Movement is one of the significant features of living beings. Animals and
plants exhibit a wide range of movements. Streaming of protoplasm in
the unicellular organisms like Amoeba is a simple form of movement.
Movement of cilia, flagella and tentacles are shown by many organisms.
Human beings can move limbs, jaws, eyelids, tongue, etc. Some of the
movements result in a change of place or location. Such voluntary
movements are called locomotion. Walking, running, climbing, flying,
swimming are all some forms of locomotory movements. Locomotory
structures need not be different from those affecting other types of
movements. For example, in Paramoecium, cilia helps in the movement of
food through cytopharynx and in locomotion as well. Hydra can use its
tentacles for capturing its prey and also use them for locomotion. We use
limbs for changes in body postures and locomotion as well. The above
observations suggest that movements and locomotion cannot be studied
separately. The two may be linked by stating that all locomotions are
movements but all movements are not locomotions.
Methods of locomotion performed by animals vary with their habitats
and the demand of the situation. However, locomotion is generally for
search of food, shelter, mate, suitable breeding grounds, favourable
climatic conditions or to escape from enemies/predators.
Cells of the human body exhibit three main types of movements, namely,
amoeboid, ciliary and muscular.
20.1 Types of
20.2 Muscle
20.3 Skeletal System
20.4 Joints
20.5 Disorders of
Muscular and
Skeletal System
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.
Ciliary 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 alongwith the atmospheric air. Passage of ova through
the female reproductive tract is also facilitated by the ciliary 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. In this chapter, you will learn about the
types of muscles, their structure, mechanism of their contraction and
important aspects of the skeletal system.
You have studied in Chapter 8 that the cilia and flagella are the outgrowths
of the cell membrane. Flagellar movement
helps in the swimming of
spermatozoa, maintenance of water current in the canal system of sponges
and in locomotion of Protozoans like Euglena. 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 and (iii) Cardiac.
Skeletal muscles 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.
Visceral muscles 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.
muscle fibre 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
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.
Let us examine a skeletal muscle in detail to understand the structure
and mechanism of contraction. 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 (Figure 20.1). Each
(muscle bundle)
Muscle fibre
(muscle cell)
Blood capillary
Figure 20.1 Diagrammatic cross sectional view of a muscle showing muscle bundles
and muscle fibres