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Muscular System

Muscular System Definition and Types


  • Muscles are the tissues that are responsible for the movement of the body, maintaining posture, and circulating blood throughout the body.
  • Around 40-50% of body weight is made up of muscles.
  • The muscular system in vertebrates is controlled by the nervous system, as the brain, nerves, and skeletal muscles work together to cause movement; collectively known as the neuromuscular system.
  • Characteristics of muscles-
    - Excitability
    - Contractility
    - Extensibility
    - Elasticity
  • Largest muscle- Gluteus maximus (the muscle that makes up your bottom)
  • Smallest muscle- Stapedius(deep inside your ear)

This concept includes-

  • Types of muscles
  • Structure of Skeletal Muscle
  • Contractile Proteins
  • Mechanism of muscle contraction
  • Laws related to muscle contraction
  • Cori’s Cycle
  • Disorders related to muscle contraction

Types of Muscles


There are 3 types of muscles present in the human body-



i. Skeletal Muscle

  • 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.
  • The peripheral portion of the central nervous system (CNS) controls the skeletal muscles, therefore, is under conscious, or voluntary control.
  • The basic unit of the skeletal muscle is the muscle fibres, which have many nuclei i.e., Syncytial.
  • Each muscle fibre is cylindrical and is covered by a cell membrane called sarcolemma.
  • These muscle fibres are striated, having light (I) and dark (A) bands.
  • Two muscle proteins or proteinaceous myofilaments/myofibrils responsible for striations are:
    a) Actin
    b) Myosin
  • The bundles of myofibrils are surrounded by a sheath of fibrous connective tissue.


ii. Smooth Muscle

  • These are also known as Visceral muscles, as these are located in the inner walls of hollow visceral organs of the body, like the alimentary canal, bladder, reproductive tract, etc.
  • Being without striation and hence smooth in appearance, these are called smooth muscles (nonstriated muscles)
  • These muscles are under the control of the Autonomic Nervous System(ANS) and hence cannot be controlled consciously. Therefore known as involuntary muscles.
  • They assist in various functions like peristalsis and transportation of gametes through the genital tract etc.
  • The non-striated (smooth) muscle cell is spindle-shaped and is uninucleated.
  • These muscles are of two types-

1) Single unit muscles-

  • Group of smooth muscles that shows synchronous contraction and relaxation are said to be single unit muscles.
  • Example- Muscles of major physiological tracts like the gastrointestinal tract.

2) Multi-unit muscles-

  • Muscles that function independently of one another.
  • Example- Arrector pili and Iridial muscles.


iii. Cardiac Muscle

  • Cardiac muscles are the muscles of the Myocardium (muscular layer of the heart wall).
  • Cardiac muscles are also under the control of the autonomic nervous system and hence are considered as involuntary muscles.
  • Cardiac muscle cells are cylindrical in shape and are uninucleated.
  • Many cardiac muscle cells assemble in a branching pattern to form a cardiac muscle and based on appearance, cardiac muscles are considered as striated.
  • Cell junctions of cardiac muscle cells fuse the plasma membranes and make the muscle cells stick together.
  • There are specialized communication junctions(gap junctions) called intercalated discs at the fusion points of muscle cells which allow the cells to contract as a unit.
  • Cardiac muscle fibres show rhythmic contraction and relaxation i.e, when one cell receives a signal to contract, the impulse travels to its neighbouring cells through intercalated discs and they are also stimulated to contract.



Q1 A complete coordinated activity of muscular _______, _________ systems leads to locomotion.

Skeletal systems and neural systems are hence termed neuromuscular systems which are a must requirement for locomotion to take place.

Q2 Define the term muscles. Give the characteristics of muscles.

  • Muscles are the tissues that are responsible for the movement of the body, maintaining posture, and circulating blood throughout the body.
  • Characteristics of muscles-
    - Excitability
    - Contractility
    - Extensibility
    - Elasticity

Q3 What are the largest and the smallest muscles present in the human body?

  • Largest muscle- Gluteus maximus (the muscle that makes up your bottom)
  • Smallest muscle- Stapedius(deep inside your ear)

Q4 Name the types of muscles present in the human body.

a) Skeletal muscle
b) Smooth muscle
c) Cardiac muscle

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