University:
Kentucky State University
Course:
BIO 301 | Human Anatomy
Academic year:

2020
Views:

447

Pages:

97
Author:

Lily Callahan

The orbit Orbital plate of frontal bone Orbital plate of ethmoid bone Lesser wing of sphenoid Greater wing of sphenoid Lacrimal bone Orbital plate of zygomatic bone Frontal process of the maxilla Orbital plate of maxilla Optic canal Posterior ethmoidal foramen Superior orbital fissue Anterior ethmoidal foramen Inferior orbital fissue Frontal process of the maxilla Infraorbital groove Orbit The orbits are bilateral structures below the anterior cranial fossa and anterior to middle cranial fossa The bony orbit is pyramidal in shape, with its base opening anteriorly onto the face and its apex extending in a posteromedial direction Has medial, lateral, superior (roof), inferior (floor) walls The apex of the pyramid is the optic foramen, whereas the base is the orbital rim Orbital Ophthalmic Ciliary Optic Contents of the orbit: 1. Eye ball 2. Extraocular muscles 3. Intraocular muscles 4. Nerves: Optic, branches of ophthalmic, branches from maxillary, divisions of oculomotor, trochlear, abducent, sympathetic fibers and ciliary ganglion 5. Ophthalmic artery and veins 6. Lacrimal apparatus 7. Fat The apex of the pyramid is the optic foramen Roof: Formed by: 1- The orbital plate of the frontal bone, which separates the orbital cavity from the anterior cranial fossa and the frontal lobe of the cerebral hemisphere 2- The lesser wing of the sphenoid Lateral wall: Formed by: 1- The orbital plate of zygomatic bone 2- The greater wing of the sphenoid Floor: Formed by: 1- The orbital plate of the maxilla: separates the orbital cavity from the maxillary sinus 2- Palatine bone Medial wall: Formed from before backward by: Medial walls are parallel to each other 1. The frontal process of the maxilla 2. The lacrimal bone 3. The orbital plate of the ethmoid 1. The frontal process of the maxilla The frontal process of maxilla and the lacrimal bones participate in the formation of the lacrimal groove which contains the lacrimal sac 2. The lacrimal bone  The orbital plate of ethmoid separates the orbital cavity from the ethmoidal air sinuses  It is a very thin wall 3. The orbital plate of the ethmoid Openings Into the Orbital Cavity 1- Supraorbital notch (Foramen): transmits the supraorbital nerve and blood vessels Openings Into the Orbital Cavity 2-Infraorbital groove and canal: Situated on the floor of the orbit They transmit the infraorbital nerve (a continuation of the maxillary nerve) and blood vessels Openings Into the Orbital Cavity 3-Infraorbital foramen: transmits the infraorbital nerve (a continuation of the maxillary nerve) and blood vessels Openings Into the Orbital Cavity 5- Anterior and posterior ethmoidal foramina: transmit anterior and posterior ethmoidal nerves and vessels Note: Anterior and posterior ethmoidal foramina are located between the roof and the medial wall Openings Into the Orbital Cavity 6-Inferior orbital fissure: Located posteriorly between the maxilla and the greater wing of the sphenoid it communicates with the infratemporal and pterygopalatine fossae. It transmits 1-Maxillary nerve and its zygomatic branch 2-Infraorbital vessels 3- Inferior ophthalmic vein (or a vein communicating with pterygoid plexus of veins) Note: inferior orbital fissure is located between the floor and the lateral wall Openings Into the Orbital Cavity 7- Superior orbital fissure: -Located between the greater and lesser wings of the sphenoid - It communicates with the middle cranial fossa. - It transmits Lacrimal nerve Frontal nerve Trochlear nerve Oculomotor nerve (upper and lower divisions) Abducent nerve Nasociliary nerve Superior ophthalmic vein Note: superior orbital fissure is located between the roof and the lateral wall Note the superior orbital fissure opens anteriorly into orbit and posteriorly into middle cranial fossa Note the inferior orbital fissure opens anteriorly into orbit and posteriorly into two fossae: one big ( infratemporal fossa) and one small (Pterygo-palatine