For NEET 2025

11TH Std. CBSE Board (NCERT)

Biology Movement and Locomotion Std : 11th

Contents of the chapter :
20.1 Types of Movement
20.2 Muscle
20.3 Skeletal System
20.4 Joints
20.5 Disorders of Muscular and Skeletal System

Introduction
• 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.

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 • 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…
o search of food,
o shelter,
o mate,
o suitable breeding grounds,
o favourable climatic conditions or
o to escape from enemies/predators.

20.1 Types of Movement

• Cells of the human body
exhibit three main types of
movements, namely…
o amoeboid,
o ciliary and
o muscular.
• 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
along with the atmospheric air.

• Passage of ova through the female

reproductive tract is also facilitated by the
ciliary movement.

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 • 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…
o types of muscles,
o their structure,
o mechanism of their contraction and
o important aspects of the skeletal system.

20.2 Muscle
• You have studied in Chapter 8 that the cilia and flagella are the outgrowths of the cell membrane.
• Flagellar movement helps in the…
o swimming of spermatozoa,
o maintenance of water current in the canal system of sponges and
o 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…
o excitability,
o contractility,
o extensibility and
o elasticity.
• Muscles have been classified using different
criteria, namely…
o location,
o appearance and
o 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

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 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.
• 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).

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 • Each 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.
• The dark band called ‘A’ or Anisotropic band contains myosin.
• Both the proteins are arranged as…
o rod-like structures,
o parallel to each other and
o 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.

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 • The thin filaments are firmly attached to the ‘Z’ line (from the German "zwischen" meaning
between).
• 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 (contains the protein called myomesin and it marks the centre of
the sarcomere).
• 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 (Figure 20.2).
• In a resting state, the edges of thin filaments on either side of the thick filaments partially overlap
the free ends of the thick filaments leaving the central part of the thick filaments.
• This central part of thick filament, not overlapped by thin filaments is called the ‘H’ zone (from
the German "heller", brighter).

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20.2.1 Structure of Contractile Proteins
• Each actin (thin) filament is made of two ‘F’ (filamentous) actins helically wound to each other.
• Each ‘F’ actin is a polymer of monomeric ‘G’ (Globular) actins.
• Two filaments of another protein,
tropomyosin also run close to
the ‘F’ actins throughout its
length.
• A complex protein Troponin is distributed at
regular intervals on the tropomyosin.
• In the resting state a subunit of troponin masks the
active binding sites for myosin on the actin
filaments (Figure 20.3a).
• Each myosin (thick) filament is also a polymerised
protein.
• Many monomeric proteins called Meromyosins constitute one thick filament.
• Each meromyosin has two important parts,
o a globular head with a short arm ie. heavy
meromyosin (HMM)
o a tail ie. light meromyosin (LMM).
• The HMM component, i.e.; the head and short
arm projects outwards at regular distance and angle
from each other from the surface of a polymerised myosin filament and is known as cross arm.
• The globular head is an active ATPase enzyme and has binding sites for ATP and active sites for
actin.

20.2.2 Mechanism of Muscle Contraction

• Mechanism of muscle contraction is best explained by the sliding filament theory which states that
contraction of a muscle fibre takes place by the sliding of the thin filaments over the thick
filaments.
• Muscle contraction is initiated by a
signal sent by the central nervous
system (CNS) via a motor neuron.
• A motor neuron alongwith the muscle
fibres connected to it constitute a
motor unit.
• The junction between a motor neuron
and the sarcolemma of the muscle
fibre is called the neuromuscular
junction or motor-end plate.
• A neural signal reaching this junction
releases a neurotransmitter (Acetyl
choline) which generates an action
potential in the sarcolemma.

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 • This spreads through the muscle fibre and
causes the release of calcium ions into the
sarcoplasm.
• Increase in Ca++ level leads to the binding of
calcium with a subunit of troponin on actin
filaments and thereby remove the masking of
active sites for myosin.
• Utilising the energy from ATP hydrolysis,
the myosin head now binds to the exposed
active sites on actin to form a cross bridge
• This pulls the attached actin filaments
towards the centre of ‘A’ band.
• The ‘Z’ line attached to these actins are also
pulled inwards thereby causing a shortening
of the sarcomere, i.e., contraction.
• It is clear from the above steps, that during
shortening of the muscle, i.e., contraction,

o the ‘I’ bands get reduced,

o the ‘A’ bands retain the length (Figure 20.5).

