Functional Anatomy Chapter 7 - Axial Skeleton

Course Information

• Course title: Functional Anatomy
• Course code: HHSC 105
• Instructor: Dr. Farnaz Gooya, MD, MSc in Immunology & Allergy, MEd in Health Professions Education
• Institution: School of Health Sciences, University of Northern British Columbia

Textbook Information

• Title: Human Anatomy
• Authors: McKinley, O'Loughlin, Pennefather-O, Brien
• Edition: Sixth Edition

Chapter 7 - Axial Skeleton

• The axial skeleton contains 80 bones
• Cranial bones: 8 bones that surround and enclose the brain
  • Unpaired: ethmoid, frontal, occipital, sphenoid
  • Paired: parietal, temporal
• Facial bones: 14 bones that form the face and have no brain contact
  • Unpaired: vomer, mandible
  • Paired: maxillae, nasal, lacrimal, zygomatic, palatine, and inferior nasal conchae
• Major Cavities of the Skull: Cranial cavity (houses the brain), orbits (eye sockets), oral cavity (mouth), nasal cavity, and paranasal sinuses

Introduction

• The skeleton forms an internal framework to support soft tissues, protect vital organs, bear the body's weight, and help us move.
• Typically, there are 206 bones in the adult skeleton.
• The total number decreases with growth and maturity.
• Bones differ in size, shape, weight, and even composition.

Skull

• The skull is composed of cranial and facial bones.
• Cranial bones surround and enclose the brain
• Frontal bone forms the forehead
• Paired parietal and temporal bones form the sides and back of the skull, respectively.
• Occipital bone forms the back of the skull.
• Facial bones form the face and do not include brain contact.
• Major cavities of the skull include cranial, oral, nasal and orbital cavities

Major Cavities of the Skull

• Cranial cavity: houses the brain
• Orbits: eye sockets
• Oral cavity: mouth
• Nasal cavity: inside the nose
• Paranasal sinuses: air-filled spaces within the skull bones surrounding the nasal cavity (e.g., frontal, ethmoidal, sphenoidal, maxillary)

Anterior View of the Skull

• Frontal bone forms the forehead.
• Orbits are formed from multiple skull bones.
• Superior orbital fissure and Inferior orbital fissure are openings within the orbits
• Nasal bones form the bony bridge of the nose.
• Glabella is a landmark area between the orbits, superior to the nasal bones.

Anterior View of the Skull (cont.)

• Left and right maxillae form most of the upper jaw
• Infraorbital foramen is an opening in each maxilla which allows blood vessels and nerves to reach the face.
• Mandible forms the lower jaw and the "chin" is called the mental protuberance.
• The nasal cavity's inferior border is marked by a prominent anterior nasal spine.
• Nasal septum divides the nasal cavity into left and right halves.
• Inferior nasal conchae are scroll-shaped bones found along the lateral walls of the nasal cavity.

Superior and Posterior Views of the Skull

• Four cranial bones are prominent in superior and posterior views: frontal, both parietal, and occipital bones.
• Coronal suture connects the frontal and parietal bones.
• Sagittal suture connects the left and right parietal bones.
• Lambdoid suture connects the parietal and occipital bones.

Superior and Posterior Views of the Skull (cont.)

• Parietal foramina conduct emissary veins from brain veins to scalp veins.
• External occipital protuberance is a bump on the back of the head.
• Lambdoid suture connects the parietal and occipital bones.

Lateral View of the Skull

• One of each parietal, temporal, zygomatic, maxilla, frontal, sphenoid bone (greater wing), sections of occipital bone, and mandible are visible
• Lacrimal bone is anterior to ethmoid and posterior to nasal bone.
• A portion of sphenoid bone articulates with the frontal, parietal, and temporal bones

Lateral View of the Skull (cont.)

• Temporal process of the zygomatic bone and zygomatic process of the temporal bone fuse to form zygomatic arch, which terminates superior to mandibular articulation.
• External acoustic meatus, lies over the external acoustic meatuses and posterior to that is mastoid process.

Sagittal Section of the Skull

• Perpendicular plate of the ethmoid bone
• Vomer
• Frontal sinus
• Sphenoidal sinus

Inferior or Basal View of the Skull

• Hard palate
• Sphenoid bone
• Parts of the occipital and temporal bone
• Foramen magnum (opening in occipital bone)

Superior Endocranial Cavity of the Skull

• The skull's internal cavity visible when the removable outer layer is (calvarium) is removed
• Prominent regions include frontal, ethmoid, sphenoid, temporal, and occipital bones.