fossa) Use the wire within each of the skull fissures to determine precisely the communications of superior and inferior orbital fissures Openings Into the Orbital Cavity 8-Optic canal: - Located in the lesser wing of the sphenoid - It communicates with the middle cranial fossa. - It transmits the optic nerve and the ophthalmic artery 9-Nasolacrimal canal: Located anteriorly on the medial wall; it communicates with the nose It transmits the nasolacrimal duct. Nasolacrimal canal MUSCLES OF THE EYE There are two groups of muscles within the orbit: 1-Extrinsic muscles of eyeball (extra-ocular muscles) involved in movements of the eyeball or raising upper eyelid 2-Intrinsic muscles within the eyeball, which control the shape of the lens and size of the pupil. The extrinsic muscles include 1. SUPERIOR RECTUS 2. INFERIOR RECTUS 3. MEDIAL RECTUS 4. LATERAL RECTUS 4 recti muscles 2 oblique muscles 5. SUPERIOR OBLIQUE 6. INFERIOR OBLIQUE 7. LEVATOR PALPEBRAE SUPERIORIS The intrinsic muscles include: 1- Ciliary muscle 2- Sphincter pupillae 3-Dilator pupillae Movements of the eyeball Elevation-moving the pupil/cornea superiorly Depression-moving the pupil/cornea inferiorly Abduction-moving the pupil/cornea laterally Adduction-moving the pupil/cornea medially Internal rotation-rotating the upper part of the pupil/cornea medially (or towards the nose) Intorsion External rotation-rotating the upper part of the pupil/cornea laterally (or towards the temple) Extorsion Common tendinous ring is a fibrous ring which surrounds the optic canal and part of the superior orbital fissure at the apex of the orbit. It is the common origin of the four recti muscles 1-Superior rectus Origin: Superior part of common tendinous ring Insertion: Anterior half of eyeball superiorly Nerve supply: Oculomotor nerve/ superior division Action: Elevation, adduction (Raises cornea upward and medially) 2-Inferior rectus Origin: Inferior part of common tendinous ring Insertion: Anterior half of eyeball inferiorly Nerve supply: Oculomotor nerve /inferior division Action: Depression, adduction (Depresses cornea downward and medially) 3-Medial rectus Origin: Medial part of common tendinous ring Insertion: Anterior half of eyeball medially Nerve supply: Oculomotor nerve/ inferior division Action: Adduction ((Rotates eyeball so that cornea looks medially) 4-Lateral rectus Origin: Lateral part of common tendinous ring Insertion: Anterior half of eyeball laterally Nerve supply: Abducent nerve [VI] Action: Abduction (Rotates eyeball so that cornea looks laterally) 5-Superior oblique Origin: Posterior part of the roof Insertion: Passes through pulley (trochlea) and is attached to lateral posterior half of eyeball (behind the equator) Nerve supply: Trochlear nerve Action: Depression, abduction, intorsion (Rotates eyeball so that cornea looks downward and laterally) 5-Superior oblique (Rotates eyeball so that cornea looks downward and laterally) AS IF YOU ARE LOOKING TO YOUR SHOULDER 6-Inferior oblique Origin: medial part of the floor (anteriorly) Insertion: lateral posterior half of eyeball ((behind the equator) Nerve supply: Oculomotor nerve/ inferior division Action: Elevation, abduction, extorsion (Rotates eyeball so that cornea looks upward and laterally) Medial rectus Lateralrectus Superior rectus Inferior rectus Inferior oblique Superior oblique The extraocular muscles do not act in isolation. They work as teams of muscles in the coordinated movement of the eyeball to position the pupil as needed For example, although the lateral rectus is the muscle primarily responsible for moving the eyeball laterally, it is assisted in this action by the superior and inferior oblique muscles The origins of the superior and inferior recti are situated about 23 °medial to their insertions, and, therefore, when the patient is asked to turn the cornea laterally, these muscles are placed in the optimum position to raise (superior rectus) or lower (inferior rectus) the cornea The superior and inferior oblique muscles can be tested. The pulley (trochlea) of the superior oblique