BIO210 Weekly Guide #4
AXIAL SKELETON;
CARTILAGE & BONE
After completing this laboratory you should be able to:
1) Recognize and name the bones and cartilages of the axial skeleton as well as their major structural features and landmarks
2) Identify the bones of the skull
3) Distinguish vertebrae from the cervical, thoracic, lumbar, sacral, and coccygeal levels
4) Name the four natural curvatures of the adult spine and describe the three major pathological curvatures
5) Distinguish between true, false, and floating ribs
6) Recognize, fully classify, and functionally characterize samples of cartilage and bone in microscopic sections
7) For any type of bone or cartilage, state where in the body it could be found
8) Recognize and describe endochondral and intramembranous bone formation and provide examples of bones formed by each process
Guide to Gross Anatomy Guide to Histology Guide to Physiology
Outline
I. Axial Skeleton {FAP Ch 7; APL Exercises 8.1, 8.2}
A. Axial vs. appendicular
B. Spinal column {FAP 7-5, 7-6}
general vertebral structure
regions
vertebral numbers and unique characteristics
ranges of motion
foramina
spinal curvatures
natural
pathological
C. Skull {FAP 7-2, 7-3}
cranium
calvarium and base
regions and bones
processes and fossa
foramina
face
regions and bones
orbits
jaws
ossicles
D. Hyoid {FAP Fig 7-13}
E. Ribs {FAP 7-7}
general structure
true ribs
false ribs
floating ribs
costal cartilages (sternal ribs)
motion of ribs
F. Sternum {FAP 7-7}
manubrium (head), body, and xiphoid
II. Cartilage {FAP 4-5; APL 5-2.2}
A. Properties
C.T. - mostly organic ground substance
semi-rigid
avascular
B. Functions
support, protection, bone models
C. Constituents
cells - chondrocytes (<--chondroblasts)
lacunae
extracellular material - fibers and ground substance (condroitin sulfate)
D. Perichondrium
outer fibrous & inner cellular layers
E. Types - properties and locations
hyaline cartilage
fibrocartilage
elastic cartilage
F. Development
appositional and interstitial
III. Bone {FAP 4-4, 6-1 to 6-6; APL 5-2.2, Unit 7}
A. Properties
C.T. - organic matrix with inorganic salts
calcium phosphate = hydroxyappetite
rigid
vascular
B. Functions
support, protection, leverage
calcium and phosphate depot
hematopoietic space
C. Constituents
cells
osteocytes (<--osteoblasts)
osteoclasts
lacunae, resorption pits
extracellular material - fibers, organic matrix, inorganic salts
D. Periosteum
outer fibrous and inner cellular layers
E. Types of Bone Tissue
compact
woven bone vs. lamellar bone
Haversian system - Haversian canals, lamellae, lacunae, canaliculi, Volkman's canals
spongy (cancellous)
trabeculae
stress and redesign
marrow spaces
hematopoiesis
intraosseous fat
F. Development
intracartilaginous (endochondral) - long, short, irregular bones
general plan - protobones, ossification centers, epiphysis, diaphysis,
epiphysial plates
6 zones
woven bone vs. lamellar bone - remodeling and repair
intramembranous - flat bones
general plan - periosteum, tables, cancellous layer
aging and osteopenia
Gross Anatomy List
Infracranial Axial Skeleton: {FAP 7-5 to 7-7; APL 8.2}
vertebral column / vertebrae
cervical (= "neck") [C1-C7]
especially atlas (C1), axis (C2), vertebra prominens (C7)
thoracic (= "chest") [T1-T12]
lumbar (= "back") [L1-L5]
sacral (= "holy" - used in sacrifices);
sacrum is five fused sacral vertebrae [S1-S5]
coccygeal (= "cuckoo" - resembles beak)
coccyx is 3-4 fused vertebrae [Cx1-Cx4]
sternum:
manubrium or head (manubrium = "handle")
body
xiphoid process (xiphoid = "sword-shaped")
ribs:
true ribs
false ribs
floating ribs
costal cartilages (costal= "rib")
hyoid (="U-shaped")
Skull: {FAP 7-2 to 7-4; APL 8.1}
cranial bones:
frontal (= "front")
occipital (= "back of head")
ethmoid (= "sieve-like")
sphenoid (= "wedge-shaped")
temporals (= "time"- where you first get gray hair)
parietals (= "wall")
facial bones:
mandible (= "lower jaw")
vomer (= "plow")
maxillae (= "upper jaw")
zygomatics (= "cheekbone")
nasals (= "nose")
lacrimals (= "tear")
palatines (= "roof of mouth")
inferior nasal conchae (= "shell")
Ossicles:
malleus (= "hammer")
incus (= "anvil")
stapes (= "stirrup")
KEY: Be able to identify bones and major features
Guide to Gross Anatomy
Vertebral Column {APL Fig 8.14, 8.15}
The vertebral column consists of 32 or 33 vertebrae, which fall in 5 regions:
7 cervical
12 thoracic
5 lumbar
5 sacral
3-4 coccygeal
The cervical, thoracic, and lumbar vertebrae are termed "true" vertebrae; they are connected by joints and can move relative to each other. The sacral and coccygeal vertebrae are termed "false" vertebrae; they are fused into the sacrum and coccyx, respectively.
