STRUCTURE OF A MYOFIBRIL -

1. The dark bands of the myofibril are termed the A-bands (Anisotropic bands).
2. Each A-band has at its middle a light zone called H-zone (Henson's line).
3. The light bands are also called I-bands (Isotropic bands).
4. Each I-band has at its centre a dark membrane termed the Krause's membrane or Dobie's line or Z disc or Z-line (Zwischenscheibe line).
5. The sarcolemma is invaginated to form T -tubules (Transverse tubules).
6. The T-tubules are present at the level of Z-line.
7. The T-tubules form a simple mechanism of transportation of nuirients and carry the signals for contraction of the myofibrils from the sarcolemma to the interior.
8. The part of the myofibril between two successive Z-lines is called sarcomere.
9. Therefore, the sarcomere comprises A-band and half of each adjacent I-band.
10. A sarcomere is about 2 to 3 mm long.
11. The sarcomere is the functional unit of contractile system in muscle. In fact each sarcomere is a bundle of primary and secondary filaments.

(i)       Primary Filaments (= Myosin Filaments). The primary filaments are thicker and confined to the A-bands only.

They are free at both the ends. They are composed of myosin (protein) and bear minute projections called cross- bridges of the protein meromyosin.

(ii)      Secondary Filaments (= Actin Filaments). The secondary filaments are thinner and occur in I-bands, but extend for some distance into the A-bands between the primary filaments. This partial over lapping of the primary fila- ments by the secondary filaments gives dark appearance to the Abands. The secondary filaments are composed of the proteins actin, tropomysin and troponin. They are attached to the Z-lines by one end and are free at the other end. The secondary filaments are more numerous than the primary filaments. Six secondary filaments surround each primary filament. "

1. The major component of muscle is water. Potassium is the most abundant mineral element in muscle.
2. Other minerals such as sodium, calcium, phosphorus and magnesium are present only in traces.
3. Muscles store glycogen. They have oxygen carrying pigment myoglobin or "muscle haemoglobin".
4. Muscles also contain ATP, phosphocreatine, creatine, urea, etc.

Posted Date: 10/1/2012 3:52:54 AM | Location : United States

Ask an Expert

Related Discussions:- Structure of myofibril, Assignment Help, Ask Question on Structure of myofibril, Get Answer, Expert's Help, Structure of myofibril Discussions

Write discussion on Structure of myofibril
Your posts are moderated

Write your message here..

Related Questions

The Integumentary system, what are some technologys used in the integumenta... what are some technologys used in the integumentaryy systems

Fusarium toxins, Another important genus of mycotoxin producers is Fusarium... Another important genus of mycotoxin producers is Fusarium, many species of which produce members of the trichothecene family of mold metabolites like deoxynivalenol, neosolaniol a

Amoeba, Place a slide of Amoeba (common species is A. proteus) under tlie l... Place a slide of Amoeba (common species is A. proteus) under tlie lnicroscope and focus it under low power (5x x 5x), and observe it carefully. Amoeba looks like an irregular colou

Photosynthesis, What are periplastidial spaces? What are periplastidial spaces?

From molecules to the first cell, From Molecules to the First Cell The ... From Molecules to the First Cell The prebiotic conditions on the earth in all probability were volcanic eruptions, lightning and heavy rains. There was no trace of free oxygen

Carbohydrate is an organic compound , The Carbohydrate sets are covalently ... The Carbohydrate sets are covalently attached to various variant proteins to form glycoproteins. Carbohydrates are a shorter percentage of the weight of glycoproteins than of prote

Define role in growth and cellular differentiation, Define Role in growth a... Define Role in growth and cellular Differentiation? The growth and differentiation of epithelial cells throughout the body are especially affected by vitamin A deficiency.  In

Auxins, Auxins Auxins are plant growth substances. The term Auxin us... Auxins Auxins are plant growth substances. The term Auxin usually refers to a chemical compound called Indole Acetic Acid (IAA), which is the major natural auxin. In plan

Biochemical reactions - nitrate assimilation, Biochemical Reactions - Nitra... Biochemical Reactions - Nitrate Assimilation Nitrate is the most readily available and preferred source of nitrogen for growth. Assimilatory reduction of NO - 3 to NH 3 is

Define fish as a rich source of protein, Define Fish as a rich source of pr... Define Fish as a rich source of protein? The edible portion is skeletal muscles of the body. Even though the skeletal muscles of different animals are basically similar, fish s