Axial Skeleton pt 1 Functions

Cranial - Frontal Bone

• forms the forehead

• also forms the supraorbital margin

• support and protect the frontal lobes of the brain

shell shaped bone forming the anterior cranium and the superior orbits

Cranial - Parietal Bones (2)

• Form the superior and upper lateral walls of the brain case (the calvaria or skullcap); protect the underlying parietal lobes of the cerebral cortex.

large bones forming most of the superior and lateral aspects of the cranium

Cranial - Temporal Bones (2)

• Form the lower lateral sides and base of the skull (middle/posterior cranial fossae); protect the temporal lobes of the brain.

• bones that form the inferolateral aspects of the skull

External auditory / acoustic meatus

a passageway that guides sound waves to the tympanic membrane (ear drum).  Deep to the tympanic membrane is the middle ear which contains three small bones (malleus, incus and stapes) that are responsible for directing sound waves from the tympanic membrane to the inner ear.

mandibular fossa

A depression on the temporal bone where the mandible articulates with the skull.  The mandibular fossa of the temporal bone and the condyle of the mandible come together to form a joint called the temporomandibular joint, permitting elevation, depression, protraction, retraction, and lateral excursion of the lower jaw for mastication (chewing) and speech.

Mastoid Process

Enlargement on the skull posterior to the earlobe.  Site of attachment for muscles that move the skull. major anchor site for neck muscles that rotate and extend the head.

Cranial - Occipital Bone

large bone forming most of the posterior wall and base of the skull

• houses and protects the cerebellum and occipital lobes.

foramen magnum

The brain stem extends through the foramen magnum to connect to the spinal cord that allows the brainstem/spinal cord to pass from the cranial cavity into the vertebral column, along with vertebral arteries.

occipital condyle

The rounded occipital condyles articulate with the atlas vertebra (C1), allowing the head to move up and down in a “yes” movement and a side-to-side tilt movement

Cranial- Sphenoid Bone

– a butterfly shaped bone in the middle of the skull forming the posterior wall of the orbits. It is considered the keystone of the skull because it articulates with all of the cranial bones uniting the neurocranium and facial skeleton; forms the posterior wall/apex of the orbits and central cranial floor.

optic foramen

o      Round hole in each posterior orbit.  It is a passageway for the Optic nerve (II) which carries visual information to the brain.

sella turcica

o      Depression on the sphenoid bone (inside the brain case) that protects and houses the pituitary gland.

Cranial - Ethmoid Bone

– the deepest bone of the skull, it lies between the nasal bones and the sphenoid

• forms the roof, upper lateral walls, and upper septum of the nasal cavity, as well as the medial orbital walls.

cribriform plate

Flat portion of the ethmoid bone on either side of the crista galli (inside the brain case).  The olfactory bulbs lie on the cribriform plate.  The olfactory foramina are the small holes in the cribriform plate that allow olfactory nerves to pass through the skull from the nasal cavity into the olfactory bulbs within the skull.

• allow sensory nerve fibers from the nasal cavity to pass directly into the olfactory bulbs for the sense of smell.

crista galli

Midline projection of the ethmoid bone into the brain case.  A membrane holding the brain in place attaches to this structure.

Sutures - sagittal suture

●      Fibrous joint between the two parietal bones along the midline of the skull, uniting the left and right parietal bones.

squamous suture

●      Fibrous joint between the parietal bone and the temporal bone on either side of the skull

• Joins the squamous part of the temporal bone to the inferior edge of the parietal bone on each lateral skull.

coronal suture

●      Fibrous joint between the parietal bones and the frontal bone

• joins the frontal bone to the right and left parietal bones across the crown of the head.

lambdoid suture

– Fibrous joint between occipital bone and the parietal bones

Facial- Mandible

the u-shaped lower jawbone.  The lower teeth are embedded in the mandible

• Forms the lower jaw; only moveable bone of the adult skull. Its alveolar process anchors and supports the lower teeth in sockets (alveoli).

coronoid process

A projection of the mandible to which a muscle moving the mandible upward attaches.

• Flattened anterior upward projection that serves as the insertion site for the powerful temporalis muscle, pulling the mandible upward during biting and chewing.

mandibular condyle

Rounded structure on the mandible that fits into the mandibular fossa on the temporal bone to form a synovial joint that allows the mandible to move.  The mandibular fossa of the temporal bone and the condyle of the mandible come together to form a joint called the temporomandibular joint.

Facial- Maxillae (2)

These two bones are fused medially and form the upper jaw.  The maxillae articulate with all the facial bones except for the mandible.  The upper teeth are embedded in the maxillae

Facial- Palatine Bones (2)

A pair of bones forming the posterior portion of the hard palate (roof of the mouth).

Lacrimal Bones (2)

●      delicate, small bones on the anterior medial wall of the orbits

nasolacrimal canal

- Passageway for the nasolacrimal duct which drains tears from the surface of the eye to the nasal cavity

Facial- Vomer Bones

a slender bone that forms the inferior part of the nasal septum.  The nasal septum is the wall in the nasal cavity formed by cartilage, the vomer, and the medial portion of the ethmoid bone.