a) Examine a typical true vertebra from the cervical, thoracic, or lumbar region and identify the following structures common to all true vertebrae except C1 and C2:
body transverse process
arches: spinous process
laminae articular processes
pedicles spinal foramen
- Identify the transverse foramina (cervical vertebrae only). The vertebral arteries pass through these.
- Identify the articular demifacets. What articulates here (see skeleton)?
b) Place two adjacent vertebrae together and observe the intervertebral foramina thus formed. Each such foramen is occupied by a dorsal root ganglion and spinal nerve.
c) Place vertebrae from the cervical, thoracic, and lumbar regions next to each other.
- List the features that you could use to distinguish them. Pay special attention to the shapes of the body, spinal foramina, and processes and the locations and orientations of articular surfaces. What structure is unique to the cervical vertebrae's transverse processes? What articular surfaces are unique to the thoracic vertebrae?
- Note the orientations of the superior and inferior articular surfaces between vertebrae in each region. These surfaces can slide somewhat relative to each other. What range of motion does this allow in each region? Try it out on the disarticulated vertebral column to confirm your guesses.
d) Examine the atlas (C1) and axis (C2).
- Note that the atlas has no body. In development its body has become fused to the axis, forming the dens. What motion does this allow at the atlanto-axial joint?
- On a skeleton note how the atlas articulates with the occipital bone of the skull. What motion does this allow at the atlanto-occipital joint?
e) Palpate the protuberances formed by the spinous processes of the vertebral column on yourself or a classmate (ask permission first!). Locate the "vertebra prominens" (C7). What ligament prevents you from feeling the spinous processes of the higher cervical vertebrae?
f) Examine the sacrum. Note that it is formed by the fusion of five vertebrae and their intervertebral disks. Identify the following:
anterior sacral foramina neural (sacral) canal auricular processes
posterior sacral foramina hiatus articular processes
middle sacral crest
g) Examine the coccyx. It is formed by the fusion of 3-4 vertebrae. Identify the following:
transverse processes cornu (horns)
h) On the skeleton and demonstration model study the intervertebral disks which separate the vertebral bodies. Each disk has an outer ring (annulus fibrosus) of tough fibrocartilage and a gelatinous core (nucleus pulposus) which is a remnant of the notochord.
i) The ligamentum nuchae is the fused supraspinous ligaments of the cervical vertebrae. What is its major role?
j) On the skeleton note the four normal flexures of the vertebral column; the cervical, thoracic, lumbar, and sacral.
- Note that the thoracic and sacral are primary flexures (present at birth), while the cervical and lumbar are secondary flexures (acquired later in life).
- At what approximate age does each secondary flexure develop, and what is the significance for posture of each?
- What are the pathological curvatures of scoliosis, kyphosis, and lordosis?
Sternum {APL Fig 8.16}
a) Observe that the sternum is composed of three parts; the manubrium, body, and xiphoid process. Locate the following:
suprasternal (jugular) notch facets for clavicle
sternal angle facets for costal cartilages
b) On yourself, palpate the length of the sternum. Identify the jugular notch and sternal angle. The sternal angle is at the level of the second costal cartilage (CC2) and is a handy reference landmark for locating deeper structures, such as the base of the heart..
Ribs {APL Fig 8.17}
a) On the skeleton observe the following:
7 pairs of "true" ribs
5 pairs of "false" ribs - the last 2 pairs are also called "floating" ribs.
- Look at the fiber representations of the costal cartilages on the skeleton. What feature of the costal cartilages is used to classify the ribs as "true, "false", and/or "floating"?
- Study closely the articulations of the heads of the ribs with the bodies of the thoracic vertebrae. Why are the articulation sites called "demifacets"?
b) Examine a typical rib (R3-R9). Locate the following:
head demifacets (for vert. body) angle
tubercle neck subcostal groove
c) Examine R1 closely. How could you tell it from the other 11 ribs? Can you figure out how to distinguish the left R1 from the right R1?
