The Human Skeleton | Parts, Functions, Labeled Diagram, Facts & Diseases


The human skeleton

The human skeleton (fig.#1.0)

Human skeleton can be branched into two division, axial skeleton, and appendicular skeleton. (fig.1.0)
  • Axial skeleton
  • Appendicular skeleton


  • Axial Skeleton

The axial skeleton adds the skill the vertebrae ribs and the sternum.

Skull

It is blending of two different types of bones i.e. the cranium and facial bones. The cranium consists of 8 bones 4 unpaired/non-joined and 2 paired/joined which secure the brain parietal and temporal are paired bones, whereas frontal, occipital, sphenoid and ethmoid are unpaired bones. Likewise that there are 14 facial bones of which 6 are paired and 2 unpaired. The paired facial bones are maxilla, zygomatic, nasal, lacrimal, Palatine, and inferior concha. The unpaired facial bones are mandible and vomer.
 it is confident of twelve pairs of ribs that articulate with the thoracic vertebrae. Ten of them attach anteriorly with the sternum, either directly or through the costal arch. The reduce two pairs of ribs are called "floating ribs" because they do not fix to the sternum. The rib cage arranges support to a semi-vacuum chamber called the "chest cavity".

Vertebral Column

Vertebral column extends from the skull to the pelvis to form the backbone, which saves the spinal cord (Fig 1.1). Normally the vertebral column has 4 curvatures which provide more strength than does the straight column. The vertebral column consists of 33 vertebrae. The vertebrae are named according to their location in the body, viz, cervical, thoracic, lumbar and pelvis.
           The cervical vertebrae include seven vertebrae which lie in the neck region.
The first two cervical vertebrae are atlas vertebra and axis vertebra. There are twelve thoracic vertebrae located in the thoracic region, five in the lumbar region and nine pelvic regions which form two sets, sacrum, and coccyx. The sacrum is formed by the fusion of anterior five vertebrae, whereas coccyx is formed by the fusion of four posterior vertebrae.
The skull & vertebral column (fig.#1.1)



Rib cage


It is composed of twelve pairs of ribs that articulate with the thoracic vertebrae. Ten of them connect anteriorly with the sternum, either directly or through the costal arch. The lower two pairs of ribs are known as "floating ribs" because they do not attach to the sternum. The rib cage provides support to a semi-vacuum chamber known as the "chest cavity".

  • Appendicular Skeleton

The appendicular skeleton consists of pectoral girdle and appendages (forelimbs), and pelvic girdle and appendages (hind limbs). (Fig 1.2)

Pectoral Girdle and Fore Limb

Pectoral girdle comprises scapula, supra scapula, and clavicle. The clavicle associated scapula with the sternum.

The forelimb consists of humerus, radius and ulna, 9 carpals, 5 metacarpals, and 14 phalanges.
The humerus forms ball and socket joint with the scapula, while at distal end humerus multistage joint with eight wrist bones called carpals. Five metacarpals form the framework of the palm of the hand. Five rows of the phalanges are attached to the metacarpals. They support the fingers.

Pelvic Girdle and Hind Limb

Pelvic girdle attaches the hind limb to the vertebral column (Fig 1.3). It consists of two coxal bones. Each is formed by the fusion of three bones ilium, ischium and pubis. The pelvic girdle supports the pelvic region.
The hind-limb consists of 1 femur, 2 tibias, and fibula, 8 tarsals 5 meta-tarsals and 14 phalanges. The femur is the proximal bone which forms a hip joint with the hipbone, it is ball and socket joint. At the distal end, the femur forms knee joint with the proximal end of two parallel bones called tibia and fibula. The distal end of the tibia and fibula form a joint with eight tarsals, which are also distally attached to five metatarsal bones of the ankle. Five rows of the fourteen phalanges of the toes are attached to metatarsals (Fig 1.4).

Joints

Joints occur where bones meet. They not only hold our skeleton together but also gives it mobility.
Joints are classified on the basis of the amount of movement allowed by them, into three categories:

  • Immovable joints
  • Slightly movable joints
  • Freely movable joints

The freely movable joints are of two types viz. hinge joint and ball and socket joint (Fig 1.5)

Joints are also classified on the basis of structure;

Fibrous Joints

These joints are held together by short fibers embedded in connective tissue. Such joints are present in the skull, and they fix teeth into the jaws.

