Axial Skeleton

Axial skeleton

Consists of 80 bones

Three major regions

• Skull - Vertebral column - Thoracic cage

Axial Skeleton protects

Brain, spinal cord, and organs in the thoracic system

Axial skeleton supports

Head, neck, and trunk

skull

made up of 22 facial bones and cranial bones

Cranial bones(cranium)

• Enclose the brain in the cranial cavity - Serve as attachment sites for head and neck muscles

Facial bones

• Form framework of face - Contain cavities for special sense organs for sight, taste, and smell - Provide openings for air and food passage - Sites of attachment for teeth and muscles of facial expression

Skull geography

• Cranial cavity (houses brain) - Middle and internal ear cavities - Nasal cavity - Orbit - Sinuses

Skull has

85 named openings

Foramina, canals, fissures

Provide passageways for the spinal cord, major blood vessels, and the 12 cranial nerves

Sutures

Interlocking joints that connect the bones in the skull

Major Sutures

• Coronal suture - Sagittal suture - Squamous suture - Lambdoid suture

Sutural bones

Tiny, irregularly shaped bones that appear within sutures

8 cranial bones

• frontal bone - parietal bones (2) - Occipital bone - Temporal bones (2) - Sphenoid bone - Ethmoid bone

Frontal bone

• Anterior portion of cranium - Most of anterior cranial fossa - Makes up the forehead and the superior portion of orbits

Occipital bone

• Most of skull's posterior wall and base - Articulates with 1st vertebra - Sites of attachment for ligamentum nuchae and many neck and back muscles

Foramen magnum

allows for brain to connect with the spinal cord

Temporal bones

2 bones form inferolateral aspects of skull and parts of cranial base

3 major regions of temporal bones

• Squamous - Tympanic - Petrous

Sphenoid bone

• complex bat-shaped bone - Keystone of cranium - articulates with all other cranial bones

ethmoid bone

• Deepest skull bone, complex shape - Forms roof of nasal cavity and superior part of nasal septum - Contributes to medial wall of orbits

14 facial bones

• Mandible - Maxillary bones (2) - Zygomatic bones (2) - Nasal bones (2) - Lacrimal bones (2) - Palatine bones (2) - Vomer - Inferior nasal conchae (2)

Mandible

• Lower jaw - Largest, strongest bone of face

Temporomandibular joint (TMJ)

Only freely movable joint in skull

Maxillary bones

2 bones, medially fused - Form upper jaw and central portion of facial skeleton - Contain maxillary sinuses (Largest of paranasal sinuses)

Keystone bones

Articulate with all facial bones except mandible

Zygomatic Bones

• 2 bones - form Cheekbones - Inferolateral margins of orbits

Nasal Bones

• 2 bones fused medially; form bridge of nose - Attach to cartilage that makes up most of external nose

Lacrimal bones

• 2 bones located in medial walls of orbits - Lacrimal fossa contains lacrimal sac (part of passage way for tears)

Palatine bones

2 bones - form posterior one-third of hard palate & posterolateral walls of the nasal cavity

Vomer

• Plow shaped - Forms inferior part of nasal septum

Inferior nasal conchae

• 2 bones - Form part of lateral walls of nasal cavity - Largest of the the three pairs of conchae

Hyoid bone

• Not bone of skull but considered part of skull - Does not articulate directly with another bone - Connected through stylohyoid ligaments

Hyoid bone is

Movable base for tongue

Hyoid bone site

Site of attachment for muscles of swallowing and speech

Orbits

• Cavities that encase eyes - Houses eye muscles and lacrimal glands

Nasal cavity

• Constructed of bone and hyaline cartilage - Divided along midsagittal plane by nasal septum - Formed by: the Perpendicular plate of ethmoid, vomer, and septal cartilage

Paranasal Sinuses

Mucosa-lined, air-filled spaces clustered around nasal cavity

Paranasal Sinuses allow

material to flow in and out, lightens skull, warms and humidifies air ,and enhances the resonance of voice

