Learning Objectives

To be able to distinguish the differences between the axial and appendicular skeleton. Identify the bony compositions on each part of the skeleton. List names of various bones of the body.

Notes, Pictures & Videos

A musical interlude to get started.

flashcards These can be very helpful.

The human skeleton is divided into two distinct parts:

The Axial Skeleton: The Skull, Sternum, Ribs, and Vertebral Column

The Appendicular Skeleton: The upper Extremities, Lower Extremities, The Shoulder Girdle, and The Pelvic Girdle (Sacrum and Coccyx is part of the Vertebral column)

(see links for pictures)

This helped me to visualize the two parts of the skeleton!


Main functions of the Skeletal System:
A skeleton provides "cages" to protect the delicate organs. For example: the ribcage helps protect the lungs, heart, etc. Moreover, it gives muscles "sides" or edges to attach to (through tendons of muscle and the tough periosteum of bone). It also maintains balance, and supports the body's shape. But all these functions are perhaps secondary to the primary function of locomotion. The bones allow the muscles of the body to move the limbs.

Hemopoiesis is also an important function of bones. This is the process of red blood cell formation and is carried out by stem cells in active red bone marrow. Much of red bone marrow becomes inactive when you reach adulthood and turns into fatty tissue called yellow bone marrow. Sites in adults for active red bone marrow are: flat bones of the skull, vertebrae, ribs, sternum, ossa coxae, and the proximal ends of the humerus and femur.

Bones come in different sizes; and shapes,the longest bone is the femur, and the shortest, the stapes. The outer layer of bones are called compact bones, and the middle, called spongy or cancellous bone, which are hollow and contain bone marrow. Joints of bones are held together by ligaments, which are fine fibers attaching to each bone at joints. In order for bones to not scrape against each other, slippery cartilage and synovial fluid are covered atop the bones.


This picture shows which parts of the skeleton are bone,
and which parts are cartilage. This picture is mainly only
showing the hyaline cartilage of the body, which is the
majority of cartilage in our bodies.

These are the different types of bones distributed
through our bodies. Can you name each of these
bones?



Take a look at the make-up of our bones (particularly long bones). Locate where the spongy/cancellous bone, the compact bone, the periosteum and endosteum, the epiphyseal growth plate or line, and where the marrow is! Notice how much different spongy bones looks than compact bone.

This video does a good job explaining structure and function.


Problems in the skeletal system:

Osteoporosis is a disease in which bones become fragile and more likely to break. If not prevented or if left untreated, osteoporosis can progress painlessly until a bone breaks. Fractures occur typically in the hip, spine, and wrist; and usually require prolonged hospitalization and major surgery. Our clinic emphasizes on prevention, early detection and prompt treatment. Early detection of bone loss can prompt treatment that may restore lost bone mass and reduce the chances of fracture. Dual-energy x-ray absorptiometry (DEXA) is the gold standard for measuring bone mineral density. This technology carries low risk and takes only a few minutes. It measures spine, hip or total body bone mineral density (BMD), providing reliability while exposing a woman to minimal radiation. It is recommended that all women aged40 years and older, or postmenopausal women who present with fractures, or who have been taking hormone replacement therapy for prolonged periods of time should receive osteoporosis screening in a regular basis.


Osteopenia:
What causes osteopenia? Bones naturally become thinner as people grow older because, beginning in middle age, existing bone cells are reabsorbed by the body faster than new bone is made. As this occurs, the bones lose minerals, heaviness (mass), and structure, making them weaker and increasing their risk of breaking. All people begin losing bone mass after they reach peak BMD at about 30 years of age. The thicker your bones are at about age 30, the longer it takes to develop osteopenia or osteoporosis. Some people who have osteopenia may not have bone loss; they may just naturally have a lower bone density. Osteopenia may also be the result of a wide variety of other conditions, disease processes, or treatments. Women are far more likely to develop osteopenia and osteoporosis than men. This is because women have a lower peak BMD and because the loss of bone mass speeds up as hormonal changes take place at the time of menopause. In both men and women, the following factors can all contribute to osteopenia:

• Eating disorders or metabolism problems that do not allow the body to take in and use enough vitamins and minerals
• Chemotherapy, or medications such as steroids used to treat a number of conditions, including asthma
• Exposure to radiation

Having a family history of osteoporosis, being thin, being white or Asian, getting limited physical activity, smoking, regularly drinking cola drinks, and drinking excessive amounts of alcohol also increase the risk of osteopenia and, eventually, osteoporosis.



Rickets:
Rickets is a softening of the bones in children potentially leading to fractures and deformity. Rickets is among the most frequent childhood diseases in many developing countries. The predominant cause is a vitamin D deficiency, but lack of adequate calcium in the diet may also lead to rickets. Although it can occur in adults, the majority of cases occur in children suffering from severe malnutrition, usually resulting from famine or starvation during the early stages of childhood. Osteomalacia is the term used to describe a similar condition occurring in adults, generally due to a deficiency of vitamin D.