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 • The myosin, releasing the ADP and Pi
goes back to its relaxed state.
• A new ATP binds and the cross-bridge is
broken (Figure 20.4).
• The ATP is again hydrolysed by the
myosin head and the cycle of cross bridge
formation and breakage is repeated
causing further sliding.
• The process continues till the Ca++ ions
are pumped back to the sarcoplasmic
cisternae resulting in the masking of actin
filaments.
• This causes the return of ‘Z’ lines back to
their original position, i.e., relaxation.
• The reaction time of the fibres can vary
in different muscles.
• Repeated activation of the muscles can
lead to the accumulation of lactic acid
due to anaerobic breakdown of glycogen
in them, causing fatigue.

• Muscle contains a red coloured oxygen storing pigment called

myoglobin.
• Myoglobin content is high in some of the muscles which gives a reddish
appearance.
• Such muscles are called the Red fibres.
• These muscles also contain plenty of mitochondria which can utilise the
large amount of oxygen stored in them for ATP production.
• These muscles, therefore, can also be called aerobic muscles.

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 • On the other hand, some of the muscles possess very less quantity of
myoglobin and therefore, appear pale or whitish.
• These are the White fibres.
• Number of mitochondria are also few in them, but the amount of
sarcoplasmic reticulum is high.
• They depend on anaerobic process for energy.

20.3 Skeletal System

• Skeletal system consists of a framework of bones and a few cartilages.
• This system has a significant role in movement shown by the body.
• Imagine chewing food without jaw bones and walking around without
the limb bones.
• Bone and cartilage are specialised connective tissues.
• Bone has a very hard matrix due to calcium salts in it and cartilage has
slightly pliable matrix due to chondroitin salts.
• In human beings, this system is
made up of 206 bones and a few
cartilages.
• It is grouped into two principal divisions –
o the axial and
o the appendicular skeleton.
• Axial skeleton comprises 80 bones distributed along the
main axis of the body.
• The skull, vertebral column, sternum and ribs constitute
axial skeleton.

• The skull is composed of two sets of bones –

o cranial and
o facial
• It totals to 22 bones.
• Cranial bones are 8 in number.

• They form the hard protective

outer covering, cranium for
the brain.
• The facial region is made up
of 14 skeletal elements which
form the front part of the skull.
• A single U-shaped bone called
hyoid is present at the base of
the buccal cavity and it is also
included in the skull.

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 • Each middle ear contains three tiny bones –
o Malleus (hammer),
o Incus (anvil) and
o Stapes (stirrup),
collectively called Ear Ossicles.

• The skull region articulates with the superior region of the

vertebral column with the help of two occipital condyles
(dicondylic skull).
• Our vertebral column is formed by 26 serially arranged units
called vertebrae and is dorsally placed.
• It extends from the base of the skull and constitutes the main
framework of the trunk.
• Each vertebra has a central hollow portion (neural canal)
through which the spinal cord passes.
• First vertebra is the atlas and it articulates with the
occipital condyles.

• The vertebral column is differentiated into…

o cervical (7),
o thoracic (12),
o lumbar (5),
o sacral (1-fused) and
o coccygeal (1-fused) regions starting from the skull.
• The number of cervical vertebrae are seven in almost all
mammals including human beings.
• The vertebral column…
o protects the spinal cord,
o supports the head and
o serves as the point of attachment for the ribs and
musculature of the back.
• Sternum is a flat bone on the ventral midline of thorax.
• There are 12 pairs of ribs.

• Each rib is a thin flat bone

o connected dorsally to the vertebral column and
o connected ventrally to the sternum.
• It has two articulation surfaces on its dorsal end and is
hence called bicephalic.
• First seven pairs of ribs are called true ribs.
• Dorsally, they are attached to the thoracic vertebrae and
ventrally connected to the sternum with the help of
hyaline cartilage.

