Lecture 7:anatomy of the Eye and Ear Quiz

The Eye and Ear

Accessory Structures of the Eye

• Eyebrows: short, coarse hair that lie over the supraorbital margins of the skull
• Eyelids (palpebrae): separated by the eyelid slit (palpebral fissure)
• Conjunctiva: lines the eyelids and the eyes; secretes mucus to lubricate the eyes

Lacrimal Apparatus

• Consists of:
  • Lacrimal glands: secrete tears
  • Lacrimal canaliculi: drain lacrimal secretions (tears) into the lacrimal sac
  • Lacrimal sac: drains excessive tears to the nasolacrimal duct
  • Nasolacrimal duct: ultimately drains into nasal cavity
• Lacrimal secretions contain mucus, antibodies, and lysozymes (destroy bacteria)
• Cleans and protects the eye

Flow of Tears

• Lacrimal gland → Excretory ducts to eye (blink) → across eye → Lacrimal puncta → Lacrimal canaliculi → Lacrimal sac (in lacrimal fossa) → Naso-lacrimal duct → Nasal cavity

Extraocular Muscles of the Eye

• Muscles:
  • Lateral rectus: moves eye laterally (abducts) - CN VI (abducens)
  • Medial rectus: moves eye medially (adducts) - CN III (oculomotor)
  • Superior rectus: elevates eye and turns it medially - CN III (oculomotor)
  • Inferior rectus: depresses eye and turns it medially - CN III (oculomotor)
  • Inferior oblique: elevates eye and turns it laterally - CN III (oculomotor)
  • Superior oblique: depresses eye and turns it laterally - CN IV (trochlear)

Eyeball

• Hollow sphere filled with fluids (humor)
• Composed of 3 layers: fibrous, vascular, and sensory

Layers of the Eyeball

• Fibrous layer (outermost):
  • Cornea: transparent and bends light rays to focus them on the retina (refraction)
  • Sclera: white opaque connective tissue (white of the eye)
• Vascular layer (middle):
  • Iris: forms most anterior part of the vascular layer with central aperture, the pupil
  • Ciliary body & Ciliary muscle: controls the shape of the lens
  • Choroid: highly vascular and forms posterior 5/6 of the vascular coat
• Sensory layer (innermost):
  • Retina: contains receptor cells (photoreceptors), the rods and cones
  • Fundus: interior lining of the eyeball, includes the retina, optic disc, and macula

Lens

• Biconvex crystal-like transparent structure
• Held in place by a suspensory ligament attached to the ciliary body

Segments of Eyeball

• Divided into 2 segments by the lens
• Anterior segment: divided into anterior and posterior chambers containing Aqueous humor
• Posterior segment: contains Vitreous body (humor)

The Ear

• Houses two senses: hearing and equilibrium (balance)
• Divided into three parts: outer (external) ear, middle ear, and inner ear

The External Ear

• Involved in hearing only
• Structures:
  • Pinna (auricle)
  • External auditory canal: narrow chamber in the temporal bone, lined with skin, and contains Ceruminous (wax) glands
  • Ends at the tympanic membrane (ear drum)

The Middle Ear or Tympanic Cavity

• Air-filled cavity within the temporal bone
• Only involved in the sense of hearing - transfer sound from external to inner ear
• Contains 3 pairs of bones (Ear Ossicles):
  • Malleus (hammer)
  • Incus (anvil)
  • Stapes (stirrup)
• Auditory tube: connects the middle ear with the throat (nasopharynx) and allows for equalizing pressure during yawning or swallowing

The Inner Ear

• Includes sense organs for hearing and balance
• Consists of the bony labyrinth and membranous labyrinth filled with perilymph and endolymph, respectively