Muscle system

Study of muscles is called mycology.

Muscle system consist muscle fibers as smallest unit.

Muscle fiber are long, thread like cells.

There are 3 types of muscles :-

Striated muscles

Smooth muscles

Cardiac muscles

1.     They are associated with bones (skeletal system) and causes limbs movement and locomotion.

2.     As they are linked with skeleton, so called skeletal muscles.

3.     Their contraction occurs by animals will, so called voluntary muscles.

4.     They easily get fatigued (easily loose their activity).

5.     A striated muscle cell is cylindrical, multinucleated with striations (strips of light & dark bands).

1.     They are not associated with skeleton. They occurs in internal organs and responsible for their movements.

2.     As they are linked with internal organs, so called visceral muscles.

3.     Their contraction is not under animal will, so called involuntary muscles.

4.     They slowly fatigued (much later than striated muscles.

5.     A smooth muscle cell is spindle shaped, uni nucleate without striations (strips).  

1.     They are also hot associated with skeleton. They occur in heart movements.

2.     As they are linked with heart only, so called cardiac muscles.

3.     They are also involuntary.

4.     They never get fatigued (never loose their activity)

5.     A cardiac muscle cell is cylindrical, uni nucleated, striated (with strips) and branched.

Striated muscles in detail :-

Striated muscle system has fibers which are cylindrical, multinucleated and with strips. These fibers are bounded by    as cell membrane and also filled with a fluid called sarcoplasm which is like cytoplasm  


Structure of striated muscle of vertebrate.

1.     A band

2.     I band

A band

I band

1.     Dark band of striated muscle fiber.

2.     It is thick.

3.     Its central part is called H zone.

4.     Its properties differ at different directions. So it is anisotropic.

5.     It is formed of myosin & action filaments.

1.     Light band of striated muscle fiber.

2.     It is thin.

3.     Its central part is called Z line.

4.     Its properties are same at every direction, so it is isotropic.

5.     It is formed of only actin filaments.

3.     H zone :- it is the central zone of a (dark) band. It is slightly light then the remaining part of a band.

4.     Z line :- it is the central line of I (light band). Two successive Z lines forms a unit called sarcomere.

5.     Sarcomere :- it is the space between 2 successive Z lines. It encloses I and A band both :

Sarcomere had 2 types of filaments :-

      i.        Actin ( primary filaments )

     ii.        Myosin (   secondary filaments )



1.     They are also called primary myofilaments.

2.     They are present in both A and I band.

3.     They are thin & have a size of 50 A (1 angstrom = 10-10 m)

4.     Head is absent.

1.     They are also called secondary myofilaments.

2.     They are present in only A -  band.

3.     They are thick and have a size of 100 Ao.

4.     Heat is present.


Actin structure

Myosin structure

Actin balls are connected to form a single actin filament and these 2 actin filaments are wraped on each other in a helical nammer.

Two filaments of tropomyosin also rear with these actin filament, and a complex troponin is present on tropomyosin at regular intervals.

It is a filament made up of many in  ero myosins and it has 2 important parts. Head and tail. Each head has 2 sites, one for actin attachment & other for ATP.

Structure of actin and myosin :- picture






Mechanism of muscle contraction:-

(sliding filament theory)

In muscle contraction myosin filaments comes in contact with thin actin filaments and rotate on them. This pulls the actin filaments toward the middle of sarcomere. Due to which :-

Z lines become closer to each other, sarcomere becomes shorter in length, H zone narrows & I band becomes narrow. So, at contraction muscle becomes shorter than before but its volume remains same.

When muscular contraction  occur :-

1.     When a muscle fiber is at rest, then myosin binding site of actin filaments is blocked by troponysinn so muscle cannot contract.

2.     But when, myosin binding site is exposed on actin filament, then muscle can contract freely.

Cori’s cycle :-

1.     Lactic acid formed in muscle is carried in blood and then to liver.

2.     In liver cells it is converted into glycogen.

3.     Then it goes to blood & converted into glucose.

4.     Then this glucose is reconverted into glycogen in muscles.

& cycle repeats. This lactic acid--> glycogen --> glucose -->glycogen   cycle is Cori’s cycle.

Cori’s cycle

Energy for muscle contraction :-

  1. Energy is utilized in the form of ATP in muscle contraction. Which is provided by myosin.


  1. Creatine phosphate Equation  

When ATP is converted into ACP then to reform ATP, extra phosphate is provided by creatine.

  1. In muscles, glycogen is stored for energy requirements & these also provide energy for their. Contraction.


Muscle fatigue:-

The process by which muscle looses its ability to contract due to prolonged contraction of muscle ex-  at exercise fatigue.

When ATP supply decreases, muscle become fatigued.

But when we breathe fast, then extra oxygen will supply more energy & muscle below free from fatigue.

Rigor mortis :- muscles need ATP to contract as well as to relax. But when animal dies, muscles have no ATP, as they loose the ability to relax as well as to contract. So, they remain in same position as they are during death. So, this rigidity of body after is called rigor mortis.

Related Keywords
11    PMT    Biology    Locomotion and Movement    Muscle system