W8 - special senses P3 the ear

Question 1

Describe the structure of the ear

Answer 1

Divided into
- External ear: collects soundwaves and channels them inward
- Middle ear: conveys sound vibrations to the oval window
- Internal ear: houses the receptors for hearing and equilibrium

Question 2

Temporal Bone

Answer 2

• External acoustic meatus: On the lateral side of the temporal bone - located anterior to the bulky mastoid process you can feel behind your ear.
  
  • Petrous part of the temporal bone: internal surface of skull base, which forms a prominent ridge separating the middle and posterior cranial fossae
  • Internal acoustic meatus: opening in the petrous part of the temporal bone. The vestibulocochlear nerve (CN VIII) together with the facial nerve (CN VII) travel via this foramen.

Question 3

Describe the structure of the external ear

Answer 3

Question 4

Describe the structure of the middle ear (tympanic cavity)

Answer 4

Question 5

Eustachian/auditory tube

Answer 5

Question 6

Auditory ossicles

Answer 6

Question 7

Describe the structure of the internal ear

Answer 7

• Contains the vestibulocochlear organ concerned with the reception of sound and the maintenance of balance.
  
  • It is often referred to as the labyrinth.
    There are two main divisions to the inner ear: the outer bony labyrinth and the inner membranous labyrinth.

Question 8

Bony Labyrinth

Answer 8

Question 9

Membranous labyrinth overview

Answer 9

Located within the osseous (bony) labyrinth, surrounded by perilymph.

Contains endolymph, which does not mix with perilymph.

Composed of communicating sacs and ducts, suspended within the bony labyrinth.

Question 10

Membranous Labyrinth Components & Their Locations

Answer 10

Utricle & Saccule: Located in the bony vestibule.

Utricle communicates with semicircular ducts and saccule.

Saccule is continuous with the cochlear duct.

Both contain maculae (sensory epithelium) with hair cells.

Hair cells are innervated by vestibular division of CN VIII.

Semicircular Ducts (3 total): Within the bony semicircular canals.

Each has an ampulla with a crista ampullaris (sensory area).

Detect rotational head movements via endolymph motion.

Hair cells are also innervated by vestibular division of CN VIII.

All open into the utricle.

Cochlear Duct: A spiral tube suspended in the cochlear canal.

Houses the organ of Corti (main structure for sound transduction).

Hair cells are innervated by cochlear division of CN VIII.

Question 11

Inner ear

Answer 11

• The membranous cochlear duct filled with endolymph is suspended inside the middle of the osseous canal.
  
  • This arrangement creates two subdivisions with the osseous canal:
    ○ scala vestibuli
    ○ scala tympani.
  • These two ‘scala’ are filled by perilymph. The scala vestibuli is continuous with scala tympani at the very tip of the cochlea.
  • The receptor organ for hearing is called the organ of Corti or spiral organ, and it is located within the membranous cochlear duct.
  • The hair cells of the spiral organ allow for transduction of auditory signals into nerve impulses.

Question 12

Name the receptor for the equilibrium and specify their location

Answer 12