Structure of the skeletal muscle
The basic structural unit is the muscle fiber'.
Developmental stages[edit | edit source]
- 'Myoblast - mononuclear formation; myoblasts fuse
- 'Myotubule - a multinucleated structure, the nuclei are arranged in an axis
- 'Muscle fiber - multinucleated formation, nuclei on the periphery
Description[edit | edit source]
Nuclei are oval, located on the periphery just below the surface. The plasma membrane, here called sarcolemma', forms tubular invaginations - T-tubules. On the surface of the fiber there is a complex of lamina basalis and networks of reticular fibers = endomysium; the entire complex follows the sarcolemma into the lumina of T-tubules. The cytoplasm, sarcoplasm, is filled with longitudinally arranged myofibrils, which form the contractile apparatus of the cell.
- Arrangement of myofibrils
- long. cross section - noticeable transverse striations
- transverse section - transverse striations cannot be observed, we observe bundles of myofibrils separated by a layer of sarcoplasm, the so-called Conheim fields
Mitochondria are located between myofibrils (long axes parallel), have a rod-like shape and are bulky. In the sarcoplasm we also find polysomes, gER, GK, glycogen stores.
T-tubules of the sarcolemma diverge perpendicularly at the interface of the light (I) and dark (A) myofibril strips. Forms a mesh, meshes surround each myofibril.
The smooth endoplasmic reticulum - the sarcoplasmic reticulum - is highly developed. It represents a reservoir of calcium ions, which are key to the initiation and progression of myofibril contraction. It has the character of tubules. The tubules form a network around the myofibrils. At the interface of the A and I strips, the myofibrils end by opening into a wide terminal cistern (a ring surrounding the entire myofibril). The cisterna adjoins the side away from the opening of the reticulum tubules to the perpendicular T-tubule of the sarcolemma. Each T-tubule has 2 cisterns (one on each side) = a complex structure (cisterna-T-tubule-cisterna) forms a triad. Among the sarcoplasm. close relationship between the reticulum and the membrane of the T-tubule → the formation of specialized districts - couplings. These are important in the process of coupling excitation and contraction. The end of the muscle fiber is conical.
At the transition in the tendon, the sarcolemma forms a deep intussusception ← penetration of bundles collagen fibers of the tendon + anchoring in the basement membrane.
Types of muscle fibers[edit | edit source]
Red fibers contain many myoglobinu = oxygen-binding protein (similar to hemoglobin), cytochrome → red color of muscle tissue. The filaments work continuously for a longer period of time. Energy by oxidative phosphorylation → many mitochondria. They contract more slowly, but persistently.
White fibers have low content of myoglobin, cytochrome, few mitochondria. They are more voluminous, capable of rapid contraction, but not sustained. It is divided into subtypes A (fast, moderately fatigable), B and C (very fast, quickly fatigable). [1]
Intermediate fibers - intermediate type
Building muscle[edit | edit source]
Skeletal muscle tissue is organized into muscles. Muscles are attached to skeletal components by means of fibrous structures. With their contractions, they ensure movement = active component of the locomotor apparatus'.
- Muscle fiber - covered with endomysium (lamina basalis + network of ret. fibers). A network of fibers embedded in the structures of the lamina → a mediator of the transmission of forces created during contraction to the fibrous structures of the muscle. The forces developed by the contraction of the individual fibers are added up. The resulting force acts in the direction of the axis of the tendon attachment. Richly vascularized.
- Fiber bundles - wrapped in perimysium = fibrous layer reinforced by networks of collagen fibers. Between the bundles there are vascular and nerve networks'. The perimysium is plastic, allowing the bundles to move relative to each other during muscle activity.
- Muscle - covered by epimysium = a layer of dense collagenous tissue'.
Links[edit | edit source]
Related Articles[edit | edit source]
References[edit | edit source]
- DANIELA, Jarkovská – JINDŘICH, Martínek. Histologie. 1. 1. edition. Praha : Karolinum, 1997. ISBN 80-7184-388-1.
