Human Skeletal System

The whole world is standing on a structure whether it is made up of iron, wood, plastic or concrete or anything else. Anything which needs support needs a hard structure. Similar to that, living things have a bony structure called “the skeletal system.” The origin of the first vertebrate was in the Ordovician period of the Palaeozoic era. During this period, there was the origin of jawless fishes in the fresh water. In this article, we are going to discuss the “Human Skeleton”.

Definition:

The hard protective or supportive part of the animal constitutes the skeletal system. The whole human body stands on this what we call skeletal system. The design of the skeleton depends on the animals mode of life, like how they live, what type of food they eat, what is their need to the environment etc.

The study of the skeleton is called Osteology or skeletology. 

For e.g. Skeleton for the aquatic animals is designed differently as compared to terrestrial animals. Different species have different structures according to their mode of living.

Type of Skeleton

1. Exoskeleton
2. Endoskeleton

Exoskeleton

• It is formed by the secretion of the skin from the epidermis.
• It is developed from the epidermis.
• The exoskeleton is always non-living in nature.
• It is found in vertebrates and non-vertebrates.
• It is composed of non-living protein material called Keratin or horn.
• e.g. Hairs, Nails, Claws, Hoofs, Feathers etc.
• It is ectodermal in origin.
• Mesodermal exoskeleton occurs in fishes, seals, crocodiles, turtles etc.

Endoskeleton

• Endoskeleton includes the hard part which is present inside the body.
• It is originated mesodermally.
• It is always living in nature.
• In vertebrates, endoskeleton is formed of bone and cartilage.
• Some invertebrates like corals, cuttlefish, and Echinodermata also possesses endoskeleton.

The Human Skeleton

The Human skeletal system consists of a framework of bones and few cartilages. This system has a significant role in movement shown by the human body.

Human Skeletal system is divided into two parts:

1. Axial Skeleton
2. Appendicular Skeleton

Axial Skeleton

It consists the upper part of the body. It has four parts

• Skull
• Vertebral column
• Ribs
• Sternum

Skull: Total Bones in human skull are 29.

The skull is composed of two sets of bones viz. Cranial and Facial bones.

Facial bones are 14 in number and 8 cranial bones are present.

Cranium – It encloses the brain. It has a large opening called foramen Magnum.

Human skull is di-condyles (with two occipital condyles)

Cranium formed of 8 bones.

All these bones of the skull are joined together by Suture.

• Coronal Suture (Between frontal and parietal)
• Lambdoid Suture (Between parietal and occipital)
• Seggital Suture (Between parietal and parietal)

Facial Bones – These are 14 in numbers.

Nasal bones – 2, Inferior Bones – 2

Vomer – 1,  Lacrimals – 2

Zygomatic or malar bones – 2, Palatines – 2

Marcillary – 2,  Mandibles – 1

Ear Ossicles

• Malleus – (1) Modification of articular bone
• Incus – (1) Modification of quadrate bone
• Stapes – (1) Modification of Hyomandibular bone

Stapes is the smallest bone of the whole skeletal system.

Hyoid Bone – 1

It is a single U shaped bone or also known as tongue bone which is present at the base of the buccal cavity. It is not vivid to any bone of axial skeleton. The muscles of tongue, larynx, neck, and pharynx are attached to this bone.

Hence

In the rabbit, there are 132 bones.

VERTEBRAL COLUMN

Our vertebral column is formed by 26 serially arranged units called vertebrae and is dorsally placed.

It has formula C­_7­ T₁₂ L₅ S₍₅₎ Co­₍₄₎

It has four curvatures which are known as cervical, thoracic, lumbar, and pelvic curvature.

It is differentiated into

Cervical – 7, Thoracic – 12

Lumbar – 5, Sacral – 1 (5 fused)

Coccygeal – 1 (4 fused), Cervical  Vertebral: (smallest vertebral)

Cervical  Vertebral: (smallest vertebrae) – The total no of cervical vertebral are 7 in almost all mammals including human being.

Atlas (C₁) – It is the first vertebral and it articulates with the occipital condyles of the skull.

• Centrum is absent
• Neural spinal is well developed and rigid.

RIBS

• There are 12 pairs of ribs present in human.
• Each rib is a flat bone connected dorsally to the vertebral column and ventrally to the sternum.
• On the dorsal end, ribs have two articulation surfaces called bicephalic.
• First, seven pairs of ribs are called true ribs. Dorsally they are attached with thoracic vertebrates and centrally connected to the sternum with the help of hyaline cartilage.
• The remaining 5 pairs are false ribs. 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 vertebra chondral ribs.
• Last two pairs of ribs (11th and 12th) of ribs are not connected ventrally and therefore called floating ribs.

The rib cage is formed by the combination of thoracic vertebrate, ribs, and sternum.

Sternum – Sternum is a flat bone which is 15 cm in length. It is divided into 3 segments viz. Manubrium, body and Xiphoid process.

Manubrium – Upper part

Body – Middle

Xiphoid Process – Lower Part. (Smallest Part)

Appendicular Skeleton

It consists the lower part of the body. It includes bones of the limbs and girdles. There are total 126 bones in man.

At late fetal age – 306 bones

At birth – 270 bones

After Birth – 206 bones (in adult stage)

Bones of Fore limb.

There are 30 bones in each forelimb.

No of bones in one forelimb

Arm Bone – Humerus – 1

Fore Arm – Radius and ulna – 2

Wrist bones – Carpals – 8

Palm – Metacarpals – 5

Digits – Phalanges – 14

Phalanges have its digital formula. There are 14 Phalanges in each hand, 3 for each finger and 2 for the thumb.

Digital formula – 2 3 3 3 3

Total of both the forelimbs is 60 limbs = 30 + 30.

Bones of hind limb

Again there are 30 bones in each hind limb.

No of bones in one hind limb

The femur is the strongest, heaviest and the largest bone in the human skeleton.

Now we will discuss some girdles. There are two types of girdles.

Pectoral Girdle

• These bones help in the articulation of the upper limbs with the axial skeleton.
• It is formed of the two halves. Each half consists of two bones i.e. Scapula + clavicle (Collar bone)
• Scapula – large triangular flat bone
• Clavicle – Weak thin cylindrical bone with two curvatures.

Pelvic Girdle (Hip Bone)

• These bones help in the articulation of lower limbs with the axial skeleton.
• It is also known as the innominate or coxal bone.
• Each coxal bone is formed by the fusion of three bones i.e. ilium, pubis, and Ischium.

JOINTS

Structural Classification

Fibrous Joints – This type of joints are immovable joints also called as synarthrosis.

Cartilaginous Joints – This type of joints are slightly movable also called as amphiarthrosis.     

Synovial Joints – These joints are most mobile and also called as Diarthrosis.

It has few types

• Plain synovial or gliding joint
• Hinge Joint
• Pivot joint
• Condylar Joint
• Ellipsoid joint
• Saddle Joint
• Ball and Socket Joint

Disease Related with Bones

• Bone Cancer
• Bone Density
• Bone infections
• Osteogenesis imperfecta
• Osteonecrosis
• Paget’s disease of bone
• Rickets
• Arthritis

Conclusion

As we have discussed earlier that ” to make the shape of our body, the skeletal system is very important.” It gives us the power to move. It supports our body and all the body organs. Bones has bone marrow inside it which makes blood cells and also acts as the storehouse for minerals such as calcium.