Skull and Hyoid {APL Figs 8.4 to 8.13, 8.18}
The skull will be examined again in much more detail during the CNS week. For now concentrate on being able to identify the bones and answering the questions below. The "exploded" skull preparation is excellent for this purpose.
a) The bones of the skull are classified as cranial (8 bones) and facial (14 bones). The cranial bones surround the brain in the cranial cavity. The facial bones obviously provide the underlying framework of the face. On a skull identify the following:
cranial bones:
2 pairs - parietals, temporals
4 single - frontal, ethmoid, sphenoid, occipital
facial bones:
6 pairs - nasals, maxillae, lacrimals, zygomatics, palatines, inferior conchae
2 single - mandible, vomer
- Why do you suppose that the sphenoid is called the "keystone of the skull? With which bones does the mandible articulate? With which skull bone does the atlas articulate?
b) Locate the following sutures on the adult and fetal skulls:
sagittal coronal
squamosal lambdoidal
c) Locate the fetal fontanels on the fetal skull model, and the corresponding points on the adult skull. These "soft spots" are membranous areas that allow the skull to distort markedly during birth and to grow rapidly during infancy. They disappear in infancy and early childhood as the adjacent bones grow. Which of these fontanels is the last to close?
d) Locate the hyoid bone on the skeleton. This bone does not articulate with any other bones and is often lost during skeleton preparation. Note the similarities of the hyoid to the mandible. We will study the hyoid in more detail during the respiratory system week.
- Palpate your own hyoid bone by pressing in lightly at the front of your throat at the notch just above your larynx. When you swallow, you should feel the hyoid bone move up past your finger into the base of the tongue.
Comparative Vertebrate Anatomy
Compare the axial bones of the human skeleton to those of the other vertebrates skeletons on display.
a) The cat belongs to the same class as the human, Class Mammalia.
- Notice that the number of cervical vertebrae is the same. All other mammals also have the same number of cervical vertebrae. Even giraffes have the same number of cervical vertebrae, namely seven.
- Do cats have the same number of thoracic vertebrae, ribs, and lumbar vertebrae as do humans? Notice that cats also, of course, have caudal (tail) vertebrae. How closely do these resemble the vertebrae from the other regions of the cat spinal column?
- Which of the spinal curvatures is present in the human, but absent in the cat? Why?
- Why do you suppose that the spinous processes are so much longer in the cat than in the human? What is different about the forces placed on quadruped and biped spinal columns, especially in the cervical region?
- Look at the whale vertebra. How many of the same structural features as the human vertebrae can you recognize? From what region of the spinal column do you think that this comes? (An examination of the dolphin partial vertebral column may help you with this question.)
- Notice the complexity of the cat hyoid bone relative to that of the human.
b) The alligator is a member of Class Reptilia.
- What are the postural differences between the aligator on the one hand, and the cat and human on the other? In particular, notice how the extremities are positioned. What does this imply about locomotion in these different vertebrates?
- Notice the flat plate-like bones of the "gastralia", on the ventral surface of the animal, caudal to the rib cage. What do you suppose is the function of these bones?
c) The pelican is a member of Class Aves.
- Notice that the sternum is greatly enlarged into a "keel" or "carina". How is this an adaptation to flight, i.e. what are the broad flat lateral surfaces of the keel for?
- Notice that the pelvic bones and sacral vertebrae are fused into a flat, thin, curved "synsacrum". What is the advantage of such a structural adaptation in a flying animal?
- Take a look at the skeleton of the emu, a flightless "ratite" bird. What are the important structural and functiona differences in its skeleton compared to that of the pelican?
d) The salamander is a member of Class Amphibia.
- How much similarity do you see between the vertebrae of the salamander and those of the human?
- Notice that the salamander has no complete rib cage, per se. What does this suggest about respiratory mechanisms in the salamander and the human? Could the salamander be a "negative pressure" breather which sucks air into the lungs by expanding the thoracic cavity?
e) The perch is a "bony fish" and is a member of Class Osteichthyes.
- Look closely at the fish vertebrae. Notice that the caudal (tail) vertebrae have a ventral "haemal" arch in addition to the dorsal "neural" arch. Are these arches and their processes completely fused to the vertebral bodies?
Guide to Histology
Cartilage and Bone {APL Fig 5.3, 7.3 to 7.5}
Cartilage and bone provide the skeletal framework of the body, as well as structural frameworks of some of the viscera. Cartilage and bone differ from C.T. proper in the chemical nature of the extracellular ground substance, as well as the fact that mature cells (chondrocytes and osteocytes) are located in distinct cavities - the lacunae. Cartilage differs from bone in the following respects:
1) The extracellular substance of cartilage is organic, while bone contains inorganic salts (principally calcium phosphate) deposited in an organic matrix.
