Session 2: The Facial Skeleton, Scalp and Face; The Orbit and Associated Cranial Nerves Flashcards
What 5 layers does the scalp consist of?
S - skin C - connective tissue A - aponeurosis L - loose connective tissue P - periosteum
Why is the superficial connective tissue layer of the scalp unique?
It is fibrous and tightly bound both to skin and underlying aponeurosis, so there is no movement between the two.
How is sliding of the scalp over the cranium possible?
Because of the layer of loose areolar connective tissue between the aponeurosis and the periosteum.
What is the layer of loose areolar connective tissue between the aponeurosis and periosteum of the scalp known as?
The subaponeurotic fascia.
Why do scalp wounds tend to bleed profusely and require suturing?
Because the dense fibrous tissue tends to hold the walls of superficial blood vessels open even when they are cut.
Why does a transverse tear to the aponeurosis cause gaping?
Due to the pull of occipitalis and frontalis muscles across the defect
Which is easier to suture, a transverse or sagittal tear in the aponeurosis?
A sagittal tear, because no gaping.
Why are wounds that penetrate the aponeurosis serious?
As infection can enter the subaponeurotic space and spread over the entire surface of the cranial vault with little obstruction.
Which blood vessels supply the scalp?
From ICA: - supratrochlear (opthalmic) - supraorbital (opthalmic) From ECA: - superficial temporal - posterior auricular - occipital
All these vessels anastomose freely with eachother
What is the nerve supply of the posterior scalp?
Greater occipital nerve (posterior rami C2)
Third occipital nerve (posterior rami C3)
What is the nerve supply of the lateral scalp?
Lesser occipital nerve (C2) Auriculotemporal nerve (Vc)
What is the nerve supply of the scalp anteriorly and up to the vertex?
Zygomaticotemporal nerve (Vb) Supraorbital neve (Va) Supratrochlear nerve (Va)
The facial nerve gives branchiomotor supply to all the muscles from which pharyngeal arch?
2nd pharnygeal arch
Which glands does the facial nerve carry preganglionic parasympathetic fibres for? (4)
Lacrimal
Submandibular
Sublingual
Nasal mucous
What does the facial nerve carry taste fibres from (via the chorda tympani branch)?
Anterior 2/3 tongue
What part of the head does the facial nerve supply general sensation to?
The skin lining the external auditory meatus
What are the 2 roots of the facial nerve?
The larger motor root and the smaller nervus intermedius (carrying sensory and parasympathetic).
Describe the course of the facial nerve (from the IAM to the stylomastoid foramen).
The two roots enter the internal acoustic foramen with the vestibulocochlear nerve (VIII), and join to form the facial nerve.
The facial nerve then enters the facial canal in the petrous temporal bone.
On the medial wall of the middle ear, the facial nerve bends posteriorly, and gives off the greater petrosal nerve at the geniculate ganglion.
On reaching the posterior wall of the tympanic cavity, the nerve runs inferiorly to emerge from the skull at the stylomastoid foramen.
What does the facial nerve do upon exiting the stylomastoid foramen?
It enters the parotid gland and divides into upper and lower divisions.
Which nerves does the upper division of the facial nerve give?
Temporal
Zygomatic
Buccal
Which nerves does the lower division of the facial nerve give?
Mandibular
Cervical
Which branches does the facial nerve give before exiting the skull through the stylomastoid foramen? (3)
Greater petrosal nerve
Nerve to stapedius
Chorda tympani
Where does the greater petrosal nerve arise?
Geniculate ganglion
What does the greater petrosal nerve carry?
Parasympathetic preganglionic fibres to the pterygopalatine ganglion.
What is the action of stapedius? What is its nerve supply?
Dampens over-vibration of the tympanic membrane and ossicles. Nerve to stapedius (VII).
Which nerve does the chorda tympani join?
Lingual nerve (Vc)
What does the chorda tympani supply?
Taste to anterior 2/3 tongue
Preganglionic parasympathetic to submandibular ganglion.
Which muscular branches of the facial nerve are given off after exiting the skull? (NOT to muscles of facial expression)
Posterior belly of digastric
Stylohyoid
Occipitalis
What does the temporal nerve (VII) supply?