Paranasal sinus found

in frontal, sphenoid, ethmoid, and maxillary bones

Functions of vertebral column

• Transmits weight of trunk to lower limbs - Surrounds and protects spinal cord - Serves as attachment point for ribs - Serves as attachment point for back, neck, and iliopsoas muscles

vertebral column

• 26 irregular bones(vertebrae) in five major regions - Flexible curved structure - Vertebrae increase in size from cervical to lumbar (bear more weight)

7

Cervical vertebrae - neck

12

Thoracic vertebrae - thoracic cage

5

Lumbar vertebrae - lower back

Saccrum

bone inferior to lumbar vertebrae, articulate with hip bones

Coccyx

terminus of vertebral column

Vertebral Column: Curvatures

Increase resilience and flexibility of spine

Cervical and lumbar curvatures

Concave posteriorly

Thoracic and sacral curvatures

Convex posteriorly

Scoliosis

abnormal lateral curve

Kyphosis

exaggerated thoracic curvature

Lordosis

lumbar curvature

Ligaments

Multiple ligaments support the vertebral column

Intervertebral Discs

Cushion-like pad composed of two parts

Nucleus pulposus

• Inner gelatinous nucleus - Gives disc elasticity and compressibility

Anulus fibrosus

• Outer collar composed of collagen and fibrocartilage - Limits the expansion of nucleus pulposus during compression & binds vertebrae together

Intervertebral Discs serve as

• shock absorbers - Compress during the day

Body or centrum

Anterior weight-bearing region

Vertebral arch

Composed of pedicles and laminae that, along with centrum, enclose vertebral foramen

Vertebral foramen

Together make up vertebral canal for spinal cord

Intervertebral foramina

Lateral openings between adjacent vertebrae for spinal nerves

Spinous process

projects posteriorly

Transverse processes (2)

project laterally

Superior articular processes (2)

protrude superiorly

Inferior articular processes (2)

protrude inferiorly

Vertebrae movements

• Flexion and extension - Lateral flexion - Rotation

C1 to C7

smallest, lightest vertebrae

C1 (atlas) and C2 (axis)

No intervertebral disc between them

C3 to C7 share following features

• Oval body - Spinous processes are bifid (except C7) - Large, triangular vertebral foramen - Transverse foramen in each transverse process

Atlas (C1)

• No body or spinous process - Movement for "Yes"

Axis (C2)

• More similar to other cervical vertebrae but has dens - Dens projects superiorly into anterior arch of atlas - Pivot for rotation of atlas - Movement for "No"

Thoracic Vertebrae

• All articulate with ribs at facets and demi facets - Circular vertebral foramen - Long, spinous process that points inferiorly (looks like giraffe)

T1 to T12

increase in size from first to last

Lumbar Vertebrae

• Large, kidney-shaped bodies and triangular vertebral foramen - Flat hatchet-shaped spinous processes point posteriorly (looks like moose) - Facet orientation provides stability, minimizing rotation

Sacrum

• 5 fused vertebrae (S1-S5) - Forms posterior wall of pelvis - Articulates with L5 superiorly, and with auricular surfaces of hipbones, forming the sacroiliac joints -

Coccyx area

-Tailbone - 3-5 fused vertebrae - Articulates superiorly with sacrum

Functions of the Thoracic Cage

• Protects vital organs of thoracic cavity - Supports shoulder girdles and upper limbs - Provides attachment sites for muscles of neck, back, chest, and shoulders

Thoracic Cage Components

• Sternum - Ribs - Costal cartilages - Thoracic vertebrae

Manubrium

• Superior portion - Articulates with clavicles and ribs 1 and 2

Body (midportion)

Articulates with costal cartilages of ribs 2 through 7

Xiphoid process - Inferior end

• Site of muscle attachment - Not ossified until ~age 40

Ribs and Their Attachments

• 12 pairs - Attach posteriorly to bodies and transverse processes thoracic vertebrae

Pairs 1 to 7

• True ribs - Attach directly to sternum via costal cartilage

Pairs 8 to 10

• False ribs - Attach indirectly to sternum by joining costal cartilage of rib above

pairs 11-12

• floating ribs - No anterior attachment

Head (posterior end)

• Articulates with facets on bodies of two adjacent vertebrae

Tubercle (lateral to neck)

Articulates posteriorly with transverse costal facet of same-numbered thoracic vertebra

Shaft

Most of rib