Bones and Axial Skeleton

Osteons

• haversian system

• elongated cylinder parallel to long axis

• weight-bearing pillars

• one placed outside the next = tree trunk rings

Osteon Maxtrix tube and fibers

• each matrix tube = lamella

• collagen fibers run in alternating directions to help with torsion/stress

• bone salts align between the fibers

Where are the osteocytes housed in? (Canaliculi)

Lacunae - hollow areas at junction of lamellae

What are canaliculi?

little canals that connect lacunae to each other and the central canal

How are canaliculi created?

Due to osteoblasts and osteocytes

• osteoblasts maintain contact via gap junctions

• osteoblasts secrete bone matrix

• trapped when it hardens = osteocytes

• leaves a system of tiny canals filled with tissue fluid (canaliculi)

• osteocytes are in a mature osteon together for communication/relay of nutrients

What causes bones to be well nourished?

Canaliculi and gap junctions

Interstitial lamellae

• incomplete lamellae

• fill gaps between forming osteons

• remnants of osteons from remodeling

Circumferential lamellae

• extend around the entire circumference of the diaphysis

• resist twisting of the long bone

Spongy Bone: Anatomy

• poorly organized

• Trabeculae aligns with lines of stress (helps with stress resistance, and carefully, precisely positioned)

• only a few cells thick with irregularly arranged lamellae

• osteocytes are interconnected by canaliculi

• no osteons

How many parts is the Axial Skeleton divided into and name each of them?

3

• Skull

• Vertebral column

• thoracic cage

What are the main functions of the axial skeleton?

• form longitudinal axis of body

• support head, neck, and trunk

• protect brain, spinal cord, thoracic organs

What are the two sets of bones in the skull?

cranium bones and facial bones

How many bones are included in the cranium bones?

8 bones

How many facial bones are there?

14 bones

What are the types of cranium bones?

1. Frontal bone

2. Parietal bones (2)

3. Temporal bones (2)

4. Occipital bone

5. Ethmoid bone

6. Sphenoid bone

What are the frontal bones?

Supraorbital foramen and glabella

Temporal Bones

• external acoustic meatus

• mastoid process

• styloid process

• internal acoustic meatus

• zygomatic process

Temporal Bones

jugular foramen and carotid foramen/canal

Occipital Bones

Foramen magnum, external occipital protuberance, and occipital condyle

Ethmoid Bones

Crista Galli (1), Cribriform Plate (2), Olfactory Foramina (3), Superior and middle nasal conchae

What are the parietal bones?

JUST the parietal bones (2)

Sphenoid Bones

Sella turcica (1), foramen lacerum (2), foramen rotundum (3), foramen ovale (4), foramen spinosum, and optic canal (6)

What does the sphenoid bone have?

Orbital fissure, greater wing, lesser wing, and pterygoid process

Sutures

Sagittal suture, coronal suture, squamous suture, and lambdoid suture

Facial Bones

1. Vomer (1)

2. Lacrimal bone (2)

3. Nasal Bone (2)

4. Zygomatic bone (2)

5. Maxilla (2)

6. Mandible (1)

7. Palatine (2)

8. Inferior nasal concha (2)

Lacrimal

lacrimal fossa

Maxilla

• infraorbital foramen

• alveolar processes

Mandible

• mandibular condyle

• mandibular notch

• coronoid process

• alveolar margins

• mental foramen

Paranasal sinuses

formed from five skull bones: frontal, sphenoid, ethmoid, and paired maxillary bones

• all contain mucosa-lined, air-filled spaces

What are the functions of Paranasal sinuses

warm and humidify air, help to lighten skull, enhance resonance of voice

Vertebral Column functions

• transmit weight of trunk to lower limbs

• surround and protect spinal cord

• provide attachment points for ribs and muscles

How many single bones are in the vertebrae?

24 single bones

• 7- cervial

• 12- thoracic

• 5- lumbar

What are the two fused bones of the vertebrae?

Sacrum and coccyx

Intervertebral discs

• fibrocartilage

• cushions and absorbs shock

• composed of two parts (nucleus pulposus and inner gelatinous)

• anulus fibrosus (outer collar of fibrocartilage)

Common Vertebral structure

What is the atlas in the cervical?

(C1): no body, enables head to nod yes

What is the axis of the cervical?

(C2): dens, acts as a pivot allowing you to move your head side to side - no

Thoracic

• larger body than cervical

• articular facet (ribs)

Lumbar

• blocklike bodies

• no facet for ribs

What are the abnormal curvatures of spine?

• Scoliosis (middle of spine is curved to the side)

• Kyphosis (top of spine is curved upwards)

• Lordosis ( bottom of spine is curved inwards)

What does the thoracic cage consists of ?

sternum, ribs, thoracic vertebrae, and costal cartilages

What are the functions of the thoracic cage?

protects vital organs, supports shoulder girdle and upper limbs, and provides attachment sites

Sternum

3 bones fused together

• manubrium (green)

• body (blue)

• xiphoid process (purple)

How many pairs of ribs do we have?

12 pairs of ribs

How many “true” ribs are there?

7 (1-7)

How many “false” ribs are there?

5 (8-12)

• 8-10: indirect cartilage attachments to sternum

Which ribs are floating ribs?

11 and 12 = no sternal attachment

What are the functions of bones?

Support, protection, anchorage, mineral and growth factor storage, blood cell formation, triglyceride storage, and hormone production

Cartilages of the skeleton

no blood vesslels

3 types: hyaline, elastic, and fibrocartilage

Hyaline

articular, costal, respiratory, and nasal

Elastic

ears and epiglottis

Fibrocartilage

Intervertebral discs, menisci, pubic symphysis