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

voluntary muscles, striated muscles

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

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

involuntary muscles

epimysium

perimysium

endomysium

Support, connection, nutrition, functional regulation

Light mirror structure

Structural and functional unit of skeletal muscle fiber - sarcomere

Ultrastructure

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.

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.

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

Irregular short cylindrical shape, branched and interconnected into a network

Cells are connected by intercalary disks and stain darker

1-2 nuclei, centered, oval

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

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.

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

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.

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.

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.

The ratio of thick and thin myofilaments is 1:12

Thick myofilament

Thin myofilaments

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.

Underdeveloped, sparsely tubular

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

Voluntary muscles: skeletal muscles

Involuntary muscles: cardiac muscle, smooth muscle

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

Myocardium: short columnar with branched anastomoses

Smooth muscle: fusiform, unbranched

Skeletal muscle: obvious

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

Smooth muscle: none

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

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

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

Smooth muscle: None, only sarcolemmal pits

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

Myocardium: sparse, doublet, Z-line level

Smooth muscle: underdeveloped

Skeletal muscle: none

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

Smooth muscle: gap junction

Skeletal muscle: sarcoplasmic reticulum

Myocardium: intercalary disc

Smooth muscle: dense bodies, dense macules