A small brief on the skeletal system .

1. SKELETAL SYSTEM
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3. INTRODUCTION
• The human skeleton is a framework of bones and few cartilage. It usually comprises a total of about
206 bones.
• This system has a significant role in the movement of body.
• Bones and cartilage are specialised connective tissues.
• Bone - hard matrix- calcium salts : : : : Cartilage - pliable matrix- chondritin salts.
The whole skeleton can be divided into two parts :
1. AXIAL SKELETON
2. APPENDICULAR SKELETON
AXIAL SKELETON (MAIN AXIS)
It comprises of 80 bones I,e.
 Skull ( 22) - It is divided into two : 1. Cranial (2) 2. Facial (14)
 Vertebral column ( 26)
( THORACIC CAGE)
 Sternum ( 1)
 Ribs ( 12) : These are further divided into : 1. True ribs
2. False ribs
3. Floating ribs
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4. APPENDICULARSKELETON
• The ones which are attached to the axis limb .
• These are further categorised as follows : A. LIMBS B. GIRDLES
( A ) Limbs are divided as -
 UPPER LIMBS
1. Humerous (1)
2. Radius + Ulna (2)
3. Carpels ( wrist 8)
4. Metacarples ( palm 5)
5. Phalanges ( digits 14)
 LOWER LIMBS
1. Femur ( 1)
2. Tibia & Febula ( 2)
3. Tarsals ( Ankle 7)
4. Metatarsals ( 5)
5. Phalanges ( 14 )
6. Patella (1)
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5. (B) Girdlesaredividedasfollows:
 PECTORAL GIRDLE
1. Clavicle
2. Scapula
 PELVIC GIRDLE
1. Ileum
2. Isterm
3. Pubis
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6. COMPOSITIONOFBONES
• A bone is structurally a complex organ . It is composed of 25 %
water, 35% organic solids ( ossien , osseomucoid and ossealbumin)
and 45% inorganic salts of calcium .The hardness of bone is due to
the presence of calcium salts.
The bone can be divided into two parts : * COMPACT BONE
* SPONGY BONE
The unit of compact bone is haversian system which is made up of
haversian canal , lamellae , lacunae. Blood vessels  nerves -
lymphatics are present here.
The ideal function of periosteum is the attachment of muscles and
tendons , also covering , protection , regeneration and healing of
fracture.
The spongy part is found in the inner part of flat bones , body of the
vertebrae and rounded ends of long bones.
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7. BONEMARROW
• It is found between the bone plates of the spongy substance and in
the bone canals .
• They are of two types : 1. RED 2. YELLOW
The bone marrow is a red jelly like mass of cellualr tissue present in all
the bones at birth . This red bone marrow is slowly converted into
yellow adipose tissue in most of the bones . ( The inner lining of bone
marrow cavity is endosteum )
FUNCTIONS :
 It forms haemoglobin and RBC.
Bone – marrow is rich in  reticulo-endotheliazl cells- protetcts
against microbial infections .
It forms granulocyte types of WBC.
It destroys old RBC ‘s.
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9. THE AXIAL SKELETON
• 1. SKULL
It is a large bony structure composed of two sets of bones ,
that is , cranial and facial bones.
CRANIUM
(Large and hollow bony case )
It consists of :
1. Frontal bone (1) 2. Occipital ( 1)
3. Parietal bone (2) 4. Temporal (2)
5. Sphenoid (1) 6. Ethamoid (1) 9

