Chapter 5: Skeletal system  021108


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·         What are the basic tissues that make the skeletal system.

·         How is bone made originally, and how is it reformatted once you get older.

·         Describe the functions of the bone.

·         How are connections between bones made.

·         What are some of the diseases and disorders of the skeletal system.

·         Be able to identify the major bones and their function.


Important Figures

5.1    Know the basic structure of bone.

5.2     Know how bone develops

5.6 Know the parts of the skeleton

5.13    Know how the knee functions

5.14    Know Flexion, extension and Hyperextension.


1.   Characteristics of Bone:   To bone or not to bone?

A.  Basic Bone functions and Structure

1)   Bones serve these 5 functions:

a)    Bones are moved by the contraction of muscles: thus, the whole body is movable.

b)   Bones enclose and protect vital organs such as the brain, lungs and female reproductive organs.

c)    The bones support and anchor muscles.

d)   Bone tissue acts as a depository for calcium, phosphorus, and other ions.

e)    Some bones are sites of red blood cell production.

2)     There are four types of bones listed according to their shapes: long (arms), short (wrist), flat (skull), and irregular (vertebrae).

3)   Bone is a connective tissue with living cells (osteocytes) and collagen fibers distributed throughout a ground substance that is hardened by calcium salts.

a)    As the bone develops, precursor cells called osteoblasts secrete collagen fibers and ground substance of proteins and carbohydrates.

b)   Eventually, osteocytes reside within lacunae in the ground substance, which becomes mineralized by calcium deposits

4)   The strong or  compact” bone tissue forms the bone’s shaft and the outer portion of its two ends: a periostem covers the bone shaft.

a)    Concentric layers surround osteons (haversian systems) and the Haversian canals at their centers, which contain blood vessels and nerves.

b)   Osteocytes (live bone cells) in the lacunae communicate by way of canaliculi.

5)   “Spongy” bone tissue may have red marrow that produces blood cells: adults have reserve yellow marrow (mostly fat), which can be converted to red marrow if blood cell production needs to be increased.

6)   Bone tissue it not dead.  It is constantly being reorganized and renewed.  The more your bones are used the stronger they become.  The less your bones are used the weaker they become.  This can be a problem for those who are confined or who are in micro gravity environments for extended periods.

B.   How bones Develop:  the pattern for your bones is first set out in cartilage that then turns into bone.

1)   Osteoblasts secrete material (Hydroxyapatite) inside the shaft of the cartilage model of long bones

2)   Calcium is deposited: cavities merge to form the marrow cavity.

3)   Eventually osteoblasts become trapped within their own secretions and become osteocytes (mature bone cells).

C.  In growing children, the epiphyses (ends of bones) are separated form the shaft by an epiphyseal plate (cartilage), which continues to grow under the influence of growth hormone until late adolescence.

2.     Growth and maintenance of the skeleton   quiz

A.   Bone is renewed constantly as minerals are deposited (by osteoblasts) and withdrawn (by osteoclasts) during the “remodeling” process.  Bone is constantly being built up and broken down depending on usage.  This is why astronauts who do note exercise loose bone mass.

1)   Bone turnover helps to maintain calcium levels for the entire body.

B.   Parathyroid hormone causes bone cells to release enzymes that will dissolve bone tissue and release calcium to the interstitial fluid and blood: calcitonin stimulates the reverse.

C.  Your bone is constantly being remodeled time and time again.

1)   Before adulthood, bone turnover is especially important in increasing the diameter of certain bones.

2)   Osteoporosis (decreased bone density) is associated with decreases in osteoblast activity, sex hormone production, exercises, and calcium uptake.

3)   Bone remodeling depends on the force that is exerted on the bone.  The greater the force the greater the deposit of bone.

4)   Regular exorcise will substantially increase your bone mass.

D.  Overview of the skeleton.

1)   The 206 bones of a human are arranged in two major divisions (axial and Appendicular).

2)   Bones are attached to bones by ligaments: bones are connected to muscles by tendons.

3.    Axial skeleton                                           quiz

A.   The Skull

1)   The skull consists of more than two dozen bones.

2)   The cranial vault, or brain case, is a grouping of eight bones.

a)    Frontal bone makes up the forehead and contains the sinuses.

b)   Temporal bones form the lower sides of the cranium and surround the ear canals.

c)     A sphenoid bone forms the eye socket.

d)   Parietal bones form a large part of the skull above the temporal bones.

e)    An occipital bone forms the back of the skull and encloses the foramen magnum, which is a passageway for the spinal cord.