Cartilaginous Joints

These joints allow little or no movement. Hyaline cartilage forms a joint between growing bone. The bones held together by fibrous cartilage are found between vertebrae at the point where coxal bones meet in front of the pelvis.

Synovial Joints

These joints contain a cavity filled with fluid and are adapted to reduce friction between the moving joints. The joint is surrounded by a layer of connective tissue called "fibrous capsule" and their inner layer the synovial membrane. Some parts of the capsule may be modified to form distinct ligamentholding the bones together.
Based on structure and movements allowed, the synovial joints can be classified further into major categories.

  • Hinge Joint

The joint that allows the movements in two directions. These are at elbow and knee. At these joints, a pair of muscles are arranged in the same plane as that of joints. One end of each muscle, the origin is fixed to the immovable bone on one side of the joint and the other end of muscles, the insertion is attached to the far side of the joint.

  • Ball and Socket Joint

The joint that allows the movement in several directions. Such joints have at least two pairs of muscles present perpendicular to each other. They provide maximum flexibility. Hip joint and shoulder joint are examples of ball and socket joints.

Skeletal deformities and their causes

The human skeleton supports an upright body. Sometimes our skeletal system becomes weak and results in deformations. The causes of the deformations are variable e.g.

Genetic Causes

Cleft palate, a condition in which palatine processes of maxilla and palatine fail to fuse. The persistent opening between the oral and nasal cavity interferes with sucking. It can lead to inhalation of food into the lungs causing aspiration pneumonia.

Microcephaly

The small-sized skull is caused by some genetic defect. 

Arthritis

covers over 100 different types of inflammatory or degenerative diseases that damage the joints.

Osteoarthritis  (O.A)  

is the most common chronic arthritis, which is a degenerative joint disease also caused by a genetic defect.

Hormonal Causes

Osteoporosis is a group of diseases in which bone resorption outpaces bone deposit. In this case, bone mass is reduced and the chemical composition of the matrix remains normal. Osteoporosis mostly occurs in aged women, which is related to decreased estrogen level. Other factors which may contribute include, insufficient exercise, diet poor in calcium and protein, smoking. etc.
Estrogen replacement therapy  (ERT)   offers the best protection against osteoporotic bone fractures.

Nutritional Causes

Osteomalacia  (soft bones)   includes a number of disorders in which the bones receive inadequate minerals. In this disease, calcium salts are not deposited and hence bones soften and weaken. Weight-bearing bones of legs and pelvis bend and deform. The main symptom is the pain when weight is put on affected bones.

Rickets

is another disease in children with bowed legs and deformed pelvis. It is caused by a deficiency of calcium in diet or vitamin 'D' deficiency. It is treated by vitamin 'D'  fortified milk and exposing skin to sunlight to cure the disorder.

Disc - Slip

Each intervertebral disc is a cushion - like PD composed of an inner semi-fluid nucleus pulposus which acts as rubber ball to give a disc its elasticity and compressibility and a strong outer ring of fibrocartilage, the annulus fibrosusThe annulus fibrosus holds together successive vertebrae.
The disc act as a shock absorber during walking, jumping, running and to a lesser extent to bend laterally. Severe or sudden physical trauma to spines for example from bending forward while lifting a heavy object may result in herniation of one or more discs. The herniated disc  (commonly known slipped disc) usually involves rupture of annulus fibrosus followed by the protrusion of the spongy nucleus pulposus. If protrusion presses on the spinal cord or on spinal nerves exiting from cord generate severe pain or even painkiller. If this fails disc may be removed surgically.

Spondylosis

It is the disease, which causes immobility and fusion of the vertebral joint.

Sciatica

It is characterized by stabbing pain radiating over the course of the sciatic nerve. It results due to injury of the proximal sciatic nerve, which might follow a fall, a herniated disc or improper administration of an injection into the buttock. This may result in a number of lower limb impairment depending on the precise nerve root injured. When the sciatic nerve is completely transected, the legs become nearly useless. They cannot be flexed and all foot-ankle movement is lost. Recovery from sciatic injury is usually slow and incomplete.

Arthritis

Arthritis is an inflammatory or degenerative disease that damage joints. It results in pain, stiffness, swelling of the joint. Acute forms of arthritis usually result from bacterial invasion and are treated with antibiotics. The membrane, lining the joint thickens, fluid production is decreased, which consequently leads to increased friction. Chronic arthritis includes osteoarthritis, rheumatoid arthritis, and gouty arthritis.

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