easily, and poor regeneration ability.

voluntary muscles, striated muscles

myocardium

Distributed in the heart and proximal large blood vessels, it contracts rhythmically, is not prone to fatigue, and has almost no regeneration ability.

involuntary muscles, striated muscles

smooth muscle

Distributed in visceral hollow organs and blood vessel walls, the contraction force is weak, long-lasting, and the regeneration ability is strong

involuntary muscles

constitute

Mainly composed of muscle cells with contractile function. There are a small amount of connective tissue, blood vessels, lymphatic vessels and nerves between muscle cells.

proper noun

Sarcoplasmic reticulum: smooth endoplasmic reticulum

sarcolemma: muscle cell membrane

Sarcoplasm: muscle cytoplasm

Muscle fiber: muscle cell-slender fiber type

skeletal muscle

Basic understanding

Skeletal muscles are the dynamic part of the locomotor system. Most of them are attached to bones and mainly exist in the trunk and limbs. They are controlled by human consciousness and are also called voluntary muscles.

Skeletal muscles are widely distributed in the human body, with more than 600 pieces, accounting for about 40% of the human body weight.

Each skeletal muscle has a certain position, shape, structure and auxiliary devices, and is rich in blood vessels, lymphatic vessels and nerve distribution to perform certain functions.

Divided according to location: head muscles, neck muscles, trunk muscles, diaphragm muscles, upper limb muscles, lower limb muscles, etc.

surrounded by dense connective tissue

composition

epimysium

Wrapped around the entire muscle

perimysium

The epimysium extends into the muscle, separates it to form muscle bundles, and is the connective tissue that wraps the muscle bundles.

endomysium

connective tissue outside each muscle fiber

Function

Support, connection, nutrition, functional regulation

composition

Myofibrils (subcellular structure of muscle cells) → myofibers (muscle cells, elongated fiber-shaped) → muscle bundles → skeletal muscle

skeletal muscle fibers

Light mirror structure

Cell body: long cylindrical shape

Nucleus: multinucleated cell, with dozens or even hundreds of nuclei in a muscle fiber, oval, located under the sarcolemma

Cytoplasm: filled with myofibrils arranged parallel to the long axis of the muscle fiber, in the form of filaments

periodic stripes

Horizontal stripes: The light and dark bands on each myofibril are arranged on the same plane, forming periodic horizontal stripes with alternating light and dark stripes.

Bright band: There is a dark Z line in the center. Under a polarized light microscope, the bright band appears as single refracted light, also known as the I band. Length variable.

Dark band: Under a polarized light microscope, the dark band is birefringent and anisotropic. It is also called the A band and has a constant length. Under an oil microscope or electron microscope, it can be observed that there is a more pigmented H band in the middle of the dark band, and a darker M line can be seen in the center of the H band.

Three belts and two lines: A, I, H belts; Z, M lines

Structural and functional unit of skeletal muscle fiber - sarcomere

Concept: A section of myofibril between two adjacent Z lines is a sarcomere, which is the basic structural unit of skeletal muscle contraction and relaxation.

Composition: Each sarcomere consists of 1/2 I band, A band, and 1/2 I band

The length of the dark band is constant, 1.5um, and the light band changes with the contraction and relaxation of skeletal muscles, with a maximum length of 2um.

A myofibril can be composed of hundreds of sarcomeres

Ultrastructure

myofibrils

Thick myofilament

Arranged along the long axis of myofibrils, thick myofilaments are only located in the dark band A

distributed

The center of the sarcomere, the center is fixed to the M line, and both ends are free

structure

Long balance 1.5 microns, diameter 15 nanometers

Myosin polymerizes regularly to form

Molecular structure of thick myofilaments - myosin

Bean sprout-shaped, divided into two parts: the head and the rod. There is a similar joint at the head-rod connection point, which can be flexed.

Head: towards both ends of thick myofilaments, it has ATPase activity and can bind to the actin of thin myofilaments to form a cross bridge.