Sutures

• Immovable joints between skull bones.
• Four major sutures: coronal (frontal and parietal), sagittal (two parietal), lambdoid (occipital and parietal), squamous (temporal and parietal).

Sutures (cont.)

• Sutural bones can sometimes be found in some sutures.
• These sutures can vary in size, number, and location.

Sutures (cont.)

• During adulthood, sutures start to disappear as bones fuse.
• Coronal, sagittal, and lambdoid sutures typically fuse during the late twenties to early forties.
• Squamous suture often doesn't fuse until late adulthood.

Bones of the Cranium

• The cranium, or skullcap, is composed of the eight bones that protect the brain.
• It consists of a roof (calvaria) and a base.
• Made of parietal, frontal, and occipital bones.
• Base is made of ethmoid, sphenoid, occipital, and temporal bones.

Anterior View of the Frontal Bone

• The frontal bone's squamous part is a vertical flattened area that ends at the Supraorbital margin
• Supraorbital foramen or notch
• Superciliary arches (brow ridges)
• Glabella sandwiched between the superciliary arches

Anterior View of the Frontal Bone (cont.)

• The orbital part of the frontal bone (inferior part) forms the roof of the orbit.
• Zygomatic process articulates with frontal process of zygomatic bone
• Frontal sinuses appear as 6 openings
• Frontal crest serves to attach falx cerebri to the bone

Lateral View of the Parietal Bone

• Parietal bones are bordered by four sutures.
• Lateral surface includes superior and inferior temporal lines and parietal eminence.
• Internal surface has grooves to accommodate blood vessels

Temporal Bone

• Temporal bone has a complex structure composed of the petrous, squamous, and tympanic parts.
• Contains inner ear sensory structures for hearing and balance.
• Mastoid process, filled with air cells, communicates with the middle ear.
• Styloid process, a thin, pointed projection

Occipital Bone

• Forms the posterior portion of the skull
• Two parts: squamous and basilar
• Foramen magnum, a large circular opening.
• Occipital condyles, smooth knobs

Sphenoid Bone

• Resembles a butterfly and is the 'keystone' of the cranium.

• Articulates with numerous bones.

• Major structural parts include: Body, greater wings and lesser wings.

Sphenoid Bone (cont.)

• Important foramina (openings) include optic canal, foramen rotundum, foramen ovale, foramen spinosum.

Ethmoid Bone

• Anterior view of the ethmoid bone highlights the ethmoidal labyrinth, perpendicular plate which forms superior part of nasal septum, crista galli, and superior nasal conchae.

Articulations of the Sphenoid and Ethmoid Bones

• The ethmoid bone is between the orbits. The sphenoid bone extends the cranial floor and is joined with several other bones including the maxilla.
• It forms part of the medial wall of each orbit as well as part of nasal septum.

Cranial Fossae

• The cranial cavity floor contains three cranial fossae
• Anterior cranial fossa formed by frontal, ethmoid, and sphenoid bones(lesser wings).
• Middle cranial fossa from parietal, sphenoid, and temporal bones.
• Posterior cranial fossa from occipital, temporal, and parietal bones.

Foramen of the Skull

• Foramina are openings through bones. Many important foramina are located in the base of the skull.

Bones of the Face

• Facial bones: 14 bones that give shape to the face and form parts of the orbital and nasal cavities
• Support teeth, and serve as attachment sites for expression and chewing muscles

Facial Bones and Selected Features

• Various facial bones and associated passageways, including their boundaries, and their relevant features in the skull (e.g., foramina, processes).

Zygomatic Bone

• Zygomatic bone is known as "cheekbones"
• It has 3 significant processes: frontal, maxillary, and temporal. These contribute to zygomatic arch as well

Vomer

• A triangular-shaped bone articulating with the maxilla and palatine along the midline of the skull.
• Forms part of the bony nasal septum with perpendicular plate of ethmoid bone

Inferior Nasal Concha

• The inferior nasal conchae are shell-like bones.
• They are located in the inferolateral wall of the nasal cavity.
• Help create turbulence in inhaled air.

Palatine Bone

• A bone with a characteristic L-shape.
• Forms part of the hard palate, nasal cavity, and orbits.
• Includes orbital processes at the medial floor of the orbit and horizontal plates form posterior part of the hard plate.

Maxilla

• Forms the central part of the face skeleton
• Forms upper jaw and parts of the hard palate, nasal cavity, and inferior parts of the orbits.
• Houses alveolus processes where upper teeth sit.
• Maxillae articulate with the zygomatic and frontal bones, via zygomatic/frontal processes

Maxilla (cont.)

