GENERAL ANATOMY OF MUSCLES

GENERAL ANATOMY OF  MUSCLE

1.Derivation of Name 

Muscle (Latin Mus= mouse) are so named because many of them resemble a mouse, with their tendons representing the tail.

Definition

•Muscle is a contractile tissue which brings about movements.

•Muscles can be regarded as motors of the body.

•Other contractile cells:

Myofibroblasts - seen in regenerating connective tissue.

Myoepitheliocytes - associated with glands.

BASIC PROPERTIES

•IRRITABILITY:

–  Sensitive to stimuli

•CONTRACTILITY:

–  When stimulated, the contracts lengthwise  leading to its shortening

•EXTENSIBILITY:

–  Once stimuli removed, the muscle fibers  return to their original length.

•ELASTICITY:

–  Muscle assumes a desired shape.

Types of muscles:

There  are  three  types of muscles :

1.Skeletal muscles

2.Smooth muscles

3.Cardiac muscles

Skeletal muscle tissue

•Attached to skeleton

•Cross-striated
•Voluntarily controlled
•Cells are cylindrical and multinucleated
•They respond quickly but fatigue easily

Cardiac muscle tissue

•Makes up myocardium of heart

•Unconsciously (involuntarily) controlled

•Microscopically appears striated

•Cells are short, branching & have a single nucleus

•Cells connect to each other at intercalated discs

Smooth (visceral) muscle tissue

•Makes up walls of organs & blood vessels

•Tissue is non-striated & involuntary

•Cells are short, spindle-shaped & have a single  nucleus

•Tissue is extremely extensible, while still retaining  ability to contract

Skeletal muscles

Synonyms

1.Striped muscles

2.Striated muscles

3.Somatic muscles

4.Voluntary muscles

Parts of a skeletal muscle

A. Two ends 

1.Origin is one end of the muscle which remains fixed during its contraction. 

2.Insertion is the other end which moves during its contraction.


In the limb muscles, origin is usually proximal to insertion.

B. Two parts

1.Fleshy part is contractile, and is

called the ‘belly’.

2.Fibrous part is non- contractile and inelastic. When cord-like or rope-like, it is called ‘tendon’ ; when flattened it is called      ‘aponeurosis’.   

Structure of striated muscle

A.  CONTRACTILE  TISSUE

• Each muscle is composed of numerous muscle fascicles.

• Each muscle fascicle has numerous muscle fibres.

• Each muscle fibre is a multinucleated, cross-striated cylindrical cell (myocyte).

MYOCYTE

•Sarcolemma- membrane

•Peripheral nuclei – Multinucleated

•Sarcoplasm- cytoplasm

•Longitudinal myofibrils

MYOFIBRIL

Each  myofibril  is  composed  of  longitudinal  protein  filaments,  called myofilaments:

– Actin (thin)

– Myosin (thick)

Each myofibril shows alternate dark and  light bands

– Dark bands :

A bands (anisotropic)

– Light bands:

I bands (isotropic).

In the middle of the A band, there is a  light H band with M line (dark) in the  middle.

In the middle of the I band there is a  dark Z disc or Krauses membrane.