SKELETAL SYSTEM
AXIAL SKELETON
CHAPTER 7
Honors Biology
Skeletal System

1.
2.
3.
4.
Composed of:
Bones
Cartilage
Joints
Ligaments


~ 20% of body mass
Divided into axial &
appendicular
Axial Skeleton

80 bones in 3 regions:
 Skull
 Vertebral
column
 Thoracic cage
Functions of the Axial Skeleton
1.
2.
Supports head, neck, and trunk
Protects brain, spinal cord, and organs of the
thoracic cavity
The Skull


Formed by:
Cranium
Enclose & protect brain
Attachment sites for head & neck muscles
1.
2.
Facial bones

1.
2.
3.
4.
5.
Form framework of face
Contain cavities for special sense organs
Provide openings for air & food passage
Secure the teeth
Anchor muscles of facial expression
Sutures

Interlocking joints between flat bones (cranium)
Newborn Skull

fontanels: “soft spots” present between
cranial bones made of unossified
mesenchyme
 eventually
replaced by mature bone
 function: provide some flexibility to fetal head
allowing skull to change shape as it passes thru
birth canal
Newborn Skull
Newborn Skull
Cranium

8 bones :
2
paired: parietal, temporal
 4 single: frontal, occipital, ethmoid, sphenoid
Frontal Bone



1.
Forms anterior cranium
Articulates posteriorly with parietal bones
Parts:
Squamous

2.
3.
Forms forehead
Supraorbital margins
Forms:


superior wall of orbits
Anterior cranial fossa: houses frontal lobes of brain
Parietal Bones


1.
most of superior and lateral aspects of the skull
forming the bulk of the cranial vault
4sutures:
Coronal suture

Parietal bones meet frontal
Sagittal suture
2.

Rt parietal bone meets lt parietal bone
Lambdoid suture
3.

Parietal bones meet occipital bone
Squamous suture
4.

Parietal bones meet temporal bones
Occipital Bone


Forms most of skull’s posterior wall & base
@ base is foramen magnum
 “large

hole” ↑brain stem, ↓ spinal cord
occipital condyles
 articulate
with 1st vertebra
Temporal Bones


1.
2.
3.
form inferolateral aspects of the skull
3 major parts:
Squamous
Tympanic
Petrous
Squamous portion : Temporal Bones


abuts squamous suture
Zygomatic process
 Meets
zygomatic bone
anteriorly forming
zygomatic arch

Mandibular fossa
 receives
condylar process of
mandible forming the
temporomandibular joint
(TMJ)
Tympanic part: Temporal Bone

surrounds external
acoustic meatus :
external ear canal
receives sound waves
& directs them
inward to ear drum
Petrous Portion: Temporal Bone

houses middle & inner ear
 Sense


organs for hearing & equilibrium
forms part of base of skull
Mastoid Process
 “lump”
just posterior to ear
 Attachment site for neck muscles

Styloid Process
 Needle-like
attachment for tongue & neck muscles
Temporal Bones
Sphenoid Bone




“bat-shaped” spans width of middle cranial fossa
Articulates with every other cranial bone
Contains sphenoid sinuses
Superior surface: sella turcica a saddle-shaped
fossa where the pituitary gland sits
 aka
hypophyseal fossa
Sphenoid Bone
Ethmoid Bone




“like a sieve”
midline of anterior part of cranial floor,
anterior to sphenoid, posterior to nasal bones
cribiforme plate: forms roof of nasal cavity,
the holes of the sieve where olfactory nerves
pass from roof of nasal cavity to brain
crista galla: triangular process which serves
as pt of attachment for meninges of brain
Ethmoid Bone
Ethmoid Bone


perpendicular plate: forms superior portion
of nasal cavity
superior & middle nasal conchae: (or
turbinate) increase vascular & mucous
membrane surface area in nasal cavities: aids
in sense of smell, warms, filters & moistens
air being inhaled. Filters because the
turbinates cause air to swirl as a result
inhaled particles strike & become trapped in
mucus
Ethmoid Bone
“Sometimes when you study anatomy, you
start seeing others differently.”
Facial Bones

shape of face changes dramatically during 1st
2 yrs of life:
 brain & cranial bones expand
 1st set of teeth erupt
 paranasal sinuses enlarge
 growth of face stops ~16 years old
Facial Bones

1.
2.
3.
4.
5.
6.
7.
8.
14 facial bones:
2 nasal bones
2 maxillae
2 zygomatic bones
1 mandible
2 lacrimal bones
2 palatine bones
2 inferior nasal conchae
1 vomer
Mandible



largest & strongest facial bone (lower jaw)
alveolar processes hold lower teeth sockets
mental foramen: dentist numb mental nerve
Maxillae





= upper jaws
*articulate with every bone in face except the
mandible
form part of floor of orbits, parts of nasal
cavity, & most of the hard palate (bony roof
of mouth)
each one has large maxillary sinus
alveolar process is small arch that contains
the alveolar sockets for upper set of teeth
Maxillae
Cleft Palate & Cleft Lip


