SKELETAL SYSTEM AND JOINT

In this post we are going to discuss briefly about the Skeletal System and Joints. 

Skeletal System :

•Skeletal system consists of a framework of bones and a few cartilages.

•This system has a significant role in movement shown by the body.

•Imagine chewing food without jaw bones and walking around without the limb bones. 

•Bone and cartilage are specialised connective tissues.

•The former has a very hard matrix due to calcium salts in it and the latter has slightly pliable matrix due to chondroitin salts. 

•In human beings, this system is made up of 206 bones and a few cartilages. 

•It is grouped into two principal divisions – the axial and the appendicular skeleton.

•Axial skeleton comprises 80 bones distributed along the main axis of the body. 

•The skull, vertebral column, sternum and ribs constitute

axial skeleton. 

•The skull is composed of two sets of bones – cranial and facial, that totals to 22 bones. 

•Cranial bones are 8 in number.

•They form the hard protective outer covering, cranium for the brain. 

•The facial region is made up of 14 skeletal elements which form the front part of the skull. 

•A single U-shaped bone called hyoid is present at the base of

the buccal cavity and it is also included in the skull. 

•Each middle ear contains three tiny bones – Malleus, Incus and Stapes, collectively called

Ear Ossicles. 

•The skull region articulates with the superior region of the vertebral column with the help of two occipital condyles (dicondylic skull).

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

•It extends from the base of the skull and constitutes the main

framework of the trunk. 

•Each vertebra has a central hollow portion (neural canal) through which the spinal cord passes. 

•First vertebra is the atlas and it articulates with the occipital

condyles. 

•The vertebral column is differentiated into cervical (7), thoracic (12), lumbar (5), sacral

(1-fused) and coccygeal (1-fused) regions starting from the skull. 

•The number of cervical vertebrae are seven in almost all mammals including human beings. 

•The vertebral column protects the spinal cord, supports the head and serves as the point of attachment for the ribs and musculature of the back. 

•Sternum is a flat bone on the ventral midline of thorax.

•There are 12 pairs of ribs. Each rib is a thin flat bone connected dorsally to the vertebral column and ventrally to the sternum.

•It has two articulation surfaces on its dorsal end and is hence called bicephalic. 

•First seven pairs of ribs are called true ribs. 

•Dorsally, they are attached to the thoracic vertebrae and

ventrally connected to the sternum with the help of hyaline cartilage. 

•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 vertebrochondral (false) ribs. 

•Last 2 pairs (11th and 12th) of ribs are not connected ventrally

and are therefore, called floating ribs. 

•Thoracic vertebrae, ribs and sternum together form the

rib cage.

•The bones of the limbs alongwith their girdles constitute the appendicular skeleton.

•Each limb is made of 30 bones. The bones of the hand (fore limb) are humerus, radius and ulna, carpals (wrist bones – 8 in number), metacarpals (palm bones – 5 in number) and

phalanges (digits – 14 in number). 

•Femur (thigh bone – the longest bone), tibia and fibula, tarsals (ankle bones – 7 in number), metatarsals (5 in number) and

phalanges (digits – 14 in number) are the bones of the legs (hind limb). 

•A cup shaped bone called patella cover the knee ventrally (knee cap).

•Pectoral and Pelvic girdle bones help in the articulation of the upper and the lower limbs

respectively with the axial skeleton. 

•Each girdle is formed of two halves. 

•Each half of pectoral girdle consists of a clavicle and a

scapula. 

•Scapula is a large triangular flat bone situated in the dorsal part

of the thorax between the second and the seventh ribs. 

•The dorsal, flat, triangular body

of scapula has a slightly elevated ridge called the spine which projects as a flat, expanded process called the acromion. 

•The clavicle articulates with this. 

•Below the acromion is a

depression called the glenoid cavity which articulates with the head of the humerus to

form the shoulder joint. 

•Each clavicle is a long slender bone with two curvatures. 

•This bone is commonly called the collar bone.

•Pelvic girdle consists of two coxal bones. 

•Each coxal bone is formed by

the fusion of three bones – ilium, ischium and pubis. 

•At the point of fusion of the above bones is a cavity called acetabulum to which the thigh

bone articulates. 

•The two halves of the pelvic

girdle meet ventrally to form the pubic symphysis containing fibrous cartilage.

Joints :

•Joints are essential for all types of movements involving the bony parts of the body.

•Locomotory movements are no exception to this. 

•Joints are points of contact between bones, or between bones and cartilages. 

•Force generated by the muscles is used to carry out movement through joints, where the joint acts as a fulcrum. 

•The movability at these joints vary depending on different factors. 

•Joints have been classified into

three major structural forms, namely, fibrous, cartilaginous and synovial.

•Fibrous joints do not allow any movement. This type of joint is shown by the flat skull bones which fuse end-to-end with the help of dense fibrous connective tissues in the form of sutures, to form the cranium.

•In cartilaginous joints, the bones involved are joined together with the help of cartilages. 

•The joint between the adjacent vertebrae in the vertebral column is of this pattern and it permits limited movements.

•Synovial joints are characterised by the presence of a fluid filled synovial cavity between the articulating surfaces of the two bones. 

•Such an arragement allows considerable movement. 

•These joints help in locomotion and many other movements. 

•Ball and socket joint (between humerus and pectoral girdle), hinge joint (knee joint), pivot joint (between atlas and axis), gliding joint (between the carpals) and saddle joint (between carpal and metacarpal

of thumb) are some examples.

Disorders of Muscular and Skeletal System :

•Myasthenia gravis: Auto immune disorder affecting neuromuscular junction leading to fatigue, weakening and paralysis of skeletal muscle.

•Muscular dystrophy: Progressive degeneration of skeletal muscle mostly

due to genetic disorder.

•Tetany: Rapid spasms (wild contractions) in muscle due to low Ca++ in body fluid.

•Arthritis: Inflammation of joints.

•Osteoporosis: Age-related disorder characterised by decreased bone mass and increased chances of fractures. Decreased levels of estrogen is a common cause.

•Gout: Inflammation of joints due to accumulation of uric acid crystals.