Sistema scheletrico

FACIAL BONES OF THE SKULL

= 14 bones (six paired bones: maxilla, palatine,

 zygomatic, nasal, lacrimal, and inferior nasal conchae

and two unpaired bones: vomer and mandible) forming

the upper and lower jaws, the nose, nasal cavity and

nasal septum, and the orbit. Maxillary Bone = (maxilla,

plural = maxillae), form the upper jaw, much of the hard

palate, the medial floor of the orbit, and the lateral base

of the nose. The curved, inferior margin of the maxillary

bone that forms the upper jaw and contains the upper teeth is the alveolar

process of the maxilla. On the anterior maxilla, just below the orbit, is the

infraorbital foramen. This is the point of exit for a sensory nerve that supplies

the nose, upper lip, and anterior cheek. On the inferior skull, the palatine

process from each maxillary bone can be seen joining together at the midline to

form the anterior three-quarters of the hard palate. The hard palate is the bony

plate that forms the roof of the mouth and floor of the nasal cavity, separating

the oral and nasal cavities.

Palatine Bone = pair of irregularly shaped bones,

 contributing to the lateral walls of the nasal cavity and

the medial wall of each orbit and the hard palate.

Zygomatic Bone = paired, forming much of the lateral

 wall of orbit and lateralinferior margins of ant orbital

opening.

Nasal Bone = two small bones that articulate (join)

 with each other to form the bony base (bridge) of the

nose, also supporting cartilages of the nose.

Lacrimal Bone = small, rectangular bone, forming the

 ant., medial wall of the orbit, forming a shallow depression called the lacrimal

fossa.

Inferior Nasal Conchae = curved bony plate that projects into the nasal cavity

 space from the lower lateral wall.

Vomer Bone = unpaired triangular-shaped, forming posterior-inferior part of

 nasal septum.

Mandible = lower jaw and only moveable bone of the

 skull. Each side of the mandible consists of a horizontal

body and posteriorly, a vertically oriented ramus of the

mandible (ramus = “branch”).

The ramus on each side of the mandible has 2 upward-going bony projections.

The more ant projection is the flattened coronoid process of the mandible,

which provides attachment for one of the biting muscles. The post projection is

the condylar process of the mandible, which is topped by the ovalshaped

condyle, that articulates (joins) with the mandibular fossa and articular tubercle

of the temporal bone. The broad U-shaped curve located between the coronoid

and condylar processes is the mandibular notch.

Hyoid Bone= independent bone that does not contact any other bone and thus

 is not part of the skull.

• It is a small U-shaped bone located in the upper neck near the level of the inf

mandible, with the tips of the “U” pointing post.

• serves as the base for the tongue above, and is attached to the larynx below

and the pharynx post.

• is held in position by a series of small muscles that attach to it either from

above or below

VERTEBRAL COLUMN

VC, also known as spinal column or spine = consists of a sequence of vertebrae

(singular = vertebra), each of which is separated and united by an intervertebral disc.

vertebrae + intervertebral discs = VC [flexible column supporting head, neck, and

body, allowing for their movements & also protecting spinal cord, which passes down

the back through openings in the vertebrae]

REGIONS OF VC

• VC originally develops as a series of 33 vertebrae, but this number is eventually

reduced to 24 vertebrae, plus the sacrum and coccyx.

• subdivided into 5 regions [vertebrae in each area named for that

region and numbered in descending order]: in the neck, 7

cervical vertebrae [designated with the letter “C” followed by its

number; sup C1 vertebra articulates (forms a joint) with the

occipital condyles of the skull, inf C1 articulates with the C2

vertebra, and so on] + 12 thoracic vertebrae [T1–T12] + 5

lumbar vertebrae [L1–L5] + single sacrum [also part of the pelvis

& formed by the fusion of 5 sacral vertebrae] + coccyx [tailbone, resulting from

the fusion of 4 small coccygeal vertebrae].

• sacral and coccygeal fusions do not start until age 20 and are not completed

until middle age

CURVATURES OF TV

• adult VC does not form a straight line, but instead has 4 curvatures along its

length, to increase VC’s strength, flexibility, and ability to absorb shock [when

load on the spine is increased, by carrying a heavy backpack for example,

curvatures increase in depth (become more curved) to accommodate the extra

weight; they then spring back when the weight is removed]

• 4 adult curvatures are classified as either primary or secondary curvatures:

primary curves are retained from the original fetal curvature, while secondary

curvatures develop after birth.