10-12 wks gestation the palatine processes of
maxillae typically join
not doing so  cleft palate +/- cleft lip
 speech
& swallowing can be affected
 many ear infections
 reparative surgery recommended 1st few wks of
life / surgery needs to be completed by 12 – 18
mos b/4 speech: speech therapy & orthodontic
care frequently necessary
Zygomatic Bones


“cheekbones”: the
temporal process of
the zygomatic bone
articulates with the
zygomatic process
of the temporal
bone
also part of floor of
orbit
Nasal Bones

form part of the bridge of the nose (rest is
cartilage)
Lacrimal Bones



thin, about the size of pinky fingernail
(smallest bones of face)
part of medial wall of each orbit
each contain lacrimal fossa that houses
lacrimal sac: gathers tears  nasal cavity
Palatine Bones

L-shaped pair of bones that form the
posterior portion of the hard palate & part of
floors of nasal cavity & orbit
Vomer

Δ shaped bone on the floor of nasal cavity
forming inferior portion of nasal septum
Inferior Nasal Conchae


inferior to the middle nasal conchae of the
ethmoid bone forming part of lateral wall of
nasal cavity
same function as superior & middle conchae:
swirling inhaled air to deposit particulates
but not involved in sense of smell
Paranasal Sinuses




In these 4 bones +
sphenoid
Mucosa-lined, airfilled with small
openings that
connect to nasal
cavity
Mucosa helps warm
& humidfy inhaled
air
add resonance to voice
Hyoid Bone






“U-shaped “
*does not articulate with any other bone in
skeleton
suspended by ligaments from styloid process
of temporal bone
in anterior neck between mandible & larynx
Function: supports tongue
*frequently fractured during strangulation
Hyoid Bone
Vertebral Column



aka spine, backbone
2/5 of person’s height
26 in adult (starts as 33, some fuse to form
sacrum & coccyx)
7
cervical
 12 thoracic
 5 lumbar
 1 sacrum
 1 coccyx
Vertebral Column



Fetus has anteriorly
concave curve
3 mos old when holds
head cervical curve
develops
lumbar curve
develops as infant sits
up, stands, walks
Intervertebral Discs

between bodies of consecutive vertebra
 under
compression they flatten & broaden
 harden, less elastic w/aging & narrow  loss of
height


annulus fibrosus: outer fibrous ring
nucleus pulposus: inner soft, highly elastic
Intervertebral Discs
Parts of a Vertebra

Body
 thicker,

anterior portion, weight bearing portion
Vertebral Foramina
 contains
vessels

spinal cord, adipose, areolar CT, blood
Spinous Process
1
of 7 processes, posterior, palpable on back of
body
Transverse Processes: on each side, extending
laterally
Vertebrae: 1st & 2nd Cervical

Atlas
 ring-shaped
 articulates
with
condyles of
occipital bone
 allows you to nod
head “yes”

Axis
 2nd
cervical v.
 allows you to shake
head “no”
Typical Cervical Vertebrae



C-3 to C7
smaller than other v.
except coccyx but
vertebral foramen
largest
all cervical v. have
extra foramen: 2
transverse foramen for
vertebral a., v., & n.
Typical Thoracic Vertebrae



T-1 to T-12
larger & stronger
than cervical v.
distinguishing
feature: articulate
with ribs (facets on
transverse
processes of T-1 to
T-10
Typical Lumbar Vertebrae



L-1 to L-5
largest & strongest
of the vertebrae
processes are short
& thick
Sacrum



triangular bone
formed by union of
S-1 to S-5
fusion begins ~16,
complete by age 30
female: shorter,
wider, more curved
S-2 to S-3
Coccyx



small triangle
formed by fusion of
4 coccygeal v. (Co-1
to Co-4), start
between 20 & 30
females points
inferiorly; males it
points anteriorly
Thorax


refers to entire chest
skeletal part of thorax is thoracic cage
 Sternum
 Ribs
Sternum



aka “breastbone”
flat bone in center of anterior thorax
3 bones that fuse by age 25
Sternum
1.





Manubrium
superior portion
suprasternal notch
clavicular notches
articulates with costal
cartilage of 1st & 2nd rib
sternal angle: where it
articulates with body
Sternum
2. Body
 middle & largest
portion
 articulates with
costal cartilage of
2nd thru 10 ribs
Sternum
3. Xiphoid Process
 cartilagenous in
infancy
 not completely
ossified until ~age
40
 avoid it during CPR
Ribs





12 pairs
increase in length 1st thru 7th then decrease in
length to 12th
1st thru 7th ribs (true ribs) have direct anterior
attachment to sternum by strip of hyaline
cartilage which contribute to elasticity of
thoracic cage
8th thru 10th ribs attach to each other & then
to cartilages of 7th rib
11th & 12th ribs: floating ribs
Ribs
Ribs


1.
2.
3.
4.
5.
all 12 attach posteriorly to vertebrae
Parts of a Rib
Head
Neck
Tubercle
Body
Costal Angle
Abnormal Curvatures of Spine



Scoliosis
lateral bending
usually in thoracic
region
Abnormal Curvature of Spine



Kyphosis
exaggeration of the
thoracic curve
seen in TB of spine,
congenital
malformation,
elderly