Orbit and the Nasal Cavity

What is the Function of the Nose?

1. Nose is a projection from the face.

2. Function is to filter dust entering the respiratory system.

What is the Structure of the Nose?

1. Bones, comprised of paired nasal bones, maxillae, frontal bone and septum.

2. Cartilages, comprised of  3 main: lateral, major alar and septal

What is the Structure of the Nasal Cavity?

1. Septum divides the chamber into two cavities

2. Internal surface, lateral wall has three projections; superior, middle and inferior conchae

3. Nasal cavity opens into nasopharynx

4. Supplied arterial branches from ophthalmic and maxillary.

5. Nerve supply from olfactory nerve, ophthalmic (V1 and maxillary V2)

Cranial Nerve 1- Olfactory

1. Type: special afferent – sensory, arises from cerebrum

2. Exit: Cribriform Plate

What is Olfaction?

1. Olfaction is aided by the air flow through the nasal cavity

2. Conchae help warm and moisten the air

3. Olfaction receptors are in the epithelium lining the roof and walls, the epithelium secretes a mucus fluid, odoriferous gases are dissolved into the fluid and then detected by the olfactory nerves

What are the Functions and the Structure of the Paranasal Sinuses?

1. Paranasal sinuses are air filled extensions of the nasal cavity

2. Paired frontal sinuses in frontal bone that drain through frontonasal duct.

3. Ethmoidal cells are invaginations in the ethmoid bone and drain into middle meatus (if anterior, or middle) or superior meatus (if posterior).

4. Sphenoidal sinuses in sphenoid bone that drain into spheno-ethmoidal recess.

5. Paired maxillary sinuses in maxilla drains into middle meatus.

The Orbit- Bones

Made up 7 bones:​

• Frontal

• Maxilla​

• Ethmoid

• Lacrimal​

• Sphenoid

• Zygomatic​

• Palatine​

The Orbit- Several Openings Into the Orbit

Several openings into the orbit:​

• Optic canal​

• CN II and ophthalmic artery​

• Superior orbital fissure​

• CN III, IV, V1 & VI​

• Inferior orbital fissure​

• CN V2​

What is the Function of the Eye?

The eyeball contains the optical apparatus for the visual system

What is the Stricture of the Eye?

1. Located in orbit, suspended by muscles

2. 3 layers

• Outer fibrous- sclera and cornea

• Vascular- iris

• Inner- retina

3. Divided into anterior, posterior, vitreous chamber

How Does the Visual Field Work?

1. Visual information received by the retina​

​2. Impulses carried through CN II (Optic nerve)​

​3. Lateral visual field is processed by contralateral portion of the occipital lobe​

Why is the Visual Field Important?

1. The crossing of visual fields between eyes is important for binocular vision​

• 3D vision​

• Depth perception​

2. Things are seen backwards and inverted​

3. Visual cortex processes the information to “flip” the image​

Cranial Nerve 2- Optic

1. Type: Special afferent – sensory, extension of forebrain

2. Exit: Optic canal

3. Special Embryology: Optic stalk grows out and lens vesicle grows in

4. Medial fibres decussate at the optic chiasm

Clinical Considerations of the Optic Nerve

Swelling of the gland can impact on the optic nerve causing disturbances in vision.​

Movement of the Eye- Extraocular Muscle

7 extraocular muscles:​

• Levator Palpebrae ​

• Superior Oblique ​

• Superior Rectus​

• Medial Rectus ​

• Lateral Rectus ​

• Inferior Rectus ​

• Inferior Oblique​

Movement of the Eye- 3 Axis

Anatomical Organisation of the Eye

What are the Extraocular Muscles Responsible for Eye Movement?

Overview of Eye Movement

Cranial Nerve 3- Oculomotor

1. Type: Somatic Motor (general somatic efferent) to extra- ocular muscles (EXCEPT= superior oblique and lateral rectus)  and (general visceral efferent-parasympathetic) via short ciliary nerves to ciliary body and sphincter pupillae.

2. Exit: Superior orbital fissure

Cranial Nerve 4- Trochlear

Cranial Nerve 6- Abducent

Clinical Considerations of Cranial Nerve 3, 4, 6

What is the Mechanism of Crying?

Parasympathetic Supply to the Lacrimal Gland

1. Sensory innervation​

• Lacrimal nerve (branch of V1)​

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2. Parasympathetic innervation​

• Secretomotor function via facial nerve (CN VII)​

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3. Sympathetic innervation​

• Vasoconstrictive (sup. cervical ganglion, via internal carotid)​

Cranial Nerve 5- Trigeminal

1. Type: Somatic (general sensory) and somatic motor to derivatives of 1^st pharyngeal arch.

2. Three divisions:​

• Ophthalmic / V1​

-Exits cranium through superior orbital fissure​

• Maxillary / V2​

-Exits cranium through foramen rotundum​

• Mandibular / V3​

-Exits cranium through foramen ovale​

V1- Ophthalmic

1. Exits the cranium via the superior orbital fissure​

2. Divides into: ​

• Lacrimal​

-Sensory innervation to lacrimal gland, conjunctiva and upper eyelid​

-Parasympathetic fibres to lacrimal gland​

• Frontal​

-Sensory innervation to upper eyelid, conjunctiva, forehead & scalp​

• Nasociliary​

-Sensory innervation to the eye, bridge of nose and mucous membranes of the paranasal sinuses​

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