Muscular Tissue

Muscular Tissue is the type of tissue that is present in the group metazoans, for the movement and locomotion. Metazoans are the multicellular organisms belongs to the kingdom Animalia whose cells differentiates to form tissues and organ. Muscular tissue provides mobility to the body organs of the organism. Muscle tissues are of three types namely striated, unstriated and cardiac muscle which are structurally and functionally different from each other.

The central role of muscle tissue is Contraction through which a muscle show the property of muscle contraction and relaxation. Myogenesis is a process occurs at the time of embryonic development which forms the muscle tissue.

Content: Muscular Tissue

  1. Definition of Muscular Tissue
  2. Types of Muscular Tissue
  3. Comparison chart of striated, unstriated and cardiac muscle

Definition of Muscular Tissue

The muscular tissue can define as the special types of white and red muscle tissues. The cells of the muscle tissue refer to as Muscle cell. Muscular tissue originates from the embryonic mesoderm. It contributes almost half of the body weight. The cells of muscular tissue are long and narrow refers to “Muscle fibres”. Its main function is to provide contractility or mobility.

Types of Muscular Tissue

Muscular tissues are of three types:

  1. Striated muscle tissue
  2. Unstriated muscle tissue
  3. Cardiac muscle tissuetypes of muscle tissue

Striated Muscle

Also refers as “Voluntary muscle” as its functioning is under the control of a central and peripheral nervous system. Striated muscles contribute about 40% of the body weight. These attach to the bones by the skeletal muscle through both the ends. There are many stripes (bands) present on the surface that’s why is also refers to as “striped muscle”.

Structure

Striated muscle tissue has a complex structure consisting of many elements.

Arrangement: These are found in bundles that are made of few muscle fibres refer as “fasciculi”. All the fasiculies attach together by the connective tissue, known as “perimycium”. The outer covering of the muscle bundle or fasciculi is made of connective tissues, known as “epimycium”.

Size: Its length varies from 1-4µm and diameter from 10-80µm.

Shape: Striated muscle is thread-like, elongated, cylindrical and unbranched.

Elements:

Sarcolemma: It is the transparent membrane that surrounds the muscle fibre. It has two layers:

  • The inner plasma membrane of muscle fibres
  • Outer fibres of the basement membrane.

Sarcoplasm: The cytoplasm of muscle fibre refers to “sarcoplasm”. Inside the sarcoplasm, there are many nuclei are present which are flat and oval in shape. Therefore striated muscles are multinucleated or can be known as “syncytial”.

There are some other structures also present inside the sarcoplasm like certain enzymes, sarcosomes (mitochondria), sarcoplasmal reticulum (endoplasmic reticulum), Golgi apparatus, glycogen and fat molecules etc.

Inside the sarcoplasm, there are three soluble proteins:

  • Myoalbumin
  • Myogen
  • Myoglobin

Sarcostyles: These also refer as myofibrils which are the long contractile filaments. Its main function is muscle contraction and relaxation.

Functions: Striated muscle helps in the body movement and also maintains body posture.
striated muscle

Unstriated Muscle

Also refers as “Involuntary muscles” as its functioning is independent i.e. does not require the control of a central and peripheral nervous system. Unstriated muscles also refer to “Smooth and Visceral muscles” because it is mainly found in the internal organs like the alimentary canal, uterus etc.

Structure

Its structure is very simple.

Arrangement: Unstriated muscles also arranged in the form of bundles, are made of muscle fibres. Inside the muscle fibre, there is a single, large, oval nucleus is present. Muscle fluid that surrounds the nucleus is called “sarcoplasm”. In the sarcoplasm, there are several filaments present that are arranged parallel and known as “myofibrils”. The filaments that are present are namely:

  • Actin filament
  • Myosin filament

These two filaments do neither show definite arrangement nor dark and light band patterns.

Size: Length ranges from 50-200µm and diameter from 2-5µm.

Shape: These muscles are long, thin, spindle-shaped and pointed at both the ends.

Types: It is of two types

  1. Helical smooth muscle
  2. Paramyosin muscles

Helical smooth muscles: In helical smooth muscle, the myofibrils are arranged helically and do not have a definite structure.
Example: This type of muscle tissue present in the species of phylum Annelida and Mollusca.

Paramyosin smooth muscles: In paramyosin smooth muscle actin and myosin filament, tropomyosin-B filaments are present in addition to myofibrils. Paramyosin occurs in the form of ribbons. It has a diameter of 15-150µm.
Example: This type of muscle tissue present in the species of phylum Mollusca.

Function: Unstriated smooth muscle plays a key role in the propulsion of food through the alimentary canal and also helps in the contraction and relaxation of muscles.
unstriated muscle

Cardiac Muscle

These are primarily found in the cardiac walls of the heart. Its structure is more or less very similar to the striated muscle. But its functioning is similar to the unstriated muscle that includes involuntary movements.

 Structure

It founds in a bundle having branched muscle fibres surrounds by sarcolemma. The muscle fibres bind to each other through septa and form a contractile network. In the cytoplasm, there are several integrated discs present in the irregular form. Numerous nuclei are also present inside the cytoplasm which are flat and oval in shape.

Size: Length ranges from 80-100µm and diameter from 15-20µm.

Shape: These are long, thick, truncated and branched.

Functions: Its main function is to pump blood throughout the body.
cardiac muscle

Comparison chart of striated, unstriated and cardiac muscle

PropertiesStriated muscleUnstriated muscleCardiac muscle
Also known as“Voluntary muscle”“Involuntary muscle”Cardiac muscle
LocationFound attached to bones Found in internal organs like: stomach, liver, gall bladder, alimentary canal, urinary bladder etcFound in the wall of heart
FunctioningPerforms voluntary movementsPerforms involuntary movementsPerforms involuntary movements
Control of muscle tissueControlled by central and peripheral nervous systemControlled by autonomic nervous systemControlled by sympathetic and para-sympathetic nervous system
SarcolemmaThickThinThin
NucleusMultinucleateUninucleateUni or Bi-nucleate
Presence of bands or striationsPresentAbsentPresent
BranchingBranchedUnbranchedBranched
Intercalated discAbsentAbsentPresent

Muscle tissues are composed of many elements like protein, water, fats, carbohydrates, pigments, enzymes etc. The main characteristic feature of muscle is that it converts chemical energy into the mechanical energy from the beginning of muscle contraction to the end of muscle relaxation.

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