Skeletal System Overview

Throughout history, the skull and crossbones flying from a pirate ship (aka the "Jolly Roger") have long been a symbol of death and dismay. But you shouldn't blame that on the bones on the flag! Without bones, our bodies wouldn't be able live and thrive, which is perhaps obvious. But less obvious is that the bones in our bodies are also quite alive and vital - they're just as living as our beating hearts and pulsing organs. 

Bones are living structures with five major functions

  1. To protect internal organs.
  2. To physically support the body.
  3. To produce vital blood cells.
  4. To store minerals.
  5. To offer purchase for muscle attachment. 

A point where two or more bones connect is called a joint. There are two different types of joints in the body:

  1. Movable joints, such as the ball-and-socket, hinge, gliding and pivot joints.
  2. Immovable joints, like the bones of the skull and pelvis, which allow little or no movement.

Ball-and-Socket Joint 

  • The ball-and-socket joint is a movable joint.
  • Both the hips and the shoulders contain ball-and-socket joints.
  • In a ball-and-socket joint, one bone has a rounded end (ball) that fits into a cuplike cavity (socket) on another bone. This provides a wide range of movement. Thus, your hips and shoulders can swing in almost any direction - unlike your fingers, elbows, knees, and so on.
  • The other movable joints in your body are pivot, hinge, and gliding joints.


  • The foot is one of the most complex mechanisms of the human body.
  • You use your feet throughout the day, taking up to 10,000 steps per day.
  • The foot is actually made up of many tiny bones, but overall it is considered a hinge joint.
  • Your toes use hinge joints, named after the back-and-forth movements made by hinges (as seen on a door). Elbows, knees and fingers also have these types of joints.
  • Hinge joints are classified as a movable joint. The other movable joints in your body are pivot, ball-and-socket and gliding joints.

Rib Cage

  • The rib cage (also known as the thoracic cage) acts as a shield that protects the heart, lungs, and other organs.
  • Both men and women have 12 pairs of ribs (24 overall) and 12 thoracic vertebrae.
  • The rib cage is also considered part of the respiratory system.
  • As a person breathes in and out, the rib cage expands and contracts along three planes: the vertical, the anteroposterior, and the transverse.

Spinal Cord

  • Your spinal cord is made of bundles of neurons that carry impulses from all parts of the body to the brain (and from the brain to all parts of your body).
  • The spinal cord is about as big around as an adult thumb at its thickest point, to about 1/4 of an inch thick at the thoracic region.
  • It is about 45 cm long in men and 43 cm long in women.
  • The joints between vertebrae are called gliding joints, where one part of a bone slides over another bone.
  • The spinal cord can be divided into 31 different segments at which points spinal nerves form.


  • Humans generally have 32 adult teeth (and 20 'baby' teeth before that).
  • Teeth have distinctive identifying features making them unique to each person.
  • The different parts of the tooth are enamel, dentin, cementum, and pulp.
  • There are four different types of teeth in the human mouth:
    1. Incisors – are the sharp-edged teeth in the front of the mouth that bite and cut food. We have 8 of these.
    2. Canines – are the pointed teeth next to the incisors that grip and tear food. We have 4 of these.
    3. Premolars – are the teeth just behind the canines. They help the canines with chopping and assist the molars with grinding. There are 8 of these in our mouths.
    4. Molars – are the teeth in the back of the mouth that pound, grind and crush food into mush so that it can be swallowed. We have 12 molars.

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