Sense Organs (Ear)

Question 1

General structure and functions of the ear

Answer 1

1. External ear
   - Receives Sound waves
2. Middle ear
   - transmits Sound waves from Air to fluids via Auditory ossicles: malleus, incus and stapes
3. Internal ear
   - contains the auditory organ (Fluid movements converted to nerve impulses
   - contains vestibular organ (responds to Gravity and movements of the Head)

Question 2

Structure of internal ear

Answer 2

• located within the Petrous part of temporal bone

1. Bony labyrinth
   - filled with perilymph
   a) vestibule (separated from Middle ear by oval window)
   b) 3 semicircular canals
   c) Cochlea
2. Membraneous labyrinth
   - filled with endolymph
   - Lined with simple squamous epithelium and sensory epithelium
   a) 2 connected sacs: utricle and saccule
   b) 3 semicircular ducts (continuous with the utricle)
   c) cochlear duct (continuous with the saccule)

Question 3

Hair cells of sensory epithelium

Answer 3

1. Type I - goblet cells
2. Type II - columnar cells

• located between supporting cells
• do not reach basement membrane
• connected to nerve endings
• contain stereocilia at apical surface
• contain kinocilium at apical surface in vestibular system

Question 4

Supporting cells of sensory epithelium

Answer 4

• nonsensory columnar cells
• on basement membrane
• span the entire thickness of epithelium

Question 5

Structure of Cochlea

Answer 5

1. Scala Media - cochlear duct, contains endolymph
2. Scala vestibuli - Above scala Media
   - begins at vestibular oval window
   - contains perilymph
3. Scala tympani - below Scala Media
   - ends at round window
   - contains perilymph

Question 6

Walls of Scala Media

Answer 6

1. Vestibular (Reissner’s) membrane
   - Upper Wall
   - seperates Scala Media from Scala vestibuli
   - thin fibrous connective tissue lined with simple squamous epithelium on Both sides
2. Stria vascularis
   - outer wall
   - stratified epithelium
   - intraepithelial capillary plexus
   - Producer endolymph
3. Basilar membrane
   - seperates Scala Media from Scala tympani
   - fibroelastic CT covered by simple squamous epithelium from Side of ST
   - Supports organ of corti

Question 7

Organ of corti

Answer 7

• all cells are divided into inner and outer cells by inner tunnel (Tunnel of corti)
• hair cells:
  1. 1 row of inner hair cells (Type I - goblet)
  2. 3-5 rows of outer hair cells (Type II - columnar)
  -> Stereocilia are covered by tectorial membrane
• supporting cells
  1. Inner and outer phalangeal cells (surround hair cells and form reticular lamina)
  2. pillar cells (outline the inner Tunnel)

Question 8

Sound transduction

Answer 8

1. Sound waves enter external ear and Cause tympanic membrane to vibrate
2. Vibration Moves auditory ossicles
3. Stapes generates at oval window pressure waves in perilymph of Scala vestibuli
4. Vestibular Membrane moves, causes pressure Wave formation in endolymph, that distorts the hair cells
5. Nerve Signal is initiated in cranial nerve VIII
6. Remaining pressure waves enter Scala tympani and exit via round window

Question 9

Structure of Christae ampullares

Answer 9

• located in ampullae of semicircular ducts
• consists of sensory epithelium ( hair cells Type I & II and supporting cells)
• stereocilia and kinocilia are in Dome-shaped gelatinous Cupula

Question 10

Function of Cristae ampullares

Answer 10

• sensory receptors for rotational movements of the head

Question 11

Structure of maculae

Answer 11

• sensory epithelium in the Walls of Utricle
• hair cells Type I & II and supporting cells
• Stereocilia and kinocilia are in gelatinous layer called otolithic membrane
• otolithic membrane contains otoliths on its surface (crystalline bodies)

Question 12

Function of maculae

Answer 12

• sensory receptors for static positions and linear acceleration of the Head
• otoliths are heavier than endolymph