LECTURE # 7
1/3/2011
DR. SHEREEN
In today’s lecture we are going to talk about the ORBIT as follows:
I - Description ( boney orbit ) .
II – Specific features.
III – Muscles.
**************************
I – DESCRIPTION :
The orbit is a pyramidal cavity with four walls , apex and base . Its base directed in front and the apex behind . The walls are : roof , floor , medial wall and lateral wall .



:
The roof is formed by the orbital plate of the frontal bone . At the end of the roof , near the apex their’s an opening called the orbital canal that connects the orbit to the middle cranial fossa .
: formed medially by the maxilla and laterally by the zygoma .
; formed by three bones :
1) Lacrimal bone ( most anteriorly ) , located on it the lacrimal sac .
** explanation : The lacrimal sac is the organ that collects
the excess tears being drained by the lacrimal
gland which is located on the superio-lateral part of the orbit .
2) Orbital plate of ethmiod .


Ethmiodal bone is a very small bone which has a fenestrated roof when viewed superiorly . This fenestrated roof is called the cerebriform plate of the ethmiod . From the roof , this bone sends three septa . One central, directed toward the nose forming part of the nasal septum, the other two septa fall creating a block between the nose and the orbit forming two things ; the lateral wall of the nose and the medial wall of orbit which is called the
.
3) Part of the Body of sphenoid .
: formed by two bones ; the zygomatic bone ant. And the greater wing of sphenoid posteriorly .
:
:
At the roof’s anterio-lateral part , there is a fossa which lies in it the lacrimal gland .
At the anterio-medial part, there’s a small spine that is attached to it fibro-cartilaginous trochlea of a muscle (called the superior oblique muscle ) .
:
Posteriorly there is a groove called infra-orbital groove. This groove will be covered by a bone forming a canal called infra-orbital canal which will continue moving on the floor until it finally exits through the infra-orbital foramen.

Lacrimal groove located on the Lacrimal bone for the lacrimal sac .
At the place of junction between the medial wall and the roof , there are two foramina located on the upper boarder of the Ethmiod bone called anterior
ethmoidal foramen and posterior ethmoidal foramen . These foramina exit from the anterio-posterior ethmoidal foramen which communicates with the cribriform plate.
ALL OF THE PREVIOSLY MENTIONED PARAGHRAPH IS VERY IMPORTANT FOR THE
COMMUNICATION BETWEEN THE ORBIT AND THE CRANIAL FOSSA .
:
On the upper and lower boarders , there are fissures . The upper one called the superior orbital fissure and the lower one called the inferior orbital fissure .
The superior orbital fissure is the one between the lateral wall and the roof WHILE the inferior orbital fissure is between the floor and the lateral wall .
: The superior orbital fissure will join the orbit with the cranial fossa .
1) Eyeball , which is very small .
2) Fat , that stabilizes the eyeball in its position ( cz it’s small ) .
3) Nerves .

4) Vessels .
5) Muscles , which are two types :
- intra-occular muscles ( situated inside the eyeball )
- Extra-occular muscles ( located on the eyeball from outside ) . Their function is to move the eye in different directions .
The eyeball consists of of three coats (layers) :
1) Fibrous coat which is made up of two parts ; the anterior part called CORNEA and the posterior part called SCLERA .
2) Vascular coat ( red in color ) , contains blood vessels .
3) Inner coat ( Nervous layer ) from where the Optic nerve leaves .
: they are seven in number . Levator
Palpebrae Superioris and extra-occular muscles ( which are 6 in # ).
*** doesn’t work on the eyeball.

Origin : from the posterior part of the roof of the orbit . Then passes ant. Until it divides into superficial and deep divisions .
Insertion : the upper eye-lid .
Nerve supply : Occulo-motor nerve ( cranial nerve # 3 )
Action : elevating the eye-lid .
*** The extra-ocular muscles are two groups : a) Recti muscles ( 4 in #) , which are straight muscles. b) Obligue muscles ( 2 in # ) , they change their direction during their course.
2)
:
Superior rectus muscles
Inferior rectus muscle .
Medial rectus muscle .
Lateral rectus muscle .
*** so named according to their position ***
the optic canal is surrounded by a cartilaginous ring , called common tendenous ring .

Origin of the recti muscles : from the common tendenous ring , the superior rectus muscle originates from the superior part , the inferior rectus from the inferior part and soooooooooo on .

Insertion : Sclera , anterior to the eqautor line .

They are two in number :
Superior oblique muscle .
Inferior oblique muscle .
:
Origin : posteriorly , at the junction between the roof and the lateral wall , just above the
Optic canal . Then it passes anteriorly on the medial wall until it reaches the spinocartilaginous trochea (which is located anterio-medially on the roof of the orbit ) , there it changes it’s direction posteriorly to be inserted on the anterior surface of the SCLERA .


Insertion : upper surface of the Sclera , behind the equator line .
:
Origin : medial aspect of the floor ( under the Lacrimal bone ) .
Insertion : lateral aspect of the Sclera .
:
** We describe the movement of the eyeball depending on the position of the SCLERA **
For example : if it is moved Up-ward : elevation
Down-ward : depression .
Inside , toward the nose : ABDuction .
Outside : ADDuction .

:
1) Medial rectus : ABDuction .
2) Lateral rectus : ADDuction .
3) Superior rectus : Elevation + medial deviation
4) Inferior rectus : Depression + medial deviation .
5) Superior Oblique : Depression + lateral deviation .
6) Inferior oblique : Elevation + lateral deviation .

NOTE :
The superior and inferior rectus ( Also the superior and inferior oblique ) have DUAL
Action ; because the axis of the orbit is Lateral NOT Horizontal . BUT the axis of the
Eyeball is directed longitudinally : that’s why these muscles have Dual ACTION .
:
If the eye is in the same horizontal level and directed medially then responsible muscle is medial rectus .
If the eye isn’t in the horizontal level ( directed upward or downward ) and show medial deviation then the responsible muscles are sup. /inf. Rectus ( respectively ).
If the eye isn’t in the same horizontal level ( downward / upward ) and show lateral deviation then the responsible muscles are superior and inferior oblique ( respectively ) .
From the superior orbital fissure emerges three motor nerves that supply all these seven muscles . These nerves are : occulo-motor ( cranial nerve # 3 ) , trochlear ( cranial n. # 4 ) and Abducent ( cranial n. # 6 ) .
-
“ ALL of the muscles are supplied by occulo -motor EXCEPT SO4 ( sup. Oblique by trochealar = cranial n. # 4 ) and LR6 ( lat. Oblique by craialn. #6 =abducent ) .
** intra-occular muscles ( also called intrinsic ) :
1) Constrictor pupili = ( Action : constriction of pupil )
2) Dilator pupili = ( Action : dilatation of the pupil )
3) Ciliary muscle = ( Action : change the reflactory power of the muscle )
*** ALL these muscles are Involuntary sooo they are innervated by
SYMPATHETIC OR PARASYMPATHETIC .
Constrictor pulpi + Ciliary : Sympathetic .
Dilator pupili : Parasympathetic .
Hope everything clear
Best of wishes 
Done by : Safa’a Al - Dalahmeh