2) Cartilage has the structural functions of support, protection, and cushioning, while bone has the additional metabolic functions of calcium and phosphate storage and hematopoiesis (formation of blood cells).
3) In order to accommodate differences 1 and 2, cartilage is avascular, while bone is highly vascular.
There are three types of cartilage, which have different fiber types, organizational schemes, and functional properties:
a) Hyaline Cartilage {APL Fig 5.3}
Hyaline cartilage is designed to be semi-rigid and provide a low-frictional surface. The collagen fibers do not stand out from the ground substance, so the matrix appears glassy or "hyaline". It is found mainly in five locations:
1) As articular cartilage covering the ends of bones in synovial joints
2) As costal cartilage
3) In the larynx, trachea, and bronchi
4) In the nasal septum
5) In the developing skeleton
- Observe the hyaline cartilage in the wall of the trachea. Notice that cartilage, like epithelium, is avascular. How does it obtain oxygen and nutrients? Identify the matrix, lacunae, and chondrocytes. Try to identify the perichondrium as the single layer of squamous cells at the periphery of the cartilage.
- How are the properties of hyaline cartilage suited to its role of holding airways open?
- Identify the hyaline cartilage covering the ends of the bones in the joint. How many chondrocytes do you see in each lacuna?
b) Elastic Cartilage {APL Fig 5.3}
Elastic cartilage is designed to be flexible and somewhat elastic, but to return to its original shape following distortion. With appropriate staining the highly branched elastic fibers stand out distinctly. It is found in the following locations (remember "e" for elastic):
1) The pinnae of the external ear
2) The larynx, principally the epiglottis
3) The walls of the Eustachian tube
4) The alae of the nostrils (or external nares)
- In the elastic cartilage slide (from the external ear), identify the central plate of elastic cartilage marked by the fine black elastin fibers embedded in the matrix between lacunae containing chondrocytes. How many chondrocytes are in each lacuna? How can you distinguish the elastic cartilage from the surrounding elastic connective tissue?
c) Fibrocartilage {APL Fig 5.3}
Fibrocartilage is specialized for resistance to compression and torsion (sideways forces). The dense collagen fibers embedded in the matrix contribute to its strength. It is found in the following locations:
1) The annulus fibrosus of each intervertebral disk
2) The menisci of the knee joints
3) Fibrous joints such as the symphysis pubis and sacroiliac joints
- Identify the fibrocartilage in the sample slide (from the symphysis pubis). Note the parallel collagen bundles separating rows of chondrocytes. How many chondrocytes do you see in each lacuna?
There are two main histological types of bone:
a) Compact Bone (lamellar or woven) {APL Figs 7.3, 7.4}
Mature compact, lamellar bone is easily identified in cross section by the concentric rings, or lamellae of the Haversian system and by the prominent lacunae. Note that the "empty" appearance of the lacunae is an artifact; the osteocytes shrink away from the lacunae walls during the fixation process.
- Identify the Haversian canals, lacunae, and canaliculi. Try to locate a Volkman's canal. What is contained in each?
- Woven bone is a form of compact bone that is deposited during initial bone formation (osteogenesis) and during healing of a fracture. It is subsequently reworked into lamellar bone. You may be able to identify some regions of woven bone in the bone formation slides below
b) Spongy Bone {APL Fig 7.2}
Spongy bone makes up the spicules which criss-cross the marrow spaces of both long and flat bones. Look for regions of spongy bone in the endochondral bone formation slide below.
Bone Formation and Growth
a) Endochondral Bone Formation {FAP Fig 6-11}
Long, short and irregular bones develop from hyaline cartilage "protobones" by the process of endochondral bone formation.
- Review the spatial zones of endochondral bone formation (corresonding to temporal or time sequence of sucessive stages) - including cartilage formation, proliferation, hypertrophy, calcification, chondrocyte death, and bone deposition. Review the changes that occur in the periosteum, the formation of osteoblasts from the inner layer of the periosteum, and the invasion of hollow bone by periosteal blood vessels.
- Identify the following six sequential zones: resting chondrocytes, proliferation, hypertrophy, calcification, degeneration, osteogenesis. Which zone is closest to the center of the bone shaft?
- Note that osteoblasts first form osteoid tissue on the calcified cartilage matrix. Ultimately this osteoid is reworked to form true lamellar bone.
- How does a bone grow in length and girth? What is the role of the epiphyseal plate?
b) Intramembranous Bone Formation
Flat bones (such as the cranial bones) develop directly, without a cartilage model, by ossification within a connective tissue membrane.
- Identify regions of intramembranous bone formation in the slide of the embryonic mouse head. Can you also identify the periosteum?
Guide to Physiology
There is no real physiological component to this week's lab.