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 • The 8th, 9th and 10th pairs of ribs do not articulate
directly with the sternum but join the seventh rib with
the help of hyaline cartilage.
• These are called vertebrochondral (false) ribs.
• Last 2 pairs (11th and 12th) of ribs are not connected
ventrally and are therefore, called floating ribs.
• Thoracic vertebrae, ribs and sternum together form the
rib cage.

• The bones of the limbs alongwith their girdles

constitute the appendicular skeleton.
• Each limb is made of 30 bones.
• The bones of the hand (fore limb) are…
o humerus,
o radius and
o ulna,
o carpals (wrist bones – 8 in number),
o metacarpals (palm bones – 5 in number)
and
o phalanges (digits – 14 in number)

o Femur (thigh bone – the longest bone),

o tibia and fibula,
o tarsals (ankle bones – 7 in number),
o metatarsals (5 in number) and
o phalanges (digits – 14 in number)
o are the bones of the legs (hind limb)
o A cup shaped bone called patella cover the knee
ventrally (knee cap).
• Pectoral and Pelvic girdle bones help in the articulation of
the upper and the lower limbs respectively with the axial
skeleton.

• Each girdle is formed of two halves.

• Each half of pectoral girdle consists of…
o a clavicle and
o a scapula
• Scapula is a large triangular flat bone situated
in the dorsal part of the thorax between the
second and the seventh ribs.

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 • The dorsal, flat, triangular body of scapula has a slightly
elevated ridge called the spine which projects as a flat,
expanded process called the acromion.
• The clavicle articulates with this.
• Below the acromion is a depression called the glenoid cavity
which articulates with the head of the humerus to form the
shoulder joint.
• Each clavicle is a long slender bone with two curvatures.
• This bone is commonly called as collar bone.

• Pelvic girdle consists of two coxal bones (Figure 20.10).

• Each coxal bone is formed by the fusion of three bones –
o ilium,
o ischium and
o pubis.
• At the point of fusion of the above
bones is a cavity called acetabulum
to which the thigh bone articulates.
• The two halves of the pelvic girdle
meet ventrally to form the pubic
symphysis containing fibrous
cartilage.

20.4 Joints
• Joints are essential for all types of movements involving the bony parts of the body.
• Locomotory movements are no exception to this.
• Joints are points of contact…
o between bones, or
o between bones and cartilages.
• Force generated by the muscles is used to carry out
movement through joints, where the joint acts as a
fulcrum.
• The movability at these joints vary depending on
different factors.
• Joints have been classified into three major structural
forms, namely…
o fibrous,
o cartilaginous and
o synovial.

• Fibrous joints do not allow any movement.

• This type of joint is shown by the flat skull bones which
fuse end-to-end with the help of dense fibrous connective
tissues in the form of sutures, to form the cranium.

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 • In cartilaginous joints, the bones involved are joined together with the help of cartilages.
• The joint between the adjacent vertebrae in the vertebral column is of this pattern and it
permits limited movements.

• Synovial joints are characterised by the presence of a fluid

filled synovial cavity between the articulating surfaces of the
two bones.
• Such an arragement allows considerable movement.
• These joints help in locomotion and many other movements.
o Ball and socket joint (between humerus and pectoral
girdle),
o hinge joint (knee joint),
o pivot joint (between atlas and axis),
o gliding joint (between the carpals) and
o saddle joint (between carpal and metacarpal of thumb)
are some examples.

20.5 Disorders of Muscular and Skeletal System

Myasthenia gravis:
• Auto immune disorder affecting neuromuscular junction
leading to…
o fatigue,
o weakening and
o paralysis of skeletal muscle.

Muscular dystrophy:
• Progressive degeneration of skeletal
muscle mostly due to genetic disorder.
Tetany:
• Rapid spasms (wild contractions) in
muscle due to low Ca++ in body fluid.
Arthritis:
• Inflammation of joints.
Osteoporosis:
• Age-related disorder.
• Characterised by
decreased bone mass and
increased chances of
fractures.
• Decreased levels of estrogen is a common cause.
Gout:
• Inflammation of joints due to accumulation of uric acid
crystals.