• During fetal development, body is flexed ant into fetal position, giving entire VC

a single curvature that is concave ant. In the adult, this fetal curvature is

retained in 2 regions of the VC, as thoracic curve, which involves thoracic

vertebrae, and sacrococcygeal curve, formed by sacrum and coccyx. Each of

these is thus called a primary curve because they are retained from original

fetal curvature of VC. secondary curve develops gradually after birth as the

child learns to sit upright, stand, and walk. Secondary curves are concave post,

opposite in direction to the original fetal curvature: cervical curve of the neck

region develops as the infant begins to hold their head upright when sitting &

later, as the child begins to stand and then to walk, lumbar curve of lower back

develops.

• In adults, the lumbar curve is generally deeper in females.

GENERAL STRUCTURE OF A VERTEBRA

Within the different regions of the VC, vertebrae vary in size and

shape, but they all follow a similar structural pattern. A typical

vertebra will consist of:

1. Body= is the ant portion of each vertebra, supporting the

body weight, so progressively increase in size and thickness

going down the VC: bodies of adjacent vertebrae are separated and strongly

united by an intervertebral disc.

2. vertebral arch= forms the post portion of each vertebra, consisting of 4 parts,

right and left pedicles + right and left laminae. Each pedicle forms one of the

lateral sides of the vertebral arch and are anchored to the post side of the

vertebral body. Each lamina forms part of the post roof of the vertebral arch.

The large opening between the vertebral arch and body is the vertebral

foramen, which contains the spinal cord. In the intact vertebral column, the

vertebral foramina of all of the vertebrae align to form the vertebral (spinal)

canal, which serves as the bony protection and

passageway for the spinal cord down the back. When

the vertebrae are aligned together in the vertebral

column, notches in the margins of the pedicles of

adjacent vertebrae together form an intervertebral

foramen, the opening through which a spinal nerve

exits from the vertebral column.

3. 7 processes arise from vertebral arch

(2) each paired transverse process projects laterally and arises from the

junction point between the pedicle and lamina.

(1) single spinous process (vertebral spine) projects post at the midline of the

back. transverse and spinous processes serve as important muscle attachment

sites

(2) sup articular process extends or faces upward

(2) inf articular process faces or projects downward

paired sup articular processes of one vertebra join with the corresponding

paired inf articular processes from the next higher

vertebra. These junctions form slightly moveable joints

between the adjacent vertebrae. The shape and

orientation of the articular processes vary in different

regions of the VC and play a major role in determining type and range of motion

available in each region.

bodies of adjacent vertebrae are separated and united by an intervertebral disc,

which provides padding and allows for movements between adjacent vertebrae.

disc consists of a fibrous outer layer called the anulus fibrosus and a gel-like

center called the nucleus pulposus. The intervertebral foramen is the opening

formed between adjacent vertebrae for the exit of a spinal nerve.

REGIONAL MODIFICATIONS OF VERTEBRAE

In addition to the general characteristics of a typical vertebra described

above, vertebrae also display characteristic size and structural features

that vary between the different vertebral column regions. Thus, cervical

vertebrae are smaller than lumbar vertebrae due to differences in the

proportion of body weight that each supports. Thoracic vertebrae have

sites for rib attachment, and the vertebrae that give rise to the sacrum

and coccyx have fused together into single bones.

CERVICAL VERTEBRAE

Typical C vertebrae, such as C4 or C5, have several characteristic features that

differentiate them from T or L vertebrae: a small body [reflecting the fact that they

carry the least amount of body weight], a bifid (Y-shaped) spinous process [spinous

processes of C3–C6 are short, but C7 is much longer],

transverse processes sharply curved (U-shaped) to

allow for passage of the cervical spinal nerves] and

also having an opening called transverse foramen

[important artery that supplies brain ascends up the

neck by passing through these openings], sup and inf

articular processes flattened and largely face upward

or downward, respectively.

first and second C vertebrae further modified, giving each a distinctive appearance:

C1 also called atlas, supporting skull on top of VC (in Greek mythology, Atlas was the

god who supported the heavens on his shoulders), does not have a body or spinous

process, instead, being ring-shaped, consisting of an ant arch and a post arch,

transverse processes longer and extending more laterally

than do the transverse processes of any other C vertebrae;

sup articular processes face upward and deeply curved for

articulation with the occipital condyles on the base of the

skull; inf articular processes flat and facing downward to join

with the sup articular processes of C2.

C2 called axis, serving as axis for rotation when turning head toward right

or left, resembling typical C vertebrae in most respects, but easily

distinguished by dens (odontoid process = bony projection extending

upward from vertebral body and joining with inner aspect of ant arch of

atlas, where is held in place by transverse ligament)

THORACIC VERTEBRAE

bodies of T vertebrae are larger than C: characteristic feature for a typical

midT is spinous process, long with a pronounced downward angle causing to overlap

the next inf vertebra; sup articular processes of thoracic vertebrae face ant and inf

post; additional articulation sites, each called a facet, where rib attached [= 2 facets

located on lat sides of body, called costal facet (costal = “rib”),being for articulation

with th