Head and Neck Anatomy: Orbit and Eye

• Study notes on the anatomy of the head and neck

The Orbit and The Eye

• The eyelids protect the eye and consist of skin, subcutaneous tissue, orbicularis oculi muscle, tarsus, and conjunctiva

Skin

• Thin and has eyelashes

Subcutaneous tissue

• Devoid of fat

Orbicularis oculi muscle

• Circular muscle that surrounds the eye opening
• Supplied by the facial nerve, and it closes the eye

Tarsus

• Dense protective plate of fibrous tissue

Conjunctiva

• Clear membrane that lines the eyelids
• Reflects to cover the anterior part of the sclera

Contents of the orbit

• Eyeball
• Includes 7 extraocular muscles

Levator palpebrae superioris muscle

• Inserted into the upper eyelid

Four recti muscles

• Superior, inferior, lateral, and medial rectus and two oblique muscles: superior and inferior oblique
• All the muscles are inserted into the eyeball
• All extraocular muscles are supplied by the oculomotor nerve, with exceptions
• Superior oblique muscle is supplied by the trochlear nerve
• Lateral rectus muscle supplied by the abducent nerve
• Levator palpebrae superioris elevates the upper eyelid
• The recti and oblique muscles move the eye in all directions

Blood Vessels

• Ophthalmic artery is a branch from the internal carotid artery
• The two ophthalmic veins, superior and inferior, drain into the cavernous sinus

Nerves

• Optic nerve arises from the retina and is a special sensory nerve for vision
• Ophthalmic nerve is a branch of trigeminal and is a general sensory nerve for touch and pain

Oculomotor

• Trochlear
• Abducent nerves are motor nerves to eye muscles
• Lacrimal apparatus includes lacrimal gland, lacrimal sac, and nasolacrimal duct

Lacrimal gland

• Located under the lateral part of the orbit roof and secretes tears

Lacrimal sac

• Located at the medial wall of the orbit and it collects tears

Nasolacrimal duct

• Drains tears to the nasal cavity

The Ear

• The ear consists of the external, middle, and inner ear

External ear

• Consists of the auricle (ear pinna) and auditory canal
• Ends at the ear drum (tympanic membrane), which separates it from the middle ear

Middle ear

• Located inside the petrous part of the temporal bone
• Contains three ossicles (malleus, incus, and stapes) and two muscles (tensor tympani and stapedius)
• Also connected to the nasopharynx by the Eustachean tube, equalizing air pressure on both sides of the ear drum

Internal ear

• Also known as the labyrinth, and is inside the petrous part of the temporal bone
• Consists of the cochlea and semicircular canals

Cochlea

• Located anteriorly and helps hearing

Semicircular canals

• Located posteriorly and responsible for equilibrium

Auditory nerve

• Auditory (vestibulo-cochlear) nerve, arises from the cochlea and semicircular canals and passes through the internal auditory meatus to enter the cranial cavity

The Nose

• The external nose is formed of bony and cartilaginous parts
• The cavity of the nose opens anteriorly on the face by anterior nasal openings (nostrils or nares)
• Posteriorly it opens into the nasopharynx by posterior nasal openings (choana)
• The nasal septum divides the cavity of the nose into right and left nasal cavities
• The anterior lower part of the septum is cartilaginous, while the posterior part is bony
• The lateral wall of the nasal cavities shows three bony elevations called turbinates or conchae (superior, middle, and inferior turbinates)
• The roof of the nasal cavities contains olfactory mucosa, from which arise the olfactory nerve fibers that carry smell sensation
• The floor of the nasal cavities is formed by the palate, which separates it from the oral cavity

Paranasal Air Sinuses

• Air-filled spaces in skull bones surrounding the nasal cavity
• Include the frontal, ethmoidal, sphenoidal, and maxillary air sinuses
• Maxillary air sinus is the largest
• Functions of paranasal sinuses: warming and humidification of air and resonance of voice

Maxillary Air Sinus

• It fills the body of the maxilla
• It is pyramidal in shape
• Apex lies laterally towards the zygomatic bone
• Base lies medially towards the nasal cavity
• The roof is related above to the orbit
• Floor is related below to the alveolar process of the maxilla

Opening of the maxillary sinus

• Opens into the nasal cavity high up in the base of the sinus, making drainage into the nasal cavity difficult

Nerves related to the sinus

• Infra orbital nerve runs in the roof of the sinus
• Anterior, middle, and posterior superior alveolar nerves run in the lateral wall of the sinus