Ear Anatomy Quiz: Outer and Middle Ear Structures

Outer Ear Anatomy

• Pinna (auricle) is covered with skin and made of elastic cartilage, consisting of the helix and lobule
• External auditory meatus (ear canal) is lined with skin and ceruminous glands and passes through the temporal bone

Tympanic Membrane

• Separates the outer ear from the middle ear
• Innervated with sensory fibers from the trigeminal and vagus nerves
• Responds to air vibrations or sound waves and transfers energy to the middle ear ossicles

Middle Ear Anatomy

• Consists of three middle ear ossicles: malleus, incus, and stapes
• Malleus (hammer) attaches to the tympanic membrane and is connected to the incus
• Incus (anvil) is connected to the stapes
• Stapes (stirrup) footplate attaches to the oval window of the inner ear, creating ossiculations in the scala vestibuli
• Middle ear muscles: stapedius inserts on the stapes, and tensor tympani inserts on the malleus
• Eustachian tube connects the middle ear to the nasopharynx

Inner Ear Anatomy

• Housed in a maze of temporal bone passages called the bony labyrinth
• Bony labyrinth is filled with perilymph and is lined with periosteum
• Bony labyrinth consists of:
  • Vestibule
  • Cochlea
  • Semicircular canals
• Membranous labyrinth lines inside the bony labyrinth
• Lined with epithelium and is filled with endolymph (high in Na+, K+)

Structures of Hearing

• Cochlea: a spiraling chamber of the bony labyrinth, lined with a membranous labyrinth with 3 separate chambers
  • Scala vestibuli (filled with perilymph) abuts the oval window
  • Cochlear duct (filled with endolymph) contains the organ of Corti
  • Scala tympani (filled with perilymph) abuts the round window
• Organ of Corti: innervated by CN-VIII, the cochlear portion of the VIII pathway to the CNS for hearing

Structures of Equilibrium

• Vestibule houses the saccule and utricle, which each contain a macula that are receptor cells for:
  • Static equilibrium (head position when still)
  • Linear acceleration (head movements in a straight line)
• Semicircular canals are lined with a membranous semicircular duct, with an ampulla at each end containing a crista ampullaris
• Receptors detect:
  • Angular rotation (head rotation)
  • Dynamic equilibrium

The Eye and Vision

• Visual receptors account for ~ 70% of all sensory input in the body
• 40% of the cerebral cortex is involved in processing visual perception
• Eye balls are the sense organs for vision

Accessory Structures of the Eye

• Eyebrows
• Eyelids with tarsal and ciliary glands
• Eyelashes
• Lateral and medial canthus (angles at the corner of the eye)
• Conjunctiva
• Lacrimal apparatus
• Extrinsic eye muscles (6)

Eye Accessory Structures

• Eyelids (palpebrae) protect the eyes from foreign objects and bright light
• Conjunctiva: a transparent mucous membrane covering the inner surface of the eyelids and anterior surface of the eye, but not the cornea