Anatomy Flashcards
What is the orbit?
The bony cavity which holds the eyeball
Name the 7 bones that make up the orbit
Frontal bone Sphenoid bone Zygomatic bone Maxilla Palatine Ethmoid Lacrimal
What is meant by the orbital plates?
The flat sections of bone found within the orbit which are thin-walled and so susceptible to fractures
Which 3 bones have an orbital plate?
Frontal
Ethmoid
Maxilla
What are the functions of the following bony features of the orbit:
-Optic canal in the sphenoid bone
-Superior orbital fissure in the sphenoid bone
-Supraorbital foramen/notch in the frontal bone
-Infraorbital foramen in the maxilla
?
- Optic canal in the sphenoid bone: entry of the optic nerve and ophthalmic artery
- Superior orbital fissure in the sphenoid bone: entry of CN III, IV and VI
- Supraorbital foramen/notch in the frontal bone: passage of the supraorbital NVB
- Infraorbital foramen in the maxilla: passage of the infraorbital NVB
The orbit is described as a pyramid shape. Where are the apex and base of the ‘pyramid’ found?
Apex: posteriorly at the optic canal
Base: the orbital rim
The 4 margins of the orbit are the lateral wall, medial wall, orbital floor and orbital roof. Which 2 of these are most susceptible to fracture? Why?
Medial wall + orbital floor
They are formed by thin orbital plates
What is a blowout fracture?
When pressure from a blow to thicker orbital bones fractures the medial wall/ orbital floor, which are formed by thinner orbital plates
What is a trap door fracture?
What is a possible consequence?
When a fracture in part of a bone in the orbital floor allows fat and other optic contents to slip through
If a nerve becomes trapped in the trap door, this can lead to parasthesia in the part of the face supplied by that nerve
Name the external sphincter muscle which completely encircles the eyeball
Orbicularis oculi
What are the 2 parts of the orbicularis oculi and what are their functions?
Orbital part: completely surrounds the orbit proper and is responsible for tight squeezing shut of the eyes
Palpebral part: lies directly on the eyelid and is responsible for gentle closing of the eye
What is the nerve supply to orbicularis oculi?
CN VII - the facial nerve (as it is a muscle of facial expression)
Name the 6 parts of the fibrous skeleton found deep to the orbicularis oculi muscle
- Superior tarsus
- Inferior tarsus
- Medial palpebral ligament
- Lateral palpebral ligament
- Tendon of levator palpebrae superioris (LPS)
- Orbital septum
The orbital septum extends from the orbital rim to the tarsi around the eyelids. What is the function of the orbital septum?
To prevent spread of infection between superficial and deep parts of the orbit
What is levator palpebrae superioris (LPS)?
A muscle responsible for elevating the upper eyelid
levator = elevate, palpebrae = eyelid, superioris = upper
Which muscle connects to LPS in the eyelid? Why is it special?
Superior tarsus muscle (Mueller’s muscle)
It is a smooth muscle so receives sympathetic innervation
What is the function of the superior tarsus muscle (Mueller’s muscle)?
Widens the parpebral fissure (i.e., opens the eyes wide) during times of sympathetic stimulation
What gland is found in the eyelid and what is its function?
The tarsal glands
Secrete lipids that line the eyelids to prevent overflow of lacrimal fluid (tears)
The lacrimal gland is found superolaterally to the orbit and its function is to secrete lacrimal fluid. What nerve innervates the lacrimal gland and what is its modality?
CN VII (facial nerve)
Parasympathetic secretomotor innervation
Describe the route of lacrimal fluid from the lacrimal gland to the nasal cavity
- Fluid washes over eye from lacrimal gland towards the medial angle
- Passes into the lacrimal lake at the medial angle
- Passes through the lacrimal puncta and into the 2 canaliculi
- Passes into the lacrimal sac - the first part of the nasolacrimal duct
- Nasolacrimal duct drains into the nasal cavity via the inferior meatus
There are 7 extraocular muscles. Name the 4 rectus muscles
Superior rectus
Inferior rectus
Medial rectus
Lateral rectus
Why are the extraocular rectus muscles called ‘rectus’?
‘Rectus’ means straight and the rectus muscles run from the posterior part of the orbit in a straight line and attach to the eyeball relatively anteriorly
What is the common origin and the common insertion of the rectus muscles?
Origin: common tendinous ring
Insertion: sclera of the eyeball
There are 7 extraocular muscles. Name the 2 oblique muscles
Superior oblique
Inferior oblique