The hu­man skele­tal sys­tem (Part Two)

Jamaica Gleaner - - SPORTS -

LAST WEEK, we looked at bone growth and for­ma­tion, func­tions and types of bone in the hu­man skele­ton. We con­tinue this week’s les­son by look­ing on the bones of the ver­te­bral col­umn and the types of joints.


The ver­te­bral col­umn, spine or back­bone con­sists of 33 spe­cialised bones called ver­te­brae. Between each ver­te­bra, there is a disc of car­ti­lage that al­lows a small amount of move­ment and act as shock ab­sorber. The ver­te­bral col­umn can be di­vided into five sec­tions.

Cer­vi­cal ver­te­brae – This is the neck re­gion and con­sists of seven ver­te­brae. They pro­vide at­tach­ment for neck mus­cles and sup­port the head and neck. The top ver­te­bra (at­las) fits into the skull and al­lows nod­ding of the head. The sec­ond ver­te­bra (axis) al­lows ro­ta­tion of the head.

Tho­racic ver­te­brae – These are 12 ver­te­brae that sup­port the ribcage and forms part of the chest area. They al­low slight bend­ing, for­ward, back­wards and side­ways.

Lum­ber ver­te­brae – These are the five largest bones of the spine. The mus­cles of the back are at­tached to them. They al­low large range of bend­ing for­ward, back­wards and side­ways. This re­gion can be eas­ily in­jured.

Sacral ver­te­brae – These five ver­te­brae are fused to­gether and form a very strong base that sup­ports the weight of the body and passes force from the legs and hip to up­per body.

Coc­cyx – These are five fused ver­te­brae. They have no spe­cial func­tion other than for mus­cle at­tach­ment.


The ver­te­bral col­umn is im­por­tant in all sport­ing move­ments, it is flex­i­ble, strong and al­lows bend­ing and stretch­ing into many dif­fer­ent po­si­tions. It is also vul­ner­a­ble to in­jury if pre­ven­ta­tive care is not taken. The ver­te­bral col­umn: I Pro­tects the spinal cord I Sup­ports the up­per body

Give a wide range of move­ment I Is im­por­tant for pos­ture I Passes force to the body parts Dis­or­ders of the spine:

Sco­l­io­sis – a side­way cur­va­ture of the spine that af­fects pos­ture, caus­ing dif­fi­culty in stand­ing straight.

Kyp­so­sis – a for­ward bend­ing of the spine that makes the per­son ap­pear to be lean­ing for­ward.


A joint is where two or more bones meet (ar­tic­u­late). There are over 100 joints in the body. Joints are di­vided into three types based on the amount of move­ment they al­low.

Fixed or im­mov­able joints (fi­brous)

In these, bones are fused to­gether by tough fi­bres. These types of joints are found in ar­eas re­quir­ing strength. Ex­am­ples are the joints between the plates of the cra­nium (skull) and the fused joints in the sacrum.

Slightly mov­able joints (car­ti­lagi­nous)

In these, a small amount of move­ment can oc­cur. The bones are linked by car­ti­lage. Car­ti­lage

IIis a tough, but flex­i­ble cush­ion of tis­sue that stops the bones from knock­ing to­gether (fric­tion) and can also com­press a lit­tle to al­low slight move­ment. Slightly mov­able joints are found between most of the ver­te­brae in the ver­te­bral col­umn and the joint between the ribs and ster­num.

Freely mov­able joints (syn­ovial)

All freely mov­able joints share fea­tures which pre­vent fric­tion between mov­ing bones. One of the main fea­tures is the pres­ence of syn­ovial fluid between the mov­ing bones. The bones are held to­gether by slightly elas­tic fi­bres called lig­a­ments, which al­lows the bones to move; any dam­age to the lig­a­ment re­sults in the joint los­ing some of its strength and sta­bil­ity.

There are six ba­sic types of syn­ovial joints (freely mov­able):

Ball and socket – These moves freely in all di­rec­tion. Lig­a­ments are of­ten used to keep the joint sta­ble. This type is only the hip and shoul­ders.

Hinge – The move­ment of this type works like a hinged door. The move­ment al­lowed is flex­ion and ex­ten­sion. This type of joint is

III­formed at the el­bows and knee.

Pivot – These joints al­low only ro­ta­tion be­cause of its ‘ring on a peg’ struc­ture. This is found between the at­las and axis ver­te­brae in the neck and between ra­dius and ulna, be­low the el­bow.

Sad­dle joints – These al­low move­ment in sev­eral planes, back, for­ward and side to side. Bones are shaped like sad­dle and fit neatly to­gether. Ex­am­ple the thumb.

Glid­ing – These al­low slight move­ment in all di­rec­tion, how­ever, lig­a­ments limit an­other. Ex­am­ples are the carpal bones of the hand ver­te­brae.

Condy­loid – These al­low move­ment in sev­eral planes, back and for­ward and side­ways. A lig­a­ment pre­vents ro­ta­tion. The rounded end of bones fit into the hol­low of an­other. Ex­am­ples are the wrist and ankles.

Joints work smoothly to­gether when we per­form sport­ing ac­tiv­i­ties. They must be ca­pa­ble of their full range of move­ment in or­der to work well. The de­mands of sport puts se­vere stress on joints. There­fore, it is es­sen­tial to warm up be­fore an ac­tiv­ity and cool down af­ter the ac­tiv­ity. Joints can be in­jured as a re­sult of im­pact, in­ter­nal forces or a mix­ture of both. Ex­am­ples sprains, torn lig­a­ments and dis­lo­ca­tion.


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