Extraocular muscles-pp4 Flashcards
What is the origin, insertion, function, and innervation for the LEVATOR PALPEBRAE SUPERIORIS muscle?
Ori: Orbital roof
Ins: Surface of upper eyelid
Fun: Elevates the upper lid, OPENING the eye
Inn: Superior division of CN III, the occulomotor nerve
What type of muscle is the SUPERIOR TARSAL muscle? Function, approximate location, and innervation.
Smooth muscle, innervated by the autonomic (Sympathetic) nervous system. Located near upper eyelid and functions to help elevate the upper lid.
How do the sympathetics enter and distribute throughout the head?
By traveling with the Internal Carotid Artery and its branches
A lesion of either the sympathetics or CN III will result in what?
Inability to raise the upper eyelid completely = PTOSIS. Caused by Levator Palpebrae Superior and Superior Tarsal muscles not receiving innervation signals.
What fills the orbit protecting the orbit and extraoccular muscles from excessive movements and force?
PERIORBITAL FAT
All of the RECTUS Muscles arise (originate) from what Common Tendinous Ring?
The ANNULAR TENDON of ZINN, which is located at the orbital apex
All of the RECTUS Muscles insert where?
ANTERIOR SCLERA of the eyeball.
-All four rectus muscles pierce Tenon’s Capsule and attach to the anterior SCLERA, a dense fibrous layer surrounding and maintaining the shape of the eyeball
All but one of the Rectus muscles are innervated by CN III, the occulomotor nerve. What is the one exception?
The Lateral Rectus Muscle, which is innervated by CN VI, ABDUCENS.
Note: Lateral rectus muscle is the ONLY muscle the ABDUCENS Nerve innervates
The Superior Oblique muscle is deflected posterolaterally before its insertion on the sclera of the posterior hemisphere. What is the name of the cartilaginous loop that does this?
TROCHLEA, which is located on the medial wall of the eye
With the exception of the Superior Oblique and Lateral Rectus Muscles, the extraoccular muscles are all innervated by what?
CN III, the occulomotor nerve
Lateral Rectus: CN VI, the Abducens nerve
Superior Oblique: CN IV, the Trochlear nerve
What two muscles move the eyeball around a single axis only? How many axis do the remaining muscles move the eyeball around?
The Medial and Lateral Rectus muscles both move the eyeball around the vertical axis ONLY.
The remainging extraoccular muscles move the eyeball around ALL 3 axis.
What is the origin, insertion, function, and innervation for the SUPERIOR RECTUS muscle?
Ori: Annular Tendon of Zinn
Ins: Anterior Sclera
Fun: Elevates and Adducts eyeball; Intorts
Inn: CN III
What is the origin, insertion, function, and innervation for the INFERIOR RECTUS muscle?
Ori: Annular Tendon
Ins: Anterior SCLERA
Fun: Depresses and Adducts eyeball; Extorts
Inn: CN III
What is the origin, insertion, function, and innervation for the LATERAL RECTUS muscle?
Ori: Annular Tendon
Ins: Anterior sclera
Fun: Abducts eyeball
Inn: CN VI
What is the origin, insertion, function, and innervation for the MEDIAL RECTUS muscle?
Ori: Annular Tendon
Ins: Anterior sclera
Fun: Adduction of eyeball
Inn: CN III
What is the origin, insertion, function, and innervation for the SUPERIOR OBLIQUE muscle?
Ori: Sphenoid, above margin of optic foramen
Ins: Posterior sclera
Fun: Depresses and abducts eyeball; intorts
Inn: CN CN IV
What is the origin, insertion, function, and innervation for the INFERIOR OBLIQUE muscle?
Ori: Maxillary portion of the orbital floor
Ins: Posterior sclera
Fun: Elevates and Abducts eyeball; Extorts
Inn: CN III
What is GRAVES OPHTHALMOPATHY disorder, also known as thyroid eye disease or TED?
An autoimmune inflammatory disorder producing PROPTOSIS as autoantibodies target the fibroblasts in the eye muscle. These fibroblasts may differentiate into FAT cells producing expansion and inflammation of fat cells and muscles leading to venous compression and edema. REMEMBER the picture from Frankenstein movie.
Why is the Trochlear nerve (CN IV) especially susceptible to pathology?
It has the longest distance of any nerve w/in the cranium to reach medial rectus muscle
CN III, IV, & VI course through the cavernous sinus en route to exiting the middle cranial fossa through the Superior orbital fissure. Why might the passage through teh cavernous sinus be problematic?
The 3 nerves are vulnerable to being lesioned as they pass through the Cavernous Sinus for a number of reasons:
- Dural venous sinuses may transmit pathogenic viruses into cavernous sinuses causing swelling and pinching of the nerves
- Internal Carotid Artery Aneurism = ballooning vessel that may compress nerves
- Pituitary Tumors - increase in size, especially laterally. May cause impingement of nerves affecting muscles in orbit.