Rod: Towards the middle of the thick muscle filaments, they are gathered into the main body of the thick muscle filaments with the help of the M line

Thin myofilaments

Across the light and dark bands, one end is fixed on the Z line, the other end passes through the I band of the light band, extends between the thick muscle filaments of the A band, and finally ends at the edge of the H band

distributed

One end is fixed on the Z line, the other end extends between the thick muscle filaments, and terminates on the outside of the H band.

structure

About 1 micron long and 5 nanometers in diameter

actin

Double helix chain, each monomer has a binding site for the myosin head

Tropomyosin

Double helix molecule embedded in the shallow grooves of the actin double helix chain

Troponin

Spherical, attached to tropomyosin molecules, capable of binding calcium ions

There are six thin filaments surrounding one thick filament

Band clear: only thin filaments

dark band

H-band: thick filaments only

Both sides: Thick and thin muscle filaments

Cross-section

1 thick filament-6 thin filaments

1 thin filament-3 thick filaments

transverse tubule

Concept: a tubular structure formed by the indentation of the sarcolemma into the sarcoplasm, perpendicular to the long axis of the muscle fiber, and anastomosed by the transverse tubule branches on the same plane, surrounding the myofibrils

Distribution: Located at the junction of light and dark zones

Function: conducts the excitement of the muscle membrane to the interior of the muscle fiber

sarcoplasmic reticulum

Concept: Specialized smooth endoplasmic reticulum in muscle fibers, located between the transverse tubules

Structural features

Longitudinal tubule

The part of the sarcoplasmic reticulum that surrounds myofibrils longitudinally

final pool

Flat sac formed by enlargement of both ends

triplet

Each transverse tubule is composed of terminal cisternae on both sides.

There are calcium pumps and calcium channels in the sarcoplasmic reticulum

There are calcium pumps and calcium channels on the sarcoplasmic reticulum membrane of striated muscle cells, which can pump calcium ions in the cytoplasm into the sarcoplasmic reticulum for storage against the concentration difference, making the calcium ion concentration in the sarcoplasm thousands of times higher than that in the sarcoplasm.

After the sarcoplasmic reticulum is excited, calcium channels open and stored calcium ions are released into the sarcoplasm, causing muscle cells to contract.

More mitochondria

glycogen

small amount of lipid droplets

Myoglobin (can combine with oxygen)

muscle satellite cells

Located on the surface of skeletal muscle fibers (between the sarcolemma and basement membrane), flat and protruding

After muscle fibers are injured, muscle satellite cells can proliferate and differentiate, participate in the repair of muscle fibers, and have stem cell properties.

Myofilament sliding principle

M line can shrink

A belt remains unchanged, I belt and H belt are shortened at the same time

shrink

Nerve impulses are conducted to the sarcolemma and then to the sarcoplasmic reticulum through the transverse tubules and triplets

The calcium ion channels of the sarcoplasmic reticulum open and a large amount of calcium ions enter the cytoplasm.

Calcium ions bind to troponin, causing the configuration or position of troponin and tropomyosin to change, releasing the steric hindrance effect of tropomyosin.

Actin binds to myosin heads, forming cross-bridge connections between thick and thin myofilaments

The cross bridge pulls the thin muscle filaments to slide towards the M line, shortening the season.

diastole

There is no action potential and calcium ions are pumped into the sarcoplasmic reticulum

Calcium ions are separated from troponin, and tropomyosin blocks the interaction between thick and thin myofilaments.

Thin myofilaments return, sarcomeres lengthen, and muscles relax

myocardium

Overview

Distributed on the walls of the heart and the walls of the large blood vessels adjacent to the heart

Contractions are automatic and rhythmic

muscleless satellite cells

Light mirror structural characteristics

shape

Irregular short cylindrical shape, branched and interconnected into a network

connect

Cells are connected by intercalary disks and stain darker

nucleus

1-2 nuclei, centered, oval

Cytoplasm

There are periodic striations, myofibrils are located on the periphery, and the perinuclear cytoplasm is lightly stained and contains lipofuscin.

Electron microscope structural features

Thick myofilaments, thin myofilaments and sarcomeres

The thick and thin myofilaments are not as obvious as skeletal muscle, and are separated into myofilament bundles of varying thicknesses by sarcoplasm and mitochondria.

Myofibrils vary in thickness

Mitochondria are abundant

The transverse tubule is at the level of the Z line

Ultrastructure

myocardium

The sarcoplasmic reticulum is sparse, the longitudinal tubules are underdeveloped, there are few terminal cisterns, and most of them form doublets.