Achondropladtic Dwarfism:
Achondroplasia is a type of autosomal dominant genetic disorder that is a common cause of dwarfism. Achondroplastic dwarfs have short stature, with an average adult height of 131 cm (4 feet 3.8 inches) for males and 123 cm (4 feet 0.6 inches) for females.

Achondroplasia is by far the most common chondrodysplasia in humans with an estimated prevalence to be one in 15,000 to 40,000 live births.[1] Achondroplasia is a result of an autosomal dominant mutation in the fibroblast growth factor receptor gene 3 (FGFR3), which causes an abnormality of cartilage formation. FGFR3 normally has a negative regulatory effect on bone growth. In achondroplasia, the mutated form of the receptor is constitutively active and this leads to severely shortened bones.

Case Study

Cartilage injuries of the knee - causes, diagnosis and treatment review

In the News

Psychology / Psychiatry; Sports Medicine / Fitness; 14 Sept 2006 - 20:00 PDT
Research Suggests That Wearing A Helmet Puts Cyclists At Risk
Drivers pass closer when overtaking cyclists wearing helmets than when overtaking bare-headed cyclists, increasing the risk of a collision, the research has found. Dr Ian Walker, a traffic psychologist from the University of Bath in the UK, used a bicycle fitted with a computer and an ultrasonic distance sensor to record data from over 2,500 overtaking motorists in Salisbury and Bristol.
Dr Walker, who was struck by a bus and a truck in the course of the experiment, spent half the time wearing a cycle helmet and half the time bare-headed. He was wearing the helmet both times he was struck. He found that drivers were as much as twice as likely to get particularly close to the bicycle when he was wearing the helmet. Across the board, drivers passed an average of 8.5 cm (3 1/3 inches) closer with the helmet than without. The research has been accepted for publication in the journal Accident Analysis & Prevention. "This study shows that when drivers overtake a cyclist, the margin for error they leave is affected by the cyclist's appearance," said Dr Walker, from the University's Department of Psychology. "By leaving the cyclist less room, drivers reduce the safety margin that cyclists need to deal with obstacles in the road, such as drain covers and potholes, as well as the margin for error in their own judgements. "We know helmets are useful in low-speed falls, and so definitely good for children, but whether they offer any real protection to somebody struck by a car is very controversial. "Either way, this study suggests wearing a helmet might make a collision more likely in the first place." Dr Walker suggests the reason drivers give less room to cyclists wearing helmets is down to how cyclists are perceived as a group. "We know from research that many drivers see cyclists as a separate subculture, to which they don't belong," said Dr Walker. "As a result they hold stereotyped ideas about cyclists, often judging all riders by the yardstick of the lycra-clad street-warrior. "This may lead drivers to believe cyclists with helmets are more serious, experienced and predictable than those without. "The idea that helmeted cyclists are more experienced and less likely to do something unexpected would explain why drivers leave less space when passing. "In reality, there is no real reason to believe someone with a helmet is any more experienced than someone without. "The best answer is for different types of road user to understand each other better. "Most adult cyclists know what it is like to drive a car, but relatively few motorists ride bicycles in traffic, and so don't know the issues cyclists face. "There should definitely be more information on the needs of other road users when people learn to drive, and practical experience would be even better. "When people try cycling, they nearly always say it changes the way they treat other road users when they get back in their cars." The study also found that large vehicles, such as buses and trucks, passed considerably closer when overtaking cyclists than cars. The average car passed 1.33 metres (4.4 feet) away from the bicycle, whereas the average truck got 19 centimetres (7.5 inches) closer and the average bus 23 centimetres (9 inches) closer.

