May: Ear Histo

Question 1

What are the function of the vestibulocochlear appartatus? What are it’s main parts?

Answer 1

Functions: related to equilibrium and hearing (stato-acoustic)
B. Parts
1. External ear
2. Middle ear
3. Internal ear

Question 2

What does the external ear do? What are it’s parts?

Answer 2

receives sound waves
A. Auricle (pinna)
B. External auditory meatus
C. Tympanic membrane:
1. external: epidermis
2. middle: dense connective tissue
3. Internal: simple cuboidal epithelium

Question 3

What does the middle ear do? What is it’s structure? What are the ossicles?

Answer 3

waves are transmitted from air to bone & by bone to inner ear.
A. Structure:
1. Bony cavity
2. Lined by simple squamous epithelium
3. Lateral wall: tympanic membrane
4. Medial wall: bone with two foramina (oval and round
windows) covered by membranes.
B. Ossicles:
1. Malleus - inserts into the tympanic membrane
2. Incus - articulates with the malleus and stapes
3. Stapes - inserts into oval window

Question 4

What are the characteristics of the inner ear? What is perilymph? Endolymph?

Answer 4

1. System of bony canals and cavities in the temporal bone (osseous labyrinth)
2. Contains fluid-filled membranous sacs (membranous labyrinth)
3. Perilymph - present between bony and membranous labyrinths
   ( Low K+; High Na+ )
4. Endolymph - present within membranous labyrinths
   ( High K+; Low Na+ )
5. Contains vestibular organ which functions to maintain equilibrium & to detect angular and linear accelerations.
6. Vibrations from the middle ear are transduced to specific nerve impulses that pass via the acoustic nerve to the CNS

Question 5

What are the parts of the osseous labyrinth of the inner ear?

Answer 5

1. Vestibule - middle portion
2. Semicircular canals -posterior portion
   a. parts:
   1) anterior (superior)
   2) posterior
   3) lateral
   b. located at rt. angles to each other
   c. ampullae - dilations in each canal
3. Cochlea - anterior portion
   a. spirally-coiled canal - 2 1/2 turns (ca. 35mm)
   b. modiolus
   1) medial part of cochlea
   2) contains channels for nerves and vessels
   c. spiral lamina - shelf of bone, projects laterally into cavity

Question 6

What are the parts of the membranous labyrinth of the inner ear?

Answer 6

1. Semicircular canals
2. Utricle
3. Saccule
4. Endolymphatic duct
5. Perilymphatic duct
6. Cochlear duct
7. Organ of Corti
8. Spiral ganglion

Question 7

What is the endolymphatic duct (part of the membranous labyrinth of the inner ear)?

Answer 7

a. Y-shaped tube; continuous with endolymphatic space
b. proximally, connects utricle and saccule
c. distally, it widens into endolymphatic sac; embedded in subdural space

Question 8

What is the perilymphatic duct (part of the membranous labyrinth of the inner ear)?

Answer 8

continuation of subarachnoid space into perilymphatic space

Question 9

What is the cochlear duct (part of the membranous labyrinth of the inner ear)?

Answer 9

a. scala vestibuli
b. scala tympani
c. helicotrema
d. scala media
1) vestibular membrane
2) membranous spiral lamina
3) stria vascularis:
- site of endolymph elaboration
- lined by cuboidal epithelium. Blood vessels in underlying C.T.
- believed to be involved in the maintenance of the ionic component of
endolymph.

Question 10

What is the organ of corti (part of the membranous labyrinth of the inner ear)?

Answer 10

a. spiral limbus - loose connective tissue.
b. tectorial membrane:
1) glycoprotein-rich amorphous structure
2) oriented in a lateral & horizontal direction
c. internal spiral tunnel - tunnel of Corti: contains fluid similar to perilymph
d. pillar cells
e. phalangeal cells
f. sensory hair cells: inner & outer

Question 11

What is the spiral ganglion (part of the membranous labyrinth of the inner ear)?

Answer 11

• contain cell bodies of bipolar neurons which project to the dorsal and ventral cochlear nuclei.