Osteology of the skull Flashcards
Which bones make up the anterior cranial fossa?
The frontal bone, the ethmoid bone and sphenoid bone
What are the bony features present in the anterior cranial fossa?
Frontal crest - bony ridge in the midline, acts as an attachment for the falx cerebri
Crista galli - upwards projection of bone, acts as another attachment for the falx cerebri
Cribriform plate - supports the olfactory bulb and has numerous foramina that transmit the olfactory nerve fibres
Lesser wings of the sphenoid bone - separate the anterior and middle fossae and act as an attachment for the tentorium cerebelli
Which foramina are present in the anterior cranial fossa?
Anterior ethmoidal foramen – transmits the anterior ethmoidal artery, nerve and vein.
Posterior ethmoidal foramen – transmits the posterior ethmoidal artery, nerve and vein.
Which bones make up the middle cranial fossa?
Consists of a central portion made of the sphenoid bone which contains the pituitary gland and lateral portions formed by the greater wings of the sphenoid bone, and the squamous and petrous parts of the temporal bones which hold the temporal lobes.
What are the bony features present in the middle cranial fossa?
Tuberculum sellae - vertical elevation of bone, forms the anterior wall of the sella turcica
Hypophyseal/pituitary fossa - sits in the middle of the sella turcica, holds the pituitary gland
Dorsum sellae - large square of bone that separates the middle cranial fossa from the posterior cranial fossa
Clinoid processes - surround the sella turcica, act as an attachment for the tentorium cerebelli
Which foramina are present in the middle cranial fossa?
Superior orbital fissure - transmits the oculomotor nerve, trochlear nerve, ophthalmic branch of the trigeminal nerve, abducens nerve
Foramen rotundum - transmits the maxillary branch of the trigeminal nerve
Foramen ovale - transmits the mandibular branch of the trigeminal nerve
Foramen spinosum - transmits the middle meningeal artery, middle meningeal vein and a meningeal branch of oculomotor nerve
Carotid canal - traversed by the internal carotid artery, which ascends into the cranium to supply the brain with blood.
Foramen lacerum - filled with cartilage
Which foramina are present in the posterior cranial fossa?
Internal acoustic meatus - transmits the facial nerve and the vestibulocochlear nerve.
Foramen magnum - transmits the medulla, meninges, vertebral arteries, spinal accessory nerve, dural veins and anterior and posterior spinal arteries.
Jugular foramina - transmits the glossopharyngeal nerve, vagus nerve, spinal accessory nerve (descending), internal jugular vein.
Hypoglossal canal - transmits the hypoglossal nerve
Which bones make up the posterior cranial fossa?
Occipital and temporal bones
House the brain stem and the cerebellum
What are the signs and symptoms of raised intracranial pressure?
Symptoms: headache, nausea, visual disturbance, later altered consciousness levels
Signs: Papilloedema, increased blind spot on visual field testing
What causes raised intracranial pressure?
Caused by space occupying lesions (tumour, haematoma, abscess) or idiopathic intracranial hypertension
Which bones make up the orbit?
Frontal Sphenoid Lacrimal Ethmoid Maxilla Zygomatic
What are the major pathways into the eye?
Optic canal - transmits the optic nerve and opthalmic artery
Superior orbital fissure - transmits the lacrimal, frontal, trochlear, oculomotor, nasociliary and abducens nerves. It also carries the superior ophthalmic vein.
Inferior orbital fissure – transmits the zygomatic branch of the maxillary nerve, the inferior ophthalmic vein, and sympathetic nerves.
Nasolacrimal canal, which drains tears from the eye to the nasal cavity, is located on the medial wall of the orbit.
Supraorbital foramen and infraorbital canal – they carry small neurovascular structures.
What is the Levator palpebrae superioris?
Originates at the posterior of the orbit at the common tendinous ring and inserts into the upper eyelid.
Action: Elevates the upper eyelid.
Innervated by the oculomotor nerve and the sympathetic fibres (superior tarsal muscles - smooth muscle fibres).
What is the superior rectus?
Originates in the deep part of the orbit at the inferior part of the common tendinous ring, runs over the top of the eyeball just behind the conjunctival sac and attaches onto the superior and anterior aspects of the sclera.
Action: Elevation, as well as some adduction and medial rotation.
Innervated by the oculomotor nerve.
What is the inferior rectus?
Originates from the inferior part of the common tendinous ring, and attaches to the inferior and anterior aspect of the sclera.
Action: Depression, as well as adduction and lateral rotation.
Innervated by the oculomotor nerve.
What is the medial rectus?
Originates from the medial part of the common tendinous ring, and attaches to the anteromedial aspect of the sclera.
Action: Adduction
Innervated by the oculomotor nerve.
What is the lateral rectus?
Originates from the lateral part of the common tendinous ring, and attaches to the anterolateral aspect of the sclera.
Action: Abduction
Innervated by the abducens nerve.
What is the superior oblique?
Originates from the body of the sphenoid bone. Its tendon passes through a trochlear, and then attaches to the sclera of the eye, posterior to the superior rectus.
Action: Depression, adduction and medial rotation of the eyeball.
Innervated by the trochlear nerve.
What is the inferior oblique?
Originates from the anterior aspect of the orbital floor. Attaches to the sclera of the eye, posterior to the lateral rectus.
Action: Elevation, abduction and lateral rotation of the eyeball.
Innervated by the oculomotor nerve.
What is the lacrimal gland?
Serous type exocrine glands that secrete lacrimal fluid onto the surfaces of the conjunctiva and cornea of the eye.
Lacrimal fluid acts to clean, nourish and lubricate the eyes. It forms tears when produced in excess.
Where is the lacrimal gland?
Located just inside the lateral margin of the orbit adjacent to the lateral margin of the levator palpebrae superioris.
What is the structure of the lacrimal gland?
The lacrimal gland is a compound tubuloacinar gland, comprised of lobules – which are formed by multiple acini. The acini contain serous cells and produce a watery serous secretion (lacrimal fluid).
What is the pathway of the lacrimal fluid?
The lacrimal fluid produced by the gland is secreted into excretory ducts, which empty into the superior conjunctival fornix. The fluid is then ‘spread’ over the cornea by the process of blinking.
After secretion, lacrimal fluid circulates across the eye, and accumulates in the lacrimal lake – located in the medial canthus of the eye. From here, it drains into the lacrimal sac via a series of canals.
