OCP C1 B Anatomy and Physiology > Skeletal System > Skeletal System

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What You'll Learn

After you finish this lesson, you will be able to:

  • Describe the functions of the skeletal system.
  • Explain how bones are classified by shape.
  • Identify the bones of the body.
  • Define a joint.

Skeletal System

The skeletal system refers to the bones that form the framework of the body. An adult human has 206 bones. The skeletal system performs these functions:

  • Provides shape and support to the body
  • Protects vital organs
  • Acts as a set of levers, and together with muscles helps a person move
  • Produces blood cells
  • Stores calcium

Types of Bones

Bones vary in shape and size depending on where they are found in the body. Bones are classified by shape.

  • Long bones are longer than they are wide. Bones of this type form the extremities, or arms and legs.
  • Short bones have a similar length and width. Bones of this type can be found in the wrists and ankles. They have an outer layer of compact bone and an inner layer of bone with a latticeworkstructure.
  • Flat bones have a broad shape. Bones of this type can be found in the skull, shoulder blades, and pelvis. They cover organs to protect them or provide a surface for large areas of muscle.
  • Irregular bones are specialized and do not fit the other types. Examples include the bones of the ear, face, and vertebrae.

Which type of bones has a broad shape to cover and protect organs or to provide a surface for large areas of muscle?

  • Long
  • Irregular
  • Short
  • Flat
  • Flat

Which type of bones forms the arms and legs?

  • Long
  • Short
  • Irregular
  • Flat
  • Long

Parts of Long Bones

The longest part of a long bone is called the diaphysis, or shaft.

Each end of the shaft is called an epiphysis. A thin layer of articular cartilage covers the epiphysis to absorb shock where two bones meet to form a joint.

The outer part of the bone is made of compact bone tissue, which does not bend easily. It is covered by the periosteum, which is a tough, fibrous tissue. This tissue contains blood vessels, lymph vessels, and osteoblasts for bone growth, repair, and nutrition.

Inside the compact bone is spongy bone. The medullary canal is a cavity in the center of the shaft where marrow is stored. It is lined by theendosteum to keep the cavity intact.


Bone Marrow

Present in long bones, marrow is important in making blood cells.

  • Red marrow is found in epiphyses and in certain flat bones. It produces red blood cells, platelets, and some white blood cells. Children have red marrow throughout their bodies. As they become adults, most of it is replaced with yellow marrow.
  • Yellow marrow, which is mostly made of fat cells, fills the medullary canal. This marrow serves as fat storage and contains blood vessels and some cells that form white blood cells.

What is another name for the shaft (longest part) of a long bone?

  • Medullary canal
  • Epiphysis
  • Periosteum
  • Diaphysis
  • Diaphysis

What part of long bones stores bone marrow?

  • Epiphysis
  • Periosteum
  • Medullary canal
  • Diaphysis
  • Medullary canal

Bone marrow is important in making red blood cells.

  • True
  • False
  • True

Sections of the Skeletal System

The skeletal system is divided into two sections, axial and appendicular.

  • The axial skeleton forms the main trunk of the body. It includes the skull, spinal column, ribs, and breastbone.
  • The appendicular skeleton forms the extremities. It includes the shoulder girdle, arm bones, pelvic girdle, and leg bones.

Which section of the skeleton forms the main trunk of the body?

  • Pelvic girdle
  • Axial
  • Appendicular
  • Shoulder girdle
  • Axial

Which section of the skeleton includes the arm and leg bones?

  • Axial
  • Skull
  • Spinal column
  • Appendicular
  • Appendicular

Axial Skeleton: Skull

The skull consists of the cranium and facial bones.

The cranium surrounds and protects the brain. The cranial bones join at points called sutures. At birth, there are two openings in the cranium called fontanels, or "soft spots." They give space for the skull to enlarge as the brain grows, and they usually close by 18-24 months of age. The 8 cranial bones include the following:

  • 1 frontal
  • 2 parietal
  • 2 temporal
  • 1 occipital
  • 1 ethmoid
  • 1 sphenoid

Axial Skeleton: Skull (continued)

Facial bones are also part of the skull. Facial bones guard and support the eyes, nose, mouth, and ears. Sinuses are air spaces in and around these bones. These spaces allow the voice to resonate to sound stronger. The 14 facial bones include the following:

  • 5 nasal
  • 2 maxilla, or upper jaw
  • 2 lacrimal, or inner aspect of the eyes
  • 2 zygomatic, or cheek
  • 2 palatine, or roof of the mouth
  • 1 mandible, or lower jaw

The mandible is the only movable bone in the face. It contains the sockets for the lower teeth. The maxilliary bones contain the sockets for the upper teeth.


Which of these skull bones surround and protect the brain?

  • Maxilla
  • Mandible
  • Cranium
  • Palatine
  • All of the above
  • Cranium

What is the name of the bone for the lower jaw?

  • Zygomatic
  • Maxilla
  • Occipital
  • Mandible
  • Mandible

Axial Skeleton: Spinal Column

The spinal column consists of 26 bones called vertebrae. It is also known as the vertebral column. It encloses and protects the spinal cordand supports the head and trunk. Discs of cartilage tissue separate the vertebrae to cushion the bones and allow movement.

