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Structure of Skeletal Muscle

Introduction

  • The basic unit of the skeletal muscle is the syncytial muscle fiber.
  • Skeletal muscles are also known as striated or striped or voluntary muscles.
  • These are attached to bones via tendons and are responsible for skeletal movements.
  • Central Nervous System (CNS) controls the skeletal muscles, therefore, is under conscious, or voluntary control.
  • These muscle fibers are striated, having light(Isotropic or I-band) and dark(Anisotropic or A-band) bands.
  • Special arrangement of proteinaceous myofilaments/myofibrils is responsible for striations.

Explanation
 

skeletal-muscle
 

  • An individual skeletal muscle may be made up of hundreds, or even thousands, of muscle fibers which are cylindrical and are bundled together in a connective tissue covering.
  • Epimysium is a connective tissue which surrounds each muscle.
  • Outside to epimysium another connective tissue is present called fascia, which surrounds and separates the muscles.
  • Each compartment of muscles contains a bundle of muscle fibers called a fasciculus.
  • Fasciculus is surrounded by a layer of connective tissue called the perimysium.
  • Within the fasciculus, individual muscle cells are present which are surrounded by connective tissue called the endomysium.

Myofibril

  • The basic unit of the skeletal muscle is the muscle fiber, which many nuclei i.e. Syncytial.
  • Each muscle fiber is cylindrical and is covered by a cell membrane called sarcolemma.
  • Each muscle fiber has parallelly arranged myofibrils/myofilaments responsible for striations i.e.,presence of light(I) and dark(A) bands.
  • The light bands or I-band or Isotropic band contains actin, whereas the dark band or A-band or Anisotropic band contains myosin.
  • Both actin and myosin are parallel to each other and are arranged as rod-like structures and also to the longitudinal axis of the myofibrils.
  • Based on the thickness,the filaments are categorised as thin and thick filaments.Actin filaments are thinner in comparison to the myosin filaments.
  • In the centre of each ‘I’ band is an elastic fibre known as ‘Z’ line.
  • The thin filaments(Actin filaments) are firmly attached to the ‘Z’ line.
  • By a thin fibrous membrane called ‘M’ line, the thick filaments in the ‘A’ band are held together in the middle of the band.
  • Alternative arrangements of the ‘A’ and ‘I’ bands are present throughout the length of the myofibrils.
  • The functional unit of contraction called a sarcomere is defined as the portion of the myofibril between two successive ‘Z’ lines.
  • ‘H’ zone is defined as the central part of thick filament which is not overlapped by thin filaments.
     

Myofibril

 

Related Topics to Structure of Skeletal Muscle in Biology

 

NCERT Biology Class 11 Chapters

The Living World Biological Classification Plant Kingdom
Animal Kingdom Morphology of Flowering Plants Anatomy of Flowering Plants
Structural Organization in Animals Cells: The Unit of Life Biomolecules
Cell Cycle and Division Transport in Plants Mineral Nutrition
Photosynthesis in Higher Plants Respiration in Plants Plant Growth and Development
Digestion and Absorption Breathing and Exchange of Gases Body Fluids and Circulation
Excretory Products and their Elimination Locomotion and Movement Neural Control and Coordination
Chemical Coordination and Integration
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