Axial Skeleton Anatomy

Bone Tissues

• Bone connective tissue is a major component.
• Nervous tissue, blood connective tissue, and articular cartilage are also present.
• The functional unit of bone is the osteon.

Functions of Bones

• Protect internal organs.
• Store and release fat.
• Produce blood cells
• Store and release minerals, like Ca2+ and PO43-.
• Facilitate movement.
• Supports the body.

Classification of Bones

• Long bones are longer than they are wide and have a shaft with ends.
• Short bones are cube-shaped.
• Flat bones are thin, flattened, and curved.
• Irregular bones have various shapes.

Gross Anatomy of Bones

• Compact bone is a dense outer layer.
• Spongy (cancellous) bone is an internal network with trabeculae.
• Spaces between trabeculae are filled with marrow.

Long Bone Structure

• Diaphysis is the bone shaft.
• Epiphyses are the bone ends.
• Metaphysis is between the epiphysis and diaphysis and contains a growth plate.
• Medullary cavity is hollow and contains yellow marrow.
• Blood vessels are present.

Long Bone Membranes

• Periosteum is the outer membrane and provides attachment for tendons/ligaments.
• Sharpey's fibers anchor the periosteum to the bone.
• Endosteum is the inner lining and aids in growth and remodeling.

Structure of Short, Irregular, and Flat Bones

• Contain bone marrow but no cavity.
• Diploë is the internal spongy bone of flat bones.

Bone Design and Stress

• Bone anatomy reflects stresses.
• Compression and tension are greatest at the external surfaces.

Bone Markings

• Projections are for muscle attachment.
• Surfaces form joints.
• Depressions and openings exist.

Skeletal System Components

• Bones, cartilage, joints, and ligaments are components of the Skeletal System.
• There are 206 bones in the body.
• The axial skeleton (80 bones) includes the skull, vertebral column, and thoracic cage.
• The appendicular skeleton (126 bones) includes the upper and lower limbs.

The Skull

• The skull is the most complex bony structure.
• It is composed of 22 bones.
• There are 8 cranial bones.
• There are 14 facial bones.

Cranial Bones

• The cranium is divided into the cranial vault and base.
• The cranium protects the brain.
• The cranium provides attachment sites for the head and neck.

Facial Bones

• Form the facial framework
• Create cavities for sight, taste, and smell
• Provide openings for air and food passage
• Hold teeth and anchor facial muscles

Skull Regions

• Bony ridges divide the skull into anterior, middle, and posterior fossae.
• The brain sits within fossae in the cranial cavity.

Skull Cavities

• Middle and inner ear cavities are in the lateral cranial base.
• The nasal cavity is behind the nose.
• Orbits house the eyeballs.
• Paranasal sinuses are in bones around the nasal cavity.

Skull Openings

• The skull has approximately 85 named openings including foramina, canals, and fissures.
• These openings provide passage for the spinal cord, blood vessels, and cranial nerves.

Cranial Bones (8)

• The paired bones are the temporal bones (2) and parietal bones (2).
• The unpaired bones are the frontal bone, occipital bone, sphenoid bone, and ethmoid bone.

Parietal Bones and Sutures

• The parietal bones form the superior and lateral skull.
• The four sutures are coronal, squamous, sagittal, and lambdoid.
• The coronal suture is between the parietal and frontal bones.
• The squamous suture is between the parietal and temporal bones.
• The sagittal suture is between the left and right parietal bones.
• The lambdoid suture is between the parietal and occipital bones.

Sutural Bones

• Sutural bones are small, irregular bones in sutures.
• Sutural bones vary in shape, size, and location.
• Not present in all individuals

Frontal Bone Features

• Forms the forehead and the roof of the orbits
• The supraorbital margin is the top of the orbits.
• The supraorbital foramen allows passage for a nerve and artery.
• The glabella is the smooth area between superciliary arches.
• Frontal sinuses contributes contributes to the anterior cranial fossa.

Occipital Bone

• Forms the posterior cranium and cranial base.
• Articulates with temporal and parietal bones.
• Forms the posterior cranial fossa.
• The Foramen magnum locates at the base.

Features of Occipital Bone

• Occipital condyles connect skull to spine for head movement.
• Hypoglossal foramen provides passage for tongue movement nerves.
• External occipital protuberance is a muscle attachment bump.
• Nuchal lines are ridges for muscle attachment.

Temporal Bones

• Inferior to the parietal bones.
• Inferolateral portion of the skull
• The temporal bones house inner ear structures.
• Serve as muscle attachment for chewing and head movement.

Parts of the Temporal Bone

• Squamous portion is a flat section forming the skull side.
• Tympanic surrounds the ear canal and protects ear structures.
• Petrous contains dense area that houses inner ear for hearing and balance.

Mastoid Process

• Bony prominence behind ear.
• Serves as a site for neck muscle attachment.
• Contains air sinuses

Petrous Part of Temporal Bone

• Projects medially and contributes to the cranial base.
• Houses the middle and inner ear cavities.
• Contributes to the middle and posterior cranial fossae.

