Structure of a skeletal muscle. (Perimysium labeled at top center.)

Sheath of connective tissue that groups muscle fibers into bundles or fascicles.

- Perimysium

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Muscle fascicle

Structure of a skeletal muscle. (Fascicle labeled at bottom right.)

A muscle fascicle is a bundle of skeletal muscle fibers surrounded by perimysium, a type of connective tissue.

Skeletal muscle

Skeletal muscles (commonly referred to as muscles) are organs of the vertebrate muscular system that are mostly attached by tendons to bones of the skeleton.

A top-down view of skeletal muscle
3D rendering of a skeletal muscle fiber
Muscle types by fiber arrangement
Types of pennate muscle. A – unipennate; B – bipennate; 
C – multipennate
ATPase staining of a muscle cross section. Type II fibers are dark, due to the alkaline pH of the preparation. In this example, the size of the type II fibers is considerably less than the type I fibers due to denervation atrophy.
Structure of muscle fibre showing a sarcomere under electron microscope with schematic explanation.
Diagram of sarcoplasmic reticulum with terminal cisternae and T-tubules.
Human embryo showing somites labelled as primitive segments.
When a sarcomere contracts, the Z lines move closer together, and the I band becomes smaller. The A band stays the same width. At full contraction, the thin and thick filaments overlap.
Contraction in more detail
(a) Some ATP is stored in a resting muscle. As contraction starts, it is used up in seconds. More ATP is generated from creatine phosphate for about 15 seconds. (b) Each glucose molecule produces two ATP and two molecules of pyruvic acid, which can be used in aerobic respiration or converted to lactic acid. If oxygen is not available, pyruvic acid is converted to lactic acid, which may contribute to muscle fatigue. This occurs during strenuous exercise when high amounts of energy are needed but oxygen cannot be sufficiently delivered to muscle. (c) Aerobic respiration is the breakdown of glucose in the presence of oxygen (O2) to produce carbon dioxide, water, and ATP. Approximately 95 percent of the ATP required for resting or moderately active muscles is provided by aerobic respiration, which takes place in mitochondria.
Exercise-induced signaling pathways in skeletal muscle that determine specialized characteristics of slow- and fast-twitch muscle fibers
Jogging is one form of aerobic exercise.
In muscular dystrophy, the affected tissues become disorganized and the concentration of dystrophin (green) is greatly reduced.
Prisoner of war exhibiting muscle loss as a result of malnutrition.

Deep fascia specialises within muscles to enclose each muscle fiber as endomysium; each muscle fascicle as perimysium, and each individual muscle as epimysium.

Lateral force transmission in skeletal muscle

Extracellular matrix .

Structure of a skeletal muscle.
Shear displacements between two adjacent muscle fibers showing the endomysium in its (a) unconstrained state and (b) after shearing.
Attachment of the perimysium to the endomysium at the perimysial junctional plates (PJPs).

Skeletal muscle is a complex biological material that is composed of muscle fibers and an ECM consisting of the epimysium, perimysium, and endomysium.


Fibrous tissue envelope that surrounds skeletal muscle.

Structure of a skeletal muscle (epimysium labeled at bottom center)

It is continuous with fascia and other connective tissue wrappings of muscle including the endomysium and perimysium.

Deep fascia

Fascia, a layer of dense connective tissue that can surround individual muscles and groups of muscles to separate into fascial compartments.

The rectus sheath (extensive vertical darker gray at left), an example of a fascia

The deep fasciae envelop all bone (periosteum and endosteum); cartilage (perichondrium), and blood vessels (tunica externa) and become specialized in muscles (epimysium, perimysium, and endomysium) and nerves (epineurium, perineurium, and endoneurium).


Type of chronic inflammation of the muscles (inflammatory myopathy) related to dermatomyositis and inclusion body myositis.

Micrograph of polymyositis. Muscle biopsy. H&E stain.

The inflammation of polymyositis is mainly found in the endomysial layer of skeletal muscle, whereas dermatomyositis is characterized primarily by inflammation of the perimysial layer of skeletal muscles.


Protective sheath that surrounds a nerve fascicle.

Transverse section of human tibial nerve (perineurium labeled at upper right)

This grouping structure is analogous to the muscular organization system of epimysium, perimysium and endomysium.

Pennate muscle

Type of skeletal muscle with fascicles that attach obliquely (in a slanting position) to its tendon.

Muscles of the iliac and anterior femoral regions. (Rectus femoris highlighted in red.)
Figure 1 Pennate muscle fiber arrangements: A, unipennate; B, bipennate; C, multipennate. Blue: anatomical cross-section. Green: physiological cross-section.
Pennation angle
Figure 2 Architectural gear ratio

In skeletal muscle tissue, 10-100 endomysium-sheathed muscle fibers are organized into perimysium-wrapped bundles known as fascicles.

Muscle tissue

Muscle tissues are soft tissues that make up the different types of muscles in most animals, and give the ability of muscles to contract.

The body contains three types of muscle tissue: (a) skeletal muscle, (b) smooth muscle, and (c) cardiac muscle. (Same magnification)
Three distinct types of muscle (L to R): Smooth (non-striated) muscle in internal organs, cardiac or heart muscle, and skeletal muscle.
Striated skeletal muscle cells in microscopic view. The myofibers are the straight vertical bands; the horizontal striations (lighter and darker bands) that are a visible result from differences in composition and density along the fibrils within the cells. The cigar-like dark patches beside the myofibers are muscle-cell nuclei.
A chicken embryo, showing the paraxial mesoderm on both sides of the neural fold. The anterior (forward) portion has begun to form somites (labeled "primitive segments").

Other tissues in skeletal muscle include tendons and perimysium.

Tenon's capsule

Thin membrane which envelops the eyeball from the optic nerve to the corneal limbus, separating it from the orbital fat and forming a socket in which it moves.

The right eye in sagittal section, showing Tenon's capsule (semidiagrammatic).

The sheaths on the recti muscles are gradually lost in the perimysium, but they give off important expansions.