Orbicularis oculi
Frontalis
What does the zygomatic nerve (VII) supply?
Muscles of the eyelid
What does the buccal nerve (VII) supply?
Buccinator
Orbicularis oris
Levator oris
What does the mandibular nerve (VII) supply?
Depressor oris
Muscles of the lower lip and chin
What does the cervical nerve (VII) supply?
Platysma
What shape is the orbit? Where does the apex point?
Cone-shaped; posteromedially.
Which walls of the orbit are almost parallel to each other?
Medial walls
Which walls of the orbit are at right angles to each other?
Lateral walls
What forms the roof of the orbit? What does it separate the orbit from?
Orbital plate of frontal bone; frontal lobe of brain.
What forms the floor of the orbit?
The maxilla with its air sinus.
What forms the lateral wall of the orbit? What does it separate the orbit from?
Zygomatic bone and greater wing of sphenoid; the temporalis muscle.
What forms the medial wall of the orbit?
The labyrinth of the ethmoid.
Which bones contribute to the orbit anteriorly?
Lacrimal bone and the frontal process of the maxilla.
What is posterior to the inferomedial angle of the orbital rim?
A depression called the lacrimal fossa which houses the lacrimal sac.
What lies beneath the lacrimal fossa?
A large foramen in the orbital floor for the nasolacrimal duct which opens into the inferior meatus of the nasal cavity.
Name the 3 intraocular muscles of the eye.
Ciliary muscle
Sphincter pupillae
Dilator pupillae
Name the 7 extraocular muscles of the eye.
Levator palpebrae superioris Superior rectus Inferior rectus Medial rectus Inferior oblique Superior oblique Lateral rectus
Where do the recti arise from?
The tendinous ring at the back of the bony orbit
Where do the recti attach?
The eyeball just behind the junction of the cornea and the sclera, i.e. just anterior to the equator of the eyeball.
Which muscles does the oculomotor nerve supply?
Medial rectus
Superior rectus
Inferior rectus
Inferior oblique
Which muscle does the trochlear nerve supply?
Superior oblique
Which muscle does the abducent nerve supply?
Lateral rectus
What is the action of the medial rectus?
Adducts the eyeball
What is the action of the inferior rectus?
Depresses and adducts the eyeball
What is the action of the superior rectus?
Elevates and adduct the eyeball
What is the action of the lateral rectus?
Abducts the eyeball
What is the action of the inferior oblique?
Elevates and abducts the eyeball
What is the action of the superior oblique?
Depresses and abducts the eyeball
What is the action of the LPS?
Elevates the upper eyelid
Where do the oblique muscles attach?
Posterior to the equator of the eyeball
Where do the axons of the optic nerve originate?
Retinal cells
What is the name for the area where the two optic nerves partly decussate?
Optic chiasma
Where do the optic tracts run to and from?
Run to the lateral geniculate body of the thalamus from the optic chiasma
What layers is the optic nerve covered by and up to which point?
Meningeal layers; dura, arachnoid and pia + CSF, up to the point where it pierces the sclera.
Is there a subarachnoid space surrounding the optic nerve?
Yes; small but definite
What causes papilloedema? What is the appearance of papilloedema?
Any increase in intracranial pressure is transmitted along the CSF of the optic nerve; swelling of the optic nerve disc.
Describe the route of the oculomotor nerve.
After exiting the midbrain, the oculomotor nerve pierces the roof of the cavernous sinus and runs in its lateral wall. Emerging from the sinus, it divides into superior and inferior divisions, which pass into the orbit through the superior orbital fissure and the tendinous ring.
Which muscles does the superior division of the oculomotor nerve supply?
LPS, superior rectus.
Which muscles does the inferior division of the oculomotor nerve supply?
Medial rectus, inferior rectus, inferior oblique.
What does the inferior division of the oculomotor nerve carry?
Parasympathetic preganglionic fibres destined for the ciliary ganglion. (to ciliary muscle and sphincter pupillae)
Where does the ciliary ganglion lie?
Between the lateral surface of the optic nerve and the lateral rectus muscle.
Which nerves supply post-ganglionic parasympathetics from the ciliary ganglion? Which structures do they supply?