Foramina of the Temporal Bone

• Jugular foramen: Passage for internal jugular vein and cranial nerves (IX, X, XI); located between the temporal bone and occipital bone.
• Carotid canal: Internal carotid artery pass through.
• Internal acoustic meatus: Passage for cranial nerves (VII, VIII).

Sphenoid Bone

• Spans the cranial floor width and resembles a bat.
• It has a body and 3 pairs of processes.
• Contains 5 openings.
• Considered the "Keystone" of the cranium.

Sphenoid Bone Landmarks

• Body is the central part.
• Sella turcica is a saddle-shaped area for the pituitary gland.
• Sphenoidal sinuses are air-filled spaces that lighten the skull.
• Greater wings are large extensions forming skull sides.
• Lesser wings are smaller extensions forming part of orbit.
• Pterygoid processes are projections for jaw muscle attachment.

Sphenoid Bone Openings

• Optic canal provides passage for the optic nerve.
• Superior orbital fissure: opening for 4 nerves controlling eye movement and vessels.
• Foramen rotundum opening for trigeminal nerve (sensation).
• Foramen ovale is the opening for trigeminal nerve (motor).
• Foramen spinosum passage for vessels supplying skull.

Ethmoid Bone

• Located between the nasal and sphenoid bones.
• Forms most of the medial bony region between nasal cavity and orbits.
• Contributes to the nasal septum.

Ethmoid Bone Landmarks

• Cribriform plate: superior surface, contains foramina
• Cribriform plate allows for olfactory nerves (CN I).
• Crista galli serves as attachment for falx cerebri.
• Perpendicular plate forms the superior part of the nasal septum.

Openings in the Ethmoid Bone

• Ethmoidal labyrinth is the location of air cells and ethmoid sinuses that lighten the skull.
• Nasal conchae are superior and middle and extend medially.

Facial Bones

• Unpaired bones: mandible, vomer
• Paired bones: maxillae, zygomatic bones, nasal bones, lacrimal bones, palatine bones and inferior nasal conchae

Mandible

• Largest and strongest facial bone.
• The only movable skull bone.
• Has a horizontal body.
• Characterized by two upright rami

Major landmarks of the Mandible

• Mandibular fossa - depression (temporal bone)
• Mandibular foramen - opening (inner ramus surface)
• Alveolar process - ridge containing tooth sockets
• Mental foramen - opening (anterior surface)
• Condylar process - articulates with mandibular fossa
• Ramus - connects body to condylar and coronoid processes

Maxillary Bones

• Articulate with all facial bones except the mandible.
• Contain maxillary sinuses.
• Form part of the inferior orbital fissure.
• Keystone bones of the face.

Facial Bones

• Zygomatic bones: lateral wall of orbits
• Nasal bones: bridge of nose

Facial bones

• Lacrimal bones: medial orbital walls
• Palatine bones: posterior part of hard palate

Facial Bones

• Vomer: inferior nasal septum
• Inferior nasal conchae: thin, curved bones form lateral walls of nasal cavity

Special Parts of the Skull

• Nasal cavity
• Paranasal sinuses
• Orbits
• Hyoid bone

Nasal Cavity Function

• Respiration
• Olfaction
• Resonance
• Sinus Connection

Paranasal Sinuses

• Air-filled sinuses within: -Frontal bone -Ethmoid bone -Sphenoid bone -Maxillary bones
• Lined by mucous membrane
• Lightens the skull

Orbits

• Eye protection
• Houses muscles, nerves, and vessels
• Supports eye movement and vision

Hyoid Bone

• Below mandible
• Only bone with no direct articulation
• Movable base for tongue

Vertebral Column

• Consists of 26 bones (adult).
• It supports trunk weight and protects the spinal cord.
• Serves as attachment sites for neck and back muscles.

Vertebral Column Regions

• 7 cervical vertebrae
• 12 thoracic vertebrae
• 5 lumbar vertebrae
• Sacrum – 5 fused bones
• Coccyx – 4 fused bones

Normal Curvatures of the Spine

• Cervical and lumbar: concave posteriorly.
• Thoracic and sacral: convex posteriorly.
• Curvatures increase resilience.

Primary and Secondary Curvatures

• Primary curvatures: thoracic and sacral, present at birth.
• Secondary curvatures: cervical and lumbar develop with walking.

Ligaments of the Spine

• Anterior longitudinal ligament
  • Attaches to vertebrae and intervertebral discs.
  • Prevents hyperextension.
• Posterior longitudinal ligament
  • Narrow, weak
  • Attaches to intervertebral discs

Intervertebral Discs

• Cushion-like pads located between the vertebrae.
• Contains nucleus pulposus and anulus fibrosus.

Intervertebral Disc Components

• Nucleus pulposus: gelatinous core, absorbs compression.
• Anulus fibrosus: outer ligament rings, inner fibrocartilage, encloses the nucleus pulposus.