Glossary

Osteology: The scientific study of bones.
Sutural bones/wormian bones: Extra bones within joints (sutures) of the skull.
Sesamoid bones: Extra bones within tendons from repeated stress as the tendon moves across a joint. (develop by intramembraneous ossification inside tendons)
C-shaped hyaline rings: Cartilaginous rings in the respiratory tract that keep the walls of the trochlea and smaller airways open.
Hyaline cartilage: A clear colored cartilage found in much of the respiratory tract, joints, growth plates, and the fetal skeleton. (most abundant c. in body)
Fibrocartilage: Act as shock absorbers found in places such as between vertebrae and in the symphasis pubis. There is an extracellular matrix with thick collagen fibers that help resist stretching and compression.
Elastic cartilage: Also with an extra cellular matrix, it is found in places in need of highly flexible support i.e. external ear, ear canal, epiglottis.
Calcification: Deposition of minerals in the matrix of bone connective tissue to make bone sturdy.
Hemopoisis/hematapoisis: The process of blood cell formation carried out by stem cells in the red bone marrow of spongy bone.
Erythropoietin: Hormone produced by the kidneys, it stimulates hematapoisis.
Ossification/Osteogenesis: To turn (cartilage) into bone.
Long bones: Typically function as levers and are bones of the upper and lower extremities.
Short bones: Cube-shaped and act to transfer forces. Bones of wrist and ankle.
Flat bones: Broad with a dense surface for muscle attachment or protection of underlying organs. Roof of skull, scapulae, sternum, ribs.
Irregular bones: Varied in shape with projections for muscle attachments or articulation. Vertebrae, several bones in skull i.e. sphenoid, ethmoid, etc.
Diaphysis: Central shaft of long bones
Medullary cavity/marrow cavity: Hollow space within diaphysis. Contains yellow marrow in adults and red marrow in growing children.
Endosteum: Lining of medullary cavity. Helps remodel medullary cavity during bone growth and repair.
Epiphysis: Knobby ends of long bones. Outer layer of compact bone and inner layer of spongy bone. At a joint surface, it is covered in hyaline cartilage called articular cartilage, which helps reduce friction and absorb shock in movable joints.
Periosteum: Tough sheath of dense irregular connective tissue around the outer surface of bone (except areas covered by art. cartilage). Serves as a place for tendon-muscle attachment to bone. **Periosteum is responsible for the growth in the width of bone by pulling stress on the periosteum.
Epiphyseal growth plate: Located between epiphysis and diaphysis in growing children/teenagers. **Composed of hyaline cartilage with high mitotic activity that helps bones grow in length.
Epiphyseal line: Remnant of e. growth plate in adults when bones are done growing.
Osteoblasts: **Lay down the ground substance that creates new bone. Secrete initial form of bone matrix called osteoid which calcifies to become bone. (happens on the outside of bone)
Osteoclasts: **Maintains matrix of bone by breaking in down. This process is called osteolysis. (happens in the inside of bone)
Intramembraneous ossification: Takes existing membranes & lays down bone tissue. Produces flat bones of the skull and some facial bones. This is why babies have soft spots- the membraneous tissue hasn't hardened yet.
Endochondral ossification: Cartilage is replaced with bone. Occurs with the majority of the skeleton.
Growth hormone/somatotrophin: Produced in pituitary gland and stimulated activity in e. growth plates.
Sex hormones-estrogen and testosterone: Dramatically accelerate bone growth at the e. growth plates at puberty.
Vitamin A: activates/stimulates osteoblasts
Vit. C: required for normal synthesis of collagen, the primary component in bone matrix.
Vit. D: stimulates the absorption and transport of calcium and phosphate ions into the blood for possible storage in the bone.
Condyle: large, smooth rounded articulating oval structure
Facet: small, flat, shallow art. surface
Head: prominent, rounded epiphysis
Alveolus: deep pit/socket in upper jaw
Fossa: flattened or shallow depression
Crest: narrow, prominent, ridge-like projection
Epicondyle: projection adjacent to a condyle
Process: any marked, bony prominence
Spine: pointed, slender process
Trochanter: massive, rough projection found only on proximal, lateral end of femur
Tubercle: small, round projection
Tuberosity: large, rough projection
Fissure: narrow, slit-like opening through a bone
Foramen: rounded passageway through a bone
Sinus: cavity or hollow space in a bone

Connections to other body systems

• Starting from the integumentary system, "Vitamin D is essential for the process of absorbing calcium and phosphorus from the small intestine for the synthesis of healthy bones" (p. 25). With the help of that system our bones will have the elements needed for osteoblasts to do their job in bone development. More than 90% of the bodies reserves for calcium are are found in the bones. Without calcium we would struggle with muscle contraction, blood clotting, and nerve impulse transmission.
• 
  
• An organ from the urinary system plays a role in the stimulation of a cell found in the red bone marrow. What organ? What hormone does it secrete? What will that hormone stimulate? The kidney controls the hormone erythropoietin. Once that hormone is released hematopoiesis can begin. It happens in nearly all parts of the body for children but in adults you can only find it in the flat bones of the skull, vertebrae, ribs, sternum, bones of the pelvis, and the proximal ends of the humerus and femur.

