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Locomotion and Movement of Human
Body: Skeletal system explanation
Movement is one of the significant features of living beings
...
Streaming of
protoplasm in the unicellular organisms like Amoeba is a simple form
of movement
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Human beings can move limbs, jaws, eyelids,
tongue, etc
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Such voluntary movements are called locomotion
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Locomotory structures need not be different from those
affecting other types of movements
...
Hydra can use its tentacles for capturing its prey
and also use them for locomotion
...
The above observations suggest
that movements and locomotion cannot be studied separately
...
Methods of locomotion
performed by animals vary with their habitats and the demand of the
situation
...

TYPES OF MOVEMENT:
Cells of the human body exhibit three main types of movements,
namely, amoeboid, ciliary and muscular
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It is effected by pseudopodia formed by the streaming of

protoplasm (as in Amoeba)
...

Ciliary movement occurs in most of our internal tubular organs which
are lined by ciliated epithelium
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Passage of
ova through the female reproductive tract is also facilitated by the
ciliary movement
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The contractile property of muscles is
effectively used for locomotion and other movements by human
beings and majority of multicellular organisms
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MUSCLE:
The cilia and flagella are the outgrowths of the cell membrane
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Muscle is a specialised tissue
of mesodermal origin
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They have special properties
like excitability, contractility, extensibility and elasticity
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Based on their location,
three types of muscles are identified: (i) Skeletal (ii) Visceral and (iii)
Cardiac
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They have a striped appearance under the microscope
and hence are called striated muscles
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They are primarily involved in locomotory
actions and changes of body postures
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They do not exhibit any striation and are smooth in appearance
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Their
activities are not under the voluntary control of the nervous system
and are therefore known as involuntary muscles
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As the name suggests, Cardiac muscles are the muscles of heart
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Based on appearance, cardiac muscles are striated
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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
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Each muscle fibre is lined by the plasma
membrane called sarcolemma enclosing the sarcoplasm
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The
endoplasmic reticulum, i
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, sarcoplasmic reticulum of the muscle
fibres is the store house of calcium ions
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Each myofibril has alternate dark and light bands on it
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The light bands contain actin and is
called I-band or Isotropic band, whereas the dark band called ‘A’ or
Anisotropic band contains myosin
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Actin filaments are thinner as compared to the
myosin filaments, hence are commonly called thin and thick
filaments respectively
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The thin filaments are firmly attached
to the ‘Z’ line
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The ‘A’ and ‘I’ bands are arranged alternately
throughout the length of the myofibrils
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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
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Describe: Structure of Contractile Proteins
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Each ‘F’ actin is a polymer of
monomeric ‘G’ (Globular) actins
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A
complex protein Troponin is distributed at regular intervals on the
tropomyosin
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Each myosin (thick) filament is also a polymerised protein
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Each meromyosin has two important parts, a globular head

with a short arm and a tail, the former being called the heavy
meromyosin (HMM) and the latter, the light meromyosin (LMM)
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e
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The globular
head is an active ATPase enzyme and has binding sites for ATP and
active sites for actin
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Muscle contraction is initiated by a signal sent by the central nervous
system (CNS) via a motor neuron
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The junction
between a motor neuron and the sarcolemma of the muscle fibre is
called the neuromuscular junction or motor-end plate
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This
spreads through the muscle fibre and causes the release of calcium
ions into the sarcoplasm
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Utilising the energy
from ATP hydrolysis, the myosin head now binds to the exposed
active sites on actin to form a cross bridge
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The ‘Z’ line attached to
these actins are also pulled inwards thereby causing a shortening of
the sarcomere, i
...
, contraction
...
e
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The myosin,

releasing the ADP and P1 goes back to its relaxed state
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The ATP is again hydrolysed by
the myosin head and the cycle of cross bridge formation and
breakage is repeated causing further sliding
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This causes the return of
‘Z’ lines back to their original position, i
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, relaxation
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Repeated activation
of the muscles can lead to the accumulation of lactic acid due to
anaerobic breakdown of glycogen in them, causing fatigue
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Myoglobin content is high in some of the muscles which gives a
reddish appearance
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These
muscles also contain plenty of mitochondria which can utilise the
large amount of oxygen stored in them for ATP production
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On the other
hand, some of the muscles possess very less quantity of myoglobin
and therefore, appear pale or whitish
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Number of mitochondria are also few in them, but the amount of
sarcoplasmic reticulum is high
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SKELETAL SYSTEM:
Skeletal system consists of a framework of bones and a few
cartilages
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Imagine chewing food without jaw bones and walking
around without the limb bones
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The former has a very hard matrix due to calcium
salts in it and the latter has slightly pliable matrix due to chondroitin
salts
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It is grouped into two principal divisions – the axial
and the appendicular skeleton
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The skull, vertebral column, sternum and ribs constitute
axial skeleton
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Cranial bones are 8 in number
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The facial region is made up of 14 skeletal elements which form the
front part of the skull
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Each middle ear contains three tiny bones – Malleus, Incus and
Stapes, collectively called Ear Ossicles
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Our vertebral column is formed by 26 serially arranged units called
vertebrae and is dorsally placed
...
Each vertebra has a
central hollow portion (neural canal) through which the spinal cord
passes
...
The vertebral column is differentiated into cervical (7),
thoracic (12), lumbar (5), sacral (1-fused) and coccygeal (1-fused)
regions starting from the skull
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The vertebral
column protects the spinal cord, supports the head and serves as the
point of attachment for the ribs and musculature of the back
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There are 12 pairs of ribs
...
It has
two articulation surfaces on its dorsal end and is hence called

bicephalic
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Dorsally, they
are attached to the thoracic vertebrae and ventrally connected to the
sternum with the help of hyaline cartilage
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These are called
vertebrochondral (false) ribs
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Thoracic vertebrae, ribs and sternum together form the rib cage
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Each limb is made of 30 bones
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Femur (thigh bone – the longest
bone), tibia and fibula, tarsals (ankle bones – 7 in number),
metatarsals (5 in number) and phalanges (digits – 14 in number) are
the bones of the legs (hind limb)
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Pectoral and Pelvic girdle bones help in the articulation of the upper
and the lower limbs respectively with the axial skeleton
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Each half of pectoral girdle consists of a
clavicle and a scapula
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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
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Below the
acromion is a depression called the glenoid cavity which articulates
with the head of the humerus to form the shoulder joint
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This bone is
commonly called the collar bone
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Each coxal bone is formed
by the fusion of three bones – ilium, ischium and pubis
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The two halves of the pelvic girdle meet
ventrally to form the pubic symphysis containing fibrous cartilage
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Locomotory movements are no exception to this
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Force generated by the muscles is used to carry out
movement through joints, where the joint acts as a fulcrum
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Joints
have been classified into three major structural forms, namely,
fibrous, cartilaginous and synovial
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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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The joint between the adjacent vertebrae in
the vertebral column is of this pattern and it permits limited
movements
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Such an arrangement allows considerable movement
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Ball and socket joint
(between humerus and pectoral girdle), hinge joint (knee joint), pivot
joint (between atlas and axis), gliding joint (between the carpals) and

saddle joint (between carpal and metacarpal of thumb) are some
examples
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Muscular dystrophy: Progressive degeneration of skeletal muscle
mostly due to genetic disorder
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Arthritis: Inflammation of joints
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Decreased levels of
oestrogen is a common cause
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