Slender, plow-shaped bone that forms the inferior and posterior part of the bony nasal septum, dividing the left and right nasal airways.

Facial - Inferior Nasal Conchae (2)

Thin curved bones on the lateral walls of the nasal cavity. They function to increase the surface area of the nasal cavity trapping foreign airborne particles in nasal mucus before they reach the lungs.

Facial - Zygomatic bones (2)

Form the cheeks and the lateral orbits

Zygomatic arch

A bridge of bone formed by projections of the temporal and zygomatic bones.  It functions as an attachment site for a muscle moving the mandible and for ligaments holding the mandible in place.

Facial - Nasal Bones (2)

●      Two bones forming the bridge of the nose

Facial - Hyoid bone

- This bone is NOT part of the skull and lies just inferior to the mandible in the anterior neck.  The hyoid bone is the only bone that is not directly attached to another bone.  It functions to anchor the throat, larynx and tongue muscles.

• Located in the anterior midline of the neck beneath the mandible. It does not articulate with any other bone; suspended by muscles and the stylohyoid ligament. Functions as a stable base for the tongue and anchors larynx and pharyngeal muscles essential for swallowing and vocalization/speech.

 

Spine Curvature - Kyphosis

Exaggerated thoracic curvature which can be caused by osteoporosis

Spine Curvature- Lordosis

●      Exaggerated lumbar curvature which can be caused by pregnancy or potbelly

Scoliosis

Abnormal lateral curvature of the vertebral column

Vertebra - Body (centrum)

Thick, cylindrical part of the vertebra responsible for bearing weight.

Vertebral Foramen

Hole formed by the vertebral body and arch.  The spinal cord and cauda equina extend through the vertebral foramen.  Together all the vertebral foramina form the vertebral canal.

Vertebra - Spinous Process

Midline, posterior projection of the vertebrae that is a site of ligament and muscle attachments for muscles that move the vertebral column and also some muscles that move the head, scapulae, and arms.

Vertebra - Transverse process

Lateral projections of the vertebrae that are sites of ligament and muscle attachments for muscles that move the vertebral column.

Cervical vertebra (C1-C7)

The smallest, lightest vertebra found in the neck

Transverse foramina

All cervical vertebrae contain an opening in both transverse processes through which the vertebral arteries supplying blood to the brain pass.

Atlas

The atlas is the first cervical vertebra (C1). It articulates with the occipital condyles to form a synovial joint that allows for lateral skull movement (side-to-side tilt) and anterior/posterior movement (nodding head “yes”)

Axis

The second cervical vertebra is the axis (C2).  It has a bony projection called the dens around which the atlas rotates allowing a “no” movement of the skull.

Thoracic vertebra (T1-T12)

●      The vertebrae that articulate with the ribs.

• Possess costal facets to articulate with the ribs, giving structural stability to the rib cage.

Lumbar vertebra (L1-L5)

Large, sturdy vertebrae in the lower back

massive bodies designed to bear the majority of upper body weight.

Vertebra - Sacrum (S1-S5)

Five fused vertebrae that form the posterior wall of the pelvis.  The sacrum articulates laterally with the two hip bones (coxae) to form the bony pelvis.  The articulation between the sacrum and the coxa is called the sacroiliac joint.

Sacral foramina

o      Along the length of the sacrum are openings through which spinal nerves exit the sacrum (analogous to intervertebral foramina)

Sacral Canal

o      The sacral canal is a continuation of the vertebral canal.  It contains the cauda equina

Sacral hiatus -

o      Inferior opening of the sacral canal.  Anesthetics can be injected into the sacral hiatus.

Coccyx (Co1-Co4)

The “tailbone” typically comprised of four fused coccygeal vertebrae

• serves as an attachment site for muscles and ligaments of the pelvic floor.

Sternum

●      the “breastbone” is located in the anterior midline of the thorax and serves as an anchor point for the clavicles and most of the ribs.  The sternum connects to the ribs via cartilage called costal cartilage which allows the thoracic cage to change shape during breathing.

Manubrium

o      Superior bone of the sternum.  The clavicles attach to the manubrium

Sternum - Body

o      Main, middle bone of the sternum

Xiphoid process

o      Inferior bone of the sternum.  Site of attachment for the linea alba which is a tissue that anchors the abdominal muscles.

Ribs (12)

●      Bones that form the walls of the thoracic cage

True ribs (1-7) -

There are seven pairs of true ribs (vertebrosternal ribs).  These are the superior seven pairs of ribs which attach directly to the sternum by their costal cartilages.

False ribs (8-12

These are the inferior five pairs of ribs.  They are called false ribs because they do not have a direct attachment to the sternum. Ribs 11 and 12 have no anterior attachment and are called floating false ribs.