The spinal column includes these vertebrae:

  • 7 cervical, or neck
  • 12 thoracic, or chest
  • 5 lumbar, or lower back
  • 1 sacrum, or back of pelvic girdle
  • 1 coccyx, or tailbone

The spinal column consists of 26 bones called _______.

vertebrae, vertebra


What is the name for the bones of the chest?

  • Thoracic
  • Lumbar
  • Cervical
  • Coccyx
  • Thoracic

What is the name for the bones of the lower back?

  • Cervical
  • Lumbar
  • Thoracic
  • Sacrum
  • Lumbar

Axial Skeleton: Thorax

The thorax is also known as the chest cavity. It helps to protect the heart and lungs.

There are 12 pairs of ribs, or costae:

  • The first 7 pairs are called "true ribs" because they are attached to the sternum, or breastbone.
  • The next 5 pairs are called "false ribs."
    • The first 3 pairs of these ribs each attach to the cartilage of the rib above it.
    • The last 2 pairs have no attachment on the front of the body and are called "floating ribs."

The sternum includes 3 parts:

  • The manubrium is the upper region. It is attached by ligaments on both sides to the clavicles, or collarbones.
  • The gladiolus is the body.
  • The xiphoid process is a small piece of cartilage at the bottom.

Why are some costae called "false ribs?"

  • They attach only to other ribs or have no attachment.
  • They are located outside of the chest cavity.
  • They are attached to the sternum with ligaments instead of cartilage.
  • They are actually made of cartilage instead of bone.

They attach only to other ribs or have no attachment.


What is the name of the breastbone?

  • Sternum
  • Thorax
  • Clavicle
  • Coccyx



Appendicular Skeleton: Shoulder Girdle

The shoulder girdle is also known as the pectoral girdle. It includes 4 bones:

  • 2 clavicles, or collarbones
  • 2 scapulas, or shoulder bones

The clavicles help brace the shoulders and prevent a person from having too much forward motion. The scapulas provide a place for the arms to be attached, and together with muscles they assist with arm movement.


Appendicular Skeleton: Arms and Hands

The bones of each arm include the following:

  • Humerus, or upper arm bone.
  • Ulna, or the lower arm bone whose upper end forms the elbow.
  • Radius, or the lower arm bone on the thumb side.

The bones of each hand include the following:

  • 8 carpals, which form the wrist.
  • 5 metacarpals, which form the palm of the hand.
  • 14 phalanges, which form the fingers.

What is the name of the collarbones?

  • Clavicles
  • Scapulas
  • Phalanges
  • Carpals
  • Clavicles

What is the name of the upper arm bone?

  • Humerus
  • Clavicle
  • Ulna
  • Radius
  • Humerus

What is the name of the wrist bones?

  • Scapulas
  • Carpals
  • Metacarpals
  • Phalanges
  • Carpals

Appendicular Skeleton: Pelvic Girdle

The pelvic girdle includes 2 os coxae, or hip bones. They attach to the sacrum in addition to connecting to each other at a joint called thesymphysis pubis. Each os coxae consists of these 3 fused sections:

  • Illium
  • Ischium
  • Pubis

The pelvic girdle supports the trunk of the body, in particular the lower soft abdominal organs. It also provides a place for the legs to be attached.


Appendicular Skeleton: Legs and Feet

The bones of each leg include the following:

  • Femur, or the thigh bone in the upper leg. It is the longest bone in the body.
  • Patella, or kneecap.
  • Tibia, or the shin in the lower leg.
  • Fibula, which is also in the lower leg.

The bones of each foot include the following:

  • 7 tarsals, which form the ankle. A large tarsal bone called the calcaneous forms the heel.
  • 5 metatarsals, which form the instep of the foot.
  • 14 phalanges, which form the toes.

How many sections are fused to make up each of the os coxae, or hip bones?

  • Two
  • Three
  • Four
  • Five
  • Three

What is the name of the upper leg bone, in the thigh?

  • Fibula
  • Ischium
  • Femur
  • Tibia
  • Femur

What is the name of the shin bone?

  • Patella
  • Illium
  • Tibia
  • Fibula
  • Tibia

What is the name of the bones for both the toes and fingers?

  • Tarsals
  • Phalanges
  • Metatarsals
  • Carpals
  • Phalanges


Joints are areas where two or more bones connect. Bands of connective tissue called ligaments help hold bones together at joints. Joints are classified by movement.

  • A diarthrosis joint is movable.
  • An amphiarthrosis joint is partially movable.
  • A synarthrosis joint is not movable.

An area where two or more bones connect is called a _______.



Not movable

synarthrosis joint



diarthrosis joint


partially movable

amphiarthrosis joint


Lesson Summary

In this lesson, you learned that:

  • The main function of the skeletal system is to give shape to and protect the body.
  • Bones are classified by shape: long, short, flat, or irregular.
  • The axial skeleton forms the main trunk of the body. It includes the skull, spinal column, ribs, and breastbone.
  • The appendicular skeleton forms the extremities. It includes the shoulder girdle, arm bones, pelvic girdle, and leg bones.
  • Joints are areas where two or more bones connect.

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