10-12 short ciliary nerves (nasociliary Va); ciliary muscle and sphincter pupillae.
Which structures pass through the superior orbital fissure? (top to bottom)
Superior opthalmic vein Lacrimal nerve (Va) Frontal nerve (Va) Trochlear nerve (IV) Superior division III Nasociliary nerve (Va) Abducent nerve (VI) Inferior division III Inferior opthalmic vein
Where does the opthalmic artery pass to enter the orbit?
Through the optic canal
Describe the path of the trochlear nerve.
After exiting the brain it enters the cavernous sinus, runs through the superior orbital fissure (but not the tendinous ring), turns medially above LPS to supply superior oblique.
Describe the path of the abducent nerve.
Pierces the dura on the posterior aspect of the clivus and travels superolaterally to enter the cavernous sinus, lying just lateral to the internal carotid artery. Leaves the sinus to pass through the superior orbital fissure and the tendinous ring to supply the lateral rectus.
Where does the opthalmic nerve (Va) pick up postganglionic sympathetic fibres? What do these sympathetic fibres supply?
In the cavernous sinus from the internal carotid plexus. They supply the vessels of the orbit, vessels and sweat glands of the forehead, and the dilator pupillae (via the long ciliary nerves of the nasociliary branch).
What are the main branches of the opthalmic nerve?
Frontal, Lacrimal and Nasociliary
What is the first major branch of the internal carotid artery?
Opthalmic artery
What does the opthalmic artery give off after entering the orbit?
Central artery of the retina and branches to the extraocular muscles.
What does the opthalmic artery give off on the lateral surface of the optic nerve?
Lacrimal artery
Where in the orbit is there an anastomosis? Which vessels is this anastomosis between?
Between the recurrent meningeal branch of the lacrimal artery (ICA) and the anterior branch of the middle meningeal artery (ECA)
Describe the course of the superior opthalmic vein.
Leaves the orbit from the superior orbital fissure to enter the cavernous sinus.
Describe the 3 possible courses of the inferior opthalmic vein.
1) may join the superior opthalmic vein
2) may pass separately through the superior orbital fissure to join the cavernous sinus
3) may pass through the inferior orbital fissure to join with the pterygoid plexus of veins in the infratemporal fossa.
What are the angles of junction of the upper and lower lids when the eyes are open known as?
The medial and lateral canthi
What is the opening between the eyelids known as?
The palpebral fissure
What are the tarsal plates?
Laminae of condensed connective tissue in each eyelid.
What attaches to the superior tarsal plate?
The main insertion of LPS.
Where do the tarsal/Meibomian glands (modified sebaceous glands) open? What do they produce and what is its function?
Skin posterior to the eyelashes. They produce an oily secretion to make the lid margins waterproof and reduce evaporation of the tears on the cornea.
What reflects at the root of each eyelid?
The palpebral conjunctiva turns into the bulbar conjunctiva by reflecting onto the anterior aspect of the eyeball.
What does closure of the eyelids form?
Conjunctival sac
What are the lines of reflection of the eyelid known as?
The superior and inferior conjunctival fornices.
Where does the lacrimal gland lie?
In a depression in the superolateral angle of the orbit.
How many lacrimal ducts are there?
12-14
Where do the lacrimal ducts open?
Into the lateral part of the superior conjunctival fornix
Which two structures bulge into the conjunctival sac medially? What else do they protrude into?
Lacrimal caruncle and plica semilunaris. The lacrimal lake, where tears are swept on blinking.
Where do tears go from the lacrimal lake?
The lacrimal canaliculi
Where do the lacrimal canaliculi (upper and lower) open into?
The lacrimal sac
Where is the lacrimal sac located?
A groove formed by the lacrimal bone and the frontal process of the maxilla.
What is the opening of the nasolacrimal duct into the inferior meatus guarded by? Why?
A fold of mucous membrane, to prevent air being forced up the dict into the sac when blowing one’s nose.
What are the bones of the facial skeleton?
6 paired: Maxillae Inferior conchae Nasal Lacrimal Palatine Zygomatic
2 unpaired:
Mandible
Vomer