General Vertebral Structure

• Body: supports weight.
• Arch: protects spinal cord.
• Foramen: opening for spinal cord.
• Spinous/Transverse processes: muscle/ligament attachment.
• Articular processes: connect vertebrae.
• Intervertebral foramina: nerve passageways..

Spinal Function

• Movement between vertebrae.
  • Flexion and extension
  • Lateral flexion
  • Rotation in the long axis

Cervical Vertebrae

• C1-C7
• Smallest and lightest
• C3-C7 wider body, short and bifid spinous process (except C7, vertebra prominens)

Features of Cervical Vertebrae

• Large, triangular foramen
• Transverse processes with transverse foramina
• Superoposteriorly facing articular facets

Atlas (C1)

• No body or spinous process.
• Supports skull.
• Superior articular facets, receive occipital condyles.
• Allows flexion/extension.
• Nodding "yes".

Axis

• Body and spinous process
• Dens projects superiorly
• Fusion of atlas body with axis
• Pivot for rotation (shake head "no")

Thoracic Vertebrae

• Articulate with ribs & heart-shaped bodies
• T1 full facet for first rib
• T１０-T12 single facet for ribs

Features of Thoracic Verteae

-Long spinous processes, point inferiorly
 -Circular vertebral foramen

• Transverse processes articulate with rib tubercles -Articular faucets at superior/inferior edges
• Allows rotation, limits flexion/extension

Lumbar Vertebrae (L 1−L 5)

• Thick bodies
• Thin transverse processes
• Short, flat, spinous processes
• Triangle vertebral foramina
• Medially facing articular facets
• Allows flexion/, prevents rotation

Sacrum (S１−S4)

-Forms posterior pelvic wall

-Five fused vertebrae -Superiorly articulates with L5 -Inferiorly articulates with coccус

Sacrum Landmarks

• Sacral promontory: bulge of first scaral vertebra into pelic cavity
• Ala: fused rib elements Superior articular process: projections one upper scarum Apex: inferior and of scarum

Sacrum Landmarks

• Transverse ridges: horizontal bridges
• Facet of superior articular process: smooth, rounded surfaces
• Median scaral crest: vertical ridge, positive midline
• Lateral scaral crest: vertical ridges, sides of median crest
• Auricular surface: lateral, ear-shaped

Sacral Foramina

• Anterior sacral formina: passage for ventral ram of sacral nerves
• Posterior sacral foramina passage for dorsal rami of sacral nerves Sacral canal Center of sacrum continuation of vertebral cana,
• Contains nerves and tissue Sacra hiatus: opening at inferior sacrum, coccyx
• Tailbone Consists of the base ( broad,upper part)
• Apex (pointed, lower end Has coccygeal cornua main part of the body also consist of the 3-5 fused vertebrae

Thoracic Cage

• Forms chest framework
• Thoracic vertebrae (posterior)
• Ribs (lateral)
• Sternum and costal cartilage (anterior)
• Protects thoracic organs
• Supports shoulder girdle and upper limbs
• Muscle attachment sites

Sternum

• Manubrium: superior, articulates with clavicles
• Bodybulk, noted for costal cartilage of ribs 1-7
• Xiphoid process inferior, ossifes around age 40

Landmarks of the Sternum

• Jugular notch central indentation, superios border of manubrium
• Sternal angle: ridge where manubrium joins body
• Clavicar notch shallow depressions for clavides, superior aspect of manubrium

Ribs

• Attach to vertebral column posteriorly
• True ribs top 7 pairs, attach to sternum via costal cartilage
• False ribsbotton 5 pairs, including floating ribs (11-12)

Landmarks of the Ribs

• Head round end, articulates with vertebral bodies
• Neckshort segment after head
• Tuberde bump new neck-body junction
• Long curves
• Costal grooves hallower groove along inner surface
• Sternal ends anterior end, articulates with sternum

Common Conditions

Cleft palate: congenital disorder failure of palate halves of fuse medially Stenosis of lumbar spine narrowing of vertebral canal, compresses spinal nerve roots

Abnormal Spinal Curvatures

Kyphosis: exaggerated thoracic curvature Lordosis accentuated lumbar curvature; “swayback

• Scoliosis abnormal rate curvature

Ossification

• Membrane, bones ossify in second month of development
• Bane tissue gross outward from ossification centers are you gonna Fontanelles innusifred membrane remenence

The Skeleton Throughout Life

• Skeleton grows until 18-21 years
• Childrenadolescents bone formation exceeds reabsorption
• Young adults formation and reabsorption balanced

Height Loss

• Reabsorption predominates, bone mass declines
• Intervertebrasdiscs loos water content
• Height loss common by age 55
• Thorax becomes more rigid

Summary

• Axial skeleton forms the central framework of the body
• Provides support and protection of ital organs
• Includes skull, -vertebral column, and ribcage
• Aging needs to bone thanes and less of bones density

Test your knowledge of the axial skeleton and its components. Questions cover the skull, vertebral column, and rib cage. Explore the primary functions and key features of this essential skeletal division.