Download extraocular muscles

The extraocular muscles are the
six muscles that control movement of
the eye and one muscle that
controls eyelid elevation (levator
palpebrae). The actions of the six
muscles responsible for eye
movement depend on the position of
the eye at the time of muscle
contraction.
Levator Palpebrae Superioris
Attachments: Originates from the lesser wing of the
sphenoid bone, immediately above the optic
foramen. It attaches to the superior tarsal plate of the
upper eyelid (a thick plate of connective tissue).
Actions: Elevates the upper eyelid.
Innervation: The levator palpebrae superioris is
innervated by the oculomotor nerve (CN III). The
superior tarsal muscle (located within the LPS) is
innervated by the sympathetic nervous system.
Recti Muscles
There are four recti muscles; superior rectus, inferior
rectus, medial rectus and lateral rectus.
These muscles characteristically originate from
the common tendinous ring. This is a ring of fibrous
tissue, which surrounds the optic canal at the back of
the orbit. From their origin, the muscles pass anteriorly
to attach to the sclera of the eyeball.
Superior Rectus
Attachments: Originates from the superior part of the
common tendinous ring, and attaches to the superior
and anterior aspect of the sclera.
Actions: Main movement is elevation. Also contributes
to adduction and medial rotation of the eyeball.
Innervation: Oculomotor nerve (CN III).
Inferior Rectus
Attachments: Originates from the inferior part of the common
tendinous ring, and attaches to the inferior and anterior aspect of the
sclera.
Actions: Main movement is depression. Also contributes to adduction
and lateral rotation of the eyeball.
Innervation: Oculomotor nerve (CN III).
Medial Rectus
Attachments: Originates from the medial part of the common
tendinous ring, and attaches to the anterio-medial aspect of the
sclera.
Actions: Adducts the eyeball.
Innervation: Oculomotor nerve (CN III).
Lateral Rectus
Attachments: Originates from the lateral part of the common
tendinous ring, and attaches to the anterio-lateral aspect of the sclera.
Actions: Abducts the eyeball.
Innervation: Abducens nerve (CN VI).
Oblique Muscles
There are two oblique muscles – the superior and inferior
obliques. Unlike the recti group of muscles, they do not
originate from the common tendinous ring.
Superior Oblique
Attachments: 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.
Actions: Depresses, abducts and medially rotates the eyeball.
Innervation: Trochlear nerve (CN IV).
Inferior Oblique
Attachments: Originates from the anterior aspect of the
orbital floor. Attaches to the sclera of the eye, posterior to the
lateral rectus
Actions: Elevates, abducts and laterally rotates the eyeball.
Innervation: Oculomotor nerve (CN III).
intraocular muscles of the eye
The ciliary muscle is a ring of smooth muscle[2][3] in
the eye's middle layer (vascular layer) that
controls accommodation for viewing objects at
varying distances and regulates the flow of aqueous
humour into Schlemm's canal. It changes the shape
of the lens within the eye, not the size of the pupil
which is carried out by the sphincter pupillae muscle
and dilator pupillae.
Nerves of the Orbit
A. Ophthalmic nerve
•Enters the orbit through the superior orbital fissure and divides into
three branches:
1. Lacrimal nerve
•Enters the orbit through the superior orbital fissure.
•Enters the lacrimal gland, giving rise to branches to the lacrimal
gland, the conjunctiva, and the skin of the upper eyelid.
2. Frontal nerve
•Enters the orbit through the superior orbital fissure.
•Runs superior to the levator palpebrae superioris.
•Divides into the supraorbital nerve , which passes through the
supraorbital notch or foramen and supplies the scalp, forehead, frontal
sinus, and upper eyelid, and the supratrochlear nerve, which passes
through the trochlea and supplies the scalp, forehead, and upper
eyelid.
3. Nasociliary nerve
Is the sensory nerve for the eye, enters the orbit through the superior
orbital fissure.
Gives rise to the following:
• A communicating branch to the ciliary ganglion.
