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TYPES OF MOVEMENT

Cells of the human body exhibit

three main types of movements, namely,

amoeboid, ciliary and muscular

a. Amoeboid movement

Some specialised cells in our body like

macrophages and leucocytes in blood

exhibit amoeboid movement.

It is effected by pseudopodia formed by

the streaming of protoplasm (as in

Amoeba).

Cytoskeletal elements like microfilaments

are also involved in amoeboid movement.

b. Ciliary movement

This type of movement occurs in most of

our internal tubular organs which are lined

by ciliated epithelium.

The coordinated movements of cilia in the

trachea help us in removing dust particles

and some of the foreign substances

inhaled along with the atmospheric air.

Passage of ova through the female

reproductive tract is also facilitated by the

ciliary movement.

c. Muscular movement

Movement of our limbs, jaws, tongue, etc,

require muscular movement.

The contractile property of muscles are

effectively used for locomotion and other

movements by human beings and majority

of multicellular organisms.

Locomotion requires a perfect

coordinated activity of muscular, skeletal

and neural systems.

MUSCLES

Muscle is a specialised tissue of

mesodermal origin. About 40-50 per cent of

the body weight of a human adult is

contributed by muscles. They have special

properties like excitability, contractility,

extensibility and elasticity. Muscles have

been classified using different criteria, namely

location, appearance and nature of regulation

of their activities. Based on their location,

three types of muscles are identified :

(i) Skeletal (ii) Visceral (iii) Cardiac.

i) Skeletal muscles

They are closely associated

with the skeletal components of the body.

They have a striped appearance under the

microscope and hence are called striated

muscles. As their activities are under the

voluntary control of the nervous system,

they are known as voluntary muscles too.

They are primarily involved in locomotory

actions and changes of body postures.

ii) Visceral muscles

They are located in the inner

walls of hollow visceral organs of the body

like the alimentary canal, reproductive tract,

etc. They do not exhibit any striation and are

smooth in appearance. Hence, they are

called smooth muscles (nonstriated

muscle). Their activities are not under the

voluntary control of the nervous system and

are therefore known as involuntary

muscles. They assist, for example, in the

transportation of food through the digestive

tract and gametes through the genital tract.

iii)Cardiac muscles

As the name suggests, Cardiac muscles are

the muscles of heart. Many cardiac muscle

cells assemble in a branching pattern to form

a cardiac muscle. Based on appearance,

cardiac muscles are striated. They are

involuntary in nature as the nervous system

does not control their activities directly

ULTRA STRUCTURE OF SKELETAL

MUSCLE

Each organised skeletal muscle in our

body is made of a number of muscle

bundles or fascicles held together by a

common collagenous connective tissue

layer called fascia.

Each muscle bundle contains a number of

muscle fibres / Muscle cell

Each muscle fibre/muscle cell is lined by

the plasma membrane called

Sarcolemma enclosing the sarcoplasm.

Muscle fibre is a syncitium as the

sarcoplasm contains many nuclei.

The endoplasmic reticulum, i.e.,

sarcoplasmic reticulum of the muscle

fibres is the store house of calcium ions.

A characteristic feature of the muscle fibre

is the presence of a large number of

parallelly arranged filaments in the

sarcoplasm called myofilaments or

myofibrils.

Each myofibril has alternate dark and

light bands on it. A detailed study of the

myofibril has established that the striated

appearance is due to the distribution

pattern of two important proteins – Actin

and Myosin.

The light bands contain actin and is

called I-band or Isotropic band, whereas

the dark band called ‘A’ or Anisotropic

band contains myosin. Both the proteins

are arranged as rod-like structures,

parallel to each other and also to the

longitudinal axis of the myofibrils.

Actin filaments are thinner as compared to

the myosin filaments, hence are

commonly called thin and thick filaments

respectively.

In the centre of each „I‟ band is an elastic

fibre called ‘Z’ line which bisects it. The

thin filaments are firmly attached to the „Z‟

line.

The thick filaments in the „A‟ band are also

held together in the middle of this band by

a thin fibrous membrane called ‘M’ line.

The „A‟ and „I‟ bands are arranged

alternately throughout the length of the

myofibrils.

The portion of the myofibril between

two successive ‘Z’ lines is considered

as the functional unit of contraction

and is called a sarcomere