and the origin of the inferior oblique muscles lie medial and anterior to their insertions. The physician tests the action of these muscles by asking the patient first to look medially, thus placing these muscles in the optimum position to lower (superior oblique) or raise (inferior oblique) the cornea Because the lateral and medial recti are simply placed relative to the eyeball, asking the patient to turn his or her cornea directly laterally tests the lateral rectus and turning the cornea directly medially tests the medial rectus Axis of eyeball Axis of orbit Inferior muscles--------------Extorsion Superior muscles------------- Intorsion LEVATOR PALPEBRAE SUPERIORIS Origin: Posterior part of the roof Insertion: Anterior surface and upper margin of superior tarsal plate, skin of upper eyelid Nerve supply: Oculomotor nerve/ superior branch Action: Elevationof upper eyelid Nerves of orbit Motor 1. Oculomotor 2. Trochlear 3. Abducent SO4LR6 Sensory 1. Opthalmic Lacrimal Frontal (General sensations) 2. Optic Nasociliary (Special sensations) Optic canal LEVATOR PALPEBRAE SUPERIORIS Superior rectus Superior oblique Lateral rectus Medial rectus Inferior rectus The tendinous ring surrounds the optic canal and the medial margin of superior orbital fissure Nerves of orbit Live Free To See No Insult At All Lacrimal nerve Frontal nerve Trochlear nerve Superior division of the oculomotor Nasociliary nerve Abducens nerve Inferior division of the oculomotor Lie within the common tendinous ring Ophthalmic artery Optic nerve Superior division of the oculomotor Optic nerve Ophthalmic artery enter the orbit via the optic canal, and so lie within the common tendinous ring Superior and inferior divisions of the oculomotor nerve Nasociliary branch of the ophthalmic nerve Abducens nerve also enter the orbit within the common tendinous ring, but they do so via the superior orbital fissure Nasociliary nerve Abducens nerve Inferior division of the oculomotor Lie outside the common tendinous ring Lacrimal nerve Trochlear nerve Frontal branch of ophthalmic nerve Lacrimal branch of ophthalmic nerve Superior ophthalmic vein Trochlear nerve all enter the orbit through the superior orbital fissure but lie outside the common tendinous ring Frontal nerve Structures which enter the orbit through the inferior orbital fissure lie outside the common tendinous ring. The close anatomical relationship of the optic nerve and other cranial nerves at the orbital apex means that lesions in this region may lead to a combination of visual loss from optic neuropathy and ophthalmoplegia from multiple cranial nerve involvement Infraorbital nerve and artery Inferior ophthalmic vein Zygomatic branch of maxillary nerve The intrinsic muscles include CILIARY MUSCLE SPHINCTER PUPILLAE DILATOR PUPILLAE Constricts pupil Ciliary muscle: Controls shape of lens; in accommodation, makes lens more globular Supplied by Parasympathetic via oculomotor nerve Dilates pupil Intrinsic Eye Muscles and their response to light At the apex of petrous bone, the free border crosses over the attached border At this point, the third and fourth cranial nerves pass forward to enter the lateral wall of the cavernous sinus CT-Brain Epidural Hemorrhage May Cause Temporal Lobe Herniation Remember that the dura is a tough structure and its tentorium as well, thus one should think about it as a real septa Compression of occulomotor nerve (III) is the first clinical sign ipsilateral pupil dilation Any intracranial mass inside the skull (tumor, bleeding…) may force its neighboring structures to herniate since the parasympathetic fibers that supply the constrictor pupil are located on the outside of the nerve and are inactivated first by compression Danger triangle of the face Superior and inferior ophthalmic veins Cavernous sinus Note: venous communication (via the ophthalmic veins) between the facial vein and the cavernous sinus Facial vein deep facial vein Pterygoid venous plexus Cavernous sinus syndrome Cavernous sinus syndrome  Sepsis from the central portion of the face or paranasal sinuses