Human Skeleton System

The Skeleton system is a frame work of bones, cartilages and ligments which consists of all organs. The bonrs are different in shape like long bones, flat bones, short bones and irregular bones.

Bascially human skeleton is divided into two categories.

1.Axial Skeleton

2.Appendicular Skeleton

      

Now let us discuss about axial skeleton in detail

AXIAL SKELETON- It includes skull, hyoid bones, vertebral column and thoracic cage.

The Skull is the frame work which supports organs of vision, hearing, smell and taste. The skul is mainly divied into two parts-

1-Head bones also called as cranial bones

2-Facial bones

There are 8 cranial bones and 14 facial bones.thus the skull consists of 22 bones. All bones of craniumm are flat bones and immovable joints which protects brain. The base of skull consists of an opening through which Medulla oblongata of the brain passes as spinal cord.

The vertebral columor back bone is 'S' shaped which consists of three vertebrae. The vertebral column is divided into 5 regions:

1.Cervical vertebrae- 7 bones

2.Thoracic vertebrae- 12 bones

3.Lumbar vertebrae- 5 bones

4.Sacral vertebrae- 5 bones 

5.Coccygeal vertebraem- 4 bones

The five Sacral bones are fused together as a single bone. The four Coccygeal bones are fuse together as another single bone. Thus total vertebrae are 26 in nummber.

The thoracic cavity includes three different types of bones:

1.Sternum- This is single bone present in the front portion of the thoracic cavity.

2.Vertebral column- This is long vertebral column or spinal cord which is present in the back portion of the thoracic cavity.

3.Ribs- The both sternum and vertebral column are connected on either side with ribs.This is also called as rib cage.

RIB Cage- It consists of 12 pairs of ribs.Each rib unites as joint with vertebral column. Ribs are of three types; True ribs, False ribs and Floating ribs.

True ribs- The first seven ribs of the rib cage are attached directly to sternum are called as true ribs.

False ribs- 8th, 9th and 10th ribs are called as false ribs. These ribs are not attach directly to sternum anmd the cartilages of the ribs attach to 7th rib.

Floating ribs- 11th and 12th pair of ribs are called as floating ribs, as they not attach to sternum.

Appendicular Bones- It found in the appendages/limbs - arms and legs, pelvis, shoulders.

There are other components to mention as well.

Let's start with the pectoral girdle. This is comprised of the clavicle, orcollarbone, and the scapula, or shoulder blade, which together give structure to the shoulder, thereby attaching the upper limbs to the axial skeleton. The clavicle has a sternal end where it attaches to the manubrium, and an acromial end, which joins the scapula. The scapula is a thin, flat bone, roughly triangular, and it has three borders, the superior, the medial or vertebral, and the lateral or axillary(outer).

From here, we move on to the upper limb. This consists of the arm, forearm, and hand. Though colloquially we think if this whole thing as an arm, when speaking in terms of anatomy, it is just this upper portion that we call the arm, so let's start there. 

In the arm we find the humerus, a typical long bone, with its greater and lesser tubercle, radial groove, medial and lateral epicondyle, radial and coronoid fossa, trochlea, and capitulum. 

Moving on to the forearm, we now see two bones, the radius and the ulna. These are connected all the way down by the interosseous membrane, a flexible ligament. The ulna is slightly longer, with its olecranon and coronoid process. The radius goes from wide to thin the other way, with a thin head, the radial tuberosity, and a radial styloid process. From there we see the hand, which has many separate bones. The carpus, or wrist, is made of eight short bones called carpals. These are the scaphoid, lunate, triquetrum, pisiform, and then the trapezium, trapezoid, capitate, and hamate. 

Next we see the five metacarpals, which make up the palm of the hand, and they are simply named one through five, from thumb to pinky. These connect to the phalanges, which are the bones that make up your fingers. 

There are fourteen of these bones per hand, three per finger, which are the distal, middle, and proximal phalanges, except the thumb which has two, as it has no middle phalanx. 

Moving back over to the torso, we see the pelvic girdle. The attaches the lower limbs to the axial skeleton just like the pectoral girdle did for the upper limbs, although this one has far less mobility and far more stability than the other. This girdle starts at the sacrum we described earlier, and continues with two hip bones. These are made of three separate bones at birth, which fuse to become one by adulthood, but we still describe the regions of the hip bone as being the illium, ischium and pubis. 

Lastly, the lower limb contains very thick bones, allowing us to run and jump effectively. The thigh is made of a single bone just like the arm, and this one is called the femur, which is the largest bone in the body. Here we see the head, with a small pit called the fovea capitis. Then the greater and lesser trochanter, the intertrochanteric crest, the gluteal tuberosity, linea aspera, medial and lateral condyles, and epicondyles, intercondylar fossa, and patella. From there, we go to the leg, which like the forearm, contains two bones, the tibia and the fibula.

Again, we see an interosseous membrane between them. In the larger tibia, we see the medial and lateral condyles, the intercondylar eminence, tibial tuberosity, anterior border, medial malleolus, and fibular notch. The fibula is much thinner, with its head and lateral malleolus. Then we get to the foot, which is similar to the hand. We see the tarsus, made of seven bones called tarsals. The biggest two, the talus and calcaneus, make up the ankle. Then there is the cuboid, the navicular, and the medial, intermediate, and lateral cuneiform bones. Next we see the metatarsus, with five long metatarsals, again numbered one through five. Also like the hand, we see fourteen phalanges, also known as the hallix.