Humans have an
internal skeleton made of bone, cartilage and connective tissue.
Human skeleton from the back
Human skeleton from the front
Axial skeleton
This part of the skeleton consists of the skull comprising the cranium, facial
bones, foramen magnum, palate and jaws, vertebral column, rib cage andbreastbone(sternum)
The skull: consists of the cranium and facial bones
The
cranium consists of eight flat bones joined together by immovable joints called
sutures. The cranium surrounds and protects the brain.
There is a large opening at the base of the skull called the
foramen magnum through which the spinal cord passes
On either side of the foramen magnum is a projection or
condyle which articulate with the first vertebra (called the atlas) to give the nodding
movement of the head
There are 15
facial bones. These are irregular bones that include cheek nasal , temple and upper and lower
jaw bones. The only movable bone is the lower jaw.
The upper and lower jaws bear the sockets for the 32 permanent teeth.
The number, type and arrangement of the teeth in an animal is indicated by a
dental formula The human dental formula is:
2.1.2.3
2.1.2.3
This formula represents the numbers of each type of tooth in half of the upper
jaw and half of the lower jaw. This formula tells us that in both the upper andlower halves there are 2 incisors, 1 canine, 2 premolars and 3 molars.
Therefore in the whole jaw there are 8 incisors, 4 canines 8 premolars and 12molars, a total of 32 teeth in all.
The vertebral column
: Consists of 33 vertebrae
The vertebral columns is divided into five regions
A
cervical (neck) region consisting of 7 vertebrae. The first of these called the
atlas supports the skull and the joint with the skull allows for the
nodding movement of the head.
The 2
nd vertebra called the
axis has a projection oo which the atlas pivots to give the side to side movement of
the head.
A
thoracic region (chest) of 12 vertebrae each of which bears a pair of ribs
A
lumbar region (lower back) the largest vertebrae as they carry the weight of the body
A
sacral region consisting of 5 fused vertebrae forming a bone called the
sacrum that forms part of the pelvic girdle which provides for the attachment of
muscles and the legs.
A
coccyx made up of 4 fused bones. These bones form the tail in those mammals that have
tails.
The vertebrae join up to each other in such a way that there is a continuous
spinal canal which runs from the base of the skull to the pelvic girdle. This canal contains
the
spinal cord.
Between the vertebrae are
discs of fibrocartilage which prevent friction between vertebrae and act as shock absorbers duringwalking, running and jumping.
Spinal nerves are able to enter and leave the spinal cord through gaps between adjacent
vertebrae.
Strong ligaments and muscles around the spine stabilise the vertebrae and help to control movement.
CURVES OF THE SPINE
When viewed from the side the vertebral column can be seen to have
four curves, with the cervical and lumbar regions curving forwards while the
thoracic and sacral regions curve backwards.
Questions & Answers
Explain the following terms .
(1) Abiotic factors in an ecosystem
Abiotic factors are non living components of ecosystem.These include physical and chemical elements like temperature,light,water,soil,air quality and oxygen etc
