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MHT-CET : Biology Entrance Exam

MHT - CET : Biology - Human Skeleton Page 1

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Skeleton : The external or internal framework which supports and protects the soft organs and tissues of the body is called skeleton.

1. Functions of Skeleton

 

  • The skeleton gives a definite shape to the body.
  • The skeleton protects delicate parts of the body such as brain, spinal cord, heart and lungs.
  • The skeleton provides surface for attachment of muscles.
  • The skeleton helps in movement and locomotion.
  • The long bones have a cavity called bone marrow in which blood cells are produced.
  • The skeleton is the reservoir of minerals like calcium and phosphorus.

 

 

2.

Divisions of the Human Skeleton

 

  • The axial skeleton - These include the skull, the vertebral column and the thoracic cage.
  • The appendicular skeleton - These include the skeleton of forelimbs and the hind limbs and the group of bones at their base to which they are joined (girdles).

 

 

3.

Skull

 

  • The skull is the skeleton of the head. It is made up of the bones of the cranium and the bones of the face (facial bones). The major part of the skull forms a protective bony covering of the brain called cranium.

         Cranium (Brain Box)
The cranium consists of eight bones, four of them median and two paired. They are:
Frontal (median)
Occipital (median)
Sphenoid (median)
Ethmoid (median)
Parietal (paired)
Temporal (paired)

         Face

There are
13 bones in addition to the frontal bone of the cranium, which form the skeleton of the face. These bones are:
Zygomatic or cheek bones (paired)
Maxilla or upper jaw (median)
Nasal (paired)
Lacrimal (paired) bones
Vomer (median)
Mandible or lower jaw (median)
Palatine (paired)
Inferior nasal conchae or turbinate (paired)

 

 

4.

Vertebral Column

 

  • The vertebral column or backbone is a characteristic feature of all vertebrates.
  • The vertebral column forms the central axis of the body.
  • The vertebral column consists of 33 ring-like bones called vertebrae. These vertebrae are connected to each other by cartilaginous pads which protect the vertebral column from shocks.
  • The vertebral column consists of 7cervical vertebrae in the neck region, 12 thoracic vertebrae at the back of the chest, 5 lumbar vertebrae at the back of the abdomen, 5 sacral vertebrae at the hip region and 4 caudal vertebrae at the end of the vertebral column.
  • Intervertebral foramina and cartilaginous discs are present between the vertebrae.
  • The continuous vertebral foramina of all vertebrae form a neural canal.

 

 

5.

A Typical Vertebra of Man

 

Lumbar Vertebrae

  • The lumbar vertebra is regarded as the typical vertebra.
  • There are 5 lumbar vertebrae in man.
  • The lumbar vertebra is large and stout consisting of a large, solid ventral body called centrum.
  • The centrum is acetous, i.e., flat.
  • The size of the centrum and the vertebrae generally increases towards the lower end.
  • Cervical vertebra has the smallest centra and the lumbar has the largest centrum.
  • Cartilaginous pieces called intervertebral discs are present in between the centra.
  • Towards the dorsal side of the centrum, there lies a bony arch called neural arch which encloses neural canal or vertebral foramen through which passes the spinal cord.
  • The neural arch bears a pair of transverse processes laterally; a single spinous process called neural spine medially; and two pairs of superior and inferior articular processes also termed as superior and inferior zygapophyses. (singular: zygapophysis).

 

 

6.

Cervical Vertebrae

 

  • The cervical vertebrae are the smallest of the vertebrae.
  • There are seven vertebrae of the neck region. Of these seven cervical vertebrae in man, the 3rd, 4th, 5th, 6th and 7th vertebrae show similar structure. Therefore, they are described as typical cervical vertebrae.
  • A typical cervical vertebrae has a small and oblong centrum with flat surfaces on both the sides.
  • The transverse processes are reduced and possess a foramen for the vertebral artery.
  • The neural arch and the neural spine are well developed.
  • The neural spine is bifid, i.e., forked.
  • Seventh cervical vertebra has an undivided neural spine. It is the largest of the cervical vertebrae and is known as vertebra prominens.
  • Atlas is the first cervical vertebra of man. Atlas is a bony ring with reduced centrum and processes.
  • The neural arch of atlas is well developed.
  • Axis is the second cervical vertebra of man. Its centrum gives off a cylindrical conical process called odontoid process. Neural arch and neural spine of axis are well developed.

 

 

7.

Thoracic Vertebra of Man

 

  • There are 12 thoracic vertebrae in man which lie in between the cervical and the lumbar vertebrae.
  • A typical thoracic vertebra consists of a heart-shaped centrum.

 

 

 

8.

Sacrum

 

  • This is a structure formed by the fusion of five vertebrae below the last lumbar.
  • The sacrum lies between the two halves of the hip bone (innominate), it articulates with a sacroiliac joint on each side. Together they form the pelvic girdle.
  • The upper part of the sacrum possesses a pair of superior articular processes for articulation of the fifth lumbar vertebra.
  • The sacrum possesses four pairs of sacral foramina for the passage of nerves.

 

 

9.

Coccyx

 

  • The coccyx represents the remnant of tail bone in human beings.
  • The anterior end of the coccyx articulates with the lower end of the sacrum.
  • It is solid without any space for nerves.
  • Each coccygeal vertebra bears a pair of lateral processes, of which the first pair is the largest.

 

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