Clinical manifestations:  Ophthalmoplegia with diminished pupillary light reflexes  Venous congestion leading to periorbital edema  Exophthalmos Pain or numbness of the face Subsequent infection or inflammation in the cavernous sinus can result in damage to any of the cranial nerves that pass through it Exophthalmos is a bulging of the eye anteriorly out of the orbit Ophthalmoplegia is the paralysis or weakness of the eye muscles Eyelids The eyelids (act like the curtains) protect the eye from injury and excessive light by their closure The upper eyelid is larger and more mobile than the lower because of its attachment to the levator palpebrae superioris The upper and lower eyelids meet each other at the medial and lateral angles. The palpebral fissure is the space between the eyelids when they are open The palpebral fissure is the entrance into the conjunctival sac The layers of the eyelids: (from anterior to posterior) 1. Skin 2. Subcutanous tissue 3. Voluntary muscle 4. The orbital septum (tarsus) 5. Conjunctiva 1 4 5 3 2 Structure of the eyelids 1-Skin and subcutaneous tissue: - Thin - Only a thin layer of connective tissue (can be easily become oedematous (with fluid or blood)) Contains: The sebaceous glands (glands of Zeis) open directly into the eyelash follicles  The ciliary glands (glands of Moll) are modified sweat glands that open separately between adjacent lashes 2- Voluntary muscle Palpebral part of orbicularis oculi 4- Orbital septum (Palpebral fascia) An extension of periosteum into both the upper and lower eyelids from the orbital margin The orbital septum is thickened at the margins of the lids to form the superior and inferior tarsal plates The lateral ends of the tarsal plates are attached by a band, the lateral palpebral ligament, to the orbital margin The medial ends of the plates are attached by a band, the medial palpebral ligament, to the orbital margin. Tarsus provides major support for each eyelid  The tarsal glands are long, modified sebaceous glands that pour their oily secretion onto the free margin of the lid; their openings lie behind the eyelashes  This oily material prevents the overflow of tears and helps make the closed eyelids airtight. (Meibomian gland) 5-The conjunctiva Is a thin mucous membrane that lines the eyelids  It is reflected at the superior and inferior fornices onto the outer surface of the eyeball (sclera) The eyelids are closed by: 1-The contraction of the orbicularis oculi and 2-The relaxation of the levator palpebrae superioris muscles in the upper eyelids The upper eyelid is elevated by: THE LEVATOR PALPEBRAE SUPERIORIS Levator palpebrae superioris Origin: posterior part of the roof of the orbit Insertion: anterior surface of superior tarsus with some fibers attaching to the skin of upper eyelid Nerve supply: oculomotor nerve/ superior division There is a collection of smooth muscle fibers insert into the upper edge of the superior tarsus (superior tarsal muscle) Superior tarsal muscle which is part of the levator palpebrae superioris, helps maintain upper eyelid elevation and are innervated by postganglionic sympathetic fibers from the superior cervical ganglion Loss of oculomotor nerve [III] function results in complete ptosis or drooping of the upper eyelid, whereas loss of sympathetic innervation to the superior tarsal muscle results in partial ptosis Horner's syndrome Horner's syndrome is caused by a lesion in the sympathetic trunk in the neck that results in sympathetic dysfunction. It is characterized by three typical features: 1-Pupillary constriction due to paralysis of the dilator pupillae muscle 2- Partial ptosis (drooping of the upper eyelid) due to paralysis of the superior tarsal muscle of the levator palpebrae superioris 3-Absence of sweating on the ipsilateral side of the face and the neck due to absence of innervation of the sweat glands ORBITAL FAT The spaces between the main structures of the orbit are occupied by fat The fat helps to stabilize the position of the eyeball and also acts as a socket within which the eye can rotate. Conditions