Skull and Intracranial Region Anatomy PDF

Anatomy of the head and neck – Skull and intracranial region Anatomy of the Head & Neck The skull and intracranial region [email protected] ANATOMY 0 Learning outcomes Ø Define the boundaries and describe the contents of the three cranial fossae Ø List the main foramina or fissures of the s...

Anatomy of the head and neck – Skull and intracranial region Anatomy of the Head & Neck The skull and intracranial region [email protected] ANATOMY 0 Learning outcomes Ø Define the boundaries and describe the contents of the three cranial fossae Ø List the main foramina or fissures of the skull and the structures that travel through these Ø List and identify the cranial venous sinuses and be aware of their clinical significance in terms of the spread of infection; Ø Describe the cavernous sinus and list its contents ANATOMY 1 The cranium or skull Ø The cranium serves to protect the brain as well as housing the special sensory organs Ø It is comprised of two parts: - Neurocranium, the group of 8 bones that effectively encloses the brain - Viscerocranium, the group of bones that form the face and mandible (jaw) Ø The bones of the viscerocranium will be revisited again at the ’Face and scalp’ lecture ANATOMY 2 The neurocranium Ø The eight bones that together form the neurocranium are: - (singular) frontal, ethmoidal, sphenoidal and occipital - (paired) temporal and parietal Frontal Parietal Temporal © Visible Body ANATOMY 3 Skull sutures 1 Ø The bones of the skull articulate either by sutures, which are almost rigid, or movable joints such as the TMJ Ø Sutures do not fully close until after birth to prevent the thin bone from breaking. Also skull bones grow at this interface to match brain growth Ø Once growth is complete the skull bones become fully ossified ANATOMY 4 Foetal skull 1. 2. 3. 4. 5. 6. 7. 8. 9. ANATOMY Future coronal suture Anterior fontanelle Anterolateral fontanelle Future squamous suture Posterolateral fontanelle Future lambda suture External acoustic meatus Future sagittal suture Posterior fontanelle 5 Skull sutures 2 Ø Images depict the principal sutures of the adult skull ANATOMY 6 Neurocranium bones – brief overview Ø Frontal: covers the forehead, part of the top of the head and the roof of the orbits Ø Parietal: on either side of the mid-sagittal suture these bones cover the lateral walls (Latin ‘paries’) and roof of the cranium Ø Occipital: (Latin ‘occiput’, which translates to ‘back of the head’) covers the posterior region of the skull Ø Temporal: cover the inferior lateral walls and part of the floor of the cranium. The term ‘temporal’ reflects the passage of time (i.e. grey hairs) Ø Sphenoid: shaped like a butterfly, this bone borders the cranial and facial skeleton. Articulates with every other cranial bone, as well as the palatine bones, zygomatic bones, maxillae and vomer Ø Ethmoid: positioned between the orbits. This bone forms the anteromedial floor of the cranium, the roof of the nasal cavity, part of the medial wall of each orbit, and part of the nasal septum ANATOMY 7 Sphenoid and ethmoid bones Ø The images below show the skull with the frontal bone removed to reveal the position of the sphenoid (left) and ethmoid (right) bones relative to the other cranial bones © Visible Body ANATOMY 8 Features of the sphenoid bone Ø The image below (© Visible Body) illustrates the different elements of this bone using colours Ø The sella turcica (‘Turkish saddle’) encloses the pituitary gland Ø The Supra-Orbital Fissure separates the lesser wing superiorly from the greater wing below Ø The left and right greater wings form part of the posterior wall of each of the eye orbits (orbital plate) (Posterior view) Sella turcica Lesser wing Greater wing Superior Anterior Body Inferior Posterior ANATOMY Optic foramen (Superior view) © Visible Body Medial pterygoid process Lateral pterygoid process 9 Features of the ethmoid bone Ø One of the more prominent features on the upper surface of the ethmoid is the crista galli (blue colour), which anchors the falx cerebri – see ‘The Brain’ lecture) Ø Lateral projections from the crista galli are the left and right cribriform plates (grey colour) that allow the passage of the olfactory nerves to the nasal cavity below Ø Inferior to the crista galli and running in the mid-sagittal plane is the perpendicular plate, which contributes in separating the left and right nasal passages Ø From each one of the Cribriform Plates there is a left or right Orbital Plate part of the medial wall of the respective eye orbit and origin of two medial projections, the superior and middle Nasal conchae – see ‘Oral and