• Maxillary sinus, a spacious cavity located adjacent to nasal cavity, housed within the maxilla

Mandible

• Forms the entire lower jaw
• Supports the lower teeth and provides attachment for masticatory muscles.
• Composed of body and two rami.
• Mandible's ramus intersects body at the angle of the mandible, supporting teeth through alveolar process

Mandible (cont.)

• Condylar process of mandible articulates with mandibular fossa of temporal bone creating TMJ

Nasal Complex

• Nasal cavities are formed by nasal bones, nasal conchae, and nasal cartilages.
• The superior border is made of parts of frontal and sphenoid bones.
• The inferior border is made of the maxillae and palatine bones.

Paranasal Sinuses

• Air-filled spaces within the skull surrounding the nasal cavities, that humidify and warm inhaled air.
• They provide resonant chambers that produce sounds during speaking.
• Maxillary sinus, is more prominent around age 5 and frontal sinus develops more around age 10

Orbital Complex/Left Orbit

• Bony cavities in the skull that hold and protect the eyes.
• Multiple bones form the orbits (e.g., mostly maxilla, frontal, lacrimal, ethmoid, sphenoid, and zygomatic)

Bones Associated with the Skull

• Auditory ossicles (malleus, incus, stapes) are tiny bones in the petrous portion of each temporal bone, to help with hearing
• Hyoid bone is located between the mandible and larynx; it serves as an attachment site for certain muscles and is crucial for swallowing

Sex Differences in the Skull

• Differences in shape and size.
• Male skulls are generally larger and more robust than female skulls.
• Superciliary arches, supraorbital margins, occipital protuberance, and mental protuberance are frequently used to determine sex.

Fetal Skull

• Infant cranial bones are connected by flexible areas of connective tissue called fontanelles
• These fontanelles allow for brain growth and flexibility during birth.
• Commonly visible are: anterior, posterior, sphenoidal, and mastoid fontanelles

Fetal Skull (cont.)

• Most significant growth in cranium occurs before age 5.
• Brain growth is almost complete by age 5.
• Cranial sutures (joints) fully developed around age 5.

Vertebral Column

• Composed of 26 bones (24 vertebrae, sacrum, and coccyx), providing vertical support, maintaining upright position, and weight transfer.
• Divided into 5 regions: cervical, thoracic, lumbar, sacrum and coccyx (superior to inferior).

Spinal Curvatures

• Cervical curvature helps support the weight of the head.
• Thoracic curvature, slightly concave; lumbar curvature, concave, helps weight transfer and maintain upright position.
• Sacral curvature is a natural concavity found at inferior end of vertebral column.

Cervical: Vertebrae

• The first cervical vertebrae is called the atlas, it lacks a body and spinous process.
• The second cervical vertebrae is called the axis. which has a process called the dens that acts as the pivot for movement

Thoracic Vertebrae

• Thoracic vertebrae are positioned superior to the lumbar region.
• They are larger than cervical vertebrae.
• They have costal facets (where ribs attach) on the body and transverse processes

Lumbar Vertebrae

• Lumbar vertebrae form the lower back (inferior to thoracic region)
• Significantly larger than thoracic and cervical vertebrae.
• They support most of the upper body weight
• They lack transverse foramina and costal facets.

Sacrum and Coccyx

• The sacrum is a large triangular bone that forms the posterior wall of the pelvic cavity.
• The sacral canal is a continuation of the vertebral canal.
• Sacrum articulates with iliac bones (hip bone) at sacroiliac joints.
• The coccyx is a small, rudimentary tailbone-shaped structure formed by fusion of 4 small vertebrae.

Thoracic Cage

• The bony structure that supports the chest wall, formed by:
• Thoracic vertebrae posteriorly, ribs laterally, and sternum anteriorly.
• Protects vital organs such as the heart, lungs, trachea, and esophagus.

Sternum

• The sternum is the breastbone, which is a flat bone located in the anterior midline of the thoracic wall.
• It is composed of three parts: manubrium (superior part), body (middle part), and xiphoid process (inferior part)

Ribs

• Ribs are elongated, curved, and flat bones. The ribs connect posteriorly with the thoracic vertebrae and end anteriorly in the thoracic wall
• Facets on the head and tubercle to articulate with the vertebral body and transverse process respectively

Ribs (cont.)

• 12 pairs of ribs.
• 1-7 true ribs connect to the sternum directly via costal cartilage;
• 8-12 false ribs don't connect directly with the sternum;
• 11-12 floating ribs don't connect to the sternum.

Aging of the Axial Skeleton

• Bones fuse together more as we age.
• Skeletal mass and density decline in older age.
• Bones become porous and brittle.
• Articulating surfaces often deteriorate in older adults.