resulting in an increased overall volume of orbital fat, e.g. hyperthyroidism (Graves’ disease), may lead to forward protrusion of the eyeball exophthalmos Lacrimal apparatus Nerve supply of lacrimal gland Sensory: The lacrimal nerve (ophthalmic nerve) Parasympathetic: The greater petrosal nerve (facial nerve) Sympathetic (postganglionic fibers): originate from the superior cervical ganglion Foramen lacerum Has an anterior opening for the pterygoid canal And a posterior opening for the carotid canal Lacrimal nerve Lacrimal nerve is joined by a branch of the zygomaticotemporal nerve (parasympathetic to lacrimal gland) 6- Finally the lacrimal nerve 5-They then pass into its zygomatic branch and the zygomaticotemporal nerve 4- Postganglionic parasympathetic fibers join the maxillary nerve. 3- Nerve to pterygoid canal passes through the pterygoid canal to the pterygopalatine ganglion 1- Greater petrosal nerve (a branch of the facial nerve) which carries the preganglioninc parasympathetic fibers The parasympathetic secretomotor nerve supply is derived from the facial nerve 2- Greater petrosal nerve joins the deep petrosal nerve to form the nerve of the pterygoid canal (vidian nerve) (at foramen Lacerum) 6- Finally the lacrimal nerve 3- Nerve to pterygoid canal passes through the pterygoid canal to the pterygopalatine ganglion 5-They then pass into its zygomatic branch and the zygomaticotemp oral nerve 4-postganglionic sympathetic fibers join the maxillary nerve. The sympathetic postganglionic fibers are derived from the internal carotid plexus 2- Deep petrosal nerve joins the Greater petrosal nerve to form the nerve of the pterygoid canal (vidian nerve) (at foramen Lacerum) 1- Deep petrosal nerve contains postganglionic sympathetic fibers from the internal carotid plexus (superior cervical ganglion) Nerves of the Orbit Optic Nerve The optic nerve enters the orbit from the middle cranial fossa by passing through the optic canal It is accompanied by the ophthalmic artery The nerve is surrounded by sheaths of pia mater, arachnoid mater, and dura mater It pierces the sclera at the posterior pole of the eyeball (optic disc) Remember that the meninges fuse with the sclera so that the subarachnoid space with its contained cerebrospinal fluid extends forward from the middle cranial fossa, around the optic nerve, and through the optic canal, as far as the eyeball. Thus, the subarachnoid space extends around the optic nerve as far as the eyeball A rise in pressure of the cerebrospinal fluid within the cranial cavity therefore is transmitted to the back of the eyeball. Papilledema A swollen optic disc caused by increased intracranial pressure Can be seen when retina is examined using an Ophthalmoscope Any increase in intracranial pressure results in increased pressure in the subarachnoid space surrounding the optic nerve Optic disc: the point of exit of the optic nerve, lacking visual receptors (blind spot) Lacrimal Nerve The lacrimal nerve arises from the ophthalmic division of the trigeminal nerve It enters the orbit through the superior orbital fissure It is joined by a branch of the zygomaticotemporal nerve (parasympathetic to lacrimal gland) Lacrimal nerve Frontal Nerve The frontal nerve arises from the ophthalmic division of the trigeminal nerve It enters the orbit through the superior orbital fissure It divides into the supratrochlear and supraorbital nerves that wind around the upper margin of the orbital cavity to supply the skin of the forehead Supratrochlear nerve Supraorbital nerve Frontal nerve Nasociliary Nerve The nasociliary nerve arises from the ophthalmic division of the trigeminal nerve. It enters the orbit through the superior orbital fissure Nasociliary nerve Branches of the Nasociliary Nerve 1- The communicating branch to the ciliary ganglion is a sensory nerve. The sensory fibers from the eyeball pass to the ciliary ganglion via the short ciliary nerves without interruption, and then join the nasociliary nerve by means of the communicating branch. 