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11. OCCIPITALBONE
• It forms the back and a part of base of the skull.
• The lower part contains a larger opening known as ‘ Foramen
Magnum’ through which spinal cord continues downward.
• The upper edges are joined with the parietal bones. ( quadrilateral
shape)
• The frontal bone in the cranium is joined with two parietal bone.
( The skull also consists the orbits which lodges the eye balls in it. The
roof of this orbit is formed by the zygomatic bone and sphenoid bone .
The floor of the orbit is formed by the maxilla. )
TEMPORAL BONES
 These are situated on the lateral sides - attached to sphenoid in
the front - parietal bone above  occipital bone behind.
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12. SPHENOIDBONE
• It is present at the base of the skull and in front of the occipital bone .
• Its shape resembles a bird named as bat.
• The body is hollow and contains two large size sinuses .
• It houses the pituitary gland.
ETHAMOID BONE
• It is cubical in shape.
• It fills the shape between the two orbits.
• They comprise of a no. of branches through which the nerve smell (
olfactory ) passes from nose to the brain.
FRONTAL BONE
• Present in front central portion.
• It is joined to parietal bones.
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13. • It is extended up to the forehead and forms the roof of orbital and nasal
cavities.
PARIETAL BONES
• They form the side walls and also the greater part of the roof of cranium.
• They are quadrilateral in shape.
FACIAL BONES
There are 14 facial bones which include :
1. Maxillae (2) 2. Palantine (2)
3. Nasal (2) 4. zygomatic (2) ( cheeck bones)
5. Lacrimal (2) 6. Turbinates (2)
7. Vomer (1) 8. Mandible (1)
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14. MAXILLA
• The maxilla is a large irregular bone.
• It forms the upper jaw and the major portion of the palate.
• The upper set of teeth are fixed in it.
• The body of the maxilla is hollow and contains the important
maxillary sinus or antrum.
( Sinusitis - during common cold , it causes inflammation within
the nose which then spreads to the maxillary sinus causing
discomfort in this area.)
NASAL BONES
• These are two small bones situated in between the
sockets of the eyes (orbits).
• They form hard ridge of the nose.
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15. LACRIMAL
• These are the smallest and fragile .
TURBINATE
• These bones are spongy and project from the outer wall of the nasal cavities.
VOMER
• It is a thin vertical bone which separates the nasal cavity.
ZYGOMATIC BONES
• Also termed as the cheeks bones.
• They unite with the maxillae in the front .
MANDIBLE
• It is the largest bone of the face which fixes it in respective sockets ,
the lower set of teeth.
( movable bone of the skull )
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16. VERTEBRALCOLUNM
• It forms a series of vertebrae and forms the axis to which
other bones of the skeleton are connected.
• The skull is situated on the pivot at the top of the vertebral
column.
• The sacrum of the vertebral column forms a part of the pelvis
which forms the lower end of the axis.
• The first seven vertebrae of the neck is termed as the cervical
vertebrae.
• The next 12 are termed as thoracic vertebrae.
• The remaining 5 are termed as lumbar vertebrae.
• The lowest 5th vertebrae forms a wedge shape structure
known as sacrum.
• The end portion of this column is termed as coccyx. (Tail) 16

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18. Functions
• Powerful and flexible pillar.
• Provides attachment to the ribs and muscles of the neck ,
chest and back.
• Protects spinal cord from shocks, accidents and jerks.
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19. A VERTEBRAE consists of an anterior circular body with two neural
arches  these two neural arches form bony ring for spinal cord 
from the bony ring three projections arise which are known as ‘
processes’  processes on each side are termed as ‘ Transverse
processes’  downwards is the Spinous processes.
The region between the body and transverse processes is termed as
the pedicle. And the region between the transverse process and
the spinous process is termed as the lamina.
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20. • Transverse process serves as attachment sites for the muscles.
• Together the pedicle and lamina create the vertebral foramen.
CERVICAL REGION –
• These vertebrae create a concave curvature .
• C3- C7  have common characteristics.
• The vertebra is oval in shape larger from side to side.
• Posterioly the spinous processes is short & points backward
Unique characteristics 
• Presence of hole in the transverse processes.
• Passage of vertebral artery through the vertebral foramen.
The C1 – ATLAS , does not have a body , instead there is an anterior
vertebral arch which replaces the body known as the anterior
tubercle and the posterior vertebral arch which replaces the
spinous processes termed as the posterior tubercle.
The C2- AXIS , it is similar to all other vertebra with the exception of
the presence of superior dens. 20

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22. THORACIC REGION
• Body is heart shaped.
• Small spinous processes .
• Vertebral foramen is circular in shape & much smaller than the vertebral
foramen of the cervical region.
• Transverse processes is present.
• Facets are also present.
(COSTAL FACETS)- Characteristic feature of each individual vertebra  which
endures the attachment to the ribs.
First thoracic vertebra is much smaller than the last one , cause of its weight
bearing action as it decends down the column.
LUMBAR VERTEBRA- (L1-L5)
• Their body is kidney shaped.
• They create a concave curvature & all 5 are similar.
• They have increased weight bearing action.
SACRUM ( 5 FUSED)
• Large triangular bone composed with 5 vertebra.
• Dorsal surface is convex & pelvic surface is concave.
• They articulate with the L5 last lumbar vertebra.
COCCYX ( 3-4 FUSED)
• Triangular shape.
• Articulates with the sacrum and tapers at the apex.
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24. • BONES OF THORAX
Formed by thoracic or dorsal vertebrae , anteriorly by the
sternum & costal cartilages.
STERNUM
• Flat & dragger in shape.
• Divided into three points
• 1. Manubrium 2. Body 3. Xiphoid process
Manubrium
• It is triangular in shape and it articulates on either side with the
clavicle , 1st & 2nd cartilages.
Body
• Attachment with 3rd – 6th ribs.
Xiphoid process
Usually cartilagenous. 24

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26. RIBS
• All ribs are combined together with their respective cartilages
forming an elastic framework with movable sides.
• There are twelve pairs of ribs bilaterally situated.
• Curved , flat , strip shaped bones .
The ribs are raised and lowered during inspiration and expiration
of air , thereby increasing & decreasing the chest cavity.
The first seven are termed as true ribs.
The last 5 are termed as false ribs.
The last two are i ,e 11th & 12th floating ribs.
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