Nasal Cavities’ lecture (Superior view) © Visible Body Anterior ANATOMY Posterior 10 Features of the sphenoid and ethmoid bones ANATOMY 11 Facial bones – brief overview 1 Ø Maxilla: (paired bones) located centrally in the facial skeleton. Together the maxilla form the upper jaw supporting upper teeth Ø Palatine: small bones with a distinct L shape. Contribute to the hard palate, the nasal cavity and eye orbit Ø Zygomatic: commonly referred to as the cheekbones. Contribute to the lateral wall of each orbit and cheeks Ø Lacrimal: the smallest bones in the skull. Contribute to the medial wall of each orbit. These bones display a groove for the passage of the tear duct, which drains tears into the nasal cavity Ø Nasal: form the bridge of the nose, with the lateral side articulating with the medial edge of the maxilla. Often fractured by blows to the nose ANATOMY 12 Facial bones – brief overview 2 Ø Vomer: makes the inferior posterior part of the nasal septum. Articulates with both the maxillae and the palatine bones. Its wings articulate superiorly with the sphenoid bone and the perpendicular plate of the ethmoid bone, forming together the bony nasal septum Ø Inferior nasal conchae: located in the lateral wall of the nasal cavity. Its superior and middle counterparts are part of the ethmoid bone, however the inferior are separate bones Ø Mandible: comprises the entire lower jaw. Its role is to supports the lower teeth and as anchor for the muscles of mastication ANATOMY 13 Some Facial bones – illustrated Lacrimal (Frontal) Nasal Nasal Zigomatic Maxilla ANATOMY Palatine Inf nasal concha © Visible Body 14 Base of the skull ANATOMY 15 Skull air sinuses Ø Around the nasal cavity are a series of air-filled cavities, that also contain mucus Ø The four main pairs of sinus cavities in the skull are - Frontal (1) - Ethmoid (2) - Sphenoid (3) - Maxillary (4) ANATOMY 16 The occipital condyle Ø The skull articulates with the cervical spine via the occipital condyle Ø These condyles are two large protuberances located laterally to the foramen magnum, roughly the frontal half, on the under surface of the occipital bone © Visible Body ANATOMY 17 The cervical vertebrae Ø The top seven vertebrae, termed cervical, provides a dual role: - weight support, relaying this force down to the lower vertebrae - head movement, through muscle action attached between the skull, cervical vertebrae and thorax Ø The first two vertebrae – atlas and axis – are non-typical, specialised to provide the greatest range of movement, both in the flexion/extension plane, as well as rotation ANATOMY 18 Exercise: structure of a cervical vertebra Ø Research the topographical features of a typical vertebra (C3-7) Ø Draw a typical vertebra, including appropriate labels Ø Revisit this topic in the first anatomy practical ANATOMY 19 Intracranial region ANATOMY 20 The intracranial region – brief overview Ø The intracranial region defines the space that contains the brain as well as the intracranial elements of both cranial and spinal nerves, blood vessels, meninges and cerebrospinal fluid Ø When viewed from above the cranial cavity shows three shallow depressions: anterior, middle and posterior, which accommodate specific portions of the brain and cerebellum. ANATOMY 21 Anterior cranial fossa Ø The bones that form the boundary of the anterior cranial fossa are: Frontal Ethmoid Frontal Lesser wing of sphenoid Ø Neuroanatomy: Frontal lobes Olfactory nerves bulbs and tracts Anterior cerebral artery ANATOMY Ethmoid Sphenoid 22 Middle cranial fossa Ø The bones that form the boundary of the middle cranial fossa are: - sphenoid (greater wings and body plus sinus) - petrous part of the temporal Ø Neuroanatomy: Temporal lobes Cavernous sinus and associated cranial nerves Optic nerves Ophthalmic artery Optic chiasm Pituitary gland Internal carotid arteries Middle meningeal artery ANATOMY Temporal Sphenoid 23 Posterior cranial fossa Ø The bones that form the boundary of the posterior cranial fossa are: - temporal - occipital Ø Neuroanatomy: Brainstem and cerebellum Sigmoid sinus Cranial nerves VII-XII Vertebral and basilar arteries Temporal Occipital ANATOMY 24 Sella turcica Ø The sella turcica is a saddle-like feature of the sphenoid bone Ø This feature encloses the pituitary gland, which protrudes from the under surface of the brain Ø It is of clinical relevance given its confined space, whereby pituitary gland tumours can press on neighbouring structures such as the optic nerve ANATOMY 25 Foramina of the skull ANATOMY 26 Anatomical structures travelling through skull foramina ANATOMY 27 Questions? Questions? Email: [email protected] ANATOMY 28