2- The long ciliary nerves, two or three in number, arise from the nasociliary nerve as it crosses the optic nerve. They contain sympathetic fibers for the dilator pupillae muscle. The nerves pass forward with the short ciliary nerves and pierce the sclera of the eyeball. They continue forward between the sclera and the choroid to reach the iris. 3-The posterior ethmoidal nerve supplies the ethmoidal and sphenoidal air sinuses 4-The infratrochlear nerve supplies the skin of the medial part of the upper eyelid and the adjacent part of the nose 5-The anterior ethmoidal nerve passes through the anterior ethmoidal foramen. After supplying an area of mucous membrane in the nasal cavity, it appears on the face as the external nasal nerve at the lower border of the nasal bone, and supplies the skin of the nose down as far as the tip 1- The communicating branch to the ciliary ganglion 2- Posterior ethmoidal nerve 3- Anterior ethmoidal nerve 4- Infratrochlear nerve 5- Long ciliary nerves Branches of the Nasociliary Nerve 3 4 2 1 Trochlear Nerve The trochlear nerve enters the orbit through the superior orbital fissure It supplies the superior oblique muscle Superior oblique Abducent nerve The abducent nerve enters the orbit through the superior orbital fissure It supplies the lateral rectus muscle lateral rectus Oculomotor Nerve The superior division of the oculomotor nerve enters the orbit through the superior orbital fissure It supplies superior rectus and levator palpebrae superioris SO4 LR6 The inferior division of the oculomotor nerve enters the orbit through the superior orbital fissure  It supplies inferior rectus, medial rectus, and inferior oblique muscles.  The nerve to the inferior oblique gives off a branch that passes to the ciliary ganglion and carries parasympathetic fibers to the sphincter pupillae and the ciliary muscle Ciliary Ganglion Is a parasympathetic ganglion About the size of a pinhead and situated in the posterior part of the orbit. It receives its preganglionic parasympathetic fibers from the oculomotor nerve via the nerve to the inferior oblique muscle The postganglionic fibers leave the ganglion in the short ciliary nerves, which enter the back of the eyeball and supply the sphincter pupillae and the ciliary muscle. It receives its postganglionic sympathetic fibers from the internal carotid sympathetic plexus (superior cervical ganglion) and run through the ganglion without interruption. Superior division Brain stem Oculomotor nerve Inferior division Postganglionic parasympathetic 1- Constrictor pupillary ms 2- Ciliary ms Preganglionic parasympathetic Short ciliary nerve Sympathetic plexus around ICA Brain stem Sensory communicating branch Long ciliary nerve Nasociliary V1 V2 Trigeminal nerveV3 Dilator pupillary ms General sensation from eyeball Ophthalmic Artery  Is a branch of the internal carotid artery It enters the orbit through the optic canal with the optic nerve It gives off numerous branches, which accompany the nerves in the orbital cavity Branches of the Ophthalmic Artery: The central artery of the retina is a small branch that pierces the meningeal sheaths of the optic nerve to gain entrance to the nerve It runs in the substance of the optic nerve and enters the eyeball at the center of the optic disc. Here, it divides into branches, which may be studied in a patient through an ophthalmoscope The central artery of the retina Occlusion of central artery of retina results in blindness The central artery of the retina Ophthalmic Veins Superior ophthalmic vein Communicates in front with the facial vein Leaves the orbit through the superior orbital fissure and enters the cavernous sinus Inferior ophthalmic vein  Leaves the orbit by: 1-Joining the superior ophthalmic vein OR 2-Passing through the superior orbital fissure on its own to join the cavernous sinus OR 3- Passing through the inferior orbital fissure to join with pterygoid venous plexus. Superior ophthalmic vein Cavernous sinus Facial vein deep facial vein Inferior ophthalmic vein Pterygoid venous plexus

The Orbit

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