Part 2 - Eye, ear, nose

• Orbit


  Eyeball and its accessory visual structures

  
• Orbits


  • Bilateral bony cavities in the facial skeleton that resemble hollow, quadrangular pyramids
  • Their bases directed anterolaterally
  • Their apices directed posteromedially
  • The medial walls are near parallel
  • Lateral walls are at right angles
  • The axes of the orbits diverge at 45°

  
• Contents of the orbit and the anterior orbital region


  • Eyeballs
  • Eyelids
  • Extra-ocular muscles
  • Nerves and vessels to eyeballs and muscles
  • Orbital fascia surrounding eyeballs and muscles
  • Mucous membrane (conjunctiva)
  • Orbital fat

  
• Boundaries of the orbit

  • Base
  • Superior wall
  • Inferior wall (floor)
  • Lateral wall
  • Medial wall
  • Apex
• Orbit


  Eyeball and its accessory visual structures

  
• Orbits


  • Bilateral bony cavities in the facial skeleton that resemble hollow, quadrangular pyramids
  • Their bases directed anterolaterally
  • Their apices directed posteromedially
  • The medial walls are near parallel
  • Lateral walls are at right angles
  • The axes of the orbits diverge at 45°

  
• Contents of the orbit and the anterior orbital region


  • Eyeballs
  • Eyelids
  • Extra-ocular muscles
  • Nerves and vessels to eyeballs and muscles
  • Orbital fascia surrounding eyeballs and muscles
  • Mucous membrane (conjunctiva)
  • Orbital fat

  
• Boundaries of the orbit


  • Base
  • Superior wall
  • Inferior wall (floor)
  • Lateral wall
  • Medial wall
  • Apex
• Periorbita


  Lines the bones forming the orbit and is continuous with other structures
• Eyelids


  • Moveable folds that cover the eyeball anteriorly
  • Protect the eye from injury and excessive light
  • Keep the cornea moist by spreading lacrimal fluid

  
• Parts of the eyelid


  • Palpebral conjunctiva
  • Bulbar conjunctiva
  • Conjunctival sac
  • Superior and inferior tarsi
  • Eyelashes
  • Medial palpebral ligament
  • Lateral palpebral ligament
  • Orbital septum

  
• Lacrimal gland


  Secrets lacrimal fluid which moistens and lubricates the surfaces of the conjunctiva and cornea
• Innervation of lacrimal gland


  1. Presynaptic parasympathetic fibres of facial nerve

  2. Postsynaptic sympathetic fibres from superior cervical ganglion

  3. Mixed fibres of communicating branch of zygomatic nerve from CN V2
• Parts of the eyeball

  • Fibrous layer (sclera and cornea)
  • Vascular layer (choroid, ciliary body and iris)
  • Inner layer (retina)

  
• Fibrous layer


  • Provides shape and resistance
  • Sclera is tough and opaque
  • Cornea is transparent
• Vascular layer


  • Choroid is dark and reddish-brown
  • Ciliary body is muscular and vascular
  • Iris is a thin contractile diaphragm with a central aperture (pupil)
• Inner layer


  • Optic part of retina has a pigmented layer and a neural layer
  • Nonvisual retina extends over the ciliary body and iris

  
• Compartments of the eyeball


  • Anterior segment (anterior chamber and posterior chamber)
  • Posterior segment

  
• Refractive media of the eyeball

  • Aqueous humor
  • Lens
  • Vitreous humor
• Extraocular muscles


  • Levator palpebrae superioris
  • Superior oblique
  • Inferior oblique
  • Superior rectus
  • Inferior rectus
  • Medial rectus
  • Lateral rectus
• Innervation of extraocular muscles

  LR6SO4AO3 (lat. rectus CN VI, Sup. oblique CN IV, all others CN III)
• Nerves of the orbit


  • Optic nerve (CN II)
  • Oculomotor (CN III)
  • Trochlear (CN IV)
  • Abducent (CN VI)
  • Ophthalmic (CN V1)
• Branches of ophthalmic nerve (CN V1)


  • Frontal
  • Supratrochlear
  • Supraorbital
  • Nasociliary
  • Long ciliary
  • Lacrimal
• Ciliary ganglion


  Group of postsynaptic parasympathetic nerve cell bodies located between the optic nerve and lateral rectus posteriorly
• Abducent (CN VI)


  Passes directly to lateral rectus
• Ophthalmic (CN V1)

  Branch of ophthalmic nerve
• Structures innervated by ophthalmic nerve


  • Frontal
  • Supratrochlear
  • Supraorbital
  • Nasociliary
  • Posterior ethmoidal
  • Anterior ethmoidal
  • Long ciliary
  • Lacrimal
• Ciliary ganglion