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SUMMARY
• Movement is an essential feature of all living beings. Protoplasmic streaming, ciliary movements,
movements of fins, limbs, wings, etc., are some forms exhibited by animals.
• A voluntary movement which causes the animal to change its place, is called locomotion.
• Animals move generally in search of food, shelter, mate, breeding ground, better climate or to
protect themselves.
• The cells of the human body exhibit amoeboid, ciliary and muscular movements.
• Locomotion and many other movements require coordinated muscular activities.
• Three types of muscles are present in our body.
• Skeletal muscles are attached to skeletal elements.
• They appear striated and are voluntary in nature.
• Visceral muscles, present in the inner walls of visceral organs are nonstriated and involuntary.
• Cardiac muscles are the muscles of the heart.
• They are striated, branched and involuntary.
• Muscles possess excitability, contractility, extensibility and elasticity.
• Muscle fibre is the anatomical unit of muscle.
• Each muscle fibre has many parallelly arranged myofibrils.
• Each myofibril contains many serially arranged units called sarcomere which are the functional
units.
• Each sarcomere has a central ‘A’ band made of thick myosin filaments, and two half ‘I’ bands
made of thin actin filaments on either side of it marked by ‘Z’ lines.
• Actin and myosin are polymerized proteins with contractility.
• The active sites for myosin on resting actin filament are masked by a protein-troponin.
• Myosin head contains ATPase and has ATP binding sites and active sites for actin.
• A motor neuron carries signal to the muscle fibre which generates an action potential in it.
• This causes the release of Ca++ from sarcoplasmic reticulum.
• Ca++ activates actin which binds to the myosin head to form a cross bridge.
• These cross bridges pull the actin filaments causing them to slide over the myosin filaments and
thereby causing contraction.
• Ca++ are then returned to sarcoplasmic reticulum which inactivate the actin.
• Cross bridges are broken and the muscles relax.
• Repeated stimulation of muscles leads to fatigue.
• Muscles are classified as Red and White fibres based primarily on the amount of red coloured
myoglobin pigment in them.
• Bones and cartilages constitute our skeletal system.
• The skeletal system is divisible into axial and appendicular.
• Skull, vertebral column, ribs and sternum constitute the axial skeleton.
• Limb bones and girdles form the appendicular skeleton.
• Three types of joints are formed between bones or between bone and cartilage – fibrous,
cartilaginous and synovial.
• Synovial joints allow considerable movements and therefore, play a significant role in locomotion.

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EXERCISES
1. Draw the diagram of a sarcomere of skeletal muscle showing different regions.
2. Define sliding filament theory of muscle contraction.
3. Describe the important steps in muscle contraction.
4. Write true or false. If false change the statement so that it is true.
(a) Actin is present in thin filament
(b) H-zone of striated muscle fibre represents both thick and thin filaments.
(c) Human skeleton has 206 bones.
(d) There are 11 pairs of ribs in man.
(e) Sternum is present on the ventral side of the body.
5. Write the difference between :
(a) Actin and Myosin
(b) Red and White muscles
(c) Pectoral and Pelvic girdle
6. Match Column I with Column II :
Column I Column II
(a) Smooth muscle (i) Myoglobin
(b) Tropomyosin (ii) Thin filament
(c) Red muscle (iii) Sutures
(d) Skull (iv) Involuntary
7. What are the different types of movements exhibited by the cells of human body?
8. How do you distinguish between a skeletal muscle and a cardiac muscle?
9. Name the type of joint between the following:-
(a) atlas/axis
(b) carpal/metacarpal of thumb
(c) between phalanges
(d) femur/acetabulum
(e) between cranial bones
(f) between pubic bones in the pelvic girdle
10. Fill in the blank spaces:
(a) All mammals (except a few) have __________ cervical vertebra.
(b) The number of phalanges in each limb of human is __________
(c) Thin filament of myofibril contains 2 ‘F’ actins and two other proteins namely __________
and __________.
(d) In a muscle fibre Ca++ is stored in __________
(e) __________ and __________ pairs of ribs are called floating ribs.
(f) The human cranium is made of __________ bones.

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