Summary of the IB SEHS Unit 1.1 (the skeletal system). You will find detailed yet summarized information on the topic, organized according to the IB syllabus (contains all necessary information to achieve a 7).
1.1: Skeletal system
made up of bones, cartilage, ligaments and joints
skeletal system represents 20% of body mass
206 bones divided into the axial skeleton and the appendicular skeleton
Skeletal functions
-protects vital organs -storage and release of minerals (calcium and
-support and maintenance of posture phosphorus)
-providing attachment points for the muscles -blood cell production
-storage of energy
Axial and appendicular skeleton
Axial skeleton Appendicular skeleton
-protects internal organs (brain, -provides attachment points for
spinal cord, heart, lungs…) muscles that enable body
movement
-acts as support and
maintenance (posture) -protects reproductive organs
-provides some attachment
points for muscles
They both act as a mineral store (calcium…), are involved in cell production (ribs, long bones…) and
energy storage (yellow marrow)
Axial skeleton
formed by 80 bones (skull, ribs, sternum, and vertebral column)
enclose important structures and main function is protection
more rigid than appendicular skeleton
skull
divided into face and cranium
protects brain, eyes and ears and contains teeth
22 bones
provides attachment for muscles involved in chewing
1.1: Skeletal system 1
, sternum
flat bone
at the bottom of the throat and runs to halfway down the center of the chest
attachment for the ribs and helps to rotect vital organs whithin the torax
ribs
curved bones that articulate with sternum at the front and the thoracic vertebrae at the back
12 pairs in total
first 7 ribs: true ribs and attach directly to the sternum
8-10 ribs: false ribs (attach to 7th rib and indirectly to the sternum)
11-12 ribs: floating ribs (not attached to sternum)
Sternum, ribs and thoracic vertebrae form thoracic cage
Thoracic cage functions: intercostal muscles (essential for breathing) are located in-between the
ribs. Protects vital organs
vertebral column
strong but flexible column
33 units: vertebrae
Parts of a vertebrae:
body: largest and flattest part
vertebral foramen: hole where spinal cord is located
intervertebral disc: outer ring or fibrocartilage (anulus fibrosus) and gel-like elastic structure in the
middle (nucleus pulposus)
Sections:
Cervical vetebrae (7): smallest ones and have more movement than thoracic and lumbar
Thoracic vertebrae (12): more restricted movement and has ribs attached to each side of vertebrae
Lumbar vertebrae (5): biggest and strongest → major role in weight-bearing + absorbs high
compression loads
Sacral vertebrae (5): weight from the body to the pelvis and legs
Coccyx (4): at around 30, coccyx fuses with sacral vertebrae. They say it helps stabilice while sitting.
1.1: Skeletal system 2
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