Unit 2B Answers
1) There are two types of ossification. What are they are what are the main steps?
a. Intramembranous Ossification – produces flat bones, facial bones
i. Ossification centers with osteoblasts form within thickened regions of
mesenchyme
ii. Osteoid is secreted and undergoes calcification
iii. Woven bone and surrounding periosteum form
iv. Lamellar bone replaces woven bone as compact and spongy bone form
b. Endochondral Ossification – produces most other bones in body
i. Fetal hyaline cartilage model develops
ii. Chondrocytes undergo hypertrophy and matrix calcifies.
iii. Periosteal bone collar forms from periosteum, creating a shell of bone around
the diaphysis
iv. Primary ossification center forms in the diaphysis. Cartilage matrix invaded
by osteoprogenitor cells, blood vessels
v. Secondary ossification centers form in the epiphyses
vi. Bone replaces cartilage through secretion of osteoid, except the articular
cartilage and epiphyseal plate
vii. Epiphyseal plate ossify and form epiphyseal lines
2) What is the difference between intramembranous and endochondral ossification vs
interstitial and appositional growth?
intramembranous and endochondral ossification are the steps in creating new bone.
Interstitial (length) and appositional (width) growth are the constant remodeling and
creating bone
3)The Skull is formed by the cranium and the facial bones. The cranium has two sets of paired
bones, they are the parietal and the temporal bones. 2B 2
4) The cribiform plate of the Ethmoid bone allow passage of the olfactory nerves which involves
your sense of smell, while the crista galli which is a small ridge of bone that attaches to the dura
mater of the brain’s meninges and holds the brain in place. 2B 2
5) The sella turcica of the sphenoid bone contains the hypophyseal fossa which encloses the
pituitary gland, while the optic canals of the sphenoid bone allows passage of the optic nerves
where some nerves cross in the optic or chiasmic groove. 2B3
6) Tiny irregularly shaped bones that appear within the sutures of the skull are referred to as
sutural or wormian bones and are different in each person. 2B3
7) The only bone in the body that does not articulate with another bone is the hyoid bone, which
is an attachment for muscles of the neck that raise and lower the larynx during swallowing and
speech. 2B 4
8)Kyphosis is a curvature of the spine that has a hunchback look to it which is associated with
osteoporosis, while lordosis is a curvature that has a swayback look to it and is associated with
pregnancy and scoliosis is a curvature that gives a “S” shape to the body. Text page 202 2B 5
9) In the intervertebral disks, the annulus fibrosis encloses the gelatinous nucleus pulposis and
acts like a shock absorber.2B 5
10) The dens of the axis or C2 fits into the vertebral foramen of the altas or C1 to allow the
head to rotate. 2B 5
11) One of the functions of the ribs is to use the intercostal muscles and diaphragm to lift and
depress the thorax during the rhythmic movements of breathing. 2B 6
12) True ribs articulate with transverse processes of vertebrae and sternum directly via costal
cartilage, where false ribs articulate with transverse processes of the vertebrae and attach to
the sternum indirectly via costal cartilage and finally floating ribs articulate with the transverse
processes of the vertebrae but have no anterior attachments. 2B6
13) In the forearm the interosseous membrane allows the rotating movement of the radius
against the ulna, allowing hand rotation. 2B7
14) The bones of the wrist are referred to as carpals, where as the bones of the palm are
referred to as metacarpals and the bones of the fingers are phalanges. The thumb is also called
the pollex which has no middle phalange. 2B 8