Divisions of Skeletal System - Human Anatomy - Lecture Notes, Study notes for Anatomy. Alagappa University


Description: Divisions of Skeletal System, Axial Skeleton, Appendicular Skeleton, Types of Bones, Bone Surface Markings, Sphenoidal Sinuses, Alveolar Process with Alveoli, Features of Skull are some points f this lecture. This lecture handout was provided by lecturer in Human Anatomy class. Important terms are bold in this handout. Few terms of the lecture are given above.
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A. Divisions of the Skeletal System
1. The 206 named bones in the adult skeleton are grouped in two major divisions
i. axial skeleton consists of the 80 bones located around the longitudinal
axis of the body:
a. skull bones
b. auditory ossicles
c. hyoid bone
d. vertebral column
e. sternum
f. ribs
ii. appendicular skeleton consists of 126 bones that form:
a. pectoral (shoulder) girdles
b. upper extremities
c. pelvic (hip) girdle
d. lower extremities
B. Types of Bones
1. Almost all bones are classified on the basis of shape into five major types:
i. long bones
ii. short bones
iii. flat bones
iv. irregular bones
v. sesamoid bones, which are (typically) small bones embedded in
2. There is one additional type of bone that is classified by location:
i. sutural (or Wormian) bones, which are located in the joints between
certain cranial bones
C. Bone Surface Markings
1. The surfaces of bones have surface markings, structural features that are
adapted to specific functions; the two major types of surface markings are:
i. depressions and openings
ii. processes
2. Important surface markings include fissure, foramen, fossa,
sulcus, meatus, process, condyle, facet, head, crest, epicondyle, line,
spinous process, trochanter, tubercle, and tuberosity.
D. Skull
1. The skull consists of 22 bones
i. 8 cranial bones that form the cranial cavity to enclose and protect the
ii. 14 facial bones that form the face
2. The 8 cranial bones (each having specific surface markings) are:
i. frontal bone
a. frontal squama (vertical plate)
b. supraorbital margin
c. supraorbital foramen
d. frontal sinuses
ii. two parietal bones
iii. two temporal bones, each one having:
a. temporal squama
b. zygomatic process (which contributes to the zygomatic arch)
c. mandibular (glenoid) fossa
d. articular tubercle
e. mastoid portion
f. external auditory (acoustic) meatus
g. mastoid “air cells”
h. mastoid process
i. internal auditory (acoustic) meatus
j. styloid process
k. stylomastoid foramen
l. petrous portion
m. carotid foramen
n. jugular foramen
iv. occipital bone
a. foramen magnum
b. occipital condyles
c. hypoglossal foramen
d. external occipital protuberance
e. superior nuchal lines
f. inferior nuchal lines
v. sphenoid bone
a. body
b. sphenoidal sinuses
c. sella turcica
d. greater wings (each having a foramen ovale)
e. lesser wings
f. optic foramen
g. superior orbital fissure
h. pterygoid processes
vi. ethmoid bone
a. lateral masses
b. ethmoidal sinuses
c. perpendicular plate
d. cribriform plate
e. olfactory foramina
f. crista galli
g. superior nasal conchae (turbinates)
h. middle nasal conchae (turbinates)
3. The 14 facial bones (each having specific surface markings) are:
i. two nasal bones
ii. two maxillae, each one having:
a. maxillary sinus
b. alveolar process with alveoli
c. palatine process
iii. two zygomatic bones, each one having:
a. temporal process (which contributes to the zygomatic arch)
iv. two lacrimal bones, each one having:
a. lacrimal fossa
v. two palatine bones, each one having:
a. horizontal plates
vi. two inferior nasal conchae (turbinates)
vii. vomer
viii. mandible
a. body
b. rami
c. angle
d. condylar process
e. temporomandibular joint
f. coronoid process
g. mandibular notch
h. alveolar process with alveoli
i. mental foramen
j. mandibular foramen
k. mandibular canal
E. Unique Features of the Skull
1. The nasal septum, formed by the vomer, septal cartilage, and perpendicular
plate of the ethmoid bone, divides the nasal cavity into right and left
2. The orbits are deep sockets (each having a roof, lateral wall, floor, and medial
wall), formed by several bones, that house the eyeballs and associated
3. The skull bones contain numerous foramina (see Table 7.4) that are
passageways for blood vessels and nerves.
4. Sutures are immovable joints located between skull bones; four notable
sutures are:
i. coronal suture
ii. sagittal suture
iii. lambdoid suture
iv. (two) squamous sutures
5. Paranasal sinuses are paired cavities located in certain skull bones;
i. they are lined with mucous membranes that are continuous with the
lining of the nasal cavity
ii. they produce mucus and serve as resonating chambers for sound
iii. they are located in the maxillae, frontal, sphenoid, and ethmoid bones.
6. Fontanels are fibrous connective tissue membrane-filled spaces located
between the cranial bones of infants; their function is to:
i. enable the fetal skull to modify its shape as it passes through the birth
ii. permit rapid growth of the brain during infancy.
Major fontanels are:
a. anterior (frontal) fontanel
b. posterior (occipital) fontanel
c. two anterolateral (sphenoid) fontanels
d. two posterolateral (mastoid) fontanels
Fontanels become ossified during the first two years of childhood.
7. The cranial fossae are three levels on the floor of the cranial cavity:
i. anterior cranial fossa
ii. middle cranial fossa
iii. posterior cranial fossa
F. Hyoid Bone
1. The hyoid bone is a U-shaped bone, located in the upper neck, that does not
articulate with any other bone.
2. It supports the tongue and is an attachment site for several tongue, neck, and
pharynx muscles.
3. Its major surface markings are:
i. body
ii. lesser horns
iii. greater horns
G. Vertebral Column
1. The vertebral column (spine or backbone) is a strong, flexible rod that:
i. surrounds and protects the spinal cord
ii. supports the head
iii. serves as a site of attachment for ribs and back muscles.
2. It is formed by 26 vertebrae:
i. 7 cervical vertebrae
ii. 12 thoracic vertebrae
iii. 5 lumbar vertebrae
iv. one sacrum formed by fusion of 5 sacral vertebrae
v. one (or two) coccyx formed by fusion of (usually) 4 coccygeal
3. Intervertebral discs are located between neighboring vertebrae (from C2
down to the sacrum):
i. each consists of an outer annulus fibrosus and an inner nucleus
ii. they form strong joints, permit various movements of the spine, and
absorb vertical shock
4. The vertebral column has four alternating normal curves:
i. anteriorly convex cervical curve
ii. anteriorly concave thoracic curve
iii. anteriorly convex lumbar curve
iv. anteriorly concave sacral curve
At birth, there is only a single anteriorly concave curve; the cervical and lumbar
(i.e., secondary) curves develop in the early months of infancy as the child
begins to hold its head erect and as the child begins to sit and walk,
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