B.   Facial bones

1)     The mandible forms the lower jaw: two maxillary bones form the upper jaw

2)     Zygomatic bones form the cheekbones : lacrimal bones form the inner eye sockets

3)     Palatine bones make up the nasal cavity: a vomer bone forms the nasal septum

C.    The vertebral column, or backbone, extends form the base of the skull to the hipbones

1)     The spinal cord extends through a cavity formed by the vertebrae.

2)     Humans have 24 separate vertebrae: 7 cervical, 12 thoracic, 5 lumbar, plus a sacrum and a coccyx (which contain fused bones)

3)   Cartilaginous intervertebral disks serve as shock absorbers but may rupture (herniate) to release fluid, which presses against adjacent nerves.

D.  The ribs and Sternum.

1)   Ribs (12 pairs) are attached to the vertebrae dorsally and serve as a scaffolding for the upper body torso

2)   Most of the ribs are attached to the sternum ventrally.

4.     Appendicular Skeleton.

A.   Pectoral girdle and upper limbs

1)   The pectoral girdle includes the bones of and attached to the shoulder.

a)    The scapula is a large, flat shoulder blade with a socket for the upper arm bone.

b)   The clavicle (collarbone) connects the scapula to the sternum.

2)   Each upper limb includes some 30 separate bones.

a)    The humorous is the bone of the upper arm.

b)   The radius and ulna extend form the hinge like joint of the elbow to the wrist.

c)    The carpels form the wrist: the metacarpals the palm of the hand and the phalanges the fingers.

B.    The pelvic girdle and lower limbs.

1)   The pelvic girdle includes the pelvis and the legs.

a)    The pelvis is made up of coaxial bones.

b)   The pelvis is broader in females than males: this is necessary for childbearing.

2)    The legs contain the body’s large bones.

a)    The femur is the longest bone, expending form the pelvis to the knee.

b)   The tibia and fibula form the lower leg: the kneecap bone is the patella.

Tarsal bones compose the ankle metatarsals the foot, and phalanges the toes.

5.     Joints

A.  A synovial joints are the most common and move freely: they include the ball and socket joints of the hips and the hinge like joints such as the knee.

1)   They are stabilized by ligaments.

2)    A capsule of dense connective tissue surrounds the bones of the joint.

3)    In osteoarthritis, the cartilage at the end of the bone degenerates.

4)    In rheumatoid arthritis, the synovial membrane becomes inflamed, the cartilage degenerates, and bone is deposited into the joint.

B.   Cartilaginous joints (such as between the vertebrae) have no gap, but are held together by cartilage and can move only a little.

C.   Fibrous joints also have no gap between the bones and hardly move: flat cranial bones are an example

6.     Diseases and disorders of the skeletal system

A.   Sprain is a stretched or torn ligament.  May take a long time to heal because the ligaments have every few cells and a poor blood supply.  A large ligament that is torn will not heal and needs to be fixed surgically.

B.   Bursitis and tendonitis

a)     Inflammation of the tendons and bursae after injury.  Located usually at joints where repetitive banging occurs.


C.    Arthritis, or inflammation of the joints.

a)     General term for joint inflammation.

b)   Mostly due to general wear and tear occurring over a lifetime, and usually in older adults.

c)    In time, the cartilage protecting the end of the joints wears out.

d)   Rheumatoid arthritis involves joint inflammation and is caused by the bodies own immune system.


7.     Terms for movement

A.   Flexion:  decreases the angle of a joint

B.   Extension:  Increases the angle of a joint

C.  Abduction:  movement of a limb away form the body's midline

D.  Adduction: movement of a limb toward the body's midline


Possible assignments: things to think about

1.     Why do some people consider bone non-living?   Is this true?  How would you counter this argument?

2.      What is the difference between bone production in a fetus and the way a bone heals after a break? 

3.      What muscles are collectively called the hamstrings, in which sports are these injured

4.     What is a slipped or herniated disc?  What are its most common causes?

5.     What is the effect of exorcising on the production of bone.

6.     Why are two types of cells (ones that break down materials and one that build up bone) required for healthy dynamic bones??


Multiple-choice questions Click on the letters to see if the answer is correct.  If you need to review click on the hyper linked words in the question or the answers.


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1)      The difference between osteoblasts and osteoclasts are


Osteoblasts make up epithelial tissue and osteoclasts are connective tissue.


Osteoclasts are osteoblasts that are trapped within the solid matrix of the bone


Osteoblasts deposit (make) bone and osteoclasts remove bone, constantly renewing the structure.


Osteoblasts secrete material inside the cartilage model of bones found in infants.


Osteoblasts work in the epiphyses and help the bones grow long.

2.      A fellow student was not wearing a helmet and crashes his motorcycle.  She says that she broke several bones in her skull.  Which of the following would be bones that he may have broken?


The sphenoid bone


The occipital bone


The mandible


The thoracic


The sacrum




Answers  1) C,D,E 2) A,B,C





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