Skull and Cervical Vertebrae Anatomy

• The presentation covers the skull and cervical vertebrae.
• The lecture notes are by Dr Ramya Rathan, Associate Professor of Anatomy, dated March 1, 2025.

Learning Objectives

• The aims are to identify the different bones of the skull, including the cranial fossae and foramina.
• Describe the typical and atypical cervical vertebrae, including their parts and structure.

Bones Forming Cranial Fossa

• The bones of the calvarium and cranial base form the cranial fossa.
• The frontal, sphenoid, temporal, parietal, occipital, and ethmoid bones comprise the cranial fossa.

Cranial Fossa

• The cranial fossa consists of the anterior, middle, and posterior cranial fossae.

Anterior Cranial Fossa

• It lodges the frontal lobes of the cerebrum.
• The floor is composted of the cribiform plate of the ethmoid bone, the orbital plate of the frontal bone, and the lesser wing of the sphenoid.
• Features include the crista galli, cribiform plate, frontal crest, jugum sphenoidale, and anterior clinoid process.
• Structures passing through the cribiform plate include olfactory nerves.
• The ethmoidal canal transmits the anterior and posterior ethmoidal vessels.

Middle Cranial Fossa

• This area lodges the hypophysis cerebri in the middle and the temporal lobe of the cerebrum laterally.
• The floor is butterfly-shaped and consists of median and lateral sections:
• The median part is formed by the body of the sphenoid.
• It presents the sulcus chiasmaticus in the front, the sella turcica behind, and the carotid groove.
• The lateral part forms the cranial surface of the greater wing of the sphenoid.
• It is also the inner surface of the squamous part of the temporal bone and the anterior surface of the petrous part of the temporal bone.

Foramen and Structures Passing

• Medial part:
  • The optic canal transmits the optic nerve.
  • The hypophyseal fossa lodges the hypophysis cerebri.
• Lateral part:
  • Supraorbital fissure.
  • Foramen ovale.
  • Foramen spinosum.
  • Foramen rotundum.
  • Foramen lacerum.

Summary of Floor of Cranial Cavity

• Foramen rotundum (middle cranial fossa/pterygopalatine fossa):
  • The [V2] Maxillary division of [V] trigeminal nerve passes through it.
• Foramen ovale (middle cranial fossa/infratemporal fossa):
  • The [V3] Mandibular division of [V] trigeminal nerve passes through it.
• Carotid canal (middle cranial fossa neck)
• Internal carotid artery
• Foramen spinosum (middle cranial fossa/infratemporal fossa):
  • The middle meningeal artery runs through it.
• Jugular foramen (posterior cranial fossa/neck)
  • [IX] Glossopharyngeal nerve
  • Vagus nerve
  • [XI] Accessory nerve
  • Internal jugular vein.
• Foramen magnum (posterior cranial fossa neck):
  • Spinal cord
  • Vertebral arteries
  • Roots of accessory nerve [XI] pass through the foramen magnum into the cranial cavity and then leave the cranial cavity through the jugular foramen.
• Cribiform plate (anterior cranial fossa/nasal cavity):
  • [I] Olfactory nerves pass through it.
• Optic canal (middle cranial fossa/orbit):
  • [II] Optic nerve
  • Ophthalmic artery.
• Superior orbital fissure (middle cranial fossa/orbit):
  • [V1] Ophthalmic division of [V] trigeminal nerve.
  • [III] Oculomotor nerve
  • [IV] Trochlear nerve
  • [VI] Abducent nerve
  • The superior ophthalmic vein
• Foramen lacerum:
  • It's filled with cartilage in life.
• Internal acoustic meatus (posterior cranial fossa/ear, and nec via stylomastoid foramen):
  • [VII] Facial nerve
  • [VIII] Vestibulocochlear nerve
  • Labrynthine artery and vein.
• Hypoglossal canal (posterior cranial fossa/neck):
  • [XII] Hypoglossal nerve.

Posterior Cranial Fossa

• This area lodges the cerebellum, pons, and medulla oblongata.
• The bones forming the floor are the sphenoid, occipital, temporal, and parietal bone.
• Features of the posterior cranial fossa :
  • A large central opening called the foramen magnum, the internal occipital crest, and the sigmoid sulcus.
• Foramen:
  • Hypoglossal canal
  • Jugular foramen
  • Internal acoustic meatus
  • Foramen magnum.

Foramina/Outlets

• Foramen Magnum: Carries the medulla, ascending portion of the spinal accessory nerve, vertebral arteries
• Located in the Posterior Cranial Fossa
• Internal Acoustic Meatus: Accommodates cranial nerves VII and VIII
• Jugular Foramen: Transmits IJV and cranial nerves IX, X, and XI
• Hypoglossal Canal: Transmits the cranial nerve XII

Cranial Nerves in Cranial Fossa

• Cribriform plate: Olfactory n (CNI)
• Optic canal: Optic n (CNII)
• Superior orbital fissure:
• Oculomotor n (CNIII)
• Trochlear n (CNIV)
• Ophthalmic n (CNV₁)
• Abducens n (CNVI)
• Foramen rotundum: Maxillary n (CNV₂)
• Foramen Ovale: Mandibular n (CNV3)
• Internal acoustic meatus:
  • Facial n (CNVII)
  • Vestibulocochlear n (CNVIII)
• Jugular foramen:
  • Glosopharyngeal n (CNIX)
  • Vagus n (CNX)
  • Accessory n (CNXI)
• Hypoglossal canal: Hypoglossal n (CNXII)

Vertebral column

• Cervical spine: 7 vertebrae (C1-C7)
• Thoracic spine: 12 vertebrae (T1-T12)
• Lumbar spine: 5 vertebrae (L1-L5)
• Sacrum: 5 (fused) vertebrae (S1-S5)
• Coccyx: 4 (3-5) (fused) vertebrae (Tailbone)

Structure of Typical Cervical Vertebra (3,4,5,6)

• Key structures are:
  • Lamina.
  • Transverse process.
  • Superior articular process.
  • Pedicle.
  • Vertebral foramen.
  • Body (centrum).

Atypical Cervical Vertebra – C1, C2, and C7

• Atlas (C1)
• Axis (C2)
• C7- Vertebra prominence

Clinical Significance of Atlas and Axis

• Atlanto-occipital joint: Allows head nodding on the vertebral column
• The dens of the axis: acts as the pivot, enabling the atlas and head to rotate side to side.
• Dislocation of C1-C2: Can result in respiratory paralysis.