Review Questions

Answers to questions are located on the "quiz answers" tab

1. The Petrous Portion is located in which bone?
a. Zygomatic bone
b. Occipital bone
*c. Temporal bone
d. Parietal bone

2. Cartilage connects what?
a. Bone to Bone
b. Muscle to Bone
c. Muscle to Muscle
d. Skin to Muscle
*e. Does not connect

3. Tendons connect what?
a. Bone to Bone
*b. Muscle to Bone
c. Muscle to Muscle
d. Skin to Muscle

4. The healing of a fractured Ulna would mainly be determined by upon which tissue?
a. Periosteum
*b. Endosteum
c. Hyaline Cartilage
d. Compact bone

5. How many phalanges are there in a normal human body?
a. 10
*b. 56
c. 42
d. 60
e. Impossible to tell

6. If I went rollerblading and accidentally hurt my scaphoid by falling down what part of the body did I hurt?
a. ankle
b. arm
c. wrist
d. hand

7. The trabecular bone which is a found in reparative phase of fracture healing is absorbed by osteoclasts, that creates a shallow pit known as _______ in the remodeling phase?
a. Howships Lacuna
b. Entheses
c. Haversian system
d. Medullary Cavity

8. The Cubital Fossa is located?
a. Upper extremity
b. Lower extremity
c. Sphenoid bone
d. Cervical Vertebrae

9. Bone marrow that produces red blood cells is found in?
a. Spongy bone
b. Strong bones
c. Developing bones
d. Compact bones

10. What is the nonliving portion of the bone mostly made of?
a. Chitin, sodium & calcium
b. Spongy bone, magnesium & calcium
c. Keratin, sulfate & sodium
d. Matrix fibers, calcium & phosphates

11. What is one example of a sesamoid bone in our body?
a. knuckles
b. olecranon fossa (elbow)
c. patellae
d. axis of the spine
e. none of the above

12. One explanation for bones becoming weaker is:
a. osteoclasts are more active than osteoblasts
b. osteocytes are more active than osteoprogeniter cells
c. osteoblasts are more active than osteoclasts
d. osteolysis is not happening in the bone matrix
e. all of the above

13. Red bone marrow:
a. Is stimulated by erythropoietin
b. Can be found in the ossa coxae
c. Is in the spongy bone of most bones in the body of a child
d. Becomes inactive and turns into fat in diaphysis
e. All of the above

14. Compact bone:
a. is also called cancelous bone
b. is only in the diaphysis
c. is a shock absorber
d. is in the frontal bone
e. none of the above

15. During fetal development and through infant and toddler years:
a. chondroblasts secrete an elastic cartilage model
b. cartilage is replaced with bone
c. minerals are deposited into hypertrophied cartilage cells
d. all cartilage cells die from loss of nutrients from calcification
e. b & c


16. The sequence of events following a bone fracture is:
a. fractured hematoma, fibrocartilage callous, the bone is remodeled, hard bony callous forms
b. fractured hematoma, fibrocartilage callous, hard bony callous forms, the bone is remodeled
c. neither are correct

17. Osteopenia:
a. Is less controllable than osteoporosis
b. Is more controllable than osteoporosis
c. Is when bones become weaker from insufficient ossification
d. Is when bones become weaker from insufficient calcification
e. a & c

18. According to an article, problems healing bone is associated with:
a. The Ilizarov apparatus
b. Individuals who smoke
c. Osteoblasts working too hard
d. Malfunction of the bladder
e. a & b


19. For more osteoclasts to work:
a. be an astronaut
b. don't pull on the periosteum
c. stay out in the sun
d. stay in bed
e. a , b, & d

20. T/F: Sesamoid bones are synonymous with sutural bones.

21. T/F: When trauma occurs in an area, a bone can develop.

22. T/F: Chondroblasts make chondrocytes, which make cartilage.

23. The vertebrae and pubis:
a. have fibrocartilage
b. have fibrocartilage and elastic cartilage
c. are composed of c-shaped rings
d. have cartilage that is clear in color

24. The matrix of bone connective tissue is:
a. sturdy and rigid
b. osseous
c. due to calcification
d. all of the above

25. Primary ossification occurs in the _____ and secondary ossification occurs in the _____.
a. epiphysis, diaphysis
b. short bones, long bones
c. diaphysis, epiphysis
d. long bones, short bones
e. a & b

26. The Ilizerov apparatus stimulates:
a. osteoblasts
b. osteoclasts
c. hyaline in epiphyseal growth plate
d. none of the above

27. Thick bones of the left arm are associated with:
a. achondroplastic dwarfism
b. endosteum
c. Roman soldier skeletons
d. stimulated osteoclasts
e. all of the above

28. A pathologic fracture can be linked to:
a. disease
b. stepping out of the car
c. vitamin D deficiency
d. all of the above
e. none of the above

29. A greenstick fracture:
a. is a complete break
b. breaks the skin
c. breaks bone into many pieces
d. happens often in growing children

30. A facet is:
a. large, smooth, and round
b. at the rounded epiphysis
c. a ridge-like projection
d. a slender process
e. none of the above

31. An additional bone that may develop in response to stress is called:
a. wormian bone
b. sutural bone
c. sesamoid bone
d. funny bone