Doublet: The transverse tubule is closely connected to the terminal cisterna on one side.

During contraction, calcium ions are taken in from outside the cells

leap disk

The transverse part of the intercalated disc is located at the level of the Z line. It has adhesive zonules and desmosomes that tightly connect the myocardial fibers.

There are gap junctions in the longitudinal part, which facilitate the exchange of chemical information and electrical impulses between cells and synchronize the contraction and contraction of the myocardium.

smooth muscle

distributed

Widely distributed in the walls of hollow organs such as digestive tracts, respiratory tracts, and blood vessels

Light mirror structural characteristics

Long fusiform, the size and shape vary depending on the location and the functional form of the organ, generally 200 microns long

No striations, cytoplasmic eosinophilia

Single core, rod-shaped or oval

Ultrastructure of smooth muscle fibers

Cytoplasm

There are no myofibrils, thick myofilaments, thin myofilaments and intermediate filaments can be seen. There are dense bodies in the cytoplasm. The intermediate filaments are connected between dense spots and dense bodies to form a spindle-shaped cytoskeleton.

cytoskeletal system

Dense bodies: small bodies with high electron density in the muscle plasma

Macula densa: an area of high electron density under the sarcolemma

Intermediate filaments: connected between macula densa and dense bodies, composed of desmin

membrane

There are dense spots on the membrane, and between the dense spots, the sarcolemma can be seen invading to form small depressions, which are equivalent to the transverse tubules of skeletal muscles and can transmit impulses.

Foveolae: a structure formed by the inlay of the sarcolemma

Thick and thin muscle filaments

The ratio of thick and thin myofilaments is 1:12

Thick myofilament

It is composed of myosin and is cylindrical in shape. There are cross bridges arranged in rows on the surface. Two adjacent rows of cross bridges drive in opposite directions.

Thin myofilaments

Composed of actin, one end is attached to the dense patch or dense body, and the other end is free and surrounds the thick muscle filaments

myofilament unit

Several thick and thin myofilaments gather to form a myofilament unit, also known as a contractile unit. There is only a small amount of sarcoplasmic reticulum in the cell. When the cell contracts, it also needs to absorb calcium ions from outside the cell.

sarcoplasmic reticulum

Underdeveloped, sparsely tubular

Smooth muscle fiber contraction principle

Based on the sliding theory between thick and thin myofilaments

Because the attachment points of thin myofilaments and cytoskeleton are distributed in a spiral shape, when the myofilaments slide, the muscle fibers twist in a spiral shape and their long axis shortens.

There are relatively developed gap junctions between smooth muscle fibers, which can transmit information molecules and electrical impulses, causing synchronous functional activities of adjacent muscle fibers.

Summarize

Comparison of three types of muscle tissue

distributed

Skeletal muscle: attached to bones

Myocardium: the wall of the heart and adjacent large blood vessels

Smooth muscle: mostly embedded in the walls of hollow organs

muscle type

Voluntary muscles: skeletal muscles

Involuntary muscles: cardiac muscle, smooth muscle

form

Skeletal muscles: long cylindrical, without branches (except tongue muscle)

Myocardium: short columnar with branched anastomoses

Smooth muscle: fusiform, unbranched

horizontal stripes

Skeletal muscle: obvious

Cardiac muscle: There are striations, which are not as obvious as skeletal muscle

Smooth muscle: none

nucleus

Skeletal muscle: multinucleated, located at the periphery of the cell

Cardiac muscle: 1-2 nuclei, located in the center of the cell

Smooth muscle: single nucleus, located in the center of the cell

specialized structure of sarcolemma

Skeletal muscle: transverse tubule, located at the junction of the A and I bands

Myocardium: transverse tubule, thicker, located at the Z line level

Smooth muscle: None, only sarcolemmal pits

sarcoplasmic reticulum

Skeletal muscle: developed, triplet, junction of light and dark bands

Myocardium: sparse, doublet, Z-line level

Smooth muscle: underdeveloped

gap junction

Skeletal muscle: none

Myocardium: adhesive zones, desmosomes, gap junctions, intercalary discs

Smooth muscle: gap junction

Other special structures

Skeletal muscle: sarcoplasmic reticulum

Myocardium: intercalary disk

Smooth muscle: dense bodies, dense macules