SKELETAL SYSTEMAXIAL SKELETONCHAPTER 7

Honors Biology

Skeletal System

Composed of:1. Bones2. Cartilage3. Joints4. 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 Skeleton1. Supports head, neck, and trunk2. Protects brain, spinal cord, and organs

of the thoracic cavity

The Skull

Formed by: Cranium

1. Enclose & protect brain2. Attachment sites for head & neck muscles

Facial bones1. Form framework of face2. Contain cavities for special sense organs3. Provide openings for air & food passage4. Secure the teeth5. 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

Forms anterior cranium Articulates posteriorly with parietal

bones Parts:1. Squamous

Forms forehead

2. Supraorbital margins3. Forms:

superior wall of orbits Anterior cranial fossa: houses frontal lobes

of brain

Parietal Bones

most of superior and lateral aspects of the skull forming the bulk of the cranial vault

4sutures:1. Coronal suture

Parietal bones meet frontal

2. Sagittal suture Rt parietal bone meets lt parietal bone

3. Lambdoid suture Parietal bones meet occipital bone

4. Squamous suture 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

form inferolateral aspects of the skull 3 major parts:1. Squamous 2. Tympanic3. 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

14 facial bones:1. 2 nasal bones2. 2 maxillae3. 2 zygomatic bones4. 1 mandible5. 2 lacrimal bones6. 2 palatine bones 7. 2 inferior nasal conchae8. 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, air-filled with small openings that connect to nasal cavity

Mucosa helps warm & humidfy inhaled air

add resonance to voice

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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 spinal cord, adipose, areolar CT, blood vessels

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

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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

all 12 attach posteriorly to vertebrae

Parts of a Rib1. Head2. Neck3. Tubercle 4. Body 5. 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