• Short ciliary nerves , which carry postganglionic parasympathetic and
sympathetic fibers to the ciliary body and iris .
• Long ciliary nerves , which transmit postganglionic sympathetic fibers
to the dilator pupillae.
• The posterior ethmoidal nerve , which passes through the posterior
ethmoidal foramen to the sphenoidal and posterior ethmoidal sinuses.
• The anterior ethmoidal nerve , which passes through the anterior
ethmoidal foramen to supply the anterior ethmoidal air cells. It divides
into internal nasal branches , which supply the septum and lateral walls
of the nasal cavity, and external nasal branches , which supply the skin
of the tip of the nose.
• The infratrochlear nerve , which innervates the eyelids, conjunctiva,
skin of the nose, and lacrimal sac.
B. Optic nerve
Consists of the axons of the ganglion cells of the retina and
leaves the orbit by passing through the optic canal.
Carries Special Sensory fibers for vision from the retina to the
brain and mediates the afferent limb of the pupillary light
reflex.
Joins the optic nerve from the corresponding eye to form the
optic chiasma.
C. Oculomotor nerve
Leaves the cranium through the superior orbital fissure.
Divides into a superior division , which innervates the superior
rectus and levator palpebrae superioris muscles, and an
inferior division , which innervates the medial rectus, inferior
rectus, and inferior oblique muscles.
Its inferior division also carries preganglionic parasympathetic
fibers to the ciliary ganglion.
D. Trochlear nerve
Passes through the lateral wall of the cavernous
sinus during its course.
Enters the orbit by passing through the superior
orbital fissure and innervates the superior oblique
muscle.
E. Abducens nerve
Enters the orbit through the superior orbital fissure
and supplies the lateral rectus muscle.
F. Ciliary ganglion
Is a parasympathetic ganglion situated behind the
eyeball, between the optic nerve and the lateral
rectus muscle
Blood Vessels of the Orbit
A. Ophthalmic artery
Is a branch of the internal carotid artery and enters the orbit
through the optic canal beneath the optic nerve.
Gives rise to the ocular and orbital vessels , which include the
following:
1. Central artery of the retina
Is the most important branch of the ophthalmic artery.
Travels in the optic nerve; it divides into superior and inferior
branches to the optic disk, Its an end artery that does not
anastomose with other arteries, and thus its occlusion results in
blindness.
2. Long posterior ciliary arteries
Pierce the sclera and supply the ciliary body and the iris.
3. Short posterior ciliary arteries
Pierce the sclera and supply the choroid.
4. Lacrimal artery
Passes along the superior border of the lateral rectus
and supplies the lacrimal gland, conjunctiva, and eyelids.
5. Medial palpebral arteries
Contribute to arcades in the upper and lower eyelids.
6. Muscular branches
Supply orbital muscles and give off the anterior ciliary
arteries, which supply the iris.
7. Supraorbital artery
Passes through the supraorbital notch (or foramen) and
supplies the forehead and the scalp.
8. Posterior ethmoidal artery
Passes through the posterior ethmoidal foramen to
the posterior ethmoidal air cells.
9. Anterior ethmoidal artery
Passes through the anterior ethmoidal
foramen to the anterior and middle ethmoidal
air cells, frontal sinus, nasal cavity, and
external nose.
10. Supratrochlear artery
Passes to the supraorbital margin and
supplies the forehead and the scalp.
11. Dorsal nasal artery
Supplies the side of the nose and the lacrimal
sac.
B. Ophthalmic veins
1. Superior ophthalmic vein
•Is formed by the union of the supraorbital, supratrochlear, and
angular veins.
•Receives branches corresponding to most of those of the
ophthalmic artery and, in addition, receives the inferior
ophthalmic vein before draining into the cavernous sinus.
2. Inferior ophthalmic vein
•Begins by the union of small veins in the floor of the orbit.
•Communicates with the pterygoid venous plexus and often with
the infraorbital vein and terminates directly or indirectly in the
cavernous sinus.