  • Group of postsynaptic parasympathetic nerve cell bodies
  • Located between the optic nerve and lateral rectus posteriorly
  • Receives nerve fibers from 3 sources: sensory fibers from nasociliary nerve, presynaptic parasympathetic fibers from oculomotor nerve, postsynaptic sympathetic fibers from internal carotid plexus
  • Short ciliary fibers arise here and supply sympathetic and parasympathetic fibers to ciliary body and iris

  
• Arteries of orbit


  • Central retinal
  • Supraorbital
  • Supratrochlear
  • Lacrimal
  • Dorsal nasal
  • Short posterior ciliaries
  • Long posterior ciliaries
  • Posterior ethmoidal
  • Anterior ethmoidal
  • Anterior ciliary
• Auricle


  • Composed of an irregularly shaped plate of elastic cartilage covered by thin skin
  • Concha of auricle is the deepest depression
  • Helix is the elevated margin
  • Lobule consists of fibrous tissue, fat and blood vessels
  • Tragus is a tongue-like projection overlapping the opening of the external acoustic meatus

  
• External acoustic meatus


  • Ear canal leading inward through the tympanic part of the temporal bone from the auricle to the tympanic membrane
  • Lateral third is slightly S-shaped and cartilaginous, lined with skin continuous with the auricular skin, with ceruminous and sebaceous glands producing cerumen
  • Medial 2 thirds are bony and lined with thin skin continuous with the external layer of the tympanic membrane
• Tympanic membrane


  • Thin, oval, semitransparent membrane at the medial end of the external acoustic meatus
  • Forms a partition between the external acoustic meatus and the tympanic cavity of the middle ear
  • Covered with skin externally and mucosa of the middle ear internally
  • Umbo is the peak of the central depression
  • Pars flaccida is the thin membrane superior to the lateral process of the malleus
  • Pars tensa is the remainder of the membrane
• Tympanic cavity


  • Narrow air-filled chamber in the petrous part of the temporal bone
  • Has 2 parts: tympanic cavity proper and epitympanic recess
  • Communications: anteromedially to the nasopharynx by the pharyngotympanic tube, posterosuperiorly to the mastoid cells through the mastoid antrum
  • Lined with mucosa continuous with the pharyngotympanic tube, mastoid cells and mastoid antrum
  • Walls: tegmental (roof), jugular (floor), membranous (lateral), labyrinthine (medial), mastoid (posterior), carotid (anterior)

  
• Mastoid antrum


  • Cavity in the mastoid process of the temporal bone
  • Separated from the middle cranial fossa by the tegmen tympani
  • Common cavity into which the mastoid air cells open
  • Lined by mucosa
• Pharyngotympanic tube


  • Connects the tympanic cavity to the nasopharynx
  • Opens posterior to the inferior nasal meatus
  • Posterolateral third is bony, the rest is cartilaginous
  • Lined by mucosa continuous with the tympanic cavity and nasopharynx
  • Function is to equalize pressure in the middle ear with atmospheric pressure
  • Walls of the cartilaginous part are normally in apposition (the tube is closed)
  • Opened by levator veli palatini and tensor veli palatini
• Contents of the middle ear


  • Auditory ossicles
  • Stapedius and tensor tympani muscles
  • Chorda tympani (branch of facial nerve)
  • Tympanic nerve plexus
• Malleus


  • Attaches to the tympanic membrane and moves with it
  • Functions as a lever
  • Head lies in the epitympanic recess and articulates with the incus
  • Neck lies against the flaccid part of the tympanic membrane, with the chorda tympani crossing the medial surface
  • Handle is embedded in the tympanic membrane, with the tendon of the tensor tympani inserting near the neck
• Incus


  • Between the malleus and stapes, articulating with both
  • Body lies in the epitympanic recess and articulates with the head of the malleus
  • Long limb is parallel to the handle of the malleus, with the interior end articulating with the stapes
  • Short limb is connected by a ligament to the posterior wall of the tympanic cavity
• Stapes


  • Smallest ossicle
  • Head is directed laterally and articulates with the incus
  • Base fits into the oval window on the medial wall of the tympanic cavity, attached to the margins by an annular ligament
  • Considerably smaller than the tympanic membrane, so vibratory force is increased 10 times but amplitude is decreased
• Tensor tympani


  • Short muscle that pulls the handle of the malleus medially
  • Tenses the tympanic membrane and reduces amplitude of its oscillations
  • Prevents damage to internal ear when exposed to loud sounds
  • Innervated by the mandibular nerve