Striated skeleton

Striated muscles are present in the limbs, body wall, tongue, pharynx, and beginning of the oesophagus. it is long and cylindrical, the fibres are unbranched, multinucleated which is bounded by sarcolemma.

features

1. Nerve supply from cranial nerve
2. Blood supply is abundant
3. Very rapid contraction
4. They soon get fatigued
5. Voluntary

Non-striated muscle

Oesophagus, urogenital tract, urinary bladder, blood vessels, and the iris of the eye. are all non-striated muscle

Feature

1. Spindle-shaped
2. Fibre unbranched, unnucleated, and bounded by plasma lemma
3. No intercalated disc
4. Nerve supply from the autonomic nervous system
5. Blood supply is scanty
6. Slow contraction
7. They do not get fatigued.
8. Involuntary

Cardiac Muscle

wall of heart

Feature

1. Short and cylindrical
2. fibres branched
3. uninucleate
4. Bounded by plasma lemma
5. Nerve supply from the autonomic nervous system
6. Blood supply abundant

Types of fibres

1. • Type I(Slow )Fibres

These are red in colour because of a large amount of myoglobin. The fibres are rich in mitochondria and oxidative enzymes, but poor in phosphorylases.

1. • Type II ( Fast ) Fibres

These are paler ( White ) in colour because of myoglobin. The fibres are rich in glycogen and phosphorylase, but poor in mitochondria and oxidative enzymes.

1. • Intermediate Fibres

Represent a variant of type II (fast) fibres which are relatively resistant to fatigue, although less than type I(slow) Fibre(Burke,etal,1973)

Structure of myofibril

Myofibril consists of a no. Of two alternating bands which are also called sections or disks.
The two bands are –

1. light band or I band also called thick filament
2. Dark band or A band also called thin filament

Sarcomere

It is defined as the structural and functional unit of a muscle.
It is a basic contractile unit of muscle
Each myofibril contains many sarcomeres arranged in series throughout the length.
Sarcomere consist of many thread-like structure called myofilaments

Myofilament

• • Actin filament

Thin filament

They are made up of

• • Head ( ATP Binding sites )
  • Tail
• Myosin filament Thick filament

  They are made up of three
  component

  • Tropomyosin
  • F-actin
  • Troponin

Muscle Contraction

It includes three stages

• Excitation–contraction coupling

there are the following steps in Excitation –contraction coupling :

• • • Excitation of muscle fibres by impulses passing through motor nerve and neuromuscular junction
    • Generation of action potential in muscle fibre
    • Entrance of action potential in cisternae sarcoplasmic reticulum
    • Contraction of muscle fibres.
    • Movement of calcium ions towards actin filaments
    • Release of calcium ions from cisternae

• Roles of troponin and tropomyosin

• • • Ca+ released Ca+ binds to troponin causing it to change shape. Shape change releases it from tropomyosin(blocker)
    • Tropomyosin moves to reveal the binding site on actin (thin filament )

• Sliding mechanism

Release of large amounts of calcium ions from cisternae of L tubules.
Binding of calcium ions with troponin it lead to
change in the position of troponin then
pulling of tropomyosin molecules away from F-actin which leads to
exposure of active sites of F- actin and
attachment of myosin head to actin.
Power stroke – then tilting of myosin head and dragging of actin filament. Detachment of myosin head and returning to original position then again
attachment of myosin head to new active sites of f- actin and dragging of actin filament – repetition of these actions.
Movement of actin filament of both sides towards each other and formation of actin -myosin complex
this lead to
contraction of muscles