Muscular System Definition and Types

Introduction:

• 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
 

Introduction:

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

Explanation
 

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.
  
  
   

FAQs

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

• 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?
Ans.

• 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.
Ans.
a) Skeletal muscle
b) Smooth muscle
c) Cardiac muscle